Marine Institute Dungarvan Harbour SPA …...Table 8.31 - Population data for Bar-tailed Godwit 57...

Marine Institute

Dungarvan Harbour SPA Appropriate Assessment

[including consideration of Helvick Head to Ballyquin SPA and Mid-Waterford

Coast SPA]

February 2014

Plan Design Enable

Dungarvan Harbour SPA - Appropriate Assessment of Aquaculture

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Marine Institute Bird Studies

Dungarvan Harbour Special Protection Area: Appropriate Assessment of Intertidal Oyster Cultivation [including consideration of Helvick Head to Ballyquin SPA and Mid-Waterford Coast SPA]

February 2014

Notice

This report was produced by Atkins Ecology for the Marine Institute for the specific purpose of the Marine Institute Bird Studies project. This report may not be used by any person other than the Marine Institute without the Marine Institute's express permission. In any event, Atkins accepts no liability for any costs, liabilities or losses arising as a result of the use of or reliance upon the contents of this report by any person other than the Marine Institute.

Document History

JOB NUMBER: RK2927 DOCUMENT REF: 2927Dg17_Dungarvan Harbour AA_Rev0.doc

1 Final TG TG & POD POD JN 25-2-2014

0 Draft for Comment TG TG & POD POD JN 4-2-2014

Revision Purpose Description Originated Checked Reviewed Authorised Date


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Executive Summary vii

Acknowledgements xiii

1. Introduction 1

Structure of this report 1

Constraints to this assessment 2

2. Methodology 5

General 5

Data sources 5

Subsites 6

Definition of habitat zones 6

Analyses of waterbird distribution 7

Assessment methodology 9

3. Conservation objectives 16

Dungarvan Harbour SPA 16

Helvick Head to Ballyquin SPA 17

Mid-Waterford Coast SPA 17

4. Screening 18




5. Status and habitats and distribution of the SCI species 20




6. Intertidal oyster cultivation in Dungarvan Harbour 27

Scope of activity 27

History of activity 27

Description of activity 29

7. Potential impacts of intertidal oyster cultivation 35

Introduction 35

Habitat changes 35

8. Assessment of impacts on the SCI species of the Dungarvan Harbour SPA 38

Introduction 38

Light-bellied Brent Goose 38

Red-breasted Merganser 41

Great Crested Grebe 42

Golden Plover 44

Grey Plover 46

Knot 49


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Dunlin 51

Bar-tailed Godwit 55

Conclusions 58

9. Assessment of impacts on the SCI species of the Helvick Head to Ballyquin SPA 59

Introduction 59

Cormorant 59

Peregrine 60

Herring Gull 61

Conclusions 64

10. Assessment of impacts on the SCI species of the Mid-Waterford Coast SPA 65

Introduction 65

Cormorant 65

Peregrine 66

Herring Gull 66

Conclusions 67

11. Assessment of cumulative impacts 68

Introduction 68

Activities 68

Species assessments 71

12. References 76

Citation: -

Gittings, T. and O’Donoghue, P. (2014). Dungarvan Harbour Special Protection Area: Appropriate

Assessment of Intertidal Oyster Cultivation [including consideration of Helvick Head to Ballyquin SPA and

Mid-Waterford Coast SPA]. Unpublished Report prepared by Atkins for the Marine Institute.

Cover Photograph – reproduced with permission. John Fox.


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List of Tables

Table 2.1 - Development of intertidal oyster cultivation in Dungarvan Harbour in relation to the

availability of waterbird data and the expected influence on waterbird population trends

assuming a negative impact from intertidal oyster cultivation 11

Table 2.2 – Criteria for assessing significance with reference to attribute 1 of the conservation

objectives 13

Table 3.1 – Attributes and targets for the conservation objectives for Light-bellied Brent Goose,

Shelduck, Red-breasted Merganser, Great Crested Grebe, Oystercatcher, Golden

Plover, Grey Plover, Lapwing, Knot, Dunlin, Black-tailed Godwit, Bar-tailed Godwit,

Curlew, Redshank and Turnstone at Dungarvan Harbour. 16

Table 3.2 – Attribute and target for the conservation objective for wetlands and waterbirds at

Dungarvan Harbour. 17

Table 5.1 – Conservation condition and population trends of the SCI assessment species at

Dungarvan Harbour. 20

Table 5.2 - Seabird population data for the Helvick Head to Ballyquin SPA 22

Table 5.3 - Seabird population data for the Mid-Waterford Coast SPA 23

Table 6.1 - Extent of area occupied by trestles between 2000 and 2013 27

Table 8.1 - Extent of habitat affected by intertidal oyster cultivation under various tidal conditions 38

Table 8.2 - Light-bellied Brent Goose distribution in NPWS BWS low tide counts of Dungarvan

Harbour, 2009/10 39

Table 8.3 - Light-bellied Brent Goose distribution in low tide counts on the Outer Sandflats zone

carried out for the trestle study, 2011 39

Table 8.4 - Population data for Light-bellied Brent Goose 40

Table 8.5 – Red-breasted Merganser distribution in high tide counts of Dungarvan Harbour 41

Table 8.6 - Population data for Red-breasted Merganser 42 Table 8.7 – Great Crested Grebe distribution in high tide counts of Dungarvan Harbour 42

Table 8.8 - Population data for Great Crested Grebe 43

Table 8.9 – Golden Plover distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10 44

Table 8.10 - Golden Plover distribution in low tide counts on the Outer Sandflats zone carried out for

the trestle study, 2011 44

Table 8.11 - Population data for Golden Plover 46 Table 8.12 - Grey Plover distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10 46

Table 8.13 - Grey Plover distribution in low tide counts on the Outer Sandflats zone carried out for the

trestle study, 2011 46 Table 8.14 - Counts of Grey Plover on flood/ebb tides in Whitehouse Bank during the trestle study,

January-March 2011 47 Table 8.15 - Predicted displacement of Grey Plover based on densities recorded in trestle-free areas

of the lower shore zone of Whitehouse Bank 48

Table 8.16 - Population data for Grey Plover 49 Table 8.17 - Knot distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10 49

Table 8.18 - Knot distribution in low tide counts on the Outer Sandflats zone carried out for the trestle

study, 2011 49

Table 8.19 - Counts of Knot on flood/ebb tides in Whitehouse Bank during the trestle study, January-

March 2011 50 Table 8.20 - Population data for Knot 51

Table 8.21 - Dunlin distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10 51

Table 8.22 - Dunlin distribution in low tide counts on the Outer Sandflats zone carried out for the trestle

study, 2011 52

Table 8.23 - Dunlin densities (number per 10 ha) in lateral zones relative to the tideline 53


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Table 8.24 - Counts of Dunlin on flood/ebb tides in Whitehouse Bank during the trestle study, January-

March 2011 53

Table 8.25 - Predicted displacement based on densities recorded in trestle-free areas of the lower

shore zone of Whitehouse Bank 54

Table 8.26 - Population data for Dunlin 54

Table 8.27 – Bar-tailed Godwit distribution in NPWS BWS low tide counts of Dungarvan Harbour,

2009/10 55

Table 8.28 – Bar-tailed Godwit distribution in low tide counts of the Outer Sandflats zone carried out

for the trestle study, 2011 55

Table 8.29 – Bar-tailed Godwit densities (number per 10 ha) in lateral zones relative to the tideline 56

Table 8.30 - Predicted displacement of Bar-tailed Godwit based on densities recorded in trestle-free

areas of the lower shore zone of Whitehouse Bank 56

Table 8.31 - Population data for Bar-tailed Godwit 57 Table 9.1 – Cormorant distribution in high tide counts of Dungarvan Harbour 60

Table 9.2 – Herring Gull distribution in low tide counts of Dungarvan Harbour 62

Table 9.3 - Herring Gull distribution in low tide counts on the Outer Sandflats zone carried out for the

trestle study, 2011 63

Table 9.4 – Herring Gull densities (number per 10 ha) in lateral zones relative to the tideline 63

List of Figures

Figure 1.1 –Dungarvan Harbour, Helvick Head to Ballyquin and Mid-Waterford Coast SPAs 4

Figure 1.2 – Special Protection Areas in the vicinity of Dungarvan Harbour 4

Figure 2.1 – Subsites used in the NPWS BWS survey and zones used for broad-scale analysis of

waterbird distribution 15

Figure 2.2 - Areas covered in the trestle study 15 Figure 5.1 - Approximate tideline alignments at low tide under various tidal conditions 24

Figure 5.2 - Intertidal biotopes in Dungarvan Harbour as mapped by Aquatic Services Unit (2009) 24

Figure 5.3 - Benthic communities in Dungarvan Harbour as mapped by NPWS (2011d) 25

Figure 5.4 - Zostera distribution in 1970 25 Figure 5.5 - Zostera distribution in 1992 and 2013 26

Figure 6.1 - Aquaculture plots in Dungarvan Harbour 30

Figure 6.2 - Date of licensing of licensed and surrendered aquaculture plots in Dungarvan Harbour 30

Figure 6.3 - Dates of first cultivation in aquaculture plots at Dungarvan Harbour 31

Figure 6.4 - Extent of oyster trestles in Dungarvan Harbour in 2000 and 2005 31



Figure 11.1 - Indicative map of disturbance pressures in Dungarvan Harbour SPA 75


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Appendix A 81

Appendix B 83

B.1 Introduction 84

B.2 Fish populations in Dungarvan Harbour 84

B.3 Red-breasted Merganser 84

B.4 Great Crested Grebe 85

B.5 References 85

Appendix C 86

C.1 Introduction 87

C.2 Shelduck 87

C.3 Lapwing 87

C.4 Black-tailed Godwit 88

C.5 References 90

Appendix D 91

D.1 Introduction 92

D.2 Methods 92

D.3 Results 95

Appendix E 98

E.1 Introduction 99

E.2 Bar-tailed Godwit diet 99

E.3 Benthic fauna of the Outer Sandflats zone in Dungarvan Harbour 100

E.4 Assessment of Bar-tailed Godwit food resources 103

E.5 References 104

List of Tables

Table B.1 - Fish species recorded in Dungarvan Harbour in the October 2008 survey 84

Table C.1 - Lapwing distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10 88

Table C.2 - Black-tailed Godwit distribution in NPWS BWS low tide counts of Dungarvan Harbour,

2009/10 88

Table C.3 - Black-tailed Godwit distribution in low tide counts of the Outer Sandflats zone carried out

for the trestle study, 2011 89

Table D.1 - Tidal exposure in the lower shore zone of Whitehouse Bank under various low tides 96

Table D.2 - Tideline lengths in the lower shore zones of Ballyrandle Sandflats and Whitehouse Bank

under various low tides 96

Table D.3 - Predicted displacement due to intertidal oyster cultivation, based on the density of birds

recorded in the trestle-free areas of the lower shore zone of Whitehouse Bank 97

Table D.4 - Predicted displacement of Bar-tailed Godwit due to intertidal oyster cultivation, based on

the density of birds recorded in the lower shore zone of Ballyrandle Sandflats 97

Table E.1 - Polychaete species recorded in the diet of Bar-tailed Godwit 99

Table E.2 - Sediment composition recorded in the 2013 benthic survey 100

Table E.3 - Composition of the benthic fauna recorded in the ASU survey 101

Table E.4 - Composition of the benthic fauna recorded in the 2013 survey 101

Table E.5 - Composition of the polychaete fauna recorded in the ASU survey 102

Table E.6 - Composition of the polychaete fauna recorded in the 2013 survey 103


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List of Figures

Figure E.1 - Sediment composition in the ASU benthic samples from the Outer Sandflats zone of

Dungarvan Harbour 105

Figure E.2 - Total polychaete frequency in benthic samples from the Outer Sandflats zone of

Dungarvan Harbour (including the ASU dig samples) 105 Figure E.3 - Total polychaete frequency in benthic samples from the Outer Sandflats zone of

Dungarvan Harbour (including the ASU core samples) 106 Figure E.4 - Frequency of large polychaetes in benthic samples from the Outer Sandflats zone of

Dungarvan Harbour (including the ASU dig samples) 106

Figure E.5 - Frequency of large polychaetes in benthic samples from the Outer Sandflats zone of

Dungarvan Harbour (including the ASU core samples) 107


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Executive Summary

This report contains the Appropriate Assessment of aquaculture on the Dungarvan Harbour Special

Protection Area (site code 004032). The Helvick Head to Ballyquin SPA (site code 004192) and the Mid-

Waterford Coast SPA (site code 004193) are also considered in this report, because of their close proximity

to the Dungarvan Harbour, and the potential usage of aquaculture areas by birds from these SPAs. The only

aquaculture activity in Dungarvan Harbour is suspended oyster cultivation using bags and trestles in the

intertidal zone (referred to as intertidal oyster cultivation hereafter).

This assessment is based on a desktop review of existing information, combined with the results of a

detailed study of waterbird distribution in the outer part of Dungarvan Harbour that was carried out as part of

a wider study of the effects of intertidal oyster culture on the spatial distribution of waterbirds (the trestle

study). Where relevant, it identifies information gaps that may affect the reliability of the conclusions of this

assessment.

Constraints to this assessment include limited information available on the spatial extent of aquaculture

activity prior to 2000, some limitations to the available data on waterbird numbers and distribution within

Dungarvan Harbour (in particular, the limited number of I-WeBS counts per winter and the lack of information

about distribution within Dungarvan harbour prior to the development of intertidal oyster cultivation), lack of

detailed information on the SCI species of the Helvick Head to Ballyquin and the Mid-Waterford Coast SPAs,

lack of information on the nature of the response of Red-breasted Merganser, Great Crested Grebe,

Cormorant and Peregrine to intertidal oyster cultivation, and lack of detailed information on other activities

potentially affecting waterbird populations within Dungarvan Harbour.

Methodology

For the purposes of analysing waterbird distribution for this assessment, the subsites used for waterbird

monitoring have been grouped into three broad zones: the Inner Harbour, the Outer Sandflats and the Outer

Bay. The Outer Sandflats zone has also been divided into Whitehouse Bank, on the southern side of the

main tidal channel, and Ballyrandle on the northern side of the main tidal channel.

The primary source of information used for the identification of potential impacts is the trestle study. This

study used the results of counts of waterbirds within oyster trestles and in areas of comparable habitat

without trestles, and quantification of the available habitat within and outside the trestles, to analyse the

relationship between waterbird distribution patterns and the presence of oyster trestles, and to identify

species that may be negatively affected by intertidal oyster cultivation and the likely scale of the resulting

displacement impacts. Four of the SCI species (Red-breasted Merganser, Great Crested Grebe, Cormorant

and Peregrine) were not covered by the trestle study and a literature review was carried out to assess the

likely main food resources of these SCI species in the Dungarvan Harbour SPA and to assess the potential

impact of intertidal oyster cultivation on these food resources.

Where potential impacts were identified, the spatial overlap between the distribution of the species and the

spatial extent of the intertidal oyster cultivation was calculated, or qualitatively assessed when quantitative

data was not available. This overlap is considered to represent the potential magnitude of the impact, as it

represents the maximum potential displacement if the species has a negative response to the activity. For

selected wader species, a detailed assessment methodology was used to quantify the potential

displacement due to intertidal oyster cultivation. This methodology used one or more methods (depending

upon the species involved) to calculate the expected numbers that would have occurred on Whitehouse

Bank during the counts carried out for the trestle study in the absence of intertidal oyster cultivation and then

scaled these displacement methods up to predict the potential displacement impacts from full occupation of

the aquaculture plots.


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The potential impact of intertidal oyster cultivation on long-term population trends was assessed by

comparing population trends in Dungarvan Harbour with national trends over periods corresponding to

various phases of the development of intertidal oyster cultivation in Dungarvan Harbour. If intertidal oyster

cultivation caused negative impacts on population trends in Dungarvan Harbour we would expect the

Dungarvan Harbour population trend to be more negative than the national trend.

The criteria used to identify potentially significant impacts is focused on the Conservation Objectives, and

their attributes, that have been defined and described for the Dungarvan Harbour SPA. Impacts that will

cause displacement of 5% or more of the total Dungarvan Harbour population of a SCI species have been

assessed as potentially having a significant negative impact.

Conservation objectives

The Special Conservation Interests (SCIs) of the Dungarvan Harbour SPA include non-breeding populations

of Light-bellied Brent Goose, Shelduck, Red-breasted Merganser, Great Crested Grebe, Oystercatcher,

Golden Plover, Grey Plover, Lapwing, Knot, Dunlin, Black-tailed Godwit, Bar-tailed Godwit, Curlew,

Redshank and Turnstone. The conservation objectives for these species are to maintain their favourable

conservation condition, which are defined by there being stable or increasing long-term population trends

and no significant decrease in numbers or range of areas used within Dungarvan Harbour.

The wetland habitats within the Dungarvan Harbour SPA and the waterbirds that utilise this resource are an

additional SCI (the wetlands and waterbirds SCI). The conservation objective for this SCI is to maintain its

favourable conservation condition, which is defined by there being no significant decrease in the permanent

area occupied by wetland habitats.

The SCIs of the Helvick Head to Ballyquin SPA are breeding populations of Cormorant, Peregrine, Herring

Gull, Kittiwake and Chough. The SCIs of the Mid-Waterford Coast SPA are breeding populations of

Cormorant, Peregrine, Herring Gull and Chough. The conservation objectives for these species are to

maintain their favourable conservation condition. NPWS have not defined site-specific attributes and targets

to define the favourable conservation condition of these species for these SPAs.

Screening

Several SCI species were screened out from further assessment because they have a neutral/positive

response to intertidal oyster cultivation (Oystercatcher, Curlew, Redshank and Turnstone) or they are not

considered to have any significant spatial overlap with the aquaculture plots in Dungarvan Harbour

(Shelduck, Lapwing, Black-tailed Godwit, Kittiwake and Chough).

The Conservation Objectives define the favourable conservation condition of the wetlands and waterbirds

SCI at Dungarvan Harbour purely in terms of habitat area. Intertidal oyster cultivation has not, and will not,

cause any change in the permanent extent of wetland habitat. Therefore, intertidal oyster cultivation is not

likely to have any significant impact on this SCI and it has been screened out from any further assessment.

SCI status

Of the Dungarvan Harbour SCI species included in this assessment, Red-breasted Merganser, Great

Crested Grebe, Golden Plover and Grey Plover have been assessed as having intermediate (unfavourable)

conservation condition and Dunlin has been assessed as having unfavourable conservation condition.

NPWS have not made any assessment of the status of the SCI species of the Helvick Head to Ballyquin and

Mid-Waterford Coast SPAs.


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Intertidal oyster cultivation in Dungarvan Harbour

There are currently 35 plots (covering 203 ha) licensed for intertidal oyster cultivation and an additional 20

plots with applications for licenses (covering 75 ha). The licensed sites and application areas are all in a

single contiguous block spanning the lower intertidal and upper subtidal zone on Whitehouse Bank in the

Outer Sandflats zone.

The aquaculture plots were first licensed in 1993, with additional licenses issued up to 2010. However,

intertidal oyster cultivation in Dungarvan Harbour began in the mid-1980s and increased over the next ten

years or so, until, by the mid-1990s it is estimated that the area occupied by trestles was at least 60% of the

2013 levels. By 2000, 82 ha was occupied by trestles and this increased to 105 ha in 2013. The recorded

oyster production increased from around 500 tonnes in 1995 to over 2000 tonnes in 2012, although the data

for 1995 may be an underestimate.

Impacts on Dungarvan Harbour SCI species

Light-bellied Brent Goose

Light-bellied Brent Goose may have a complex interaction with intertidal oyster cultivation, but at Dungarvan

Harbour, the available evidence indicates that it currently has a neutral or positive association with this

activity. However, intertidal oyster cultivation in Dungarvan Harbour may have caused, or contributed to, the

complete loss of a large seagrass (Zostera) bed. Zostera is normally a favoured feeding habitat for Light-

bellied Brent Goose. Light-bellied Brent Goose continue to occur within the same area, but now feed on

algae covering the trestles. Zostera may have a higher nutritive value as a food resource for Brent Goose

and is generally the preferred food resource when available. Therefore some displacement of Light-bellied

Brent Goose might be expected to have occurred due to the reduced quality of the food resource (algae) that

has replaced the Zostera bed. However, the actual displacement that has occurred will depend upon the

quality of the habitat elsewhere in Dungarvan Harbour.

The Light-bellied Brent Goose population trend at Dungarvan Harbour has been consistently more positive

than the national trend. Therefore, there is no evidence that the development of intertidal oyster cultivation

has affected the long-term population trends of Light-bellied Brent Goose at Dungarvan Harbour.

Red-breasted Merganser and Great Crested Grebe

Red-breasted Merganser and Great Crested Grebe are mainly fish-eating species. Intertidal oyster

cultivation is likely to have neutral or positive impacts on the availability of prey resources for these species

in the areas occupied by the activity, compared to areas of similar habitat elsewhere in Dungarvan Harbour.

Therefore, intertidal oyster cultivation is not likely to cause any displacement of these species.

The population trends of both species at Dungarvan Harbour are similar to the national trend. Therefore,

there is no evidence that the development of intertidal oyster cultivation has affected the long-term

population trends of these species at Dungarvan Harbour.

Golden Plover

The limited available data indicates that Golden Plover avoid oyster trestles and this pattern would be

expected from knowledge of their ecology. The area now occupied by oyster trestle blocks covers a large

part of Whitehouse Bank and extends close to the area apparently favoured by Golden Plover. It seems

reasonable to suppose that, in the absence of the oyster trestles, Golden Plover flocks would also occur

within the northern part of the area now occupied by oyster trestle blocks. However, intertidal oyster

cultivation does not appear to have caused significant displacement of Golden Plover from Whitehouse Bank

and the potential future expansion of intertidal oyster cultivation is unlikely to affect the overall occurrence of

Golden Plover within the northern part of Whitehouse Bank.


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The 1995/96-2007/08 population trend of Golden Plover at Dungarvan Harbour (-19%) was significantly

more negative than the national trend (-2%). However, the more recent trend data indicates that the scale of

the national decrease up to 2010/11 is probably broadly comparable to the scale of decrease at Dungarvan

Harbour over the same period. Golden Plover counts tend to be highly variable (due to their pattern of usage

of intertidal habitats) so precise quantitative interpretation of trends at infrequently counted individual sites

(such as Dungarvan Harbour) is unlikely to be ecologically meaningful. Overall, therefore, there is no

evidence that the development of intertidal oyster cultivation at Dungarvan Harbour has affected the long

term population trends of Golden Plover.

Grey Plover, Knot, Dunlin and Bar-tailed Godwit

Four of the SCI species included in this assessment (Grey Plover, Knot, Dunlin and Bar-tailed Godwit) have

strong negative associations with intertidal oyster cultivation and, at Dungarvan Harbour, have significant

spatial overlap with the aquaculture plots. Based on numbers present outside oyster trestle blocks at low

tide, the predicted displacement levels for these species due to full occupation of the aquaculture plots are

9% (Grey Plover), 4% (Dunlin) and 3% (Bar-tailed Godwit). However, these predicted impacts do not take

account of any large-scale displacement impacts from intertidal oyster cultivation.

Grey Plover, Knot and Dunlin feed in large numbers on the upper shore zone of Whitehouse Bank on

flood/ebb tides when the tideline is above the oyster trestle area but usually largely leave Whitehouse Bank

around low tide when the tideline is within the oyster trestle area. If these movement patterns are due to their

avoidance of intertidal oyster cultivation, then the level of intertidal oyster cultivation in 2011 may have

caused displacement of around 10% (Grey Plover), 18% (Knot) and 30% (Dunlin) of their respective

Dungarvan Harbour populations. However, it is also possible that some of the difference between the

flood/ebb tide and low tide numbers on Whitehouse Bank may reflect birds moving away from Whitehouse

Bank at the stage of the tide when the tideline reaches the lower shore zone due to factors unrelated to the

presence of oyster trestles, such as the exposure of suitable habitat elsewhere.

Bar-tailed Godwit did not occur in larger numbers in Whitehouse Bank on flood/ebb tides, compared to at low

tide, but much larger numbers occur on similar intertidal habitat on Ballyrandle Sandflats. This could also

indicate large-scale displacement impacts due to intertidal oyster cultivation. However, although the overall

biotope type has been classified as the same, the presence of a tidal channel running through the

Ballyrandle Sandflats is likely to affect the habitat and there are some minor but consistent differences in

sediment composition between the Ballyrandle Sandflats and Whitehouse Bank. The abundance of large

polychaetes (which are the favoured prey item of Bar-tailed Godwit) appear to be generally higher in the

Ballyrandle Sandflats compared to Whitehouse Bank, although the available data is too limited to draw

definitive conclusions. Therefore, it seems plausible that the major component of the differences in densities

of Bar-tailed Godwit between the Ballyrandle Sandflats and the trestle-free areas of Whitehouse Bank is due

to differences in food resources, although some displacement effect on areas adjoining trestles may also be

occurring.

The long-term population trends of all four of these species at Dungarvan Harbour are similar to, or more

positive than, the national trends. Therefore, there is no evidence that the development of intertidal oyster

cultivation at Dungarvan Harbour has affected the long-term population trends of these species at

Dungarvan Harbour.


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Impacts on Helvick Head to Ballyquin and the Mid-Waterford Coast SCI species

Cormorant

Dungarvan Harbour in general, and the intertidal oyster cultivation area in particular, may provide potential

foraging habitat for the Cormorant populations of these SPAs but that these areas are not likely to be of

major importance in providing food resources for these populations.

Intertidal oyster cultivation is likely to have neutral or positive impacts on the availability of prey resources for

Cormorant in the areas occupied by the activity, compared to areas of similar habitat elsewhere in

Dungarvan Harbour. Therefore, intertidal oyster cultivation is not likely to cause any displacement of

Cormorant within Dungarvan Harbour.

There is no evidence that large-scale aquaculture at Dungarvan is causing negative impacts on fish

population through reduced recruitment or through indirect food web effects. The lack of negative signals

from the long-term population trends of other fish-eating species (Red-breasted Merganser and Great

Crested Grebe) also indicates that there have been no major impacts on the fish populations. Moreover,

Dungarvan Harbour is not likely to be of major importance in providing food resources for SPA Cormorant

population.

Peregrine

It seems likely that the intertidal oyster cultivation area provides potentially suitable feeding habitat and is

within the foraging range of at least one pair of each of the SPA Peregrine populations. However, the

availability of high quality food resources closer to the pair from the Helvick Head to Ballyquin SPA, the

distance of the intertidal oyster cultivation area from the Mid-Waterford Coast pair, and the low numbers of

waterbirds that will be present during most of the Peregrine’s breeding season, indicate that the intertidal

oyster cultivation area is probably not of major importance as feeding habitat for the Peregrine populations of

these SPAs.

Intertidal oyster cultivation may reduce the quality of the feeding habitat by interfering with Peregrine

foraging behaviour. However, given that the intertidal oyster cultivation area is likely to be of low importance

for the nearest breeding pair from each SPA, it is unlikely that intertidal oyster cultivation will significantly

affect food resources for these pairs. Therefore, intertidal oyster cultivation is considered unlikely to affect

the conservation condition of the Peregrine populations of either SPA.

Herring Gull

Dungarvan Harbour in general, and the intertidal oyster cultivation area in particular, are likely to potential

foraging habitat for the Herring Gull populations from both SPAs.

Herring Gull generally appears to have a neutral response to intertidal oyster cultivation. At Dungarvan

Harbour, there was some evidence of a minor negative response by roosting Herring Gulls. However,

Herring Gulls from the SPA populations are unlikely to be visiting Dungarvan Harbour to roost. Foraging

Herring Gulls do not appear to show an avoidance response to intertidal oyster cultivation. Therefore,

intertidal oyster cultivation is not likely to affect Herring Gull food resources and is considered unlikely to

affect the conservation condition of the Herring Gull populations of either SPA.

Cumulative impacts

This assessment considered the potential cumulative impacts of the combined effects of intertidal oyster

cultivation in combination with other activities within the SPA (including beach recreation, water-based

recreation, hand collection of shellfish, bait digging, and effluent discharge).


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On Whitehouse Bank, horse riding may cause displacement of Golden Plover across the low tide period.

Intertidal oyster cultivation is not considered to be causing, or likely to cause, significant levels of

displacement of Golden Plover, due to the extensive availability of suitable roosting habitat in the upper

shore zone. High levels of disturbance from horse riding to this upper shore zone could, in combination with

intertidal oyster cultivation, cause significant displacement impacts.

On the Ballyrandle Sandflats, bait digging, shellfish gathering and intertidal walking may all cause

displacement of Knot, Dunlin and Bar-tailed Godwit across the low tide period, with Dunlin also possibly

displaced from the Inner Harbour due to bait digging. This displacement could, in combination with intertidal

oyster cultivation, cause a significantly greater displacement impact than the impact of intertidal oyster

cultivation by itself.

Horse riding on Whitehouse Bank, and watersport recreation in the Inner Harbour, may also cause

displacement of Grey Plover, Knot, Dunlin and Bar-tailed Godwit on ebb/flood tides. This will not have a

direct in-combination effect with intertidal oyster cultivation, as the latter will only have displacement impacts

close to low tide when the tideline is within the lower shore zone. However, if the carrying capacity of

Dungarvan Harbour for these species was limited, displacement could cause reduced survivorship. In this

scenario, displacement of these species from the Inner Harbour and Whitehouse Bank on ebb/flood tides

due to horse riding and/or watersport recreation (and, for Knot, Dunlin and Bar-tailed Godwit, displacement

from the Ballyrandle Sandflats during low tide) could, in combination with intertidal oyster cultivation, cause a

significantly greater impact on survivorship than the impact of intertidal oyster cultivation by itself.

It is also possible that shellfish gathering on the Ballyrandle Sandflats could affect food resources for Knot,

so resource depletion due to shellfish gathering could, in combination with intertidal oyster cultivation, cause

a significantly greater impact on survivorship than the impact of intertidal oyster cultivation by itself.

The long-term population trends of Golden Plover, Grey Plover, Knot, Dunlin and Bar-tailed Godwit at

Dungarvan Harbour do not indicate any site-specific factors causing negative impacts to their populations.

Therefore, there is no evidence that current levels of disturbance in-combination with intertidal oyster

cultivation are causing negative impacts to the conservation condition of any of these species at Dungarvan

Harbour.


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Acknowledgements We are grateful to Brian O’Loan (BIM), Jim Harty (Dungarvan Shellfish), Cliona Mhic Ghiolla Chuda and

Michael Burke (Bia Mara Deise Teo) and Yannick Fournier (PKA) for providing information about the history,

and current activity, of the intertidal oyster cultivation industry in Dungarvan Harbour. Francis Beirn (Marine

Institute) provided useful comments on an earlier draft of this report. We are also grateful to Paul Walsh for

information about bird distribution at Dungarvan Harbour, while Olivia Crowe (BirdWatch Ireland) and Lesley

Lewis and David Tierney (NPWS) assisted with the provision of bird data. We also thank Sjoerd Duijns

(Royal Netherlands Institute for Sea Research (NIOZ)) for information about Bar-tailed Godwit ecology and

Robert Wilkes (EPA) for information about the Zostera populations at Dungarvan Harbour.


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1. Introduction

1.1 Atkins (Ecology) was commissioned by the Marine Institute to provide ornithological services in

relation to the appropriate assessment of aquaculture and shellfisheries on coastal Special

Protection Areas (SPAs).

1.2 This report contains the Appropriate Assessment of aquaculture in Dungarvan Harbour. The

aquaculture sites are within the Dungarvan Harbour SPA (site code 004032) and this SPA is the

primary focus of this assessment. There are also two other SPAs in the vicinity: Helvick Head to

Ballyquin SPA (site code 004192) and Mid-Waterford Coast SPA (site code 004193). These SPAs

are also considered. The boundaries of these SPAs are shown in Figure 1.1 and Figure 1.2. The

only aquaculture activity in Dungarvan Harbour is suspended oyster cultivation using bags and

trestles in the intertidal zone (referred to as intertidal oyster cultivation hereafter). The subject of

the assessment are areas that have either already been licensed for intertidal oyster cultivation, or

for which there are applications for such licenses; these are collectively referred to as aquaculture

plots.

1.3 This assessment is based on a desktop review of existing information, combined with the results

of a detailed study of waterbird distribution in the outer part of Dungarvan Harbour that was

carried out as part of a wider study of the effects of intertidal oyster cultivation on the spatial

distribution of waterbirds (Gittings and O’Donoghue, 2012). Where relevant, it identifies

information gaps that may affect the reliability of the conclusions of this assessment.

1.4 The data analysis and report writing was done by Tom Gittings. Paul O’Donoghue assisted with

project design, document preparation and undertook document review. Data entry was carried out

by David Kelleghan.

1.5 Scientific names and British Trust for Ornithology (BTO) species codes of bird species mentioned

in the text are listed in Appendix A.

Structure of this report

1.6 The structure of the report is as follows:

Section 2 of the report describes the methodology used for the assessment.

Section 3 of the report lists the Special Conservation Interests (SCIs) of the Dungarvan

Harbour SPA, and describes the Conservation Objectives, and their attributes and targets,

that have been defined for these SCIs.

Section 4 of the report contains a preliminary screening assessment that screens out SCIs

that do not show any significant spatial overlap with the activities being assessed. It also

includes a habitat screening that is used to define which of the remaining SCIs are assessed

in relation to activities affecting particular habitat zones.

Section 5 of the report contains a brief summary of the status and distribution of the SCI

species, and their habitats, in the Dungarvan Harbour SPA. This section only contains a very

brief summary of distribution patterns; detailed analyses of distribution patterns of individual,

species are carried out, as appropriate, in the impact assessment sections of relevant

activities later in the document.

Section 6 discusses the history of intertidal oyster cultivation in Dungarvan Harbour and

provides a description of the current and proposed future extent of the activity and the nature

of its operations.

Section 7 discusses the potential impact of intertidal oyster cultivation on waterbirds.


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Section 8-10 presents detailed assessments of the likely impact of intertidal oyster cultivation

in Dungarvan Harbour on the SCIs of the Dungarvan Harbour, Helvick Head to Ballyquin and

Mid-Waterford Coast SPAs.

Section 11 contains an assessment of cumulative impacts.

Constraints to this assessment

1.7 The spatial extents of the aquaculture plots have been derived from shapefiles supplied by the

Marine Institute (dated 30/10/2013). We understand that detailed information on the activity being

assessed is currently being compiled by BIM through an aquaculture profiling exercise. This

information was not available at the time of writing; as this may reduce the area of trestles actively

farmed our assessment can be viewed as a conservative impact assessment.

1.8 There are no maps available of the extent of aquaculture activity prior to 2000. While information

on the history of the development of aquaculture activity between 1985 and 2000 has been

obtained from interviews with producers, there is considerable uncertainty about the exact area

occupied by trestles and relative intensities of the activity pre- and post-2000. This affects the

interpretation of long-term population trends as indicators of potential impacts.

1.9 Detailed information on tidal dynamics and bathymetrics in Dungarvan Harbour is known to exist

in a report commissioned by BIM in 1993 (referred to in the CLAMS report; CLAMS, 2002 &

O’Loan, 2014) and in the UISCE MarGIS model developed by BIM (Brian O’Loan, BIM, pers.

comm.). However, this information was not available to us at the time of writing. Instead we used

mapping of tidelines by eye, combined with interpretation of aerial imagery to generate the

estimates of tideline lengths and intertidal areas that we required for quantitative impact

assessments.

1.10 The I-WeBS dataset for Dungarvan Harbour includes limited numbers of counts for most winters.

This affects the interpretation of population trends for species that tend to have high variability in

their monthly counts. Only limited information on the derivation of the long-term population trends

is presented in NPWS (2012c), with graphs of the trends not presented for all the species, and

without details of which months were included in the indices and the level of imputed counts

required.

1.11 There is no information available on the distribution of waterbirds within Dungarvan Harbour prior

to the development of intertidal oyster cultivation. Therefore, it is difficult to make assessments

about large-scale displacement impacts.

1.12 There is relatively good information available on the low tide distribution of waterbirds in

Dungarvan Harbour in mid-late winter through the NPWS BWS counts and the trestle study, but

information for the autumn/early winter period is limited to two counts in 2009. The I-WeBS

dataset only include subsite counts for the winters of 2010/11 and 2011/12. Therefore, information

on the high tide distribution of waterbirds in Dungarvan Harbour is limited.

1.13 There is limited information available on the population sizes and distribution of SCI species within

the Helvick Head to Ballyquin and Mid-Waterford Coast SPAs, and no information available on

their population trends and conservation condition, or on the extent to which the birds from these

SPAs visit Dungarvan Harbour.

1.14 There is a strong site-specific evidence base for the assessment of displacement impacts from

intertidal oyster cultivation on most of the SCI species associated with intertidal and shallow

subtidal habitats. However, the assessment of impacts on Red-breasted Merganser, Great

Crested Grebe, Cormorant and Peregrine is based mainly on interpretation of their habitat

preferences and food resource requirements.


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1.15 The assessment of cumulative impacts provides a general assessment of issues such as

recreational impacts, but without detailed information on other activities it is not possible to

precisely quantify these potential impacts. General comments are, however, included as

appropriate.


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Figure 1.1 –Dungarvan Harbour, Helvick Head to Ballyquin and Mid-Waterford Coast SPAs.

Figure 1.2 – Special Protection Areas in the vicinity of Dungarvan Harbour.


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2. Methodology

General

2.1 This assessment is based on a desktop review of existing information about waterbird population

trends and distribution in Dungarvan Harbour, combined with the results of a detailed study of

waterbird distribution in the outer part of Dungarvan Harbour that was carried out as part of a

wider study of the effects of intertidal oyster cultivation on the spatial distribution of waterbirds

(Gittings and O’Donoghue, 2012; referred to hereafter as the oyster trestle study) in addition to a

number of site familiarisation site visits by both TG and PO’D.

Data sources

2.2 The SPA boundaries are derived from NPWS shapefiles (which were last updated on

17/08/2011).

2.3 The spatial extents of the aquaculture plots have been derived from shapefiles supplied by the

Marine Institute (dated 30/10/2013).

2.4 The spatial extents of historical and existing intertidal oyster cultivation activity have been derived

from the following sources:

Digitisation of the extent of oyster trestles shown on OSI orthophotography (2000 and 2005)

GPS mapping of the extent of oyster trestles in 2007 (supplied by Brian O’Loan, BIM; see

also O’Loan, 2014), early 2011 (Gittings and O’Donoghue, 2012) and 2013 (supplied by the

Marine Institute).

GPS mapping of access routes in 2013 (supplied by the Marine Institute).

2.5 Information on the development and current practices of intertidal oyster cultivation activities in

Dungarvan Harbour was obtained from interviews with major producers (Jim Harty of Dungarvan

Shellfish, Cliona Mhic Ghiolla Chuda and Michael Burke of Bia Maras Deise Teo, and Yannick

Fournier of PKA) in December 2013, as well as information from the CLAMS report (CLAMS,

2002).

2.6 The bird data sources used for the assessment are as follows: -

Published mean annual peak counts for the early 1970s and mid-1980s (Sheppard, 1993);

Irish Wetland Bird Survey (I-WeBS) counts 1994/95-2010/11;

NPWS Baseline Waterbird Survey (NPWS BWS) 2009/10 counts;

The descriptions of waterbird distribution within Dungarvan Harbour in the SPA Conservation

Objectives Supporting Document (NPWS, 2011c);

Consultation with the I-WeBS coordinator (Paul Walsh, pers. comm.);

Data collected during the oyster trestle study (Gittings and O’Donoghue, 2012), including

unpublished data not presented in the report;

Data from the Seabird2000 dataset (see Mitchell et al., 2004) and from seabird surveys

carried out in 2008 (JNCC Seabird Colony Data; http://jncc.defra.gov.uk/page-4460).

2.7 The distribution of biotopes in Dungarvan Harbour is taken from two sources: the habitat

distribution map of intertidal biotopes in Aquatic Services Unit (2009) and the map showing the

distribution of benthic communities in NPWS (2011d).


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2.8 The extent and timing of exposure of intertidal habitats is based on observations made during

survey work in the oyster trestle study (Gittings and O’Donoghue, 2012), including unpublished

data not presented in the report, supplemented by observations in September 2013 and mapping

of tideline alignments from aerial imagery (see Appendix D).

2.9 The depths of subtidal habitats are based on Admiralty Chart data, and represent the depth below

the lowest astronomical tide.

2.10 Data on the timing and height of low tides were obtained from the United Kingdom Hydrographic

Offices Admiralty EasyTide website (http://easytide.ukho.gov.uk/).

2.11 Information on other activities (such as recreational use and shellfish gathering) was obtained

primarily from the data on potentially disturbing activities recorded during the NPWS BWS counts

and the oyster trestle study, supplemented by the general descriptions within the CLAMS report

(CLAMS, 2002).

Subsites

2.12 Dungarvan Harbour was divided in 28 subsites for the NPWS BWS survey (Figure 2.1), and these

subsites (or amalgamations of some of these subsites) were also used for I-WeBS counts in

2010/11 and 2011/12. I-WeBS count data for Dungarvan Harbour prior to 2010/11 is not divided

into subsites. For the purposes of analysing waterbird distribution, the subsites have been divided

into three broad zones: the Inner Harbour, the Outer Sandflats and the Outer Bay (Figure 2.1).

The Outer Sandflats zone has also been divided into Whitehouse Bank (subsites 0M420 and

421), on the southern side of the main tidal channel, and Ballyrandle (subsite 0M425) on the

northern side of the main tidal channel (Figure 2.1).

Definition of habitat zones

2.13 Three broad habitat zones have been defined for this assessment: intertidal, shallow subtidal (<

0.5 deep) and deep subtidal (> 0.5 m deep). The rationale for the distinction between the shallow

and deep subtidal zones is that Light-bellied Brent Goose generally does not feed in waters

greater than 0.5 m deep. In addition, we divided the intertidal habitat on Whitehouse Bank into

lower shore and upper shore zones, with the boundary corresponding to the upper limit of the

oyster trestles (as mapped in 2011) and the approximate upper limit of the aquaculture plots

(Figure 2.1).

2.14 The biotope maps (Figure 5.2 and Figure 5.3) show boundaries between the intertidal and

subtidal zones: i.e., the lower limits of the mapped biotopes. However, these boundaries are

apparently derived from Admiralty Chart mapping (for the Aquatic Services Unit map) and from

Ordnance Survey Discovery Series mapping (for the NPWS map). The Admiralty Chart mapping

mainly dates from 1896-1912, while the Discovery Series mapping appears to be based on the

1930s six inch mapping. Therefore, the details of the boundaries between the intertidal and

subtidal zones are likely to have changed.

2.15 The actual extent of tidal exposure in the critical areas of the Outer Sandflats zone will also vary

considerably between neap and spring low tides and will vary continuously over the course of a

single low tide period. Therefore, we used our own mapping data, supplemented by aerial

imagery, to calculate tideline lengths and areas of exposed intertidal habitat for use in our

assessment.

2.16 Our mapping data came primarily from the trestle study (Gittings and O’Donoghue, 2012). In this

study, we mapped the tideline position during five counts of the entire Outer Sandflats zone and

another 13 counts on eight dates of a 2-3 km section of Whitehouse Bank. We also mapped the

tideline in Ballyrandle in September 2013. This tideline mapping was used in conjunction with

aerial imaging that represented the tideline during an extreme neap and a mean low tide to map


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the tideline alignment at extreme neap (1.4-1.5 m), neap (1.1 m), mean (0.7 m) and spring (0.4 m)

low tides and at intermediate tides between these (see Appendix D). In addition to providing

tideline alignments at full low tide under the relevant tide, these tideline alignments show how the

tideline moves through the lower shore zone across the low tide period.

Analyses of waterbird distribution

2.17 The analyses of waterbird distribution in this assessment focuses on distribution patterns of

feeding, or potentially feeding birds, as the main potential impacts will be to the availability and/or

quality of feeding habitat. Most waterbird species will roost at high tide in shoreline or terrestrial

areas, which will not be affected by the activities being assessed. However, we have included

assessment of potential impacts on roosting birds, where relevant.

2.18 Waterbird distribution has been mainly analysed by reviewing count data across subsites from the

I-WeBS, NPWS BWS and trestle study datasets. However, we have only calculated percentage

distributions where we consider the data to be consistent (i.e., excluding counts with poor

coverage and/or low numbers). In addition, NPWS BWS flock map data has also been used.

I-WeBS

2.19 Waterbird distribution has been monitored as part of the Irish Wetland Bird Survey (I-WeBS) each

winter since 1995/96, apart from 2009/10. The I-WeBS scheme aims to carry out monthly counts

each winter between September and March in all sites that are important for non-breeding

waterbird populations. However, this level of coverage is not always possible to achieve in a

volunteer-based scheme. At Dungarvan Harbour, between one to five counts (mean 2.4) have

been carried out each winter. Most counts have been carried out in the mid-winter period

(December-February). The counts are carried out by a coordinated team of three volunteers,

normally all on the same day around the high tide period.

2.20 Most of the Dungarvan Harbour I-WeBS dataset consists of a single count for the entire site. It is

only for 2010/11 and 2011/12, that I-WeBS data for individual subsites, or groups of subsites, is

available. Therefore, our analyses of waterbird distribution from I-WeBS data is restricted to those

two winters.

NPWS BWS

2.21 Details of the NPWS BWS methodology and results at Dungarvan Harbour are described in

Cummins and Crowe (2010) and NPWS (2011c).

Counts

2.22 In the winter of 2009/10, waterbird counts were carried out as part of the National Parks and

Wildlife Service’s Baseline Waterbird Survey (NPWS BWS). Four low tide and one high tide count

were carried out, as well as a separate high tide roost survey. The counts were carried out by a

coordinated team of professional counters. Each count was completed in a single day and there

was complete coverage on each count, apart from one minor subsite (0M426) that was not

covered during the December count (Cummins and Crowe, 2010).

2.23 The NPWS BWS counts were carried out from land-based vantage points. This means that birds

within the trestle blocks on Whitehouse Bank would generally not have been visible and the

counts will have underestimated the numbers of birds occurring on Whitehouse Bank for species

that do not completely avoid the trestles.

2.24 The NPWS BWS counted feeding and roosting birds separately. However, we have not analysed

their distribution separately. In general, birds at low tide usually roost in the same area as they

feed and often the roosting birds are mainly just roosting for short periods of time before resuming


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feeding. Therefore, the division between feeding and roosting may be a matter of chance

depending upon the exact timing of the count.

NPWS BWS flock maps

2.25 As part of the NPWS BWS the approximate position of the main flocks encountered were

mapped. These flock map data have been used to supplement the analyses of species

distribution from the I-WeBS and/or NPWS BWS counts. In particular, the flock map data is useful

in indicating relationships between species distributions and broad topographical/habitat zones,

such as biotopes, edges of tidal channels, upper shore areas, etc.

2.26 There are some limitations to the interpretation of flock map data because of the difficulties of

accurately mapping positions of distant flocks from shoreline vantage points and also the different

observers may have varied in the extent to which they mapped flocks.

Trestle study

2.27 Dungarvan Harbour was included in a study carried out of the relationship between intertidal

oyster cultivation and waterbird distribution (Gittings and O’Donoghue, 2012). This work included

an extensive study across six sites (Dungarvan Harbour) and an intensive study at Dungarvan

Harbour.

2.28 In the extensive study, five coordinated counts were carried out at Dungarvan Harbour between

January and early March 2011 covering the entire Outer Sandflats zone (apart from the mixed

substrata and eulittoral rock biotopes). The zone was divided into 15 sectors (Figure 2.2). On

each count the numbers of all waterbird species were counted in each sector and their location

(within or outside trestle blocks), position (tideline or intertidal) and activity (feeding or

roosting/other) were recorded.

2.29 The intensive study covered a 2-3 km stretch of shore on Whitehouse Bank (Figure 2.2): the 2 km

stretch was covered on each count and used for the main data analyses, while the additional 1 km

stretch was covered on some of the counts. This area contained a mixture of large blocks of

trestles, small blocks of trestles and clear areas. The study area was divided into seven

longitudinal sectors (i.e., sectors orientated perpendicular to the shoreline) and five lateral bands

(i.e., bands that are parallel to the shoreline). The study area was designed so that the tideline

passed through each sector with broadly similar timing.

2.30 Counts for the intensive study were carried out on eight dates during January-March 2011. On

each date, one or two complete counts were carried out, with a total of 13 complete counts being

achieved. Numbers, activity, location (within/outside trestle areas) and position (tideline or

intertidal) of birds in each band of each sector were recorded.

2.31 The extensive and intensive study counts were all carried out during a five hour period centred on

the low tide, which corresponds to the exposure period of the lower shore zone in Whitehouse

Bank. Some additional counts were also carried out on Whitehouse Bank on an opportunistic

basis on ebb/flood tides before the tideline reached the lower shore zone. These counts provide

information on bird usage of Whitehouse Bank during the period when the trestles were not

exposed.


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Assessment methodology

Identification of potential impacts

2.32 Potential negative impacts to SCI species have been identified where the activity may cause

negative impacts to prey resources, where there is evidence of a negative response to the activity

by the species from previous work, and/or where a negative response is considered possible by

analogy to activities that have similar types of impacts on habitat structure and/or by analogy to

ecologically similar species.

2.33 The primary source of information used for the identification of potential impacts is the trestle

study (Gittings and O’Donoghue, 2012). This study used the results of counts of waterbirds within

oyster trestles and in areas of comparable habitat without trestles, and quantification of the

available habitat within and outside the trestles, to analyse the relationship between waterbird

distribution patterns and the presence of oyster trestles. The main analyses used were: ordination

analyses to investigate the influence of oyster trestles on waterbird assemblages (with the position

of species in the ordination providing an indication of their association with oyster trestles); and

comparison of observed numbers within trestle blocks with numbers predicted assuming that birds

are distributed evenly across available habitat. The results of the analyses were used to identify

consistent patterns of positive or negative association with oyster trestles across the sites studied

and categorised species into the following groups: neutral/positive association, negative

association, exclusion response, and variable response (response may vary between sites).

2.34 The trestle study was carried out during periods with typical levels of husbandry activity.

Therefore, the effects of disturbance due to husbandry activity associated with intertidal oyster

cultivation are included in the categorisation of species responses and such disturbance impacts

are not analysed separately in this assessment. However, potential disturbance impacts from

other activities (such as recreational activities) are included in the cumulative assessment.

2.35 The trestle study focused on species associated with the intertidal and/or shallow subtidal

habitats. Three of the SCI species (Red-breasted Merganser, Great Crested Grebe and

Cormorant) are primarily associated with deep (>0.5 m) subtidal habitats, while Peregrine is a

raptor that may feed over intertidal habitats, and the trestle study does not provide information on

their responses to intertidal oyster cultivation. A literature review was carried out to assess the

likely main food resources of these SCI species in the Dungarvan Harbour SPA (see Appendix B)

and to assess the potential impact of intertidal oyster cultivation on these food resources.

Assessment of impact magnitude

Displacement impacts

2.36 Where potential impacts from intertidal oyster cultivation on a SCI species have been identified, or

cannot be ruled out, the spatial overlap between the distribution of the species and the spatial

extent of intertidal oyster cultivation was calculated, or qualitatively assessed when quantitative

data was not available. This overlap is considered to represent the potential magnitude of the

impact, as it represents the maximum potential displacement if the species has a negative

response to intertidal oyster cultivation. Where appropriate, information on species habitat usage

was used to refine the assessment of likely impact magnitude.

2.37 For selected wader species, a detailed assessment methodology was used to quantify the

potential displacement due to intertidal oyster cultivation (see Appendix D). This methodology

used one or more methods (depending upon the species involved) to calculate the expected

numbers that would have occurred on Whitehouse Bank during the 2011 trestle counts in the

absence of intertidal oyster cultivation and then scaled these displacement methods up to predict

the potential displacement impacts from full occupation of the aquaculture plots.


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2.38 The basic method used the mean density of birds recorded on the lower shore zone of

Whitehouse Bank in areas outside the trestle blocks during the trestle study and the percentage of

the lower shore zone of Whitehouse Bank occupied by trestles under the typical tidal conditions

across the trestle study counts to calculate the expected numbers. The difference between the

observed and expected numbers, adjusted for neap tides (see Appendix D), was then used as a

measure of the number of birds potentially displaced due to intertidal oyster cultivation in early

2011. The numbers recorded in I-WeBS counts in January and February 2011 was then used to

express this displacement as a percentage of the total Dungarvan Harbour population. This

method was used for Grey Plover, Dunlin and Bar-tailed Godwit, but could not be applied to Knot

because they occurred too rarely in the lower shore zone to allow meaningful density calculations.

2.39 The basic method assumes that intertidal oyster cultivation is not causing large-scale

displacement (i.e., it is not affecting the occupancy of habitat adjoining oyster trestles). However,

the counts of birds on ebb/flood tides indicated that this assumption was not correct. For Grey

Plover, Dunlin and Knot much larger numbers were generally recorded on ebb/flood tides

compared to at low tide on the same day. It is reasonable to assume that, given the lack of habitat

variation between the upper and lower shore zones in Whitehouse Bank, in the absence of

intertidal oyster cultivation, the numbers recorded on ebb/flood tides and at low tide on the same

day would be similar. Therefore, the mean difference between the ebb/flood tide and low tide

counts, adjusted for neap tides (see Appendix D) was taken as an alternative measure of potential

displacement due to intertidal oyster cultivation.

2.40 Bar-tailed Godwit did not occur in larger numbers on Whitehouse Bank during ebb/flood tides

compared to at low tide. However, the distribution data showed that Bar-tailed Godwit occur in

much higher numbers in Ballyrandle compared to Whitehouse Bank despite the lack of differences

in intertidal biotopes between these two areas. This is an indication of possible large-scale

displacement due to intertidal oyster cultivation. Therefore, for Bar-tailed Godwit, the mean

density of birds recorded on the lower shore zone of Ballyrandle during the trestle study was used

to calculate an alternative measure of potential displacement, using the same process as the

basic method above. However, it should be noted that this method may strongly overestimate the

potential displacement impact.

2.41 To predict the displacement impacts from full occupation of the aquaculture plots we first

calculated the percentages of tideline and intertidal habitat that would be occupied during neap,

mean and spring low tides. We then used the basic method, as above, to calculate the

displacement impacts for each of these tidal conditions and took the mean of the three as the

overall displacement impact.

2.42 We did not carry out any further adjustment to the 2011 displacement impacts calculated using

the ebb/flood tide method and the Ballyrandle densities. Large-scale displacement, if it occurs,

represents an avoidance of the general area including areas not occupied by trestles. Therefore,

large-scale displacement would not be expected to be linearly correlated with the area occupied

by trestles.

Impacts on population trends

2.43 A large intertidal oyster cultivation industry in Dungarvan Harbour has been present for the past

25 years or so. If intertidal oyster cultivation, of the scale being assessed, is likely to have impacts

on population trends this should be detectable from species population trends in Dungarvan

Harbour over the same period. Therefore, to assess the potential impact on population trends we

have assessed species population trends in relation to the periods defined in Table 2.1. For each

of these periods we have compared the Dungarvan Harbour population trend with the national


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trend. If intertidal oyster cultivation caused negative impacts on population trends in Dungarvan

Harbour we would expect the Dungarvan Harbour population trend to be more negative than the

national trend. Where the Dungarvan Harbour population trend is similar to, or more positive than,

the national trend, we have concluded that there is no evidence that intertidal oyster cultivation

has caused negative impacts to the Dungarvan Harbour population trend. It could be argued that,

if both trends are negative, the overall national trend reflects widespread pressures (including

aquaculture activities) across many of the important sites and the Dungarvan Harbour population

decrease may still have been caused by intertidal oyster cultivation. However, the development of

intertidal oyster cultivation in Dungarvan Harbour in the late 1980s/early 1990s generally predates

widespread intertidal aquaculture activity elsewhere in Ireland, so the national population trends

during this period will not have been influenced by widespread aquaculture activity.

2.44 There are some limitations to the above interpretation of species population trends. The only

available data for the 1970s and the 1980s are the published mean annual peak counts in

Sheppard (1993). Without access to the original data it is not possible to look at the variation in

species numbers and assess how reliable the mean annual peaks are as indication of the overall

population levels. Mean annual peaks have now been superseded by calculation of trend indices

to provide more reliable population trends but we do not have any such trend analyses for the

crucial period between the mid-1980s and the mid-1990s. The population trends from 1995/96-

2007/08 should be more reliable. However, the limited number of I-WeBS counts per winter mean

that there are either a high number of imputed counts or the indices are based on a small number

of counts per winter. Either way, the indices could easily be biased by anomalous counts in

winters when there were few counts.

Table 2.1 - Development of intertidal oyster cultivation in Dungarvan Harbour in relation to the

availability of waterbird data and the expected influence on waterbird population trends assuming a

negative impact from intertidal oyster cultivation.

Period Intertidal oyster cultivation* Waterbird data Expected influence on

population trend activity trend pop trend

early 1970s

none

minimal increase

mean annual peak

counts

-

none

mid 1980s

initial trials, only small

scale activity

major increase

mean annual peak

counts (1984/85-1986/87)

-

major negative

mid-1990s

60%-80% of current levels

moderate increase

and movement upshore

mean annual peak

counts (1995/96-1998/99)

population trends

(1995/96-2007/08)

negative

late-2000s

90% of current levels

- -

* see paragraphs 6.2-6.6

Assessment of impact significance

2.45 The methodology used for this Appropriate Assessment is focussed on the Conservation

Objectives, and their attributes, that have been defined and described for the Dungarvan Harbour

SPA (NPWS, 2011c, 2012). These conservation objectives are the same for all the SCI species.

2.46 Conservation Objective 1 defines two types of attributes to assess conservation condition: long

term population trends and numbers or range (distribution) of areas used. This assessment

focuses on assessing potential impacts on the spatial distribution of the SCI waterbird species

within Dungarvan Harbour and, in particular, whether the activities will cause displacement of a


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significant proportion of the Dungarvan Harbour population from the affected area(s). If the

activities are not predicted to cause significant displacement, then the activities are not likely to

affect the long term population trends. If the activities are predicted to cause significant

displacement, then the activities could affect the long term population trends (but see below). In

the cases where the activities are predicted to cause significant displacement, the impacts on

distribution and population size are assessed separately.

2.47 The basis for the assessments are datasets that indicate the distribution of waterbird species

between different broad sectors of Dungarvan Harbour (the I-WeBS and NPWS BWS counts) and

the distribution within the main areas containing oyster trestles (the trestle watch study), and the

information on species responses to intertidal oyster cultivation (the trestle watch study). The

datasets allow calculation, or qualitative assessment, of the proportion of the Dungarvan Harbour

population that would be affected if aquaculture activities cause displacement of birds from areas

occupied by the activities under consideration. This approach can be considered as a very simple

form of habitat association model and represents a conservative form of assessment (see Stillman

and Goss-Custard, 2010): the population-level consequences of displacement will depend upon

the extent to which the remaining habitat is available (i.e., whether the site is at carrying capacity).

In general this assessment method “will be pessimistic because some of the displaced birds will

be able to settle elsewhere and survive in good condition” (Stillman and Goss-Custard, 2010).

2.48 The assessment of potential disturbance impacts is based mainly on the potential for disturbance

to cause displacement of birds from areas they would otherwise occupy. However, where there is

limited availability of alternative habitat, or where the energetic costs of moving to alternative

habitat is high, disturbance may not cause displacement of birds but may still have population-

level consequences (e.g., through increased stress, or reduced food intake, leading to reduced

fitness) (Gill et al., 2001). However, assessing these types of potential impacts would require

detailed population modelling, which would require a major research effort that is beyond the

scope of this assessment.

Assessment of significance

2.49 The significance of any potential impacts identified has been assessed with reference to the

attributes and targets specified by NPWS (2012) for this conservation objective. Potential negative

impacts are either assessed as significant (if the assessment indicates that they will have a

detectable effect on the attributes and targets) or not significant. The significance levels of

potential positive impacts have not been assessed.

Attribute 1 – Long term population trends

2.50 The criteria that we have used for assessing significance with reference to attribute 1 of the

conservation objectives are summarised in Table 2.1 and are described below.

2.51 If the impact is predicted to cause spatial displacement of >25% of the total Dungarvan Harbour

population of a SCI species, then the impact could, pessimistically, cause the long term population

trend to show a decrease of 25% or more. Therefore, the impact would be potentially significant

with reference to attribute 1 of the conservation objective.

2.52 If the long-term population trend of the species is a decrease of 25% or more, and the impact is

predicted to cause spatial displacement of 5% or more (see criteria under Attribute 2), then the

impact could prevent the potential recovery of the population. Therefore, the impact would be

potentially significant with reference to attribute 1 of the conservation objective.

2.53 If the long-term population trend of the species is a decrease of less than 25%, but the

combination of the long-term population trend and the predicted spatial displacement (where the

latter is assessed to be significant; see criteria under Attribute 2) would equal or exceed 25%,

then the impact could cause the long term population trend to show a decrease of 25% or more.


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Therefore, the impact would be potentially significant with reference to attribute 1 of the

conservation objective.

Table 2.2 – Criteria for assessing significance with reference to attribute 1 of the conservation

objectives.

Long-term population decrease (P)

Spatial displacement (S)

Additional criteria Impact

- ≥ 25% - Significant

≥ 25% ≥ 5% - Significant

< 25% ≥ 5% P + S ≥ 25% Significant

Attribute 2 – Number or range (distribution) of areas used

2.54 Assessing significance with reference to attribute 2 is more difficult because the level of decrease

in the numbers or range (distribution) of areas that is considered significant has not been specified

by NPWS. There are two obvious ways of specifying this threshold: (i) the value above which

other studies have shown that habitat loss causes decreases in estuarine waterbird populations;

and (ii) the value above which a decrease in the total Dungarvan Harbour population would be

detectable against background levels of annual variation.

2.55 There have been some studies that have used individual-based models (IBMs; see Stillman and

Goss-Custard, 2010) to model the effect of projected intertidal habitat loss on estuarine waterbird

populations. West et al. (2007) modelled the effect of percentage of feeding habitat of average

quality that could be lost before survivorship was affected. The threshold for the most sensitive

species (Black-tailed Godwit) was 40%. Durell et al. (2005) found that loss of 20% of mudflat area

had significant effects on Oystercatcher and Dunlin mortality and body condition, but did not affect

Curlew. Stillman et al. (2005) found that, at mean rates of prey density recorded in the study, loss

of up to 50% of the total estuary area had no influence on survival rates of any species apart from

Curlew. However, under a worst-case scenario (the minimum of the 99% confidence interval of

prey density), habitat loss of 2-8% of the total estuary area reduced survival rates of Grey Plover,

Black-tailed Godwit, Bar-tailed Godwit, Redshank and Curlew, but not of Oystercatcher, Ringed

Plover, Dunlin and Knot. Therefore, the available literature indicates that generally quite high

amounts of habitat loss are required to have significant impacts on estuarine waterbird

populations, and that very low levels of displacement are unlikely to cause significant impacts.

However, it would be difficult to specify a threshold value from the literature as these are likely to

be site specific.

2.56 If a given level of displacement is assumed to cause the same level of population decrease (i.e.,

all the displaced birds die or leave the site), then displacement will have a negative impact on the

conservation condition of the species. However, background levels of annual variation in recorded

waterbird numbers are generally high, due to both annual variation in absolute population size and

the inherent error rate in counting waterbirds in a large and complex site. Therefore, low levels of

population decrease will not be detectable (even with a much higher monitoring intensity than is

currently carried out). For example, a 1% decrease in the baseline population of Turnstone would

be a decrease of two birds. The minimum error level in large-scale waterbird monitoring is

considered to be around 5% (Hale, 1974; Prater, 1979; Rappoldt, 1985). Therefore, any

population decrease of less than 5% is unlikely to be detectable and, for the purposes of this

assessment, 5% has been taken to be the threshold value below which displacement effects are

not considered to be significant. This is a conservative threshold, as error levels combined with

natural variation are likely to, in many cases; prevent detectability of higher levels of change. This

threshold is also likely to be very conservative in relation to levels that would cause reduced

survivorship (see above).


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Summary

2.57 Impacts have been assessed as potentially having a significant negative impact on attribute 1 of

the conservation objectives (the species’ long-term population trend), if they are predicted to

cause:

Displacement of 25% or more of the Dungarvan Harbour total; or

Significant displacement levels (i.e., 5% or greater; see below) that combined with current

long-term population trends, could result in a long-term population decline of 25%; or

Significant displacement levels (i.e., 5% or greater; see below) where the current long-term

population trends is already equal to or greater than 25%.

2.58 Impacts that will cause displacement of 5% or more of the total Dungarvan Harbour population of

a SCI species have been assessed as potentially having a significant negative impact on attribute

2 of the conservation objectives (the species’ distribution within Dungarvan Harbour). In this

context, displacement may involve birds moving to other areas within the SPA or leaving the site

altogether.

2.59 The 25% threshold has been derived from the NPWS conservation objectives. The 5% threshold

is based on the rationale presented above (paragraphs 2.54-2.56).


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Figure 2.1 – Subsites used in the NPWS BWS survey and zones used for broad-scale analysis of

waterbird distribution.

Figure 2.2 - Areas covered in the trestle study.


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3. Conservation objectives

Dungarvan Harbour SPA

Qualifying features

3.1 The Special Conservation Interests (SCIs) of the Dungarvan Harbour SPA include non-breeding

populations of Light-bellied Brent Goose, Shelduck, Red-breasted Merganser, Great Crested

Grebe, Oystercatcher, Golden Plover, Grey Plover, Lapwing, Knot, Dunlin, Black-tailed Godwit,

Bar-tailed Godwit, Curlew, Redshank and Turnstone.

3.2 In addition:

The wetland habitats contained within Dungarvan Harbour SPA are identified to be of

conservation importance for non-breeding (wintering) migratory waterbirds. Therefore the wetland

habitats are considered to be an additional Special Conservation Interest.

(NPWS, 2012)

3.3 The SCIs are divided into Selection Species and Additional Special Conservation Interests.

However, this distinction has no relevance for the Appropriate Assessment process and is,

therefore, not referred to further in this assessment.


SCI species

3.4 The conservation objectives for the Light-bellied Brent Goose, Shelduck, Red-breasted

Merganser, Great Crested Grebe, Oystercatcher, Golden Plover, Grey Plover, Lapwing, Knot,

Dunlin, Black-tailed Godwit, Bar-tailed Godwit, Curlew, Redshank and Turnstone non-breeding

populations at Dungarvan Harbour are to maintain their “favourable conservation condition”

(NPWS, 2011c).

3.5 The favourable conservation conditions of these species at Dungarvan Harbour are defined by

various attributes and targets, which are shown in Table 3.1.

Table 3.1 – Attributes and targets for the conservation objectives for Light-bellied Brent Goose,

Shelduck, Red-breasted Merganser, Great Crested Grebe, Oystercatcher, Golden Plover, Grey Plover,

Lapwing, Knot, Dunlin, Black-tailed Godwit, Bar-tailed Godwit, Curlew, Redshank and Turnstone at

Dungarvan Harbour.

Attribute Measure Target Notes

1 Population trend

Percentage trend

Long term population trend stable or increasing

Waterbird population trends are presented in part four of the Conservation Objectives Supporting Document [NPWS, 2011c].

2 Distribution Number and range of areas used by waterbirds

There should be no significant decrease in the numbers or range of areas used by waterbird species, other than that occurring from natural patterns of variation

As determined by regular low tide and other waterbird surveys. Waterbird distribution from the 2009/10 waterbird survey programme is discussed in Part Five of the conservation objectives supporting document [NPWS, 2011c.

Source: NPWS (2012)

Attributes are not numbered in NPWS (2012), but are numbered here for convenience


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Wetlands and waterbirds

3.6 The conservation objective for wetlands and waterbirds at Dungarvan Harbour is to “maintain the

favourable conservation condition of the wetland habitat in Dungarvan Harbour SPA as a resource

for the regularly-occurring migratory waterbirds that utilise it” (NPWS, 2012).

3.7 The favourable conservation condition of the wetland habitat at Dungarvan Harbour is defined by

a single attribute and target, which is shown in Table 3.2.

Table 3.2 – Attribute and target for the conservation objective for wetlands and waterbirds at

Dungarvan Harbour.

Attribute Measure Target Notes

Habitat area Hectares The permanent area occupied by the wetland should be stable and not significantly less than the area of 2,291 ha other than that occurring from natural patterns of variation.

The wetland habitat area was estimated as 2,291 ha using OSi data and relevant orthophotographs. For further information see Part Three of the Conservation Objectives Supporting Document

Source: NPWS (2011c)

Helvick Head to Ballyquin SPA

Qualifying features

3.8 The Special Conservation Interests (SCIs) of the Helvick Head to Ballyquin SPA are breeding

populations of Cormorant, Peregrine, Herring Gull, Kittiwake and Chough.


3.9 The conservation objectives for the Cormorant, Peregrine, Herring Gull, Kittiwake and Chough

breeding populations at Helvick Head to Ballyquin are to maintain or restore their “favourable

conservation condition” (NPWS, 2011a).

3.10 NPWS have only published generic conservation objectives for the Helvick Head to Ballyquin

SPA. Therefore, there are no site-specific attributes and targets to define the favourable

conservation condition of these species.

Mid-Waterford Coast SPA

Qualifying features

3.11 The Special Conservation Interests (SCIs) of the Mid-Waterford Coast SPA are breeding

populations of Cormorant, Peregrine, Herring Gull and Chough.


3.12 The conservation objectives for the Cormorant, Peregrine, Herring Gull and Chough breeding

populations at Mid-Waterford Coast are to maintain or restore their “favourable conservation

condition” (NPWS, 2011a).

3.13 NPWS have only published generic conservation objectives for the Mid-Waterford Coast SPA.

Therefore, there are no site-specific attributes and targets to define the favourable conservation

condition of these species.


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4. Screening


Preliminary screening

4.1 All of the SCI species (Light-bellied Brent Goose, Shelduck, Red-breasted Merganser, Great

Crested Grebe, Oystercatcher, Golden Plover, Grey Plover, Lapwing, Knot, Dunlin, Black-tailed

Godwit, Bar-tailed Godwit, Curlew, Redshank and Turnstone) make significant use of subtidal

and/or intertidal habitat in Dungarvan Harbour. The intertidal oyster cultivation covered in this

assessment will affect 278 ha of intertidal habitat and have the potential to cause significant

changes to habitat structure and/or food availability. Therefore, the activities being assessed could

potentially have significant impacts on SCIs that use subtidal and/or intertidal habitat.

4.2 The trestle study (Gittings and O’Donoghue, 2012) showed that Oystercatcher, Curlew, Redshank

and Turnstone have neutral or positive responses to intertidal oyster cultivation. Therefore, these

species can be screened out from further assessment.

4.3 The other SCI species either have negative responses to oyster trestles (Shelduck, Golden

Plover, Grey Plover, Lapwing, Knot, Dunlin, Black-tailed Godwit and Bar-tailed Godwit) or

uncertain or unknown responses (Light-bellied Brent Goose, Red-breasted Merganser and Great

Crested Grebe).

4.4 Shelduck and Lapwing have negative responses to intertidal oyster cultivation but occur almost

exclusively in the Inner Harbour zone of Dungarvan Harbour, while Black-tailed Godwit, which

also has a negative response to intertidal oyster cultivation, only uses the northern side of the

Outer Sandflats zone. The distribution of these species does not overlap with the areas affected

by intertidal oyster cultivation, and the habitat condition in Whitehouse Bank are considered to be

generally unsuitable for these species (see Appendix C). Therefore, these species have been

screened out from further assessment.

4.5 Therefore, full appropriate assessment is required for the following species: Light-bellied Brent

Goose, Red-breasted Merganser, Great Crested Grebe, Golden Plover, Grey Plover, Knot,

Dunlin, and Bar-tailed Godwit.

Wetlands and waterbirds

4.6 The Conservation Objectives define the favourable conservation condition of the wetlands and

waterbird SCI at Dungarvan Harbour purely in terms of habitat area.

4.7 None of the activities being assessed will cause any change in the permanent area occupied by

wetland habitat. Therefore, the activities being assessed are not likely to have any significant

impact on this SCI and it has been screened out from any further assessment.


Preliminary screening

4.8 The Helvick Head to Ballyquin SPA is around 2 km from the intertidal oyster cultivation area at

their nearest points. Therefore, there is potential for birds from the SPA populations to occur

within the licensed area, if the habitat conditions are suitable.

4.9 Two of the SCI species (Kittiwake and Chough) are unlikely to have any spatial overlap with

aquaculture activities in Dungarvan Harbour. Kittiwake is a seabird that usually feeds in open

marine waters. They may come in to the outer part of Dungarvan Bay but do not usually feed in


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intertidal habitat, even when it is covered at high tide. Chough feeds in terrestrial habitats and

does not utilise intertidal or subtidal habitats.

4.10 The SPA populations of the other three SCI species (Cormorant, Peregrine and Herring Gull)

could have spatial overlap with aquaculture activities in Dungarvan Harbour (see Section 9).

These species have an unknown or uncertain response to intertidal oyster cultivation. Therefore,

full appropriate assessment is required for these species.


4.11 The Mid-Waterford Coast SPA is around 6 km from the intertidal oyster cultivation area at their

nearest points. Therefore, there is potential for birds from the SPA populations to occur within the

licensed area, if the habitat conditions are suitable.

4.12 One of the SCI species (Chough) is unlikely to have any spatial overlap with aquaculture activities

in Dungarvan Harbour, as it feeds in terrestrial habitats and does not utilise intertidal or subtidal

habitats.

4.13 The SPA populations of the other three SCI species (Cormorant, Peregrine and Herring Gull)

could have spatial overlap with aquaculture activities in Dungarvan Harbour (see Section 10).

These species have an unknown or uncertain response to intertidal oyster cultivation. Therefore,

full appropriate assessment is required for these species.


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5. Status and habitats and distribution of the SCI

species


Waterbird monitoring

5.1 Waterbird distribution around high tide has been monitored by as part of the Irish Wetland Bird

Survey (I-WeBS) during most winters since 1994/95 (see paragraphs 2.19-2.20).

Waterbird status

5.2 The conservation condition and trends of the Dungarvan Harbour SCI species included in this

assessmentare summarised in Table 5.1. Species with unfavourable conservation condition are

Red-breasted Merganser, Great Crested Grebe, Golden Plover and Grey Plover (intermediate

(unfavourable)) and Dunlin (unfavourable). These species also have decreasing all-Ireland trends.

Table 5.1 – Conservation condition and population trends of the SCI assessment species at

Dungarvan Harbour.

Special Conservation Interests (SCIs)

Site Conservation Condition

12 year site

population trend

1

5 year site population

trend2

Current all-

Ireland Trend

3

Current international

trend4

Light-bellied Brent Goose Favourable +91.1 +27.3 +58 Increase

Red-breasted Merganser Intermediate (unfavourable) -15.4 -9.4 -11 n/c

Great Crested Grebe Intermediate (unfavourable) -14.5 -20 -18 Decline

Golden Plover Intermediate (unfavourable) -18.5 -29.3 -2.2 Decline

Grey Plover Intermediate (unfavourable) -11.2 -2.8 -33.1 Decline

Knot Favourable +10 +29.5 -2.91 Decline

Dunlin Unfavourable -38.4 -16.6 -46.5 Stable (alpina)

Bar-tailed Godwit Favourable +6.7 -14.5 +1.5 Stable

Source: Tables 4.2 and 4.2 in NPWS (2011)

n/c = not calculated. 1site population trend analysis, 12 yr = 1994–2007;

2 site population trend analysis, 5 yr = 2002–

2007; 3all-Ireland trend calculated for period 1994/95 to 2008/09;

4 international trend after Wetland International (2006)

Waterbird habitats and distribution

Tidal patterns

5.3 The mean low water neap for Dungarvan Harbour is 1.1 m, while the mean low water spring is 0.4

m (www.visitmyharbour.com/harbours/east-and-south-of-ireland/dungarvan-helvick/). Therefore,

the mean low water level has been defined as 0.7 m for the purposes of this assessment.

5.4 The intertidal habitat within the Inner Harbour zone is more or less fully exposed on all low tides.

However, the extent of tidal exposure in the Outer Sandflats varies considerably between neap

and spring low tides. Under extreme neap tides (1.4-1.5 m) the tideline barely reaches the lower

shore zone and the oyster trestles are largely not exposed, while under extreme spring tides (0-

0.2 m) the tideline falls to well below the area currently occupied by trestles. The approximate

patterns of tidal exposure under neap, mean and spring low tides are shown in Figure 5.1.

Habitats

5.5 The intertidal habitats in the Dungarvan Harbour SPA were classified into 12 biotopes by Aquatic

Services Unit (2009; Figure 5.2) while the mapping in NPWS (2011d) only distinguishes three


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broad benthic communities (Figure 5.3). Both sets of mapping show the broad division between

the sandy sediments in the Outer Sandflats zone and the more muddy sediments in the Inner

Harbour. The Outer Sandflats zone is mapped as the Polychaetes and Angulus tenuis in littoral

fine sand (LS.LSa.FiSa.Po.Aten) biotope by Aquatic Services Unit (2009) and the fine sand with

Angulus tenuis and Scolopos armier community complex by NPWS (2011d). The Aquatic

Services Unit map shows important habitat distinctions that are not represented in the NPWS

map, including the area of mixed substrata (LR.FLR.Eph.EphX) and eulittoral rock

(LR.MLR.BF.FserF) biotopes on the Ballyrandle side of the Outer Sandflats zone and the

distinction between the sediments on the outer and inner sides of the Cunnigar (which is obvious

in the field). However, it is not clear how reliable the boundaries of some of the minor biotope

areas are: for example, Lanice conchilega beds occur much more widely across the lower shore

zone of Whitehouse Bank than indicated by the biotope map.

5.6 The subtidal habitats in the Outer Bay Zone and along the main tidal channel are mainly less than

5 m deep (Admiralty Chart data; depths are relative to the lowest astronomical tide). The subtidal

biotopes have not been mapped.

5.7 Historically, Dungarvan Harbour has supported sizeable seagrass (Zostera) beds, which are an

important habitat for various waterbird species (including Light-bellied Brent Goose). These were

first mapped in 1970 (Guiry and Kilty, 1972). At this time, there were three beds: a large bed on

the outer part of Whitehouse Bank, another bed just inside the Cunnigar and a third small bed at

Ringnasilloge (Figure 5.4). All three beds were still present in 1992, but the Whitehouse Bank bed

had been substantially reduced in size (Figure 5.5; NATURA Environmental Consultants and

Robinson, 2003)1. By 2013, both the Whitehouse Bank and Ringnasilloge beds had disappeared

and the Cunnigar bed had reduced in size (data supplied by Robert Wilkes, EPA). The area

previously occupied by the Whitehouse Bank bed is now largely occupied by oyster trestles, and

the the loss of this bed is considered to be likely to be a direct result of the development of

intertidal oyster cultivation in Dungarvan Harbour (see paragraphs 7.3-7.5). The Ringnasilloge bed

may have been lost due to smothering by opportunistic macroalgae, while the Cunnigar bed

shows recent signs being affected by blanketing by opportunistic green seaweeds (Robert Wilkes,

EPA, pers. comm.).

Distribution

5.8 Detailed analyses of species distribution patterns are included in the impact assessment sections

of relevant activities later in this document. The following text summarises the broad distribution

patterns derived from these analyses.

5.9 Species associated with intertidal habitat occur mainly in the Inner Harbour and/or Outer Sandflats

zone. The habitat differences between these zones influence the distribution of some species with

Shelduck and Lapwing largely confined to the Inner Harbour while Golden Plover and Bar-tailed

Godwit are largely confined to the Outer Sandflats zone. However, other species occur across

both zones. Within the Inner Harbour zone, the area between the Cunnigar and the River Brickey

tidal channel appears to be favoured by several species (also reflecting biotope differences). In

the Outer Sandflats zone, Knot, Black-tailed Godwit and Bar-tailed Godwit show a strong

preference for the Ballyrandle Sandflats, while Grey Plover mainly occurs on Whitehouse Bank.

Several species (including Grey Plover, Knot and Dunlin can occur on Whitehouse Bank in large

numbers on ebb/flood tides moving to Inner Harbour as the tideline reaches the lower shore zone.

5.10 Species associated with subtidal habitats show contrasting distribution patterns (at high tide) with

Red-breasted Merganser occurring mainly in the Inner Harbour and Outer Sandflats zones, Great

1 Note that the digitisation of the 1970 and 1992 Zostera mapping was approximate so minor differences in the position

and extent of the beds are not necessarily real.


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Crested Grebe mainly in the Outer Bay and Outer Sandflats zones and Cormorant mainly in the

Inner Harbour and Outer Bay zones.


SCI species status and distribution

5.11 No information is available on Peregrine status or distribution in this SPA.

5.12 Population data for seabird colonies in this SPA is included in the Seabird 2000 dataset, while

more recent data on some colonies is also included (Table 5.2). However, there has been no

assessment of the conservation condition of the SCI seabird species in this SPA. Herring Gulls

are distributed along most of the coastline of the SPA, with the main colony at Helvick Head, while

Cormorant is restricted to a few scattered colonies.

Table 5.2 - Seabird population data for the Helvick Head to Ballyquin SPA.

Cormorant Herring Gull

Site 1999 2008 1999 2008

Crobally to Paulsworth 23 5 14

Ballymacart to Crobally 2 6 3

Ballymacart East 3 2

Mine Head West 2 10 4

Seaview to Ballycurreen 2 18 6

Mine Head East 11 8

Ballynamona 63 21 6

Seaview to Ballycurreen 1 2

Muggort's Bay 1 11

Helvick Head 1 41

Totals 83 25 116 37

All figures are occupied nests or occupied territories


5.13 No information is available on Peregrine status or distribution in this SPA.

5.14 Population data for seabird colonies in this SPA is included in the Seabird 2000 dataset (Table

5.2). However, there has been no assessment of the conservation condition of the SCI seabird

species in this SPA. Herring Gulls are distributed along most of the coastline of the SPA, while

Cormorant are restricted to a few scattered colonies.


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Table 5.3 - Seabird population data for the Mid-Waterford Coast SPA.

Site Cormorant Herring Gull

Ballyvoile Head 2 7

Ballyvoile Head 1 37 6

Island 3

East of Island 1 8

Stradbally West 1

Ballyvoorey to Stradbally 2 9

Stradbally Gull Island 39 16

Ballyvoorey to Stradbally 1 1

Ballydowane to Stradbally3 2

Ballydowane to Stradbally1 6

Bunmahon to Ballydowane3 13

Bunmahon to Ballydowane2 29 17

Bunmahon to Ballydowane1 24

Kilmurrin to Bunmahon 3 1



Dunbrattin Head east 2

Kilmurrin east 6

Dunbrattin Head west 21

Kilfarassy Stack 24 5

Kilfarassy Islands 9

Sheep Island 4

Garrarus East 2

Garrarus Gull Island 19

Illaunglass 13 6

Great Newtown Head South 3

Totals 161 176

All figures are occupied nests or occupied territories. All data from 1999-2000.


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Figure 5.1 - Approximate tideline alignments at low tide under various tidal conditions.

Figure 5.2 - Intertidal biotopes in Dungarvan Harbour as mapped by Aquatic Services Unit (2009).


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Figure 5.3 - Benthic communities in Dungarvan Harbour as mapped by NPWS (2011d) (reproduced

with permission).

Figure 5.4 - Zostera distribution in 1970.


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Figure 5.5 - Zostera distribution in 1992 and 2013.


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6. Intertidal oyster cultivation in Dungarvan Harbour

Scope of activity

6.1 Within the Dungarvan Harbour SPA there are currently 35 plot licensed (covering 203 ha) for

intertidal oyster cultivation (Figure 6.1). There are an additional 20 plots with applications for

licenses (covering 75 ha) for intertidal oyster cultivation. The licensed sites and application areas

(collectively referred to as aquaculture plots, hereafter) are all in a single contiguous block

spanning the lower intertidal and upper subtidal zone on Whitehouse Bank in the Outer Sandflats

zone.

History of activity

6.2 Aquaculture plots were first licensed in 1993, with additional licenses issued up to 2010 (Figure

6.2). However, the licensing date is not an accurate indication of the start of cultivation. In fact.

intertidal oyster cultivation began in Dungarvan Bay in 1983 when trestles were placed in the inner

bay, west of the Cunnigar. However, this area was too muddy and was found to be unsuitable for

intertidal oyster cultivation. The activity then switched to the Whitehouse Bank, where the first

trestles were installed in 1985, at the southern end of the area now occupied by the main block of

trestles (Plot T04/004; Figure 6.3). It is estimated that 100 trestles were placed in 1986 (based on

0.5 million seed at a density of 5000 seed/trestle. The activity by this producer (Dungarvan

Shellfish) increased steadily over the next few years with annual inputs of seed reaching 2 million

seed by 1990, and with 4 million half-grown oysters in the same year.

6.3 Intertidal oyster cultivation by Bia Mara Deise Teo began in 1989 with 500-1000 trestles in a plot

towards the southern end of Whitehouse Bank (Plot T04/017; Figure 6.3). By 1994, this operator

had 10,000-20,000 trestles distributed across two plots, with 10 million seed and 200 tonnes of

mussel for sale in 1995. The Fisherman’s Co-op started operation in 1991 in small plots at the

southern end of Whitehouse Bank. Details of the development of cultivation in the plots held by

the other major operator in Dungarvan (PKA) are not available.

6.4 The extent of the areas occupied by trestles in various years since 2000 is shown in Figure 6.4-

Figure 6.6. Between 2000 and 2011 there was a gradual shift landward, with little change in the

alignment of the trestles between 2011 and 2013. The areas occupied by trestles in these years

are shown in Table 6.1. There was an overall increase of 23 ha across this period, with the main

increase taking place between 2005 and 2011.

Table 6.1 - Extent of area occupied by trestles between 2000 and 2013.

Year Trestle area Increase rate Source

2000 82 ha OSI orthophotography

2005 88 ha 1.2 ha/year OSI orthophotography

2011 102 ha 3.0 ha/year Trestle study

2013 105 ha 1.5 ha/year Marine Institute


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Text Figure 6.1. Oyster production in Dungarvan Bay from data supplied by BIM.

6.5 Production data is available from 1996 (Text Figure 6.1). This shows two main phases of

increase: from 1996-2000 and from 2002-2007. The first phase of increase may represent an

increase in productive area (i.e., an increase in the area occupied by trestles), but may also, in

part at least, be an artefact of poor quality data at the start of that period. The second phase of

increase probably represents, in part at least, increased efficiency of production. The area

occupied by trestles only increased by around 25% between 2000 and 2013 while production has

increased by nearly 100%. In 2003/04, a big clean-up operation was carried out and the trestles

were re-arranged into double-rows (Brian O’Loan, pers. comm.; O’Loan, 2014). It should also be

noted that the reliability of the production data has been questioned by the producers, and, in

particular, the data for 1995/96 is considered to be an underestimate (according to the operators).

6.6 For the purposes of this assessment, it is necessary to assess the likely extent of oyster trestles

over the period from 1985-2000 so that waterbird population trends can be related to the

development of intertidal oyster cultivation activity. From the information reviewed above, it is

clear that there was minimal activity during 1984/85-1986/87 (the period corresponding to the

waterbird monitoring data from the mid-1980s). Taking account of the probable underestimate of

production levels in 1995/96, there was little change in production levels between the mid-1990s

and 2000. Combining the information from Figure 6.2 and Figure 6.3 suggests that production had

begun by the mid-1990s in most of the plots with trestles present in 2000. De Grave (1998) refers

to the site they studied in 1995 as “the most north-eastern site” which had been in production for

about six years and occupied an area of 12.5 ha; this would correspond to the area occupied by

trestles in 2000 in the two most northern plots that had been licensed by 1995 (excluding the very

thin plot at the extreme northern end). The rates of increase in trestle area between 2000 and

2013, if extrapolated backwards, would give an area of 67-76 ha occupied by trestles in 1995 (80-

90% of the area occupied in 2000 and 64-73% of the area occupied in 2013). Therefore, it seems

reasonable to assume that the area occupied by trestles in the late 1990s was not much smaller

than the area occupied in 2000. A minimum figure for the area occupied by trestles in 1995 of at

least 60% of the 2013 levels has been used in this assessment.


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Description of activity

6.7 This section presents only a brief summary of the main characteristics of the activity as detailed

aquaculture profiling is being carried out by BIM.

6.8 All existing and proposed aquaculture activity in Dungarvan Harbour involves suspended oyster

cultivation using bags and trestles in the intertidal zone (intertidal oyster cultivation). The oyster

trestles vary in height but are typically do not exceed 0.5 m height and their height above the

sediment is often less as they sink into the sediment. Some plots at Dungarvan Harbour hold taller

trestles.

6.9 The trestles are usually arranged in paired rows with a separation of around 4 m between rows

and with wider (10-20 m) access lanes (Plates 6.1 and 6.2). The rows are usually orientated more

or less perpendicularly to the tideline. Prior to 2003/04, the trestles were arranged in blocks of four

rows (Brian O’Loan, BIM, pers. comm.).

6.10 Oyster spat is supplied by hatcheries and is placed in mesh bags. These mesh bags placed on

top of the trestles, where they are on-grown until they are ready for harvesting (Plate 6.3). The

function of the trestles is to keep the animals off the seabed, preventing grit getting inside the

oysters, providing increased water flow and allowing suitable shell growth. The mesh bags

facilitate handling and prevent predation (Heffernan, 1999).

6.11 Oyster husbandry activities at Dungarvan Harbour take place during most low tides throughout

most of the year, although there may be quite periods in summer (July/August) and around

Christmas. Workers usually access the trestles by driving tractors across the beach and will often

drive through shallow water on the receding tide to make the most use of the time available. The

tractors use three access routes: from the slip at Moat at the southern end of Whitehouse Bank,

from the car park at the southern end of the Cunnigar and from the Cunnigar around 500 m north

of the car park (Figure 6.1). Tractors also frequently travel between plots by travelling across open

areas of intertidal habitat: in particular, tractors frequently drive along the intertidal habitat

adjacent to the upper edge of the main block of trestles and across the open intertidal habitat

separating the main block of trestles from trestle blocks to the south. During the trestle study, 9-13

tractors were present on the beach on each count day.

6.12 Typically a group of around 5-10 workers work along one-three adjacent rows of trestles (Plate

6.4). Husbandry activities involve turning the mesh bags every spring tide to rid the bags of any

settled silt, stop the growth of oyster shell into the mesh and destroy fouling organisms

(Heffernan, 1999). The level of husbandry activity appears to vary between plots, with some areas

having very “clean” bags and other areas having bags covered with seaweed.

6.13 Only a proportion of the trestles hold oyster bags at any one time. During the trestle study, trestles

were moved in some plots, and the occupancy (placement of bags on the trestles) of different

parts of individual trestle blocks frequently changed between consecutive counts.


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Figure 6.1 - Aquaculture plots in Dungarvan Harbour.

Figure 6.2 - Date of licensing of licensed and surrendered aquaculture plots in Dungarvan Harbour.


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Figure 6.3 - Dates of first cultivation in aquaculture plots at Dungarvan Harbour.

Figure 6.4 - Extent of oyster trestles in Dungarvan Harbour in 2000 and 2005.


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Plate 1 - Oyster trestles at Dungarvan Harbour showing typical arrangement of single and paired rows and

variation between clean bags and bags with covering of algae.

Plate 6.2 - Access lane in the main oyster trestle block at Dungarvan Harbour.


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Plate 6.3 - Oyster bag on a trestle at Ballymacoda Bay.

Plate 6. 4 - Oyster husbandry activity at Dungarvan Harbour.


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7. Potential impacts of intertidal oyster cultivation

Introduction

7.1 This section provides a review of the potential impacts of suspended oyster cultivation using bags

and trestles in the intertidal zone (referred to hereafter as intertidal oyster cultivation). It provides a

framework for the detailed assessment of likely impacts on individual species in Sections 8-9.

Habitat changes

Habitat structure

7.2 Intertidal oyster cultivation causes a significant alteration to the intertidal habitat through the

placement of physical structures (oyster trestles) on the intertidal habitat. This alteration may alter

the suitability of the habitat for waterbirds by interfering with sightlines and/or creating barriers to

movement. Based on the characteristics of species showing positive/neutral or negative

responses to trestles, we have hypothesised, based on the results of the trestle study, that trestles

may interfere with flocking behaviour causing species that typically occur in large, tightly packed

flocks to avoid the trestles. Trestles could also interfere with the visibility of potential predators

causing increased vigilance and reduced foraging time, while they may also interfere with the

ability of hunting raptors to detect and capture prey.

Food resources

Zostera

7.3 Intertidal oyster cultivation may cause impacts to seagrass (Zostera) beds, which are an important

food resource for various waterbirds including Light-bellied Brent Goose

7.4 A number of studies have reported negative impacts from off-bottom oyster cultivation on Zostera

(Everett et al., 1995; Skinner et al., 2013; Tallis et al., 2009; Wisehart et al., 2007), although

longline cultivation may only have minor impacts (Tallis et al., 2009), while hanging basket

cultivation has been reported to have negligible impacts (Bulmer et al., 2012). In addition, while

impacts may be detected in controlled small-scale studies (as in the studies cited above), Ward et

al. (2003) found that development of off-bottom oyster cultivation was not associated with large-

scale, long-term changes in Zostera distribution. The above studies are all from New Zealand and

North America and variously attribute the impacts on Zostera to sedimentation/erosion effects

and/or shading. The potential impacts of vehicular traffic associated with husbandry activity does

not appear to have been considered in the above research.

7.5 In Dungarvan Harbour, the loss of the major Zostera bed on Whitehouse Bank has coincided with

the development of intertidal oyster cultivation in this area and has been described as being

“probably due to the extensive traffic to the oyster farm” (Robert Wilkes, EPA, pers. comm.). The

area originally occupied by the Zostera bed is now largely occupied by oyster trestles (Figure 5.4

and Figure 5.5; see also footnote to paragraph 5.7). However, another (albeit small) Zostera bed

has also disappeared during the same time period and the remaining bed is substantially reduced

in size (see paragraph 5.7). These other beds are physically separated from the intertidal oyster

cultivation area and their decline/disappearance must be due to unrelated factors. Therefore, it is

possible that other processes within Dungarvan Harbour could have contributed to, or entirely

caused, the disappearance of the Whitehouse Bank Zostera bed. However, given the well-

established negative association between off-bottom oyster cultivation and Zostera beds, and

based on the precautionary principle, we have assumed for the purposes of this assessment that

intertidal oyster cultivation has been a significant contributory factor in the disappearance of the

Whitehouse Bank Zostera bed.


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Benthic fauna

7.6 Intertidal oyster cultivation may cause impacts to benthic invertebrates through sedimentation and

eutrophication, and this could potentially affect food resources for waterbird species.

7.7 In a review of the literature, Dumbauld et al. (2009) found variation in the effects of intertidal

oyster cultivation on the benthic fauna. In studies in England, France and New Zealand, intertidal

oyster cultivation caused increased biodeposition, lower sediment redox potential and reduced

diversity and abundance of the benthic fauna. However in studies in Ireland and Canada, few

changes in the benthic fauna were reported, due to high currents preventing accumulation of

biodeposits.

7.8 The Irish study referred to above was carried out at Dungarvan Harbour (De Grave et al., 1998).

This study compared an oyster trestle block (in the north-eastern section of the main block of

trestles) with a control site approximately 300 m away, with both areas being at the mean tide

level. Within the trestle block areas underneath trestles and areas in access lanes were

compared. The study found no evidence of elevated levels or organic matter or high densities of

organic enrichment indicator species within the trestle blocks. There were minor differences in the

benthic community between the control area and the areas sampled under the trestles (higher

densities of Nephtys hombergii, Bathyporeia guiiliamsoniana, Gammarus crinicomis,

Microprotopus maculatus and Tellina tenuis including increased abundance of Capiteila capitata

in the latter area), but these were considered to be probably due to increased predation by

epifaunal decapods and fishes. There appeared to be stronger changes in the benthic community

in the access lanes with increased densities of three polychaete species (Scolopos armiger,

Eteone longa and Sigalion mathildae) and higher overall diversity, and these changes were

considered to be due to the compaction of the habitat by vehicular traffic.

7.9 In more recent work commissioned by the Marine Institute, Kennedy et al. (in prep.) looked at

benthic invertebrates along access tracks, under trestles and in close controls at a number of sites

nationally, including Dungarvan Harbour. There was a strong site effect from the study in that

significant differences were observed using a variety of invertebrate response (dependent)

variables among the sites. Access routes were considered more disturbed than trestle and control

locations; most likely due to the influence of compaction from regular vehicle movements.

Abundance (among other variables) was significantly higher in control and trestle samples when

compared with those derived from access routes. No noticeable difference between control and

trestle samples was detected. Therefore, the site-specific research indicates that intertidal oyster

cultivation in Dungarvan Harbour is unlikely to have had major impacts on food resources for

waterbirds that feed on benthic fauna (F O’Beirn pers comm.).

Fish

7.10 Dumbauld et al. (2009) also reviewed studies of the effects of bivalve shellfish aquaculture on

nekton (fish and mobile invertebrates such as crabs). There was only one study that specifically

examined intertidal oyster cultivation using bags and trestles (Laffargue et al., 2006). This study

found that, in an experimental pond mesocosm, sole used the oyster trestles as resting areas

during the day, moving out into the open areas (which simulated tidal flats) to forage at night and

the authors considered that the “oyster trestles offered cover, camouflage, and safety and were

therefore attractive to sole (as artificial reef-structuring effects)”. Similarly, De Grave et al., (1998)

noted that the trestles in their Dungarvan Harbour study site acted as refuges for scavenging

crabs and shrimps. There were also a number of studies reviewed by Dumbauld et al. (2009) of

related types of oyster cultivation (included suspended culture in subtidal waters, rack and bag

systems, longlines and oyster grow-out cages). These all involve placing physical structures in the

intertidal or subtidal waters and the potential impacts from organic enrichment and benthic

community changes associated with oyster cultivation, so provide some degree of analogous

situations to intertidal oyster cultivation using bags and trestles. These have generally found either


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little differences between oyster cultivation areas and nearby uncultivated habitats, or higher

densities of nekton in the oyster cultivation areas.

7.11 In addition to the alteration of the physical habitat, aquaculture could also, theoretically, have

impacts on fish populations through reduced recruitment (due to direct consumption of eggs and

larvae by the cultured bivalves), and/or through indirect food web effects (e.g., consumption of

organic matter by the cultured bivalves that would have otherwise been available to support

fishes; Gibbs, 2004). Carrying capacity modelling of the proposed introduction of suspended

culture of green mussels into a New Zealand bay indicated that large-scale bivalve culture could

cause the replacement of zooplankton by the cultured bivalves as the major grazers in the system

with consequent impacts on pelagic fish (Jiang and Gibbs, 2005). However, Leguerrier et al.’s

(2004) model of the impact of oyster cultivation on a food web in a French bay indicated that

oyster cultivation caused secondary production to increase benefitting fish populations,

particularly those that used the mudflats as a nursery area. Lin et al.’s (2009) model and

observations of the removal of oyster cultivation from a eutrophic lagoon in Taiwan indicated that

reef fish populations were enhanced by oyster cultivation but pelagic and soft-bottom fish

increased following the removal of the oyster cultivation.

7.12 Central Fisheries Board undertook fish surveys in Dungarvan Harbour (Colligan Estuary) in 2008

as part of the WFD “fish stock surveys of transitional waters” (CRFB, 2009). Beach seine nets

captured 10 species; species which frequent the open sand flat such as sand goby, lesser

sandeel and sand smelt, which have also been recorded in the diet of Red-breasted Merganser

and Great Crested Grebe, were all recorded in good numbers (Appendix B). The prey items taken

by these fish include small crustaceans / amphipods (sand goby); zooplankton, fish larvae and

small invertebrates (lesser sand eel) and plankton (sand smelt); this, together with the abundance

of these fish species on the sandflats, would suggest that the sort of ecological impacts referred to

above are not occurring in Dungarvan Harbour.

7.13 Furthermore, the Transitional Fish Classification Index (TFCI), developed as part of the Water

Framework Directive, indicates that the Colligan Estuary (i.e. Dugarvan Harbour) is classed as

‘Good’ (EQR = 0.70). Thus, data on fish species abundance and diversity recorded by CRFB

(2009) would not point to large-scale bivalve culture causing ecosystem changes with associated

reductions in fish populations within Dungarvan Harbour. Furthermore, by virtue of trestles acting

as an artificial reef they may in fact be having a positive impact through providing shelter and

foraging opportunities for some species.

Disturbance

7.14 Intertidal oyster cultivation requires intensive husbandry activity (see Section 6.11) and this may

cause impacts to waterbirds using intertidal and/or shallow subtidal habitats through disturbance.

Disturbance will not affect high tide roosts, or waterbirds that mainly, or only, use trestle areas

when they are covered at high tide (such as Red-breasted Merganser, Great Crested Grebe and

Cormorant), because no husbandry activity takes place during the high tide period.

7.15 There is a very extensive literature on the impact of disturbance from human activity on

waterbirds. However, the trestle study (Gittings and O’Donoghue, 2012) examined the combined

potential effects of habitat alteration and disturbance from husbandry activity. The sites included in

the study included some with very high levels of husbandry activity. Therefore, it is not necessary

to consider the disturbance component of the potential impacts separately for the species covered

by the trestle study.


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8. Assessment of impacts on the SCI species of the


Introduction

8.1 This section presents a detailed assessment of the potential impacts of the existing and proposed

intertidal oyster cultivation in Dungarvan Harbour on the SCI species of the Dungarvan Harbour

SPA, excluding those SCI species that have already been screened out (see Section 4).

8.2 Information on species responses to oyster trestles is based mainly on the results of the trestle

study (see paragraph 2.33).

8.3 For the species where we have carried out detailed quantitative assessment of displacement

impacts, the basis for the assessment is the availability of habitat during the four-five hour period

centred on low tide (the period during which the lower shore zone on Whitehouse Bank is

exposed). The availability of tideline and intertidal habitat under various tidal conditions and the

percentages of these habitats occupied by trestles under various scenarios is summarised in

Table 8.1. Therefore all displacement impacts predicted in these assessments refer to

displacement during this four-five hour period centred on low tide.

8.4 The area occupied by trestles is not exposed outside the four-five hour period centred on low tide

and no husbandry activity takes place outside this period. Therefore, disturbance from husbandry

activities will not cause any displacement impacts outside the four-five hour period centred on low

tide and will not cause impacts to any high tide roosts.

Table 8.1 - Extent of habitat affected by intertidal oyster cultivation under various tidal conditions.

Neap low tide Mean low tide Spring low tide

Total area in lower shore zone 183 ha 180 ha 267 ha

% of total area

Trestles (2011) 19% 49% 38%

Licensed 22% 53% 60%

Licensed plus application 42% 88% 85%

see Appendix D for details of calculations

Light-bellied Brent Goose

Distribution within Dungarvan Harbour

8.5 In 2009/10, 20-50% of the Light-bellied Brent Goose population were recorded in the Outer

Sandflats during NPWS BWS low tide counts of Dungarvan Harbour (Table 8.2). In early 2011,

83-353 Light-bellied Brent Goose were recorded in counts of the entire Outer Sandflats zone,

representing 7-38% of the total Dungarvan Harbour population as recorded by I-WeBS counts

during this period (Table 8.3). Combing the data from 2009/10 and 2011, the mean proportion of

the Dungarvan Harbour population in the Outer Sandflats zone was 28%. The relative distribution

of birds within the Outer Sandflats zone between Whitehouse Bank and the northern side of the

bay varied between counts across this period (Table 8.2 and Table 8.3), with a mean across the

counts of 49% occurring on Whitehouse Bank.


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Table 8.2 - Light-bellied Brent Goose distribution in NPWS BWS low tide counts of Dungarvan

Harbour, 2009/10.

Date Inner Harbour Outer Sandflats

Whitehouse Bank Ballyrandle Sandflats

07/10/2009 306 180 129

17/11/2009 439 94 106

17/12/2009 963 188 54

11/02/2010* 750 424 123

* 8 birds were also recorded in the Outer Bay on 11/02/2010

Table 8.3 - Light-bellied Brent Goose distribution in low tide counts on the Outer Sandflats zone

carried out for the trestle study, 2011.

Date Ballyrandle Sandflats Whitehouse Bank

06/01/2011 96 194

22/01/2011 123 37

03/02/2011 56 27

21/02/2011 154 49

03/03/2011 225 128

Total Light-bellied Brent Goose counts for Dungarvan Harbour in early 2011: 1110 on 27/01/2011 and 917 on 14/02/2011

(I-WeBS data)

8.6 Within Whitehouse Bank, Light-bellied Brent Goose mainly occurred on the tideline with small

groups typically moving north swimming in shallow water below the tideline and feeding on the

trestles as they encountered them. Occasionally, small flocks occurred on intertidal habitat above

the tideline within the upper shore zone.

Response to oyster trestles

General patterns

8.7 The trestle study concluded that Light-bellied Brent Goose showed a variable response to oyster

trestles: at some sites observed numbers within the oyster trestle blocks were broadly in line with

predicted numbers, while at other sites the observed numbers were generally lower than the

predicted numbers. Differences between sites may reflect differences in the management of the

trestles: the geese feed on algae attached to the trestles so more intensive management may

reduce the food availability. There are also likely to be seasonal differences in the pattern of

usage of the trestles, as algal cover of the trestles will be highest in the autumn and will gradually

decline over the winter. The fieldwork for the trestle study was carried out during the late winter

period, so the results of this study may underestimate Light-bellied Brent Goose usage of areas

occupied by trestles. We also have some anecdotal evidence that Light-bellied Brent Goose may

be more sensitive to disturbance than other waterbird species, so the intensity of husbandry

activity relative to the area occupied by the trestles may affect the patterns of usage.

8.8 In recent work at Donegal Bay (Gittings and O’Donoghue, 2013), Light-bellied Brent Goose flock

distribution within trestle blocks broadly corresponded to the distribution of trestle blocks with high

algal cover, and the timing of their occurrence corresponded to times when no tractors were

present within the trestle blocks. However, this timing pattern could, alternatively, be explained by

an association with times when the tide is flooding/ebbing over the trestle blocks, making it easier

for the geese to graze on the algae, which is lifted by the tide. Other anecdotal evidence in

support of a disturbance factor being important includes the fact that at one of the sites

(Ballymacoda Bay) in the trestle study where Light-bellied Brent Goose generally showed a

negative response, the one day on which observed numbers were higher than predicted numbers

was the only day on which there were no husbandry activity. Another supporting observation is


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that on a visit to Dungarvan Harbour on 17th March 2013, an exceptional count of 690 Light-bellied

Brent Goose within the trestle blocks was recorded (T. Gittings, unpublished data); there was no

husbandry activity taking place on this bank holiday.

Dungarvan Harbour

8.9 In Dungarvan Harbour, the trestle study found that the observed numbers within the oyster trestle

blocks were broadly in line with predicted numbers, both when comparing the distribution across

the entire Outer Sandflats zone, and in the more detailed analysis of distribution within the

southern part of Whitehouse Bank.

Impact assessment

Displacement

8.10 Light-bellied Brent Goose may have a complex interaction with intertidal oyster cultivation, but at

Dungarvan Harbour, the available evidence indicates that it currently has a neutral or positive

association with this activity. However, intertidal oyster cultivation in Dungarvan Harbour appears

to have caused, or contributed to, the complete loss of a large Zostera bed (see paragraph 7.3-

7.5). Zostera is normally a favoured feeding habitat for Light-bellied Brent Goose. Light-bellied

Brent Goose continue to occur within the same area, but now feed on algae covering the trestles.

Zostera may have a higher nutritive value as a food resource for Brent Goose (Burton, 1959-60;

Mathers and Montgomery; 1997) and is generally the preferred food resource when available

(e.g., Mathers and Montgomery; 1997). Therefore some displacement of Light-bellied Brent

Goose might be expected due to the reduced quality of the food resource (algae) that has

replaced the Zostera bed. However, the actual displacement that has occurred will depend upon

the quality of the habitat elsewhere in Dungarvan Harbour.

8.11 As Light-bellied Brent Goose currently has a neutral or positive association with intertidal oyster

cultivation, further expansion of the activity should not cause any spatial displacement.

Long-term population trends

8.12 The Dungarvan Harbour Light-bellied Brent Goose population has undergone a huge increase

over the past 50 years, since Ruttledge (1966, quoted by Guiry and Kielty, 1972) gave a

population size for Dungarvan Harbour of 30. The population has been assessed as being in

favourable conservation condition with a 91% increase in its population index between 1995/96

and 2007/08 (NPWS, 2011c). This is substantially higher than the overall national trend over this

period (58%). The smoothed index shows a consistent gradual increase over most of this period,

with a sharp acceleration in the rate of increase at the end of the period. The population trend at

Dungarvan Harbour has been consistently more positive than the national trend (Table 8.16).

Therefore, there is no evidence that the development of intertidal oyster cultivation in the late

1980s, the period of major expansion in the 1990s and the intensification of the activity in the

2000s has affected the long-term population trends of Light-bellied Brent Goose at Dungarvan

Harbour.

Table 8.4 - Population data for Light-bellied Brent Goose.

Period Parameter Dungarvan Harbour National

1970s mean annual maxima 200 c. 10,000

1984/85-1986/87 mean annual maxima 694 20,018


1995/96-2007/08 population trend of smoothed index +91% +58%

2008/09-2011/12 mean annual maxima 1629

8.13 Data sources: Sheppard (1993; 1970s and 1984/85-1986/87); Crowe et al. (2008; National 1994/95-2007/08); I-WeBS

data (Dungarvan 1994/95-1996/97 and 2008/09-2011/12); NPWS (2011c; 1995/96-2007/08)


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Red-breasted Merganser


8.14 Red-breasted Merganser show a variable distribution pattern in high tide counts of Dungarvan

Harbour, occurring in all three zones, with their distribution between the Inner Harbour and Outer

Sandflats varying between counts, but the numbers in the Outer Bay zone were low on all counts

(Table 8.5). Across these counts a mean of 34% of the total count occurred in the Outer Sandflats

zone.

Table 8.5 – Red-breasted Merganser distribution in high tide counts of Dungarvan Harbour.

Zone Inner Harbour

Outer Sandflats Outer Bay

Date Whitehouse Bank Ballyrandle

27/01/2010 9 13 5 5

27/01/2011 14 7 6

14/02/2011 23 5 3

20/12/2011 40 2 5

17/02/2012 7 8 17 6


8.15 Red-breasted Merganser occurs mainly in subtidal habitat. The trestle study focused on intertidal

habitat and did not make any conclusions about the patterns of association between Red-

breasted Merganser and oyster trestles.

8.16 While the oyster trestles occur mainly in the intertidal zone, they will be covered at high tide. Red-

breasted Merganser generally feed in inshore waters, often close to the tideline, and the zone

occupied by oyster trestles will be within an area of potentially suitable habitat at high tide and, in

part, during neap low tides.

8.17 No information is available on the response of Red-breasted Merganser to intertidal oyster

cultivation. In Dungarvan Harbour, Red-breasted Merganser probably mainly feed on small

estuarine fish (such as gobies, smelt and sandeel) and mobile invertebrates (such as crabs and

shrimps; see Section B.3). In general intertidal oyster cultivation is likely to either have no effect

on, or increase local abundances of these species (see paragraph 0). There is no evidence that

large-scale aquaculture at Dungarvan is causing negative impacts on fish population through

reduced recruitment or through indirect food web effects (see paragraph 7.11). If such ecosystem-

scale effects occurred they would be manifested through impacts on long-term population trends.

They would not cause displacement of birds from the areas occupied by intertidal oyster

cultivation, as these effects would reduce the overall availability of prey resources within the entire

site rather than the distribution of prey resources within the site.

Impact assessment

Distribution

8.18 Intertidal oyster cultivation is likely to have neutral or positive impacts on the availability of prey

resources for Red-breasted Merganser in the areas occupied by the activity, compared to areas of

similar habitat elsewhere in Dungarvan Harbour. Therefore, intertidal oyster cultivation is not likely

to cause any displacement of Red-breasted Merganser.


8.19 The Dungarvan Harbour Red-breasted Merganser population has been assessed as being in

intermediate (unfavourable) conservation condition with a 15% decrease in its population index


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between 1995/96 and 2007/08 (NPWS, 2011c). The data summarised in Table 8.16 shows a

slightly greater negative trend at Dungarvan Harbour compared to the national trend. However,

with such a small population size the population trends will be heavily influenced by stochastic

variation so this difference in the trends cannot be regarded as strong evidence of an impact from

intertidal oyster cultivation. Therefore, there is no evidence that the overall food supply for Red-

breasted Merganser within Dungarvan Harbour has been affected by intertidal oyster cultivation to

such an extent as to affect long-term population trends.

Table 8.6 - Population data for Red-breasted Merganser.


1970s mean annual maxima 25-50 n/a

1984/85-1986/87 mean annual maxima 50 3000


1995/96-2007/08 population trend of smoothed index -15 -11


Data sources: Sheppard (1993; 1970s and 1984/85-1986/87); Crowe et al. (2008; National 1994/95-2007/08); I-WeBS


Great Crested Grebe


8.20 In high tide counts of Dungarvan Harbour, Great Crested Grebe occurred mainly in the Outer

Sandflats and Outer Bay zones, and within the Outer Sandflats zone occurred mainly on the

Ballyrandle side of bay (Table 8.5).

Table 8.7 – Great Crested Grebe distribution in high tide counts of Dungarvan Harbour.

Zone Inner Harbour

Outer Sandflats Outer Bay

Date Whitehouse Bank Ballyrandle

27/01/2010 2 4 1 0

27/01/2011 3 0 13 20

14/02/2011 3 0 50 6

20/12/2011 5 0 5 30

17/02/2012 4 10 20 78


8.21 Great Crested Grebe occur mainly in subtidal habitat. The trestle study focused on intertidal

habitat and did not make any conclusions about the patterns of association between Great

Crested Grebe and oyster trestles.

8.22 While the oyster trestles occur mainly in the intertidal zone, they will be covered at high tide. Great

Crested Grebe generally feed in inshore waters and the zone occupied by oyster trestles will be

within area of potentially suitable habitat at high tide and during neap low tides.

8.23 No information is available on the response of Great Crested Grebe to intertidal oyster cultivation.

Great Crested Grebe probably mainly feed on small estuarine fish (such as gobies, smelt and

sandeel) and may also feed on larger pelagic fish (such as sprat and cod; see Section B.3). In

general intertidal oyster cultivation is likely to either have no effect on, or increase local

abundances of these species (see paragraph 0). There is no evidence that large-scale

aquaculture at Dungarvan is causing negative impacts on fish population through reduced

recruitment or through indirect food web effects (see paragraph 7.11). If such ecosystem-scale

effects occurred they would be manifested through impacts on long-term population trends. They


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would not cause displacement of birds from the areas occupied by intertidal oyster cultivation, as

these effects would reduce the overall availability of prey resources within the entire site rather

than the distribution of prey resources within the site.

Impact assessment

Distribution


resources for Great Crested Grebe in the areas occupied by the activity, compared to areas of

similar habitat elsewhere in Dungarvan Harbour. Therefore, intertidal oyster cultivation is not likely

to cause any displacement of Great Crested Grebe.


8.25 The Dungarvan Harbour Great Crested Grebe population has been assessed as being in

intermediate (unfavourable) conservation condition with a 15% decrease in its population index

between 1995/96 and 2007/08, compared to a national decrease of 18% (NPWS, 2011c). The

mean annual maxima in recent years is higher than that for the mid-1990s (Table 8.16). However,

Great Crested Grebe counts at Dungarvan Harbour are highly variable, probably at least partly

reflecting the effect of weather conditions on the accuracy of counts of the Outer Bay zone.

Moreover, with such a small population size the population trends will be heavily influenced by

stochastic. Therefore, there is no evidence that the overall food supply for Great Crested Grebe

within Dungarvan Harbour has been affected by intertidal oyster cultivation to such an extent as to

affect long-term population trends.

Table 8.8 - Population data for Great Crested Grebe.


1970s mean annual maxima n/a n/a



1995/96-2007/08 population trend of smoothed index -15% -18%





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Golden Plover


8.26 In 2009/10, large Golden Plover numbers were recorded on three of the four counts (Table 8.9).

On each occasion, the majority of the birds occurred in 0M420 (the subsite covering the northern

part of the Whitehouse Bank).

Table 8.9 – Golden Plover distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10.

Zone Inner Harbour

Outer Sandflats

Date Whitehouse Bank Ballyrandle Sandflats

07/10/2009 190 1400 153

17/11/2009 0 8990 0

17/12/2009 389 6150 13

11/02/2010 12 0 0

8.27 In 2011, the Golden Plovers recorded in counts of the entire Outer Sandflats zone, were mainly on

the northern side of the bay on three of the four counts, and on the Whitehouse Bank in the other

count (Table 8.10).

Table 8.10 - Golden Plover distribution in low tide counts on the Outer Sandflats zone carried out for

the trestle study, 2011.


22/01/2011 209 2

03/02/2011 200 00

21/02/2011 0 460

03/03/2011 109 0

Total Golden Plover counts for Dungarvan Harbour in early 2011: 692 on 27/01/2011 and 68 on 14/02/2011 (I-WeBS data)

8.28 Within Whitehouse Bank, the Golden Plover flock was recorded at the northern edge of the lower

part of the sandflats, adjacent to the tidal channel, on 17th December 2009, and in the northern

part of the area on the upper sandflats close to the dunes on 7th October and 17

th November 2009

and 21st February 2011.


General patterns

8.29 Golden Plover were not recorded in sufficient numbers for inclusion in any of the analyses in the

trestle study. Therefore, the trestle study did not make any conclusion about their response to

trestles.

8.30 In the non-breeding season, Golden Plover mainly feed in agricultural fields and use intertidal

habitat as a roosting habitat (although, typically, a small percentage of the birds in the roosting

flocks will be feeding). They favour open mudflats and sandflats away from the shoreline, or other

cover, where they occur in compact flocks, often with several thousand birds in a single flock at

favoured sites. However, at high tide they will roost with other waders in high tide roosts in

shoreline and saltmarsh habitats. Given, these habitat requirements, it seems extremely unlikely

that they would ever make significant use of areas occupied by oyster trestle blocks.

Dungarvan Harbour

8.31 In the trestle study, Golden Plover were recorded on four of the five counts that were carried out

of the entire Outer Sandflats zone. A total of 980 birds were recorded on these counts with none


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recorded within the trestle blocks. Golden Plover were not recorded on any of the additional

counts of the Whitehouse Bank study area.

Impact assessment

Distribution

8.32 The limited available data indicates that Golden Plover avoid oyster trestles and this pattern would

be expected from knowledge of their ecology. Golden Plover mainly use intertidal habitat for

roosting and appear to favour open tidal flats with unobstructed views (at low tide). Therefore,

areas occupied by trestle blocks would not be suitable habitat.

8.33 Golden Plovers usually occur in very compact flocks when roosting in intertidal habitat. Therefore,

even very large flocks occupy only a small area of intertidal habitat. However, while it would seem

that in a large site such as Dungarvan Harbour there should be large areas of potentially suitable

habitat, Golden Plover flocks typically seem to favour particular areas. This is illustrated by the

positions of the large Golden Plover flocks recorded in 2009.

8.34 The area now occupied by oyster trestle blocks covers a large part of Whitehouse Bank and

extends close to the area apparently favoured by Golden Plover. It seems reasonable to suppose

that, in the absence of the oyster trestles, Golden Plover flocks would also occur within the

northern part of the area now occupied by oyster trestle blocks. However, the fact that the largest

flocks recorded in the 2009/10 low tide counts still occurred on Whitehouse Bank in close

proximity to the trestle blocks indicates that intertidal oyster cultivation has not had a significant

impact on the number and range of areas used by Golden Plover.

8.35 Most of the potential future expansion of intertidal oyster cultivation will not affect areas that

appear to be favoured by Golden Plover. There is one application plot (T04/041) at the northern

end of the area currently occupied by oyster trestles, which extends to within 100 m of one of the

Golden Plover flock locations recorded in 2009/10. It is possible that development of this plot

might reduce the utilisation of the adjacent area by Golden Plover. However, given the current

patterns of occurrence of Golden Plover flocks, it seems unlikely that this would affect the overall

occurrence of Golden Plover within the northern part of Whitehouse Bank.

Population trends

8.36 The Dungarvan Harbour Golden Plover population has been assessed as being in intermediate

(unfavourable) conservation condition with a 19% decrease in its population index between

1995/96 and 2007/08 (NPWS, 2011c). This is substantially greater than the overall national

decline over this period (-2%). The smoothed index shows a stable/slightly increasing trend over

most of this period, with a sharp decrease since 2004/05 (NPWS, 2011c); this pattern is very

similar to that shown by the smoothed national index (Boland and Crowe, 2012). Very high

numbers were recorded in low tide counts in November and December 2009, but I-WeBS counts

in 2010/11 and 2011/12 have been very low. Nationally, the decreasing trend shown up to

2008/09 (Boland and Crowe, 2012) has continued with the unsmoothed index reaching its lowest

ever values in 2009/10 and 2011/12 (Crowe et al., 2012).

8.37 The Golden Plover population trends at Dungarvan Harbour do not show any clear evidence of

impact from the development of intertidal oyster cultivation (Table 8.16). In particular, there

appears to have been a large increase in the population at Dungarvan Harbour over the period of

the initial development of the activity, while the national population remained broadly stable. While

there has been a decrease in recent years, this is mirrored by the national trends. Up to 2007/08,

the decrease at Dungarvan Harbour had been much larger than the national decrease. However,

the more recent trend data indicates that the scale of the national decrease up to 2010/11 is

probably broadly comparable to the scale of decrease at Dungarvan Harbour over the same

period. Golden Plover counts tend to be highly variable (due to their pattern of usage of intertidal


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habitats) so precise quantitative interpretation of trends at infrequently counted individual sites is

unlikely to be ecologically meaningful. Overall, therefore, there is no evidence that the

development of intertidal oyster cultivation at Dungarvan Harbour has affected the long term

population trends of Golden Plover.

Table 8.11 - Population data for Golden Plover.


1970s mean annual maxima n/a 200,000+







Grey Plover


8.38 In 2009/10, large Grey Plover numbers were recorded on all four low tide counts (Table 8.12). On

three of the counts, 80-100% of the total occurred in the Inner Harbour. On the fourth count, 50%

of the total occurred in the Outer Sandflats on Whitehouse Bank. On this count, Whitehouse Bank

was counted relatively early (2-4 hours before low tide) compared to the other counts (1 hour

before after low tide). Therefore, the February count probably captured the Grey Plover flock on

the ebb tide before the tideline reached the trestle blocks and the Grey Plovers moved off

Whitehouse Bank (see paragraph 8.43).

Table 8.12 - Grey Plover distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10.

Inner Harbour

Outer Sandflats

Date Whitehouse Bank Ballyrandle Sandflats

07/10/2009 128 0 0

17/11/2009 162 1 0

17/12/2009 136 26 3

11/02/2010 92 91 1

8.39 In 2011, the Grey Plovers recorded in counts of the entire Outer Sandflats zone, were mainly on

the northern side of the bay on three of the four counts, and on the Whitehouse Bank in the other

count (Table 8.13).

Table 8.13 - Grey Plover distribution in low tide counts on the Outer Sandflats zone carried out for the

trestle study, 2011.


06/01/2011 2 23

22/01/2011 0 50

03/02/2011 0 20

21/02/2011 0 16

03/03/2011 0 54

Total Grey Plover counts for Dungarvan Harbour in early 2011: 56 on 27/01/2011 and 243 on 14/02/2011 (I-WeBS data)

8.40 Within Whitehouse Bank, the Grey Plover recorded during the trestle study counts mainly

occurred in the trestle-free areas within the southern half. This reflected the distribution of trestle-

free lower shore habitat: most of the lower shore zone in the northern half of Whitehouse Bank is


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occupied by trestles. However, Grey Plover were recorded on some counts in the northern half of

the upper shore zone of Whitehouse Bank above the trestles. Grey Plover rarely occurred in the

trestle-free northernmost section of the lower shore zone of Whitehouse Bank. This may have

been due to the drier sand conditions near the tidal channel and/or its isolation from the main

Grey Plover habitat in the southern half of Whitehouse Bank. During, these counts Grey Plover

rarely occurred in the upper shore zone of Whitehouse Bank, and when they did they were usually

close to the lower boundary of this zone. This reflects the timing of the counts around the middle

of the low tide period. On the flood and ebb tide, when the tideline was within the upper shore

zone, Grey Plover regularly occurred in this zone (see paragraph 8.43).


General patterns

8.41 The trestle study concluded that Grey Plover has an exclusion response to oyster trestles (i.e.

oyster trestles blocks cause complete exclusion of Grey Plover from the areas occupied by the

trestle blocks). While there was only limited data for this species that could be included in the

formal analyses; observations of the flock behaviour of these species at Dungarvan Harbour (see

below) provided strong evidence of avoidance of the oyster trestle blocks. Therefore, the study

concluded that predictions of the impact of oyster trestle blocks should assume complete

exclusion of Grey Plover from the affected area with a high degree of confidence.

Dungarvan Harbour

8.42 In the trestle study, Grey Plover were recorded on all of the five counts that were carried out of the

entire Outer Sandflats zone. A total of 165 birds were recorded on these counts with only four

recorded within the trestle blocks. Grey Plover were also recorded on 10 of the 14 additional

counts of the Whitehouse Bank study area. A total of 187 birds were recorded on these counts

with only five recorded within the trestle blocks.

8.43 Observations during this study on the distribution and movements of Grey Plover on flood and ebb

tides provided further evidence of their avoidance of the trestle blocks. Flocks of 50-80 Grey

Plover were recorded on several occasions on the upper sandflats of Whitehouse Bank above the

main oyster trestle block when the lower sandflats (including the trestle blocks) were covered by

the tide (Table 8.14). On most of these occasions these flocks were not present on Whitehouse

Bank when counts were carried out at low tide. On one occasion part of the flock that had been

feeding above the main oyster trestle block were observed flying across the Cunnigar into the

inner part of Dungarvan Harbour, as the tideline receded towards the oyster trestle blocks.

Table 8.14 - Counts of Grey Plover on flood/ebb tides in Whitehouse Bank during the trestle study,

January-March 2011.

Date Flood/ebb tide count Low tide count

22 January 50 before 50

03 February 57 before 20


21 February 17 before 16*

03 March 82 after 51

07 March 14 before

4 62 after

* the birds recorded in the low tide count on 21 February were in the upper shore zone towards the end of the count as the

tideline was receding rapidly through the upper part of the lower shore zone


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Impact assessment

Distribution

8.44 Intertidal oyster cultivation appears to cause complete exclusion of Grey Plover from the areas

occupied by oyster trestles. Therefore, in the absence of intertidal oyster cultivation, Grey Plover

would be expected to occur within areas currently occupied by oyster trestles.

8.45 If the densities of Grey Plover recorded during the trestle study in the lower shore zone of

Whitehouse Bank outside the trestle blocks were representative of the densities that would have

occurred throughout this zone in the absence of the trestle blocks, a mean of 13 additional birds

would have been expected to have occurred during these counts. Allowing for neap tides, the

overall displacement of Grey Plover in 2011 predicted on this basis is 10 birds, amounting to 4%

of the Dungarvan Harbour population (Table 8.15). Full occupation of the existing licenses would

only cause a 1% increase in the predicted level of displacement, while full occupation of the

existing licenses and the application plots would cause a 5% increase (Table 8.15).

8.46 The counts carried out on flood/ebb tides also give an indication of the potential numbers that

might occur on Whitehouse Bank in the absence of intertidal oyster cultivation. There was a mean

across these counts of 51, compared to a mean of 21 in the low tide counts carried out on the

same days, and a mean of 19 across all low tide counts. Allowing for neap tides, the overall

displacement of Grey Plover in 2011 predicted on this basis is 25 birds, amounting to 10% of the

Dungarvan Harbour population.

8.47 Therefore, our estimates of the displacement of Grey Plover due to intertidal oyster cultivation in

2011 range from 10 (based on density calculations) to 25 (based on numbers present on the

flood/ebb tides). The differences in these estimates may indicate that the presence of trestles

affects the suitability of habitat adjoining the trestles (possibly due to disturbance impacts from

husbandry activity, although Grey Plover are relatively tolerant of disturbance; see paragraph

11.23). It may also simply reflect birds feeding in the northern half of the upper shore zone being

pushed up against the trestles as the tideline advances and being forced to fly to avoid the

trestles. It is also possible that some of the difference may reflect birds moving away from

Whitehouse Bank at the stage of the tide when the tideline reaches the lower shore zone due to

factors unrelated to the presence of oyster trestles, such as the exposure of suitable habitat

elsewhere.

Table 8.15 - Predicted displacement of Grey Plover based on densities recorded in trestle-free areas

of the lower shore zone of Whitehouse Bank.

numbers % of site pop

Dungarvan Harbour population in Jan-Feb 2011 243*

Predicted numbers in absence of trestles 33 13%

Predicted displacement

2011 extent of trestles 10 4%

full occupation of licensed plots

13 5%

full occupation of all aquaculture plots

22 9%

* January 2011 I-WeBS count presumed to be an underestimate

Population trends

8.48 The Dungarvan Harbour Grey Plover population has been assessed as being in intermediate

(unfavourable) conservation condition with an 11% decrease in its population index between

1995/96 and 2007/08 (NPWS, 2011c). However, the overall population trends for Grey Plover at

Dungarvan Harbour have generally followed the national trends fairly closely (Table 8.16), and the

decrease at Dungarvan Harbour between 1995/96 and 2007/08 was smaller than the overall


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national decrease over the same period. Therefore, there is no evidence that the development of

intertidal oyster cultivation in the late 1980s, the period of major expansion in the 1990s and the

intensification of the activity in the 2000s has affected the long-term population trends of Grey

Plover at Dungarvan Harbour.

Table 8.16 - Population data for Grey Plover.


1970s mean annual maxima 100 750-1500






data (Dungarvan 1994/95-1996/97 and 2008/09-2011/12); NPWS (2011c; 1995/96-2007/08).

Knot


8.49 In 2009/10, Knot was recorded on all four low tide counts with 60-100% of the birds within the

Inner Harbour (Table 8.17).

Table 8.17 - Knot distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10.

Inner Harbour Outer Sandflats

Date


07/10/2009 137 7 86

17/11/2009 299 79 98

17/12/2009 697 0 8

11/02/2010 724 5 0

8.50 In 2011, the Knot recorded in counts of the entire Outer Sandflats zone, were mainly on the

northern side of the bay (Table 8.18). However, during flood/ebb tides, large flocks of Knot

frequently occurred on Whitehouse Bank (see below).

Table 8.18 - Knot distribution in low tide counts on the Outer Sandflats zone carried out for the trestle

study, 2011.


06/01/2011 166 0

22/01/2011 0 0

03/02/2011 0 0

21/02/2011 356 92

03/03/2011 145 36

Total Knot counts for Dungarvan Harbour in early 2011: 340 on 27/01/2011 and 551 on 14/02/2011 (I-WeBS data)


General patterns

8.51 The trestle study concluded that Knot has an exclusion response to oyster trestles (i.e. oyster

trestles blocks cause complete exclusion of Knot from the areas occupied by the trestle blocks).

While there was only limited data for this species that could be included in the formal analyses,

observations of the flock behaviour of these species at Dungarvan Harbour (see below) provided


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strong evidence of avoidance of the oyster trestle blocks. Therefore, the study concluded that

predictions of the impact of oyster trestle blocks should assume complete exclusion of Knot from

the affected area with a high degree of confidence.

Dungarvan Harbour

8.52 In the trestle study, Knot were recorded on three of the five counts that were carried out of the

entire Outer Sandflats zone. A total of 795 birds were recorded on these counts with none

recorded within the trestle blocks. Knot were also recorded on two of the 14 additional counts of

the southern part of Whitehouse Bank. A total of 210 birds were recorded on these counts with

none recorded within the trestle blocks.

8.53 Observations during this study on the distribution and movements of Knot on flood and ebb tides

provided further evidence of their avoidance of the trestle blocks. Flocks of 60-250 Knot were

recorded on several occasions on the upper sandflats of Whitehouse Bank above the main oyster

trestle block when the lower sandflats (including the trestle blocks) were covered by the tide

(Table 8.19). On most of these occasions these flocks were not present on Whitehouse Bank

when counts were carried out at low tide, although on one date higher numbers were recorded on

the low tide count.

Table 8.19 - Counts of Knot on flood/ebb tides in Whitehouse Bank during the trestle study, January-

March 2011.







07 March 23 before

0 250 after

* the birds recorded in the low tide count on 21 February were in the upper shore zone towards the end of the count as the

tideline was receding rapidly through the upper part of the lower shore zone

Impact assessment

Distribution

8.54 Intertidal oyster cultivation appears to cause complete exclusion of Knot from the areas occupied

by oyster trestles. Therefore, in the absence of intertidal oyster cultivation, Knot would be

expected to occur within areas currently occupied by oyster trestles.

8.55 The counts carried out on flood/ebb tides give an indication of the potential numbers that might

occur on Whitehouse Bank in the absence of intertidal oyster cultivation. There was a mean


same days, and a mean of 26 across all low tide counts.

8.56 Knot were only recorded in the lower shore zone of Whitehouse Bank on three of the twelve

counts during the trestle study. Therefore, it appears that Knot feed in the upper shore zone of

Whitehouse Bank on the ebb/flood tides, but usually leave Whitehouse Bank when the tideline

reaches the lower shore zone, presumably due to the presence of trestles in that zone.

8.57 Total I-WeBS counts of the Knot population in Dungarvan Harbour in early 2011 were 340 on

27/01/2011 and 551 on 14/02/2011. Therefore, taking account of neap tides, the level of intertidal

oyster cultivation in 2011 may have been causing the displacement of 18% of the Dungarvan

Harbour population.


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8.58 Full occupation of the licenses and application plots will not significantly increase the scale of this

displacement impact, as the the existing level of intertidal oyster cultivation already appears to be

causing more or less complete displacement.


8.59 The Dungarvan Harbour Knot population has been assessed as being in favourable conservation

condition with a 10% increase in its population index between 1995/96 and 2007/08 (NPWS,

2011c). The smoothed index shows a stable trend over most of this period, with a gradual

increase since 2005/06 (NPWS, 2011c). This increase compares to a national decrease of 3%

over the same period. There was a decrease in the Knot population at Dungarvan Harbour

between the mid-1980s and the mid-1990s, but this appears to have been a continuation of a

trend begun in the 1970s, and mirrors a national decline (Table 8.16). Therefore, there is no

evidence that the development of intertidal oyster cultivation in the late 1980s, the period of major

expansion in the 1990s and the intensification of the activity in the 2000s has affected the long-

term population trends of Knot at Dungarvan Harbour.

Table 8.20 - Population data for Knot.


1970s mean annual maxima 1900 25,000-60,000



1995/96-2007/08 population trend of smoothed index +10% -3%




Dunlin


8.60 In 2009/10, Dunlin were recorded on all four low tide counts with 90-95% of the birds within the

Inner Harbour (Table 8.17).

Table 8.21 - Dunlin distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10.



07/10/2009 325 8 10

17/11/2009 835 15 42

17/12/2009 2422 43 215

11/02/2010 2868 26 256

Note: counts of Whitehouse Bank are likely to be underestimates as birds feeding within the trestle blocks will not have

been detectable.

8.61 In 2011, the Dunlin recorded in counts of the entire Outer Sandflats zone, were on both sides of

the bay (Table 8.18). During flood/ebb tides, large flocks of Dunlin frequently occurred on

Whitehouse Bank (see below).


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Table 8.22 - Dunlin distribution in low tide counts on the Outer Sandflats zone carried out for the



06/01/2011 202 347

22/01/2011 115 17

03/02/2011 9 15

21/02/2011 191 597

03/03/2011 91 298

Total Dunlin counts for Dungarvan Harbour in early 2011: 1212 on 27/01/2011 and 1381 on 14/02/2011 (I-WeBS data)

8.62 Within Whitehouse Bank, at low tide, most Dunlin within the lower shore zone occurred on, or

close to the tideline along most of the length of the sandflats. However, they did not occur in the

trestle-free area at the northern end of Whitehouse Bank. This may have been due to the drier

sand conditions near the main tidal channel. Dunlin flocks were also recorded on some counts on

the lower part of the upper sandflats.


General patterns

8.63 The trestle study concluded that Dunlin has a negative response to oyster trestles and there was

a high degree of confidence attached to this conclusion. Dunlin do not completely avoid trestles,

but densities within trestle blocks were lower (by factors of 2-8 times) than in comparable areas

outside trestle blocks. There was some evidence suggesting that the avoidance effect is stronger

in large flocks compared to small flocks, possibly due to oyster trestles interfere with flocking

behaviour by making it difficult for individuals in large flocks to remain in contact as they become

dispersed across several lines of trestles. A negative response by Dunlin to oyster trestles was

also reported by Kelly et al. (1996).

Dungarvan Harbour

8.64 In the analysis of Dunlin distribution across Whitehouse Bank from the extensive study, observed

numbers within the oyster trestle blocks were lower than the predicted numbers on all five counts.

In the intensive study, when large flocks were not present and predicted numbers were low (< 50),

observed numbers within the oyster trestle blocks were similar to predicted numbers. However, on

the three intensive study counts when higher numbers were present, observed numbers within the

oyster trestle blocks were much lower than the predicted numbers.

8.65 In the intensive study, mean densities were around five times higher outside the trestle blocks

compared to within the trestle blocks (Table 8.23). However, differences in densities between

areas within and outside trestle blocks in the lateral zone containing the tideline were not

significant due to the high variability in densities between counts (Friedman’s 2 = 0.091, p-value

= 0.763).


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Table 8.23 - Dunlin densities (number per 10 ha) in lateral zones relative to the tideline.

Outside trestle blocks Within trestle blocks

Lateral zone Mean SD Mean SD

Zone 0 54.4 136.3 11.8 12.0

Zone 1 4.4 8.4 1.3 1.5

Zone 2 2.7 6.8 0.7 1.6

Lateral zones were bands of intertidal habitat parallel to the tideline numbered sequentially from 0 to 2 to indicate their

proximity to the tideline, with zone 0 containing the tideline.

8.66 Observations during the trestle study on the distribution and movements of Dunlin on flood and

ebb tides provided further evidence of their avoidance of the trestle blocks. Flocks of 200-1000

Dunlin were recorded on several occasions on the upper sandflats of Whitehouse Bank above the

main oyster trestle block when the lower sandflats (including the trestle blocks) were covered by

the tide (Table 8.24). On most of these occasions much lower numbers were present on

Whitehouse Bank when counts were carried out at low tide, and on one occasion part of the flock

were observed flying across the Cunnigar into the inner part of Dungarvan Harbour, as the tideline

receded towards the oyster trestle blocks.

Table 8.24 - Counts of Dunlin on flood/ebb tides in Whitehouse Bank during the trestle study,

January-March 2011.







07 March 47 before

7 700 after

* most (578) of the birds recorded in the low tide count on 21 February were in the upper shore zone towards the end of

the count as the tideline was receding rapidly through the upper part of the lower shore zone.

Impact assessment

Distribution

8.67 Intertidal oyster cultivation appears to cause reduced utilisation by Dunlin of areas occupied by

oyster trestles compared to other areas of comparable habitat. Therefore, in the absence of

intertidal oyster cultivation, Dunlin would be expected to occur in higher densities within areas

currently occupied by oyster trestles. However, the overall extent of Dunlin distribution within

Dungarvan Harbour is probably not affected by intertidal oyster cultivation.

8.68 If the densities of Dunlin recorded during the trestle study in the lower shore zone of Whitehouse

Bank outside the trestle blocks were representative of the densities that would have occurred

throughout this zone in the absence of the trestle blocks, a mean of 40 additional birds would

have been expected to have occurred during these counts. Allowing for neap tides, the overall

displacement of Dunlin in 2011 predicted on this basis is 29 birds, amounting to 2% of the

Dungarvan Harbour population (Table 8.25). Full occupation of the existing licenses and the

application plots would increase the displacement impact to 5% (Table 8.15).

8.69 The counts carried out on flood/ebb tides also give an indication of the potential numbers that

might occur on Whitehouse Bank in the absence of intertidal oyster cultivation. There was a mean


same days, and a mean of 74 across all low tide counts. Allowing for neap tides, the overall


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displacement of Dunlin in 2011 predicted on this basis is 389 birds, amounting to 30% of the

Dungarvan Harbour population.

8.70 Therefore, our estimates of the displacement of Dunlin due to intertidal oyster cultivation in 2011

range from 29 (based on density calculations) to 389 (based on numbers present on the flood/ebb

tides). The differences in these estimates may indicate that the presence of trestles affects the

suitability of habitat adjoining the trestles. This could be due to disturbance impacts from

husbandry activity; large Dunlin flocks may be very sensitive to disturbance (Laursen et al., 2005).

It may also simply reflect birds feeding in the northern half of the upper shore zone being pushed

up against the trestles as the tideline advances and being forced to fly to avoid the trestles. It is

also possible that some of the difference may reflect birds moving away from Whitehouse Bank at

the stage of the tide when the tideline reaches the lower shore zone due to factors unrelated to

the presence of oyster trestles, such as the exposure of suitable habitat elsewhere.

Table 8.25 - Predicted displacement based on densities recorded in trestle-free areas of the lower

shore zone of Whitehouse Bank.


Dungarvan Harbour population in Jan-Feb 2011 1297




full occupation of licenses 35 3%

full occupation of aquaculture plots

61 4%


8.71 The Dungarvan Harbour Dunlin population has been assessed as being in unfavourable

conservation condition with a 38% decrease in its population index between 1995/96 and 2007/08

(NPWS, 2011c). This compares to an overall national decline of 47% over this period. The

smoothed index shows a steady decrease over most of this period, with a possible flattening of

the rate of decline since around 2005/06 (NPWS, 2011c). Between the mid-1980s and the mid-

1990s the Dungarvan Harbour Dunlin population increased slightly in line with the national trend

(Table 8.16). Therefore, there is no evidence that the development of intertidal oyster cultivation in

the late 1980s, the period of major expansion in the 1990s and the intensification of the activity in

the 2000s has affected the long-term population trends of Dunlin at Dungarvan Harbour.

Table 8.26 - Population data for Dunlin.










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Bar-tailed Godwit


8.72 In 2009/10, Bar-tailed Godwit were recorded on all four low tide counts with 71-100% of the birds

within the Outer Sandflats zone (Table 8.27).

Table 8.27 – Bar-tailed Godwit distribution in NPWS BWS low tide counts of Dungarvan Harbour,

2009/10.



07/10/2009 10 0 257

17/11/2009 63 2 153

17/12/2009 2 15 452

11/02/2010 122 41 860

Note: counts of Whitehouse Bank are likely to be underestimates as birds feeding within the trestle blocks will not have

been detectable

8.73 In 2011, the Bar-tailed Godwits recorded in counts of the entire Outer Sandflats zone, were mainly

on the northern side of the bay, apart from one count when the overall numbers present were low

(Table 8.28). Numbers of Bar-tailed Godwit recorded on counts of Whitehouse Bank during

flood/ebb tides were comparable to the numbers recorded during low tide counts of Whitehouse

Bank on the same day.

Table 8.28 – Bar-tailed Godwit distribution in low tide counts of the Outer Sandflats zone carried out

for the trestle study, 2011.


06/01/2011 57 178

22/01/2011 671 105

03/02/2011 500 65

21/02/2011 485 113

03/03/2011 326 71

Total Bar-tailed Godwit counts for Dungarvan Harbour in early 2011: 1000 on 27/01/2011 and 979 on 14/02/2011 (I-WeBS

data)

8.74 Within Whitehouse Bank, at low tide, nearly all Bar-tailed Godwits occurred on, or close to the

tideline along most of the length of the sandflats. However, they did not occur in the trestle-free

area at the northern end of Whitehouse Bank. This may have been due to the drier sand

conditions near the main tidal channel.

8.75 On Ballyrandle Sandflats, Bar-tailed Godwit are often concentrated around the Glendine River

tidal channel, but also occur along the tideline to the south at the eastern side of the bay and, at

low tide, along the tideline that extends out towards the main tidal channel below the mixed

substrata and eulittoral rock biotope areas.


General patterns

8.76 The trestle study concluded that Bar-tailed Godwit has a negative response to oyster trestles and

there was a high degree of confidence attached to this conclusion. Bar-tailed Godwit do not

completely avoid trestles, but densities within trestle blocks were lower (by factors of 2-9 times)

than in comparable areas outside trestle blocks. There is evidence suggesting that the avoidance

effect is stronger in large flocks compared to small flocks, possibly due to oyster trestles


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interfering with flocking behaviour by making it difficult for individuals in large flocks to remain in

contact as they become dispersed across several lines of trestles.

Dungarvan Harbour

8.77 In the analysis of Bar-tailed Godwit distribution across the entire Outer Sandflats zone from the

extensive study, observed numbers within the oyster trestle blocks were lower than the predicted

numbers on four of the five counts. In the analysis of Bar-tailed Godwit distribution within a 2 km

section of the lower shore zone of Whitehouse Bank observed numbers within the oyster trestle

blocks were lower than the predicted numbers on 14 of the 17 counts.

8.78 In the intensive study, mean densities were around twice as high outside the trestle blocks

compared to within the trestle blocks (Table 8.29) and this difference was significant (F1,11 = 9.79,

p = 0.001).

Table 8.29 – Bar-tailed Godwit densities (number per 10 ha) in lateral zones relative to the

tideline.

Lateral zone Outside trestle blocks Within trestle blocks

Mean SD Mean SD

Zone 0 5.8 2.8 2.3 1.4

Zone 1 0.2 0.5 0.2 0.1

Zone 2 0.0 0.1 0.0 0.1


proximity to the tideline, with zone 0 containing the tideline

Impact assessment

Distribution

8.79 Intertidal oyster cultivation appears to cause reduced utilisation by Bar-tailed Godwit of areas

occupied by oyster trestles compared to other areas of comparable habitat. Therefore, in the

absence of intertidal oyster cultivation, Bar-tailed Godwit would be expected to occur in higher

densities within areas currently occupied by oyster trestles. However, the overall extent of the Bar-

tailed Godwit distribution within Dungarvan Harbour is probably not affected by intertidal oyster

cultivation.

8.80 If the densities of Bar-tailed Godwit recorded during the trestle study in the lower shore zone of

Whitehouse Bank outside the trestle blocks were representative of the densities that would have

occurred throughout this zone in the absence of the trestle blocks, a mean of 24 additional birds

would have been expected to have occurred during these counts. Allowing for neap tides, the

overall displacement of Bar-tailed Godwit in 2011 predicted on this basis is 15 birds, amounting to

2% of the Dungarvan Harbour population, while full occupation of the licenses and application

plots would increase the displacement to 3% (Table 8.25).

Table 8.30 - Predicted displacement of Bar-tailed Godwit based on densities recorded in trestle-free

areas of the lower shore zone of Whitehouse Bank.


Dungarvan Harbour population in Jan-Feb 2011 990




full occupation of licenses 19 2%

full occupation of aquaculture plots

31 3%


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8.81 Much higher numbers of Bar-tailed Godwit usually occur on the Ballyrandle Sandflats in an area

that is classified as the same biotope-type as Whitehouse Bank. Therefore, it is possible that

intertidal oyster cultivation has affected the large-scale distribution pattern of Bar-tailed Godwits in

Dungarvan Harbour. If the densities of Bar-tailed Godwit recorded during the trestle study on the

northern side of the Outer Sandflats zone were representative of the densities that would have

occurred on Whitehouse Bank in the absence of the trestle blocks, a mean of 225 additional birds

(around 23% of the Dungarvan Harbour population) would have been expected to have occurred

during these counts.

8.82 Although the overall biotope type has been classified as the same on both side of the bay in the

Outer Sandflats zone, the presence of a tidal channel running through the sandflats on the

northern side of the bay is likely to affect the habitat and there are some minor but consistent

differences in sediment composition between the Ballyrandle Sandflats and Whitehouse Bank

(see Appendix E). The occurrence of Black-tailed Godwits on the northern side of the bay, in

contrast to their absence from Whitehouse Bank (see Appendix C.4) is also an indicator of habitat

differences. Bar-tailed Godwits do feed intensively along the tidal channel, although they are also

widely distributed around the tideline throughout this side of the bay. The absence of large flocks

of Bar-tailed Godwits on ebb/flood tides on Whitehouse Bank (when the tideline is above the

trestle zone) is also an indication that habitat conditions on Whitehouse Bank are less favourable

compared to the northern side of the bay. The abundance of large polychaetes (which are the

favoured prey item of Bar-tailed Godwit; Duijns et al., 2013) appear to be generally higher in the

Ballyrandle Sandflats compared to Whitehouse Bank, although the available data is too limited to

draw definitive conclusions (see Appendix E). Therefore, it seems plausible that the major

component of the differences in densities of Bar-tailed Godwit between the Ballyrandle Sandflats

and the trestle-free areas of Whitehouse Bank is due to differences in food resources, although

some displacement effect on areas adjoining trestles may also be occurring.


8.83 The Dungarvan Harbour Bar-tailed Godwit population has been assessed as being in favourable

conservation condition with a 7% increase in its population index between 1995/96 and 2007/08

(NPWS, 2011c). This compares to an overall national increase of 2% over this period. The

smoothed index shows a very gentle increasing trend over most of this period, with a slight

decline from 2005/06 (NPWS, 2011c). Between the mid-1980s and the mid-1990s the Dungarvan

Harbour Bar-tailed Godwit population remained stable in contrast to an apparent national

decrease (Table 8.16). Therefore, there is no evidence that the development of intertidal oyster

cultivation in the late 1980s, the period of major expansion in the 1990s and the intensification of

the activity in the 2000s has affected the long-term population trends of Bar-tailed Godwit at

Dungarvan Harbour.

Table 8.31 - Population data for Bar-tailed Godwit.





1995/96-2007/08 population trend of smoothed index +7% +2%





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Conclusions

8.84 Intertidal oyster cultivation may have caused, or contributed to the loss of a major Zostera bed

due to intertidal oyster cultivation. This may have caused some local displacement of Light-bellied

Brent Goose but does not appear to have affected their long-term population trends. However, the

current and proposed future extent of intertidal oyster cultivation is not likely to cause significant

impacts to the Dungarvan Harbour population of Light-bellied Brent Goose.

8.85 Intertidal oyster cultivation is not likely to cause significant impacts to the Dungarvan Harbour

populations of Red-breasted Merganser, Great Crested Grebe and Golden Plover.

8.86 Intertidal oyster cultivation is likely to be causing significant displacement impacts to Grey Plover,

Knot and Dunlin (based on the observed displacement of birds that occurs when the tideline

reaches the area occupied by trestles), but does not appear to have affected their long-term

population trends.

8.87 Intertidal oyster cultivation is causing some displacement impacts to Bar-tailed Godwit, but these

are not significant (assuming that habitat/food resources explain the higher numbers on the

Ballyrandle Sandflats) and do not appear to be affecting their long-term population trends.


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Introduction


intertidal oyster cultivation in Dungarvan Harbour on the SCI species of the Helvick Head to

Ballyquin SPA, excluding those SCI species that have already been screened out (see Section 4).

Cormorant

Occurrence in Dungarvan Harbour

9.2 No information is available about the occurrence of visiting Cormorant from the Helvick Head to

Ballyquin SPA within Dungarvan Harbour. However, an assessment of likely patterns of

occurrence can be made, based on information about the species breeding dispersion and

foraging behaviour.

9.3 The main Cormorant colony within the SPA occurs at Ballynamona (see paragraph 5.12), which is

around 5 km from the intertidal oyster cultivation area, or 10 km for a Cormorant flying along the

coastline, while the other recorded Cormorant colonies within the SPA are more distant. The

mean foraging range of Cormorants from their breeding colonies is 8.5 km, with a mean maximum

of 32 km and a maximum of 50 km (Seabird Wikispace; http://seabird.wikispaces.com/).Therefore,

the intertidal oyster cultivation area is within the potential foraging range of the SPA population,

but may only be a peripheral area.

9.4 In winter, Cormorant regularly occur within Dungarvan Harbour but it is not known to what extent,

if any, Cormorants use Dungarvan Harbour in summer. In a study of Cormorant diet at several

Irish coastal breeding colonies West et al. (1975), found that birds at the Lambay Island, Mattle

and Little Saltee colonies were taking fish species associated with estuarine habitats. At Mattle

and Little Saltee, wrasse predominated (77% and 85% of the diet by weight, respectively)

indicating that the birds were mainly feeding in marine habitats. However, West et al. (1975)

considered that, due to the absence of wrasse from their diet, the Lambay Island birds were

mainly feeding in the estuaries at Rush and Malahide rather than in the marine waters around

Lambay Island. However, birds from the Keeragh Island colony appeared to be feeding

exclusively on marine fish, despite Keeragh Island being closer to estuarine habitat compared to

the Little Saltee. The diet of Cormorants from two other breeding colonies (Great Saltee and

Roaninish) was studied by Tierney et al. (2011). Again, wrasse predominated forming 65-70% of

the diet by item, but some flatfish were taken indicating some foraging in estuarine habitats.

9.5 Overall, therefore, the available evidence from both the typical foraging range and diets of

breeding Cormorants indicates that both Dungarvan Harbour in general and the intertidal oyster

cultivation area in particular, may provide potential foraging habitat for the SPA Cormorant

population but that these areas are not likely to be of major importance in providing food

resources for this population.


9.6 In winter high tide counts of Dungarvan Harbour most Cormorant were recorded in the Inner

Harbour and Outer Bay zones, although there was one high count from Whitehouse Bank (Table

9.1). During the trestle study, Cormorant were regularly seen feeding in subtidal habitat close to

the tideline on Whitehouse Bank and were also observed roosting on trestles.


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Table 9.1 – Cormorant distribution in high tide counts of Dungarvan Harbour.

Zone Inner Harbour Outer Sandflats Outer Bay

Date

Whitehouse Bank Ballyrandle

27/01/2010 17 1 6

27/01/2011 17 1 21

14/02/2011 15 1 21

20/12/2011 12 32

17/02/2012 9 20 3


9.7 No evidence is available about the response of Cormorants to oyster trestles.

9.8 Cormorant are fish-eating birds. In general intertidal oyster cultivation is likely to either have no

effect on, or increase local abundances of fish (see paragraph 0). There is no evidence that large-

scale aquaculture at Dungarvan is causing negative impacts on fish population through reduced

recruitment or through indirect food web effects (see paragraph 7.11). If such ecosystem-scale

effects occurred they could be manifested through both displacement of birds (reduced usage of

Dungarvan Harbour) and/or impacts on long-term population trends.

Impact assessment


resources for Cormorant in the areas occupied by the activity, compared to areas of similar habitat

elsewhere in Dungarvan Harbour. Therefore, intertidal oyster cultivation is not likely to cause any

displacement of Cormorant within Dungarvan Harbour.

9.10 It is not possible to directly assess whether intertidal oyster cultivation is affecting the overall

availability of prey resources in Dungarvan Harbour through ecosystem-scale effects (see

paragraph 9.8). However, the lack of negative signals from the long-term population trends of

other fish-eating species (Red-breasted Merganser and Great Crested Grebe; see paragraphs

8.19 and 8.25) indicates that there have been no major impacts on the fish populations. Moreover,

Dungarvan Harbour is not likely to be of major importance in providing food resources for SPA

Cormorant population.

Peregrine


9.11 No information is available about the occurrence of visiting Peregrine from the Helvick Head to

Ballyquin SPA within Dungarvan Harbour. However, an assessment of likely patterns of


foraging behaviour.

9.12 The recorded breeding dispersion of Peregrine in Britain and Ireland varies from 2-5 km (nearest

neighbour difference; Ratcliffe, 1996). The “Waterford Coast” is cited as an example of “close

nesting” with “12 pairs spaced 2.02 km apart on suitable continuous cliff sections in 1991”

(Ratcliffe, 1996). Five pairs of Peregrine were recorded within the SPA in 2002 (NPWS site

synopsis). The SPA covers a 15 km length of coastline, which would give a breeding dispersion of

3 km. Therefore, there must be one nest site close to the northern end of the SPA and the

geometry of the coastline means that any nest site along the northern 3 km of the SPA coastline

would be within 2 km of the intertidal oyster cultivation area.

9.13 Peregrine regularly feed in intertidal areas during winter, exploiting the availability of large

numbers of waterbirds, which provide them with potential prey, and inland breeding Peregrines


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will often move to the coast in winter for this reason. They are likely to hunt over Whitehouse Bank

during winter. During the breeding season, the importance of intertidal areas diminishes as there

are few waterbirds present to provide potential prey for Peregrines: in Dungarvan Harbour the

only waterbirds breeding in intertidal habitat are Shelduck and Ringed Plover, although non-

breeding populations of some species will also be present. However, where Peregrines are

breeding, they will presumably continue to hunt over intertidal areas at times during the breeding

season. Also, juvenile Peregrines will remain around their nest sites into July/August, when the

numbers of waterbirds will build up again. Data on prey taken by breeding Peregrine in northern

Britain during March-July (Ratcliffe, 1996) show that Peregrine continue to take significant

numbers of waterbirds during this period. However, most of the frequently taken wader species

(Lapwing, Golden Plover, Snipe, Woodcock and Curlew were likely to be locally breeding in

terrestrial habitats. Ratcliffe (1996) classifies Peregrine breeding habitats in Britain into six

categories, based on their prey resources. In the “ordinary coast” category, which may correspond

to much of the Helvick Head to Ballyquin SPA, around one-third of the prey-type by weight

comprises waders and gulls and terns. However, the large seabird colonies around Helvick Head

are likely to provide a major component of the diet of Peregrines breeding at northern end of the

SPA.

9.14 Peregrines are territorial during the breeding season and their foraging range may depend upon

the local population density: for example, Peregrines in north-east Scotland mainly feed within 2

km of their nest site, but their foraging range can be extended to 6 km or more, while in

continental Europe, the foraging ranges may extend up to 15 km or more from nest sites (Cramp

and Simmons, 2004). The foraging range of breeding Peregrines will be dictated by the availability

of food resources and at coastal eyries close to large seabird colonies, “Peregrines often hunt

directly from the eyrie and kill within a few hundred metres” (Ratcliffe, 1996).

9.15 In conclusion, it seems likely that the intertidal oyster cultivation area provides potentially suitable

feeding habitat and is within the foraging range of at least one pair of the SPA Peregrine

population. However, the availability of high quality food resources closer to this pair (the Helvick

Head seabird population), and the low numbers of waterbirds that will be present during most of

the Peregrine’s breeding season, indicate that the intertidal oyster cultivation area is probably not

of major importance as feeding habitat for the SPA Peregrine population.


9.16 No evidence is available about the response of Peregrine to oyster trestles. However, it seems

likely that oyster trestles will interfere with their foraging behaviour by obscuring potential prey and

providing refuges for prey to escape to.

Assessment

9.17 Intertidal oyster cultivation may reduce the quality of the feeding habitat by interfering with

Peregrine foraging behaviour. However, given that the intertidal oyster cultivation area is likely to

be of low importance for the nearest SPA breeding pair, it is unlikely that intertidal oyster

cultivation will significantly affect food resources for this pair. Therefore, intertidal oyster cultivation

is considered unlikely to affect the conservation condition of the Helvick Head to Ballyquin SPA

Peregrine population.

Herring Gull

Occurence in Dungarvan Harbour

9.18 No information is available about the occurrence of any visiting Herring Gull from the Helvick

Head to Ballyquin SPA within Dungarvan Harbour. However, an assessment of likely patterns of


foraging behaviour.


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9.19 Herring Gull breed along most of the coastline of the SPA with the main colony at Helvick Head

(see paragraph 5.12), which is around 2 km from the intertidal oyster cultivation area and holds

around one-third of the SPA population. Cramp and Simmons (2004) quote foraging ranges from

breeding colonies in various studies ranging from 22-63 km, while Ratcliffe et al. (2000, quoted by

Langston, 2010) gave a foraging range of 40 km from breeding colonies. Therefore, the intertidal

oyster cultivation area is within the potential foraging range of the SPA population.

9.20 In winter Herring Gulls regularly roost and feed in intertidal and subtidal habitat within the intertidal

oyster cultivation area, but it is not know to what extent, if any, Herring Gulls from the SPA

colonies visit this area in summer. The Herring Gull has a very wide and varied diet. However, a

number of studies have shown that breeding Herring Gulls often rely heavily on food resources

from the intertidal zone (Garthe et al., 1999; Kim and Monaghan, 2006; Kubetzki and Garthe,

2003; Pierotti and Annett, 1991; Rome and Ellis, 2004). At some breeding colonies Herring Gulls

have been found to predominantly feed on fish (Furness and Barrett, 1985) or fish and garbage

(Nogales et al., 1995), with fish being mainly obtained from scavenging behind trawlers rather

than by direct predation (Nogales et al., 1995). However, both these examples were located on

offshore islands (Alisa Crag in south-west Scotland and Hornøy in north Norway) without any

extensive intertidal habitat nearby. Given the proximity of the intertidal oyster cultivation area to

the main breeding colony and the availability of suitable food resources, as indicated by the use of

the area in winter, it is likely that the intertidal oyster cultivation area is providing food resources

for the SPA population.

9.21 Overall, therefore, the available evidence from both the typical foraging range and diets of

breeding Herring Gull indicates that both Dungarvan Harbour in general and the intertidal oyster

cultivation area are likely to potential foraging habitat for the SPA Herring Gull population.


9.22 In winter high low tide counts of Dungarvan Harbour Herring Gull were recorded from all three

zones, with the highest numbers in the Outer Sandflats zone (mainly on Whitehouse Bank), which

held 40-70% of the total count (Table 9.2). In low tide counts of the entire Outer Sandflats zone

during the trestle study, most Herring Gulls occurred on Whitehouse Bank (Table 9.3). There was

a high proportion of roosting birds in these counts (mean 62% roosting) and the count of 149 on

21/02/2011 included a flock of 70 roosting on sandflats in the lower shore zone outside the trestle

blocks.

Table 9.2 – Herring Gull distribution in low tide counts of Dungarvan Harbour.

Zone Inner Harbour Outer Sandflats Outer Bay

Date

Whitehouse Bank Ballyrandle

27/01/2010 13 23 1 13

27/01/2011 24 39 1 37

14/02/2011 44 26 34

17/02/2012 40 169 22 17


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Table 9.3 - Herring Gull distribution in low tide counts on the Outer Sandflats zone carried out for the



06/01/2011 8 33

22/01/2011 1 43

03/02/2011 4 149

21/02/2011 38 56

03/03/2011 27 34


General patterns

9.23 Across all the sites covered by the trestle study, Herring Gull had a neutral response to oyster

trestles with observed numbers within trestle blocks similar to the predicted numbers. However,

the response of Herring Gull to intertidal oyster cultivation was classified as variable due to the

results of the intensive study in Dungarvan Harbour (see paragraph 9.24).

Dungarvan Harbour

9.24 In the analysis of Herring Gull distribution across the entire Outer Sandflats zone from the

extensive study, observed numbers within the oyster trestle blocks were similar to the predicted

numbers. However, in the analysis of Herring Gull distribution within a 2 km section of the lower

shore zone of Whitehouse Bank observed numbers within the oyster trestle blocks were

consistently lower than the predicted numbers and mean densities were around 1.25 times as

high outside the trestle blocks compared to within the trestle blocks (Table 9.4) but this difference

was not significant (F1,11 = 0.04, p = 0.852). These differences reflected the large proportions of

roosting Herring Gulls. In a re-analysis of the data for this present assessment, excluding the

roosting birds, the observed numbers within the oyster trestle blocks were scattered around the

1:1 line indicating no avoidance of the trestle blocks by the feeding birds (Text Figure 9.1),

although this analysis is based on small total counts (only four of the 13 counts included in the

analysis had total counts of ten or more)2. Given the neutral response to trestles observed across

the sites included in the extensive study, it seems reasonable to assume that foraging Herring

Gulls do not avoid trestle blocks at Dungarvan Harbour. In fact, Herring Gulls were frequently

observed feeding on top of the trestles.

Table 9.4 – Herring Gull densities (number per 10 ha) in lateral zones relative to the tideline.

Outside trestle blocks Within trestle blocks

Lateral zone Mean SD Mean SD

Zone 0 10.3 12.2 8.2 7.9

Zone 1 0.1 0.2 0.0 0.0

Zone 2 0.0 0.0 0.0 0.0


proximity to the tideline, with zone 0 containing the tideline

2 This analysis was not included in Gittings and O’Donoghue (2012) because that study only included analyses with at

least six qualifying counts, where a qualifying count was defined as having a total of ten or more birds.


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Text Figure 9.1 - Observed compared to predicted occurrence of feeding Herring Gull within oyster

trestle blocks in a 2 km section of shoreline at Whitehouse Bank. Data points with observed values of

1 and 4 have been displaced slightly for clarity.

Impact assessment

9.25 Roosting Herring Gulls may show an avoidance response to intertidal oyster cultivation at

Dungarvan Harbour. However, Herring Gulls from the SPA population are unlikely to be visiting

Dungarvan Harbour to roost.

9.26 Foraging Herring Gulls do not appear to show an avoidance response to intertidal oyster

cultivation. Therefore, intertidal oyster cultivation is not likely to affect Herring Gull food resources

and is considered unlikely to affect the conservation condition of the Helvick Head to Ballyquin

SPA Herring Gull population.

Conclusions

9.27 Intertidal oyster cultivation in Dungarvan Harbour is unlikely to cause significant impacts to the

populations of Cormorant, Peregrine and Herring Gull in the Helvick Head to Ballyquin SPA.


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Introduction


intertidal oyster cultivation in Dungarvan Harbour on the SCI species of the Mid-Waterford Coast

SPA, excluding those SCI species that have already been screened out (see Section 4).

Cormorant


10.2 No information is available about the occurrence of visiting Cormorant from the Mid-Waterford

Coast SPA within Dungarvan Harbour. However, an assessment of likely patterns of occurrence

can be made, based on information about the species breeding dispersion and foraging

behaviour.

10.3 The main Cormorant colony within the SPA occurs at Ballyvoile Head (see paragraph 5.14), which

is around 7 km from the intertidal oyster cultivation area and holds around 25% of the SPA

population. Therefore, the intertidal oyster cultivation area is within the potential foraging range of

the SPA population, but may only be a peripheral area (see paragraph 9.3). Information on the

diets of breeding Cormorants (see paragraph 9.4) indicates that both Dungarvan Harbour in

general, and the intertidal oyster cultivation area in particular, may provide suitable foraging

habitat for the SPA Cormorant population. However, these areas are not likely to be of major

importance in providing food resources for this population given their likely peripheral position in

the foraging range of the SPA population.


10.4 In winter high tide counts most Cormorants occur in the Inner Harbour and Outer Bay zones,

although there has been a high count from Whitehouse Bank (see paragraph 9.6).


10.5 Intertidal oyster cultivation is likely to either have no effect on, or cause increased local

abundances of fish (see paragraph 9.8); there is no evidence that large-scale aquaculture at

Dungarvan is causing negative impacts on fish population through reduced recruitment or through

indirect food web effects (see paragraph 7.11). If such ecosystem-scale effects occurred they

could be manifested through both displacement of birds (reduced usage of Dungarvan Harbour)

and/or impacts on long-term population trends.

Impact assessment


resources for Cormorant in the areas occupied by the activity, compared to areas of similar habitat

elsewhere in Dungarvan Harbour. Therefore, intertidal oyster cultivation is not likely to cause any

displacement of Cormorant within Dungarvan Harbour.

10.7 It is not possible to directly assess whether intertidal oyster cultivation is affecting the overall

availability of prey resources in Dungarvan Harbour through ecosystem-scale effects (see

paragraph 9.8). However, the lack of negative signals from the long-term population trends of

other fish-eating species (Red-breasted Merganser and Great Crested Grebe; see paragraphs

8.19 and 8.25) indicates that there have been no major impacts on the fish populations. Moreover,


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Dungarvan Harbour is not likely to be of major importance in providing food resources for SPA

Cormorant population.

Peregrine

Occurrence within Dungarvan Harbour

10.8 No information is available about the occurrence of visiting Peregrine from the Mid-Waterford

Coast SPA within Dungarvan Harbour. However, an assessment of likely patterns of occurrence

can be made, based on information about the species breeding dispersion and foraging

behaviour.

10.9 Seven pairs of Peregrine were recorded within the SPA in 2002 (NPWS site synopsis). The SPA

covers a 25 km length of coastline, which would give a breeding dispersion of 3.5 km. Therefore,

there must be one nest site close to the western end of the SPA within 6-9 km of the intertidal

oyster cultivation area. This distance would mean that the intertidal oyster cultivation area could

be within the foraging range of Peregrine breeding at the western end of the SPA but, if so, would

probably only be a peripheral area (see paragraph 9.14). The habitat within the intertidal oyster

cultivation area provides potentially suitable foraging habitat, although the availability of suitable

prey in this habitat is likely to be limited during the most of the breeding season (see paragraph

9.13). However, the peripheral position of the intertidal oyster cultivation area in the likely foraging

range of this pair, and the limited availability of suitable prey in the intertidal oyster cultivation area

during most of the Peregrine’s breeding season, indicate that the intertidal oyster cultivation area

is probably not of major importance as feeding habitat for the SPA Peregrine population.


10.10 No evidence is available about the response of Peregrine to oyster trestles. However, it seems

likely that oyster trestles will interfere with their foraging behaviour by obscuring potential prey and

providing refuges for prey to escape to.

Assessment

10.11 Intertidal oyster cultivation may reduce the quality of the feeding habitat by interfering with

Peregrine foraging behaviour. However, given that the intertidal oyster cultivation area is likely to

be of low importance for the nearest SPA breeding pair, it is unlikely that intertidal oyster

cultivation will significantly affect food resources for this pair. Therefore, intertidal oyster cultivation

is considered unlikely to affect the conservation condition of the Mid-Waterford Coast SPA

Peregrine population.

Herring Gull


10.12 No information is available about the occurrence of any visiting Herring Gull from the Mid-

Waterford Coast SPA within Dungarvan Harbour. However, an assessment of likely patterns of


foraging behaviour.

10.13 Herring Gull breed along most of the coastline of the SPA (see paragraph 5.14), with around 20%

of the SPA population within 10 km of the intertidal oyster cultivation area, and around 60% within

15 km. Therefore, the intertidal oyster cultivation area is well within the potential foraging range of

the SPA population (see paragraph 9.19). The habitat within the intertidal oyster cultivation area

provides potentially suitable foraging habitat (see paragraph 9.20).


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10.14 Therefore, the available evidence from both the typical foraging range and diets of breeding

Herring Gull indicates that both Dungarvan Harbour in general and the intertidal oyster cultivation

area are likely to potential foraging habitat for the SPA Herring Gull population.


10.15 In winter low tide counts most Herring Gulls occurred in the Outer Sandflats zone, particularly on

Whitehouse Bank (see paragraph 9.22).


General patterns

10.16 Across all the sites covered by the trestle study, Herring Gull had a neutral response to oyster

trestles with observed numbers within trestle blocks similar to the predicted numbers. However,

the response of Herring Gull to intertidal oyster cultivation was classified as variable due to the

results of the intensive study (see paragraph 9.24).

Dungarvan Harbour

10.17 Herring Gulls generally show a neutral response to oyster trestles (see paragraph 9.24) but, at

Dungarvan Harbour, roosting Herring Gulls appear to avoid the trestles. However, foraging

Herring Gulls did not avoid the trestle blocks at Dungarvan Harbour and were frequently observed

feeding on top of the trestles (see paragraph 9.25).

Impact assessment

10.18 Roosting Herring Gulls may show an avoidance response to intertidal oyster cultivation at

Dungarvan Harbour. However, Herring Gulls from the SPA population are unlikely to be visiting

Dungarvan Harbour to roost.

10.19 Foraging Herring Gulls do not appear to show an avoidance response to intertidal oyster

cultivation. Therefore, intertidal oyster cultivation is not likely to affect Herring Gull food resources

and is considered unlikely to affect the conservation condition of the Mid-Waterford Coast SPA

Herring Gull population.

Conclusions

10.20 Intertidal oyster cultivation in Dungarvan Harbour is unlikely to cause significant impacts to the

populations of Cormorant, Peregrine and Herring Gull in the Mid-Waterford Coast SPA.


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11. Assessment of cumulative impacts

Introduction

11.1 This section presents an assessment of potential cumulative impacts from intertidal oyster

cultivation in combination with other activities. Light-bellied Brent Goose, Red-breasted

Merganser, Great Crested Grebe, Cormorant, and Herring Gull are not included in this

assessment because the main assessment has concluded that these species are likely to have a

neutral or positive response to intertidal oyster cultivation. Therefore, as the species included in

this assessment are only associated with intertidal habitat, activities only affecting deep subtidal

habitat such as boat traffic are not included in this assessment.

Activities

11.2 An indicative distribution map of the activities considered in this assessment is shown in Figure

11.1. This is based on the mapping of activities during the trestle study and the NPWS BWS

counts, with the distribution of activities not recorded in these studies inferred from the information

provided in CLAMS (2002) and the distribution of habitat/topographical features suitable for such

activities.

Disturbance generating activities

Beach recreation

11.3 The Cunnigar is a popular location for recreational activity. During the trestle study, visitors, often

with dogs, were present on every count day. Typically visitors would walk along the length of the

Cunnigar, but rarely ventured onto the sandflats, although occasionally the dogs would run out a

few hundred metres. Horse riders were also recorded on every count day, often riding the full

length of the sandflats ranging widely across the upper shore zone, but rarely venturing into the

lower shore zone (due to the presence of the trestles). No other beach recreation activities were

recorded on Whitehouse Bank during the trestle study.

11.4 The other main recreational area in Dungarvan Harbour is Abbeyside Strand along the north-

western side of the Ballyrandle Sandflats (CLAMS, 2002). Walkers, often with dogs, were also

observed here on each count day during the trestle study with some walking out onto the

sandflats along the mixed substrata biotope area (although some of this activity may have been

associated with shellfish gathering; see below). Horse-riding was also recorded in this area during

the NPWS BWS counts.

11.5 There is also pedestrian access to the shoreline around much of the Inner Harbour zone and

along the eastern side of the Ballyrandle Sandflats. These are mainly roads, but there is a

dedicated pedestrian walkway along the old railway line crossing the Glendine Estuary at the

upper edge of the Ballyrandle Sandflats.

Water-based recreation

11.6 Water-based recreational activities were not recorded during either the trestle study or NPWS

BWS counts. However, various activities are reported to occur (CLAMS, 2002). Windsurfing is

described as a year-round activity with most popular areas being the Ballyrandle Sandflats

between Abbeyside Strand and Ballynacourty Pier. The canoeing season runs from April-

September with the main launching areas at Ballynacourty, Abbeyside, Clonea Strand and to a

lesser extent Dungarvan quays. Powered motorsports (water skiing, power boating and jet skiing)

mainly occur in the Inner Harbour west of the Cunnigar with the season running from March-

September/October.


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Hand collection of shellfish

11.7 The mixed substrata/eulittoral rock biotope area on the Ballyrandle Sandflats is a popular shellfish

gathering area (CLAMS, 2002) with winkle pickers recorded here on each count day during the

trestle study and on three of the four NPWS BWS low tide counts. Winkle pickers were also

recorded, but less frequently during the trestle study, on the western shoreline of Whitehouse

Bank within the narrow littoral rocky shore zone, and along the shoreline of the Outer Bay during

the NPWS BWS low tide counts.

Bait digging

11.8 Bait digging occurs along the shoreline at Ringnasilloge in the Inner Harbour, at Abbeyside Strand

along the north-western side of the Ballyrandle Sandflats and along the eastern shoreline of

Ballyrandle Sandflats north of Ballynacourty Pier (CLAMS, 2002). Bait digging was recorded on

the Ballyrandle Sandflats on one of the trestle study count days and two of the NPWS BWS

counts, and was also recorded on Whitehouse Bank (presumably at the southern end) on one of

the NPWS BWS counts.

Potential impacts

11.9 There is an extensive and complex literature on the impacts of disturbance from human activities

on waterbirds in intertidal and shallow subtidal habitats. It is difficult to use this literature to make

specific predictions about the nature and extent of potential disturbance impacts as the effects of

disturbance vary between species and, within species, vary between sites and within sites.

However, in general, with beach walks and/or when access is mainly along the shoreline (i.e., in

with little activity in the intertidal or shallow subtidal zone), disturbance impacts, while causing

local (a few hundred metres) displacement of birds, does not appear to affect the large-scale

distribution of birds across sites (e.g., Colwell and Sundeen, 2000; Lafferty, 2001; Gill et al., 2001;

Neumann et al., 2008; Trulio and Sokale, 2008; Yasué, 2006; but see Burton et al., 2002) or

survivorship (Durell et al., 2007; but see Stillman et al., 2012). Disturbance in the intertidal zone

will generally have greater impacts (Stillman et al., 2012) and, where disturbance rates are high

and/or concentrated areas of species food resources are affected, may cause significant impacts

to large-scale distribution (Mathers et al., 2002) and/or survivorship (Durell et al., 2008; Goss-

Custard et al., 2005; Stillman et al., 2012; West et al., 2008). However, some studies of shellfish

gathering in the intertidal zone have concluded that it does not affect waterbird populations (Dias

et al., 2008; Navedo and Masero (2007).

11.10 The main concentration of activity in the intertidal is on the Ballyrandle Sandflats. Walkers along

the Cunnigar are unlikely to cause much disturbance as they rarely venture away from the

shoreline, but horse riding across Whitehouse Bank may cause significant disturbance impacts.

During the trestle study horse riders were observed on several dates riding through the tideline on

ebb/flood tides causing disturbance to large numbers of birds. At low tide, horse riders do not

cause much disturbance as the oyster trestles prevent them from having access to the lower

shore zone where most waterbirds occur.

11.11 Boat activity will generally not affect waterbirds in intertidal and shallow subtidal activity. However,

some types of recreational watersports activities can occur in very shallow waters and have been

observed to cause disturbance to waterbirds. For example, we have observed jet skiers in

Ballycotton Bay travelling up tidal channels and across shallowly flooded areas causing

disturbance to important feeding and roosting areas. In Cork Harbour, kayakers and windsurfers

in the Aghada area can come close into the shoreline causing disturbance to high tide roosts.

These activities will mainly take place around the high tide period but may cause disturbance to

feeding waterbirds in intertidal and shallow subtidal habitat on ebb/flood tides.


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Activities affecting waterbird food resources

Bait digging and shellfish collecting

11.12 Bait digging and shellfish collecting will remove food resources that would otherwise be available

for consumption by waterbirds and may also cause mortality to not-target species (Masero et al.,

2006). Therefore, if these activities are extensive and/or affect concentrated food resources they

could cause waterbird distribution (by causing displacement from depleted areas) and/or

survivorship (by reducing the overall carrying capacity of the system).

11.13 In Dungarvan Harbour, bait digging appears to be a low intensity activity being recorded on two of

the four count days during the NPWS BWS low tide counts, and with only a single bait digger

observed on one of the five count days in the Ballyrandle Sandflats during the trestle study. This

compares to bait digger numbers of 46-544 throughout the year in the Masero et al. (2006) study.

Therefore, it seems unlikely that bait digging is having measurable impacts in terms of resource

depletion or physical habitat disturbance in Dungarvan Harbour.

11.14 Shellfish gathering is a more intensive activity in Dungarvan Harbour, particularly in the main

shellfish gathering area in the mixed substrata and eulittoral rock biotopes on the Ballyrandle

Sandflats, where it was recorded on each count day during the trestle study (with a mean of five

gatherers per count day). As the shellfish resource (periwinkles) is of limited extent, shellfish

gathering may, therefore, be causing some level of resource depletion.

Effluent discharge

11.15 Organic and nutrient inputs to estuaries increase productivity and may increase food resources for

waterbirds. Therefore, adverse impacts to waterbirds might be expected to be caused by declines

in organic and nutrient inputs associated with improvements in wastewater treatment There are a

number of studies that document the effects of organic and nutrient loading from effluent

discharges on the benthic fauna and typically the zones affected by individual discharges are

restricted to within a few hundred metres of the outfall (Burton et al., 2002). The available

evidence on the effects of nutrient reductions on estuarine waterbird populations is limited but, to

date, no significant impacts have been reported (Burton et al., 2002, 2003). One study (Alves et

al., 2012) has reported localised (within 100 m) association between wastewater inputs and bird

distribution; in this study the outfalls discharged in the intertidal zone and streams of sewage ran

across the intertidal habitat.

11.16 At Dungarvan Harbour, raw sewage was discharged into the harbour via a marine outfall at

Abbeyhole (to the north of the end of the Cunnigar; Figure 11.1) until the opening of a new

wastewater treatment plant in 2008 with discharge of treated effluent into the outer bay at

Ballynacourty Point. Therefore, it is possible that the reduced nutrient loading in the Inner Harbour

since 2008 may cause reductions in food supply for waterbirds. Based on the available research

evidence, any such impacts are likely to be restricted to the immediate vicinity of the outfall

location: i.e., the extreme western end of the Ballyrandle Sandflats and the western side of the

northern end of the Cunnigar. The western end of the Ballyrandle Sandflats has a narrow intertidal

zone and is partially isolated from the main sandflat area by the mixed substrata biotope area,

while the intertidal zone on the western side of the northern end of the Cunnigar is also relatively

narrow and has limited exposure periods. The NPWS BWS in 2009/10 took place only a short

time after the cessation of the Abbeyhole discharge and should, therefore, still reflect any

influences that the nutrient input at Abbeyhole was having on waterbird distribution. The flock map

data show no obvious association of any of the SCI species with the above areas. Therefore,

there is no evidence to indicate that the cessation of the discharge of raw sewage at the

Abbeyhole outfall will cause a significant reductions in food supply for any of the SCI species, and

it is not necessary to consider potential in-combination effects with intertidal oyster cultivation.


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Species assessments

Golden Plover

11.17 Golden Plover mainly occur on Whitehouse Bank with small numbers occurring at times in the

Inner Harbour zone and on the Ballyrandle Sandflats (see paragraphs 8.26 and 8.27). Therefore,

activities on the Ballyrandle Sandflats and in the Inner Harbour are unlikely to have significant

effects on this species.

11.18 On Whitehouse Bank, horse riding may cause displacement of Golden Plover across the low tide

period. Intertidal oyster cultivation is not considered to be causing or likely to cause significant

levels of displacement of Golden Plover, due to the extensive availability of suitable roosting

habitat in the upper shore zone. However, high levels of disturbance from horse riding to this

upper shore zone could, in combination with intertidal oyster cultivation, cause significant

displacement impacts.

11.19 Golden Plover have been recorded feeding on periwinkles (Cramp and Simmons, 2004).

However, they use the intertidal habitat in Dungarvan Harbour for roosting and do not occur in the

shellfish gathering areas. Therefore, resource depletion due to shellfish gathering is unlikely to be

causing significant impacts to the Golden Plover population.

11.20 The analysis of long-term population trends of Golden Plover at Dungarvan Harbour do not

indicate any site-specific factors causing negative impacts to the population (see paragraph 8.37).

Therefore, there is no evidence that any in-combination effects of disturbance with intertidal oyster

cultivation is causing negative impacts to the conservation condition of Golden Plover at

Dungarvan Harbour.

Grey Plover

11.21 Grey Plover occur mainly in the Inner Harbour zone and, particularly during ebb/flood tides, on

Whitehouse Bank (see paragraphs 8.38-8.39). Therefore, the main concentration of disturbance

pressures on the Ballyrandle Sandflats will not have significant effects on this species. The NPWS

BWS low tide count data and flock maps indicate that, within the Inner Harbour zone, Grey Plover

mainly occur to the east of the Glendine River tidal channel away from the bait digging area, while

in the Outer Sandflats zone their distribution does not overlap with bait-digging and shellfish

gathering activities.

11.22 On Whitehouse Bank, horse riding may cause displacement of Grey Plover on ebb/flood tides,

while in the Inner Harbour watersport recreation may also cause displacement of Grey Plover on

ebb/flood tides (although this impact would be limited to the autumn period when the impacts of

disturbance are likely to be less severe). This will not have a direct in-combination effect with

intertidal oyster cultivation, as the latter will only have displacement impacts close to low tide

when the tideline is within the lower shore zone. However, if the carrying capacity of Dungarvan

Harbour for Grey Plover was limited, displacement could cause reduced survivorship. In this

scenario, displacement of Grey Plover on ebb/flood tides due to horse riding and/or watersport

recreation could, in combination with intertidal oyster cultivation, cause a significantly greater

impact than the impact of intertidal oyster cultivation by itself.

11.23 Grey Plover appears to be relatively tolerant of disturbance impacts (Burton et al., 2002; Stillman

et al., 2012; West et al., 2008; but see Pfister et al., 19923). The long-term population trends of

Grey Plover at Dungarvan Harbour do not indicate any site-specific factors causing negative

impacts to the population (see paragraph 8.48). Therefore, there is no evidence that any in-

3 Note the full text of this paper was not available for review.


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combination effects of disturbance with intertidal oyster cultivation is causing negative impacts to

the conservation condition of Grey Plover at Dungarvan Harbour.

Knot

11.24 Knot occur mainly in the Inner Harbour zone, but significant numbers can occur in the Outer

Sandflats zone in the Ballyrandle Sandflats at low tide and on Whitehouse Bank during ebb/flood

tides (see paragraphs 8.49 and 8.50). Therefore, their distribution overlaps with most of the

recreational and harvesting activities considered in this assessment (apart from the bait-digging in

the Inner Harbour and the shellfish gathering along the southern side of the Outer Sandflats and

Outer Bay zones).

11.25 On the Ballyrandle Sandflats, bait digging, shellfish gathering and intertidal walking may all cause

displacement of Knot across the low tide period. As Knot already appear to be displaced from

Whitehouse Bank by intertidal oyster cultivation during the four-five hour period around low tide,

displacement of Knot from Ballyrandle Sandflats could, in combination with intertidal oyster

cultivation, cause a significantly greater displacement impact than the impact of intertidal oyster

cultivation by itself.

11.26 On Whitehouse Bank, horse riding may cause displacement of Knot on ebb/flood tides, while in

the Inner Harbour watersport recreation may also cause displacement of Knot on ebb/flood tides

(although this impact would be limited to the autumn period when the impacts of disturbance are

likely to be less severe). This will not have a direct in-combination effect with intertidal oyster

cultivation, as the latter will only have displacement impacts close to low tide when the tideline is

within the lower shore zone. However, if the carrying capacity of Dungarvan Harbour for Knot was

limited, displacement could cause reduced survivorship. In this scenario, displacement of Knot

from Whitehouse Bank during low tide and from the Inner Harbour and Whitehouse Bank on

ebb/flood tides due to horse riding and/or watersport recreation could, in combination with

intertidal oyster cultivation, cause a significantly greater impact on survivorship than the impact of

intertidal oyster cultivation by itself.

11.27 Knot often occur in mixed substrata biotopes. They feed on bivalve shellfish and, while they

typically specialise on mussels and/or cockles, they have been recorded feeding on periwinkles

(Cramp and Simmons, 2004). Therefore, it is possible that, if the carrying capacity of Dungarvan

Harbour for Knot was limited, resource depletion due to shellfish gathering could, in combination

with intertidal oyster cultivation, cause a significantly greater impact on survivorship than the

impact of intertidal oyster cultivation by itself.

11.28 The analysis of long-term population trends of Knot at Dungarvan Harbour does not indicate any

site-specific factors causing negative impacts to the population (see paragraph 8.59). Therefore,

there is no evidence that any in-combination effects of disturbance and/or resource depletion from

shellfish gathering with intertidal oyster cultivation is causing negative impacts to the conservation

condition of Knot at Dungarvan Harbour.

Dunlin

11.29 Dunlin occur mainly in the Inner Harbour zone, but significant numbers can occur in the Outer

Sandflats zone in the Ballyrandle Sandflats at low tide and, particularly during ebb/flood tides, on

Whitehouse Bank (see paragraphs 8.60 and 8.61). Therefore, their distribution overlaps with most

of the recreational and harvesting activities considered in this assessment (apart from the shellfish

gathering along the southern side of the Outer Sandflats and Outer Bay zones).

11.30 Bait digging in the Ballyrandle Sandflats and the Inner Harbour, and shellfish gathering and

intertidal walking on the Ballyrandle Sandflats may all cause displacement of Dunlin across the

low tide period. As Dunlin already appear to be substantially displaced from Whitehouse Bank by

intertidal oyster cultivation during the four-five hour period around low tide, displacement from


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Ballyrandle Sandflats and the Inner Harbour could, in combination with intertidal oyster cultivation,

cause a significantly greater displacement impact than the impact of intertidal oyster cultivation by

itself.

11.31 On Whitehouse Bank, horse riding may cause displacement of Dunlin on ebb/flood tides, while in

the Inner Harbour watersport recreation may also cause displacement of Dunlin on ebb/flood tides

(although this impact would be limited to the autumn period when the impacts of disturbance are

likely to be less severe). This will not have a direct in-combination effect with intertidal oyster

cultivation, as the latter will only have displacement impacts close to low tide when the tideline is

within the lower shore zone. However, if the carrying capacity of Dungarvan Harbour for Dunlin

was limited, displacement could cause reduced survivorship. In this scenario, displacement of

Dunlin from Ballyrandle during low tide and from the Inner Harbour and Whitehouse Bank on

ebb/flood tides due to horse riding and/or watersport recreation could, in combination with

intertidal oyster cultivation, cause a significantly greater impact on survivorship than the impact of

intertidal oyster cultivation by itself.

11.32 Dunlin typically feed in soft intertidal sediments and rarely feed in large numbers on mixed

substrata or eulittoral rock biotopes, while periwinkles have not been recorded in their diet (Cramp

and Simmons, 2004). Therefore, resource depletion due to shellfish gathering is unlikely to be

causing significant impacts to the Dunlin population.

11.33 The analysis of long-term population trends Dunlin at Dungarvan Harbour do not indicate any site-

specific factors causing negative impacts to the population (see paragraph 8.71). Therefore, there

is no evidence that any in-combination effects of disturbance with intertidal oyster cultivation is

causing negative impacts to the conservation condition of Dunlin at Dungarvan Harbour.

Bar-tailed Godwit

11.34 Bar-tailed Godwit mainly occur in the Outer Sandflats zone, favouring the Ballyrandle Sandflats

but with significant numbers also usually occurring on Whitehouse Bank (see paragraphs 8.72

and 8.73. In the Inner Harbour zone, significant numbers can occur at times, but they appear to be

largely restricted to the eastern side of the River Brickey tidal channel. Therefore, their distribution

overlaps with most of the recreational and harvesting activities considered in this assessment

(apart from the bait-digging in the Inner Harbour and the shellfish gathering along the southern

side of the Outer Sandflats and Outer Bay zones).

11.35 Shellfish gathering, bait digging and intertidal walking on the Ballyrandle Sandflats may all cause

displacement of Bar-tailed Godwit across the low tide period. Assuming that the differences in

density between Ballyrandle Sandflats and Whitehouse Bank are due to differences in

habitat/food resources (see paragraph 8.82), intertidal oyster cultivation is not causing, and is not

predicted to cause, significant levels of displacement (see paragraph 8.80). However,

displacement from Ballyrandle Sandflats could, in combination with intertidal oyster cultivation,

cause overall displacement levels to become significant.

11.36 On Whitehouse Bank, horse riding may cause displacement of Bar-tailed Godwit on ebb/flood

tides, while in the Inner Harbour watersport recreation may also cause displacement of Bar-tailed

Godwit on ebb/flood tides (although this impact would be limited to the autumn period when the

impacts of disturbance are likely to be less severe). This will not have a direct in-combination

effect with intertidal oyster cultivation, as the latter will only have displacement impacts close to

low tide when the tideline is within the lower shore zone. However, if the carrying capacity of

Dungarvan Harbour for Bar-tailed Godwit was limited, displacement could cause reduced

survivorship. In this scenario, displacement of Bar-tailed Godwit from Whitehouse Bank during low

tide and from the Inner Harbour and Whitehouse Bank on ebb/flood tides due to horse riding

and/or watersport recreation could, in combination with intertidal oyster cultivation, cause a

significantly greater impact on survivorship than the impact of intertidal oyster cultivation by itself.


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11.37 Bar-tailed Godwit typically feed in soft intertidal sediments and rarely feed in large numbers on

mixed substrata or eulittoral rock biotopes. While periwinkles have been recorded in their diet

(Cramp and Simmons, 2004), they predominantly feed on polychaete worms (see Appendix E.2).

Therefore, resource depletion due to shellfish gathering is unlikely to be causing significant

impacts to the Bar-tailed Godwit population.

11.38 The analysis of long-term population trends of Bar-tailed Godwit at Dungarvan Harbour does not

indicate any site-specific factors causing negative impacts to the population (see paragraph 8.71).

Therefore, there is no evidence that any in-combination effects of disturbance with intertidal oyster

cultivation is causing negative impacts to the conservation condition of Bar-tailed Godwit at

Dungarvan Harbour.


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Figure 11.1 - Indicative map of disturbance pressures in Dungarvan Harbour SPA.


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12. References

Alves, J. A., Sutherland, W. J., & Gill, J. A. (2012). Will improving wastewater treatment impact

shorebirds? Effects of sewage discharges on estuarine invertebrates and birds. Animal

Conservation, 15(1), 44–52.

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Appendix A

Scientific names


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Common name Scientific names BTO code

Light-bellied Brent Goose Branta bernicla hrota PB

Shelduck Tadorna tadorna SU

Red-breasted Merganser Mergus serrator RM

Great Crested Grebe Podiceps cristatus GG

Cormorant Phalacrocorax carbo CA

Peregrine Falco peregrinus PE

Oystercatcher Haematopus ostralegus OC

Golden Plover Pluvialis apricaria GP

Grey Plover Pluvialis squatarola GV

Lapwing Vanellus vanellus L.

Knot Calidris canutus KN

Dunlin Calidris alpina DN

Black-tailed Godwit Limosa limosa BW

Bar-tailed Godwit Limosa lapponica BA

Curlew Numenius arquata CU

Redshank Tringa totanus RK

Turnstone Arenaria interpres TT

Herring Gull Larus argentatus HG

Kittiwake Rissa tridactyla KI

Chough Pyrrhocorax pyrrhocorax CF


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Appendix B

Diet of Red-breasted Merganser and Great

Crested Grebe


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RK2927/2927Dg17_Dungarvan Harbour AA.doc 84

B.1 Introduction

B.1.1 This appendix presents an assessment of the likely diet of Red-breasted Merganser and Great

Crested Grebe at Dungarvan Harbour.

B.1.2 The assessment is based on a review of information contained within the Food sections of the

relevant species accounts in Cramp and Simmons (2004), supplemented by additional sources

where relevant. Unless otherwise stated, all information has been taken from Cramp and

Simmons (2004).

B.1.3 The assessment focuses on the relevant habitats and/or seasons.

B.2 Fish populations in Dungarvan Harbour

B.2.1 A fish stock survey was carried out in Dungarvan Harbour in October 2008 (CRFB, 2009). This

included seine net sampling at six sites and fyke net sampling at four sites. The sites were mainly

located around the main tidal channel near the tip of the Cunnigar and along the eastern shore of

the Outer Sandflats zone, with one site in the upper section of the Colligan Estuary.

B.2.2 A total of 16 species were recorded with Common Goby being the most abundant species,

followed by Lesser Sand Eel and Sand Smelt (Table B.1). The 2-Spotted Goby were associated

with rocky habitat along the eastern shore of the Outer Sandflats zone. The low number of

Flounder was noted as being a “little surprising” as they are usually abundant in estuaries.

Table B.1 - Fish species recorded in Dungarvan Harbour in the October 2008 survey

Species Total numbers

Chelon labrosus Thick Lipped Grey Mullet 1

Platichthys flesus Flounder 9

Sprattus sprattus Sprat 2

Pomatoschistus microps Common Goby 301

Pleuronectes platessa Plaice 7

Ammodytes tobianus Lesser Sandeel 164

Atherina prebyter Sand Smelt 101

Hyperoplus lanceolatus Greater Sandeel 3

Ciliata mustela 5-Bearded Rockling 21

Salmo trutta Sea Trout 1

Merlangus merlangus Whiting 1

Gadus morhua Cod 1

Pollachius pollachius Pollock 7

Gobiusculus flavescens 2-Spotted Goby 28

Syngnathus acus Greater Pipefish 1

Scyliorhinus canicula Lesser-Spotted Dogfish 4

Source: CRFB (2009)

B.3 Red-breasted Merganser

B.3.1 Gobies are generally an important prey item for Red-breasted Merganser (Cramp and Simmons,

2004) so the abundance of Common Goby in Dungarvan Harbour suggest that it is likely to be a

major component of the diet of the Dungarvan Harbour Red-breasted Merganser population. The

other common species (Lesser Sandeel and Sand Smelt) are also recorded in the diet of Red-

breasted Merganser, and smelt were a major component of the diet in one study quoted by Cramp

and Simmons (2004).


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B.3.2 Larger pelagic species such as cod and sprat, which Red-breasted Merganser also feed on, may

prove more energy rich when available, given the larger average biomass of these species. Large

pelagic species were generally rare in the fish population sampled by CRFB (2009), but may be

more frequent in the Outer Bay zone (which was not sampled). However, the limited distribution

data available indicates that Red-breasted Merganser occur less frequently in the Outer Bay zone

compared to the Outer Sandflats and Inner Harbour zones (see paragraph 8.14). Therefore, large

pelagic species may not be an important component of the diet of the Dungarvan Harbour Red-

breasted Merganser population.

B.3.3 Mobile invertebrates such as small shore crabs, mysids (shrimp like crustaceans) and common

shrimp are also an important component of the diet of Red-breasted Merganser (Cramp and

Simmons, 2004). The mixture of muddy and sandy biotopes should support abundant mysids and

shrimps that favour mud and mixed sediment, while crabs can hide in the refugia of the mixed

substatra and eulittoral rock biotopes on Spit Bank, as well as in the artificial refugia provided by

the oyster trestles. It is therefore likely that abundant invertebrates are available and may

represent an important part of the diet of Red-breasted Merganser in Dungarvan Harbour.

B.3.4 Other important prey species for Red-breasted Merganser include sticklebacks and Coalfish, but

these were not recorded in the Dungarvan Harbour (CRFB, 2009).

B.4 Great Crested Grebe

B.4.1 Great Crested Grebe, favour small prey items, between 6.5-10 cm long, with younger birds

favouring prey at the lower end of the range (Gwiazda, 1996, in addition to studies quoted by

Cramp and Simmons, 2004). The species can prey on sticklebacks but other fish such as gobies

are a more important prey item in transitional waters (Doornbus, 1984, in addition to studies

quoted by Cramp and Simmons, 2004). Therefore, the abundance of Common Goby in

Dungarvan Harbour suggests that it is likely to be a major component of the diet of the Dungarvan

Harbour Great Crested Grebe population. The other common species (Lesser Sandeel and Sand

Smelt) are not recorded in the diet of Great Crested Grebe by Cramp and Simmons (2004),

although this may reflect the limited number of studies of Great Crested Grebe diet in

brackish/marine habitats reviewed.

B.4.2 Sprat has also been found to be important food item to Great Crested Grebe in the Netherlands

(Doornbus, 1984) while cod was recorded in the diet of Great Crested Grebe in Denmark (Cramp

and Simmons, 2004). Large pelagic species were generally rare in the fish population sampled by

CFRB (2009), but may be more frequent in the Outer Bay zone (which was not sampled). Great

Crested Grebe can occur in large numbers in the Outer Bay zone (see paragraph 8.20).

Therefore, large pelagic species may also be an important component of the diet of the

Dungarvan Harbour Great Crested Grebe population.

B.5 References

Cramp, S. & Simmons, K.E.L. (2004). Birds of the Western Palaearctic interactive (DVD-ROM).

CFRB (2009). Sampling fish for the Water Framework Directive - Transitional Waters 2008:

Colligan Estuary. The Central and Regional Fisheries Board.

Doornbus, G. (1984). Piscivorous birds on the saline lake Grevelingen, The Netherlands:

Abundance, prey selection and annual food consumption. Netherlands Journal of Sea

Research 18 (3-4), 457-479.

Gwiazda, R. (1996). Foraging ecology of the Great Crested Grebe (Podiceps cristatus L.) at a

mesotrophic-eutrophic reservoir. Hydrobiologia (1-3), 39-43.


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Appendix C

Distribution of Shelduck, Lapwing and Black-

tailed Godwit in Dungarvan Harbour


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C.1 Introduction

C.1.1 Shelduck, Lapwing and Black-tailed Godwit have been screened out from detailed assessment

because their distribution within Dungarvan Harbour does not significantly overlap the activity

being assessed, and it is considered that their distribution has not been modified by the existing

levels of the activity. This appendix presents the data that justifies this screening decision.

C.2 Shelduck

C.2.1 In 2009/10, Shelduck were recorded exclusively within the Inner Harbour zone, during the NPWS

BWS counts. In 2010/11 and 2011/12, Shelduck were recorded exclusively within the Inner

Harbour zone, during I-WeBS counts. Shelduck typically roost at high tide on subtidal habitat

close to their low tide feeding areas. Therefore, unlike many other species, their high tide

distribution is likely to be very similar to their low tide distribution, so high tide count data will

usually provide a good indication of their potential use of intertidal feeding habitat (see Burton et

al., 2004; Murphy et al., 2006).

C.2.2 During January-March 2011, Shelduck were not recorded in any of the waterbird counts carried

out at Dungarvan Harbour for the trestle study. These included five low tide counts of the entire

Outer Sandflats zone, and an additional 14 low tide counts (on eight separate dates) of the

southern section of Whitehouse Bank.

C.2.3 Shelduck generally favour the muddier intertidal sediments (Lack, 1986) and their distribution

within sites is strongly linked to the distribution of Hydrobia ulvae, a mud snail, which is their

preferred prey (Bryant & Leng, 1975; Murphy et al., 2006). The habitat conditions in the Outer Bay

zone are generally not very suitable for Shelduck, and Hydrobia ulvae was only recorded in low

numbers in occasional samples from the Outer Bay zone during the ASU biotope survey (Aquatic

Services Unit, 2009).

C.2.4 The available data indicate that Shelduck do not occur within the Outer Bay zone of Dungarvan

Harbour and the habitat conditions within the Outer Bay zone are generally not very suitable.

Therefore, there is not any significant spatial overlap between Shelduck distribution within

Dungarvan Harbour and the areas affected by intertidal oyster cultivation within Dungarvan

Harbour, so intertidal oyster cultivation will not have any significant impacts on the Dungarvan

Harbour Shelduck population.

C.3 Lapwing

C.3.1 In 2009/10, Lapwing were recorded on all four low tide counts and occurred almost exclusively

within the Inner Harbour (Table C.1).


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Table C.1 - Lapwing distribution in NPWS BWS low tide counts of Dungarvan Harbour, 2009/10


Date


07/10/2009 101 0 0

17/11/2009 949 0 14

17/12/2009 1188 0 0

11/02/2010 1201 0 0

C.3.2 In the trestle study, Lapwing were only recorded on one of the five counts that were carried out of

the entire Outer Sandflats zone (a count of three birds on the northern side of the bay) and were

not recorded on any of the additional counts of the Whitehouse Bank study area.

C.3.3 In the non-breeding season, Lapwing mainly feed in agricultural fields and use intertidal habitat as

a roosting habitat (although, typically, a small percentage of the birds in the roosting flocks will be

feeding). However, unlike Golden Plover, they seem to have a preference for the muddier, more

enclosed intertidal habitats and probably rarely occur on open sandflats. In studies of habitat

preferences of waders on the coast of the Orkney Islands, Lapwing were found to show a strong

preference for muddy shores, compared to sand, boulder and gravel shores (Summers et al.,

2002). In other sites studied as part of the trestle study, Lapwing occurred almost exclusively in

shoreline areas and/or areas with muddy sediments (T. Gittings and P. O’Donoghue, unpublished

data).

C.3.4 The available data indicate that significant numbers of Lapwing do not occur within the Outer Bay

zone of Dungarvan Harbour and the habitat conditions within the Outer Bay zone are generally

not very suitable. Therefore, there is not any significant spatial overlap between Lapwing

distribution within Dungarvan Harbour and the areas affected by intertidal oyster cultivation within

Dungarvan Harbour, so intertidal oyster cultivation will not have any significant impacts on the

Dungarvan Harbour Lapwing population.

C.4 Black-tailed Godwit

C.4.1 In 2009/10, Black-tailed Godwit were recorded on all four low tide counts with 78-99% of the birds

within the Inner Harbour (Table C.2).

Table C.2 - Black-tailed Godwit distribution in NPWS BWS low tide counts of Dungarvan Harbour,

2009/10


Date


07/10/2009 1223 9 226

17/11/2009 228 2 0

17/12/2009 670 0 189

11/02/2010 724 0 17

C.4.2 In 2011, the Black-tailed Godwits recorded in counts of the entire Outer Sandflats zone, were

entirely on the northern side of the bay (Table C.3). In contrast to wader species (Grey Plover and

Knot) that showed an exclusion responses to oyster trestles (see Section 8), Black-tailed Godwits

were not recorded on counts of Whitehouse Bank carried out on ebb/flood tides (when the lower

shore area occupied by oyster trestles was not exposed) in 2011.


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Table C.3 - Black-tailed Godwit distribution in low tide counts of the Outer Sandflats zone carried out

for the trestle study, 2011


06/01/2011 136 0

22/01/2011 4 0

03/02/2011 3 0

21/02/2011 15 0

03/03/2011 0 0

Total Black-tailed Godwit counts for Dungarvan Harbour in early 2011: 1648 on 27/01/2011 and 223 on 14/02/2011 (I-

WeBS data)

C.4.3 In high tide counts where distribution has been recorded between subsites, there is only a single

record of 3 Black-tailed Godwits from the Outer Sandflats zone. The main roosting areas appear

to be in the Brickey Lower and Upper subsites (0M416 and 417), and in the Duck’s Pool and Old

Railway subsites (0M423 and 424). The birds recorded from the northern side of the Outer

Sandflats zone during low tide counts presumably come from the latter roosting area.

C.4.4 Black-tailed Godwits are typically associated with muddier sediments, compared to Bar-tailed

Godwits, and the habitat conditions in the Outer Sandflats zone would generally not be considered

optimum for this species. However, Black-tailed Godwits can feed on open sandflats in large

numbers (e.g., at Dundalk Bay; T. Gittings, personal observations) and do appear to make

significant use of the northern side of the Outer Sandflats zone. It may be that the tidal channel

within this area provides suitable feeding conditions.

C.4.5 Given, the lack of any significant numbers of Black-tailed Godwits recorded on low tide or

ebb/flood tide counts of Whitehouse Bank, and the overall distribution pattern of Black-tailed

Godwits recorded in Dungarvan Harbour, it seems reasonable to conclude that the habitat

conditions in Whitehouse Bank are not generally suitable for this species.

C.4.6 The available data indicate that significant numbers of Black-tailed Godwit do not occur within the

Whitehouse Bank and there is no evidence to suggest that their distribution has been modified by

the presence of oyster trestles. Therefore, there is not any significant spatial overlap between

Black-tailed Godwit distribution within Dungarvan Harbour and the areas affected by intertidal

oyster cultivation within Dungarvan Harbour, so intertidal oyster cultivation will not have any

significant impacts on the Dungarvan Harbour Black-tailed Godwit population.


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C.5 References

Aquatic Services Unit (2009). A survey of mudflats and sandflats in Ireland: an intertidal soft

sediment survey of Dungarvan Harbour. Unpublished report commissioned by the Marine

Institute.

Bryant, D. M. & Leng, J. (1975). Feeding distribution and behaviour of Shelduck in relation to food

supply. Wildfowl 26, 20-30. (Quoted by NPWS, 2011c).

Burton, N.H.K., Armitage, M.J.S., Musgrove, A.J. & Rehfisch, M.M. (2002). Impacts of man-made

landscape features on numbers of estuarine waterbirds at low tide. Environmental

Management, 30, 857–64.

Murphy, S., Lewis, L. J. & Kelly, T. C. (2006). The spatial ecology of wildfowl in Courtmacsherry

Bay, southern Ireland, with particular reference to the Shelduck Tadorna tadorna. Irish Birds

8, 51-58.

Summers, R. W., Underhill, L. G., & Simpson, A. (2002). Habitat preferences of waders

(Charadrii) on the coast of the Orkney Islands: twelve species of wader were surveyed on

494 coastal sections, revealing features in addition to substratum type that are important in

habitat selection. Bird Study, 49(1), 60–66.


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Appendix D

Quantitative assessment of spatial

displacement


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D.1 Introduction

D.1.1 This appendix includes full details of the methodologies used to make quantitative predictions of

potential spatial displacement due to intertidal oyster cultivation for Grey Plover, Knot, Dunlin and

Bar-tailed Godwit.

D.1.2 These assessments of spatial displacement refers to the four-five hour period around low tide and

all bird count data and calculations of tideline lengths and exposed intertidal area refer to the

lower shore zone, unless otherwise stated.

D.1.3 Count sectors referred to in this appendix are defined in Figure 2.2.

D.2 Methods

D.2.1 During the trestle study we mapped the position of the tideline by eye within each count sector at

the time the sector was counted. This mapping covered a range of tides from extreme spring (0.2

m) to mean (0.8 m) low tides. We consider this mapping to be reasonably accurate for

Whitehouse Bank because the observer was on the sandflats during the count and could use the

mapped position of the trestle blocks, and of the aquaculture marker buoys and poles as

reference points. However, the tideline mapping for the Ballyrandle Sandflats was carried out from

the shoreline and its accuracy was likely to have been affected by the distances involved and the

lack of appropriate base mapping and/or mapped reference points. We also carried out tideline

mapping at Ballyrandle Sandflats on 13/09/2010 on a 0.6 m low tide, using aerial imagery showing

the alignment of the Glendine River tidal channel and the position of the mixed substrata and

eulittoral rock biotopes to allow more accurate mapping of the tideline.

D.2.2 Our tideline mapping could not be simply used to define the entire tideline at low tide on these

dates. The tideline was continuously moving throughout the counts, so each section mapped

represented the position of the tideline at the time that section was counted. Therefore, we used

aerial imagery to obtain accurate mapping of the overall tideline alignments.

D.2.3 We initially mapped tideline alignments from two aerial images: the 2000 OSI orthophotography

and the aerial imagery included in the Bing maps mapping of Dungarvan. These sources gave us

an indication of the tideline alignment at the upper edge of the lower shore zone (corresponding

approximately to an extreme neap low tide; the Bing maps imagery) and in the middle of the lower

shore zone (corresponding approximately to a mean low tide; the 2000 OSI orthophotography).

We then used our mapping of tideline positions during the trestle study (in sections mapped at full

low tide), in conjunction with these tideline alignments, to map the position of the tide during mean

and spring low tides. We did not have any tideline mapping corresponding to a neap low tide.

However, the mean low water neap (1.1 m) is around halfway between the mean low tide (0.75 m)

and the low tide height when the trestles are not exposed (1.4-1.5 m; referred to as an extreme

neap). Therefore, we assumed that the neap low tide would be around halfway between the mean

low tide and the tideline alignment at the upper edge of the lower shore zone. We then mapped

(by eye), tideline alignments halfway between extreme neap, neap, mean and spring low tides.

This gave us seven typical tideline alignments in total: extreme neap, extreme neap-neap, neap,

neap-mean, mean, mean-spring and spring low tides.

D.2.4 We did not map the tideline alignment in the eulittoral rock biotope on the Ballyrandle Sandflats as

this area becomes exposed much earlier than the adjoining intertidal habitat. We did not map the

tideline alignment in the trestle-free area at the northern end of Whitehouse Bank (CS4) as this

area was little used by waterbirds and was excluded from our analyses. At the southern end of

Whitehouse Bank, narrow sandbanks are exposed below the tideline on the lower tides. While we


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mapped the alignment of these during our surveys, we have not included these in our mapping of

typical tideline alignments. These sandbanks have steeply shelving shorelines and, therefore, do

not provide much tideline habitat.

D.2.5 We used each of the typical tideline alignments to clip the polygons representing the count

sectors, the 2011 mapping of the trestle blocks and the aquaculture plots and calculated the

extent of intertidal habitat exposed in each of these under each category of low tide.

D.2.6 For our analyses we needed to calculate the mean percentage of tideline and exposed intertidal

habitat within the 2011 trestle blocks and the aquaculture plots across the low tide period during

neap, mean and spring low tides.

D.2.7 The total area exposed at full low tide will only give a snapshot of distribution of exposed intertidal

habitat between open areas and trestle blocks or aquaculture plots across the low tide period.

Instead we calculated the distribution of exposed intertidal habitat between open areas and trestle

blocks or aquaculture plots on Whitehouse Bank during neap, mean and spring low tides as the

means of the exposed intertidal habitat on tidelines up to the relevant tideline as follows:

Neap low tide: extreme neap, extreme neap-neap and neap low tides

Mean low tide: extreme neap-neap, neap, neap-mean and mean low tides

Spring low tide: neap, neap, neap-mean, mean, mean-spring and spring low tides

D.2.8 During neap low tides, the tideline remains close to the lower edge of the upper shore zone.

Therefore, some of the upper shore zone can be considered to be within the influence of the

tideline throughout the low tide period. To account for this we included 50% of the area of the

southern two upper shore count sectors (CS1 and CS2) and 33% of the area of the northern

upper shore count sector (CS3; excluding the area north of the trestle blocks) within our

calculations of exposed intertidal area during neap low tides.

D.2.9 We did not calculate exposed intertidal areas for the Ballyrandle Sandflats as Bar-tailed Godwit

(the only species for which we carried out calculations including Ballyrandle Sandflats) occurred

almost exclusively on the tideline.

D.2.10 As the tideline is continuously moving during this period, the tideline position at full low tide will

only give a snapshot of its distribution between open areas and trestle blocks or aquaculture plots.

However, because the tideline geometry (as opposed to position) is relatively constant across the

low tide period, the total area exposed at full low tide will give a good approximation of the

average distribution of the tideline between open areas and trestle blocks or aquaculture plots

across the low tide period, assuming that it moves at more or less constant speed during this

period. Therefore, we used the percentages of the areas of intertidal habitat exposed within the

2011 trestle blocks and the aquaculture plots at neap, mean and spring low tides to represent the

percentages of the tideline within the 2011 trestle blocks and the aquaculture plots across the low

tide period during neap, mean and spring low tides.

D.2.11 In the Ballyrandle Sandflats, the tideline alignment is more complex and the total area exposed at

low tide does not give a good indication of the average distribution of the tideline across the low

tide period. Therefore, for the analysis of Bar-tailed Godwit including the Ballyrandle Sandflats we

calculated the mean tideline lengths on Ballyrandle Sandflats and Whitehouse Bank during neap,

mean and spring low tides as the means of the tideline lengths on all tidelines up to the relevant

tideline (as defined above for calculations of exposed intertidal areas). We excluded sections of


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tidelines on Ballyrandle Sandflats that were within the mixed substrata biotope from these

analyses.

D.2.12 To assess potential displacement due to intertidal oyster cultivation, based on the density of birds

recorded in the trestle-free areas of the lower shore zone of Whitehouse Bank, we followed the

following procedure:

We calculated the mean count of birds on the tideline and in intertidal habitat outside trestle

blocks in the lower shore zone of Whitehouse Bank (excluding sector CS4, which was rarely

used by Grey Plover, Dunlin and Bar-tailed Godwit) during the 2011 trestle study. We

included all the counts from the extensive study (n = 5), as well as the counts from the

intensive study that included the additional study area (sector OY1; n = 7).

We used the mean percentages of the tideline and of exposed intertidal habitat within the

trestle blocks across mean-spring low tides (the range of tides included in the trestle study

counts) to calculate the number of additional birds that would have been expected to occur if

there were no trestles present and if birds had been distributed at the same density across

the habitat, using the following formula:

Expected number = mean tideline count/% of tideline outside trestle blocks + mean intertidal

count/% of intertidal habitat outside trestle blocks

The intensive study counts did not include sector OY4. This sector is largely occupied by

trestles and Grey Plover and Dunlin were not recorded in this sector during the extensive

study counts. For Bar-tailed Godwit, which did occur in this sector during the extensive study

counts we adjusted the observed numbers by a factor of 1.25 to represent the additional

birds that would be expected to occur in this sector (based on the distribution of birds in the

extensive study counts).

We used the mean percentages of the tideline and of exposed intertidal habitat within

aquaculture plots during neap, mean and spring low tides to estimate the potential

displacement impacts from full occupation of these plots. We multiplied these percentages by

the expected numbers calculated in step 2 above to calculate the actual numbers of birds

likely to be displaced. For Dunlin and Bar-tailed Godwit, we adjusted these figures for the fact

that not all birds are excluded from trestle blocks, by subtracting the expected number

multiplied by the density reduction factor (0.2 for Dunlin and 0.5 for Bar-tailed Godwit; see

paragraphs 8.65 and 8.78).

We assessed the significance of the potential displacement impacts by comparing the

numbers of birds likely to be displaced with the total Dungarvan Harbour population.

D.2.13 We did not use this method for Knot as it rarely occurred in the lower shore zone on Whitehouse

Bank.

D.2.14 We assessed the potential displacement due to intertidal oyster cultivation, based on the density

of birds recorded in the lower shore zone of Ballyrandle Sandflats. We only carried out this

assessment for Bar-tailed Godwit, as Grey Plover, Knot and Dunlin do not consistently occur in

higher numbers on Ballyrandle Sandflats. We only used densities of birds on the tideline, as

almost all Bar-tailed Godwits occurred on the tideline.

D.2.15 We calculated the density of Bar-tailed Godwits on the tideline on each of the five extensive study

counts (Ballyrandle Sandflats was not counted during the intensive study), using the relevant


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mean tideline length for the low tide type on each count day. We used these densities to calculate

the expected numbers that would be expected if the birds occurred at the same density along the

tideline on Whitehouse Bank on each count day. We then subtracted the numbers recorded on

Whitehouse Bank to give the predicted displacement of birds.

D.2.16 We did not carry out any further adjustment of these displacement impacts to reflect average tidal

conditions or full occupation of the aquaculture plots. Large-scale displacement, if it occurs,

represents an avoidance of the general area including areas not occupied by trestles. Therefore,

large-scale displacement would not be expected to be linearly correlated with the area occupied

by trestles.

D.2.17 We assessed the potential displacement due to intertidal oyster cultivation, based on the numbers

of birds recorded on ebb/flood tides on Whitehouse Bank. For each count day where we had a

count from the ebb or flood tide we subtracted the low tide count from the ebb/flood tide count. On

one count day we had counts from both the ebb and flood tide and we used the mean of those

counts. All the intensive study counts included in this analysis included the additional study area

(sector OY1). The intensive study did not include the upper shore zone, but any significant flocks

of the relevant species in the upper shore zone on the low tide counts were noted and included in

the low tide count totals.

D.2.18 We took the mean of the difference between the ebb/flood tide and low tide counts as the overall

displacement impact, representative of mean and spring low tides.

D.2.19 We did not carry out any counts during neap low tides. During neap low tides, the tideline remains

close to the lower edge of the upper shore zone and some of the upper shore zone can be

considered to be within the influence of the tideline throughout the low tide period. Therefore,

displacement impacts might be expected to be lower during neap low tides due to the availability

of tideline-influenced trestle-free upper shore habitat. To adjust our estimates of displacement

impacts for this factor, we multiplied our estimate of the mean number of birds displaced by 5/6

(because on one-third of the tides approximately half the available habitat will not be influenced by

trestle blocks).

D.2.20 We did not carry out any further adjustment of these displacement impacts to reflect full

occupation of the aquaculture plots. Large-scale displacement, if it occurs, represents an

avoidance of the general area including areas not occupied by trestles. Therefore, large-scale

displacement would not be expected to be linearly correlated with the area occupied by trestles.

D.2.21 We did not use this method for Bar-tailed Godwit as numbers on ebb/flood tides were similar to

low tide numbers.

D.3 Results

D.3.1 The total tidal exposure within the lower shore zone of Whitehouse Bank (excluding sector CS4)

and the percentages within trestles and aquaculture plots are shown in Table D.1. The tideline

lengths within the lower shore zones of Ballyrandle Sandflats (excluding mixed substrata and

eulittoral rock biotope areas) and Whitehouse Bank (excluding sector CS4) are shown in Table D..


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Table D.1 - Tidal exposure in the lower shore zone of Whitehouse Bank under various low tides

Low tide type

Total area (ha)

% within

Trestles (2011)

Aquaculture plots

Licenses Applications All

Extreme neap 108 0% 3% 7% 10%

Extreme neap-neap

145 9% 14% 15% 29%

Neap 183 19% 22% 20% 42%

Neap-mean 136 42% 46% 39% 86%

Mean 180 49% 53% 35% 88%

Mean-spring 223 45% 59% 29% 89%

Spring 267 38% 60% 25% 85%

Table D.2 - Tideline lengths in the lower shore zones of Ballyrandle Sandflats and Whitehouse Bank

under various low tides

Low tide type Tideline length (m)

Ballyrandle Sandflats Whitehouse Bank

Extreme neap 3672

Extreme neap-neap 4883 4082

Neap 4296 3949

Neap-mean 4518 3812

Mean 4507 3666

Mean-spring 4892 3523

Spring 5410 3403

D.3.2 The predicted displacement of Grey Plover, Dunlin and Bar-tailed Godwit, based on the density of

birds recorded in the trestle-free areas of the lower shore zone of Whitehouse Bank, is shown in

Table D.. The predicted displacement of Bar-tailed Godwit, based on the density of birds recorded

in the lower shore zone of Ballyrandle Sandflats, is shown in Table D..

D.3.3 The full results of the assessments of potential displacement impacts based on numbers recorded

on ebb/flood tides are included in the relevant species accounts in the main assessment (Section

8).


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Table D.3 - Predicted displacement due to intertidal oyster cultivation, based on the density of birds

recorded in the trestle-free areas of the lower shore zone of Whitehouse Bank

Species Scenario Predicted number of birds displaced

Neap low tides Mean low tides Spring low tides Overall

Grey Plover

2011 trestles 4 14 13 10

Licenses 5 16 18 13

All aquaculture plots 10 28 28 22

Dunlin

2011 trestles 12 38 37 29

Licenses 14 43 49 35


Bar-tailed Godwit

2011 trestles 8 21 17 15

Licenses 9 23 26 19


Table D.4 - Predicted displacement of Bar-tailed Godwit due to intertidal oyster cultivation, based on

the density of birds recorded in the lower shore zone of Ballyrandle Sandflats

Date Tide Ballyrandle Sandflats Whitehouse Bank

Count Density Count Predicted Displacement

06/01/2011 normal 57 13 178 49 -129

22/01/2011 spring 671 142 105 521 416

03/02/2011 normal 500 110 65 426 361

21/02/2011 spring 485 103 113 377 264

03/03/2011 normal 326 72 71 278 207


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Appendix E

Assessment of food resources for Bar-tailed

Godwit in Dungarvan Harbour


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E.1 Introduction

E.1.1 This appendix reviews the available data on the benthic fauna of Dungarvan Harbour and

assesses the whether there are differences in the potential food resources available for Bar-tailed

Godwit between the Ballyrandle Sandflats and Whitehouse Bank.

E.2 Bar-tailed Godwit diet

E.2.1 The Bar-tailed Godwit diet is largely dominated by polychaetes. Duijns et al. (2013) found that

across five major wintering sites in Europe (including Dublin Bay), polychaetes formed over 90%

of their diet (by frequency of occurrence), although there was variation between sites and, in

Dublin Bay, bivalves were also important (70% polychaetes and 30% bivalves). The ragworm

(Hediste diversicolor) was the most common prey item at four of the five sites, with the bloodworm

(Glycera alba) being the most frequent at the fifth site (Dublin Bay). Ragworm were also the only

prey actively selected for (i.e., consumed more frequently than expected from their relative

abundance) by the godwits.

E.2.2 Scheiffarth (2001) found some seasonal variation in their diet in the Wadden Sea, with

polychaetes comprising 99% of the prey items of both sexes in winter, while, in spring, bivalves

formed 20% of the diet of males. Smith and Evans (1973) reported that the main prey item of Bar-

tailed Godwit at Lindisfarne in northern England was the lugworm (Arenicola maritima) with other

important prey including ragworms and “a variety of small oligochaetes, polychaetes and

molluscs”.

E.2.3 The various polychaete species reported in the diet of Bar-tailed Godwit are listed in Table E.1.

The diet is dominated by a few species of large polychaetes and small polychaetes (maximum

body length less than 50 mm) are rarely taken.

Table E.1 - Polychaete species recorded in the diet of Bar-tailed Godwit

Maximum length/mm

Frequency of occurrence in diet

Species Duijns et al (2013) Scheiffarth (2001)

Alitta succinea 190 1%

Alitta virens 900 4%

Anaitides sp. 50-100 3%

Arenicola marina 120-200 4% 38%

Eteone longa 30 2%

Eunereis longissima 200-500 < 1%

Glycera alba 75 2%

Harmothoë impar 32

Hediste diversicolor 60-120 76% 41%

Lanice conchilega 300 1% 9%

Nephtys hombergii 90-200

Phyllodoce mucosa 50 1%

Pygospio sp. 15 2%

Sabellaria spinulosa 1%

Scoloplos armiger 120 1% 78%

The data for Duijns et al. (2013) is the total frequency across all five sites included in their study


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E.3 Benthic fauna of the Outer Sandflats zone in Dungarvan Harbour

E.3.1 Data from two benthic surveys are available: the benthic survey carried out for the biotope

mapping of Dungarvan Harbour (Aquatic Services Unit, 2009) and sampling of selected sites in

2013 (RPS Group, unpublished).

E.3.2 The benthic survey carried out for the biotope mapping of Dungarvan Harbour (Aquatic Services

Unit, 2009) sampled 35 stations across Dungarvan Harbour, of which 11 were in the Outer

Sandflats zone (excluding some stations located in marginal habitats). At each station core and

dig samples were taken and notes were recorded on the sediment composition, etc.

E.3.3 In 2013, some limited sampling was carried out to compare the benthic fauna within the area

occupied by trestles, with an access area and a control area on Whitehouse Bank, and with two

areas in the Ballyrandle Sandflats. In each area, ten core samples were taken.

E.3.4 The sediments in all the samples taken during the Aquatic Services Unit (2009) survey were

dominated by fine sands (Figure E.1). However, the sediment composition appeared to be more

variable in Whitehouse Bank (compared to the Ballyrandle Sandflats) with three samples with high

very fine sand components and one sample with a high medium sand component. The Ballyrandle

Sandflats had higher mud content (mean 3.34%, 95% C.I. = 0.00-8.37%, n = 5) compared to the

Whitehouse Bank samples (mean 2.43%%, 95% C.I. = 1.98-2.88%, n = 6). The organic content

was higher in the Whitehouse Bank samples (mean LOI = 1.285%, 95% C.I. = 1.155-1.415%, n =

6) compared to the Ballyrandle Sandflats samples (mean LOI = 1.024%, 95% C.I. = 0.789-

1.258%, n = 5). The Ballyrandle Sandflats samples had an anoxic layer at 1-2 cm depth (5 cm in

one sample), compared to 6-10 cm depth in the Whitehouse Bank samples (no anoxic layer in two

samples).

E.3.5 The sediment composition recorded in the samples taken in the 2013 survey is summarised in

Table E.2. The Ballyrandle Sandflats samples had a higher mud content and lower gravel and

organic content compared to the Whitehouse Bank samples.

Table E.2 - Sediment composition recorded in the 2013 benthic survey

Location Site Mean LOI

mean % sediment composition:

gravel sand mud

Ballyrandle

Site A 0.91 0.0% 94.7% 5.2%

Site B 0.75 0.0% 96.1% 3.8%

Total 0.83 0.0% 95.4% 4.5%

Whitehouse Bank

Access route 0.97 0.3% 98.6% 1.1%

Control 1.13 0.1% 98.6% 1.3%

Trestle block 0.99 0.4% 99.4% 0.2%

Total 1.03 0.3% 98.9% 0.9%

From analysis of data supplied by James Forde, RPS Group, 09/01/2014.


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E.3.6 In the ASU samples, bivalves were more frequent, and polychaetes less frequent, on Whitehouse

Bank compared to the Ballyrandle Sandflats (Table E.3).

Table E.3 - Composition of the benthic fauna recorded in the ASU survey

Mean abundance/sample

Core samples Dig samples

Class Ballyrandle Sandflats


Whitehouse Bank

Annelida 1.0 0.3 0.2 0.8

Bivalvia 11.6 36.5 5.6 14.2

Clitellata 1.2 1.0 0.0 0.0

Gastropoda 1.4 0.2 0.2 0.0

Malacostraca 13.8 17.0 7.0 2.8

Palaeonemertea 0.2 0.0 0.0 0.0

Polychaeta 51.4 27.3 21.6 9.2

E.3.7 The benthic fauna in the core samples from the 2013 survey was dominated by polychaetes with

bivalves, Clitellata and gastropods frequent in some areas (Table E.4).

Table E.4 - Composition of the benthic fauna recorded in the 2013 survey


Class Site A Site B Access route Trestle block Control

Bivalvia 8% 7% 7% 36% 11%

Clitellata 20% 2% 0% 0% 5%

Collembola 0% 0% 7% 0% 3%

Gastropoda 26% 4% 0% 0% 5%

Malacostraca 1% 8% 0% 4% 14%

Nemertea incertae sedis

0% 0% 0% 1% 3%

Polychaeta 45% 78% 86% 59% 57%

From analysis of data supplied by James Forde, RPS Group, 09/01/2014

E.3.8 The polychaete fauna recorded in the ASU and 2013 surveys is shown in Table E.6. Ragworms,

which were generally the most favoured prey item in Duijns et al.’s (2013) study, were very rare

throughout the areas sampled.


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Table E.5 - Composition of the polychaete fauna recorded in the ASU survey

Length (mm)

mean number per sample

core samples dig samples

Species Whitehouse

Bank Ballyrandle Sandflats

Whitehouse Bank

Ballyrandle Sandflats

Scoloplos armiger 120 8.8 22.2 0.8 0.8

Owenia fusiformis 50 0.3 5.8 2.2 8.4

Lanice conchilega 300 1.5 1.6 1.7 4

Euclymene oerstedii

1 0.8 2.2 4.4

Spio martinensis 32 4.2 2.2

Pygospio elegans 15 2.2 4

Nephtys hombergii 2 3 0.4 0.5 0.4

Galathowenia oculata

30 0.2 4

Nephtys cirrosa 60-100 1.8 0.8 0.5 0

Magelona filiformis 50-100 0.3 2.2

Phyllodoce mucosa

50 0.7 0.6 0.2 0.6

Tharyx sp. A 11 0 2

Capitella capitata (complex)

120 0.5 1

Spiophanes bombyx

10-20 0.8 0.2 0.2 0

Nemertea indet. 0 0.6 0 0.4

Glycera tridactyla 100 0 0.6 0 0.2

Arenicola marina 120-200 0.5 0.2

Additional species recorded: Aricidea minuta, Eteone foliosa, Eteone longa, Eumida indet., Exogone hebes, Fabricia

sabella, Glycera juv., Glycera juvenile, Goniada maculata, Goniada maculata, Lagis koreni, Lineus bilineatus, Magelona

johnstoni, Malmgrenia marphysae, Malmgrenia marphysae, Mediomastus fragilis, Melinna palmata, Mysella bidentata,

Nereis longissima, Notomastus latericeus, Orbinia latreillei, Orbinia latreillii, Perinereis cultrifera, Polydora caulleryi,

Sigalion mathildae, Spio martinensis, Streptosyllis websteri, Travisia forbesii.

Body lengths from: http://species-identification.org, www.marinespecies.org and www.marlin.ac.uk

http://www.marlin.ac.uk/


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Table E.6 - Composition of the polychaete fauna recorded in the 2013 survey

Body length (mm)


Species Site A Site B Access route

Trestle block

Control

Pygospio elegans 15 4% 4% 76% 28% 47%

Scoloplos (Scoloplos) armiger

120 44% 9% 8% 10% 15%

Nephtys hombergii 90-200 3% 7% 8% 20% 19%

Exogone (Exogone) naidina

5 11% 23% 0% 2% 0%

Magelona filiformis 50-100 16% 9% 0% 4% 0%

Maldanidae 0% 0% 0% 22% 5%

Aricidea (Aricidea) minuta

15 0% 25% 0% 0% 0%

Owenia fusiformis 50 12% 4% 0% 4% 1%

Eteone longa 30 8% 1% 0% 2% 7%

Lanice conchilega 300 1% 3% 4% 4% 0%

Caulleriella killariensis

11 0% 7% 0% 0% 0%

Capitella 100 0% 3% 0% 2% 0%

Polychaeta 0% 0% 4% 0% 0%

Pholoe inornata 8 0% 0% 0% 2% 1%

Spionidae 0% 0% 0% 0% 3%

Pholoe baltica 1% 1% 0% 0% 0%

Hediste diversicolor 60-120 0% 2% 0% 0% 0%

Sphaerodoropsis 2 0% 2% 0% 0% 0%

Phyllodoce mucosa 50 0% 0% 0% 0% 1%

Magelona johnstoni 170 0% 1% 0% 0% 0%

Notomastus 300 0% 1% 0% 0% 0%

From analysis of data supplied by James Forde, RPS Group, 09/01/2014. Body lengths from: http://species-

identification.org; www.marinespecies.org and www.marlin.ac.uk

E.3.9 The frequency of all polychaetes and of large polychaetes (maximum body length > 50 mm) in

benthic samples from the Outer Sandflats zone of Dungarvan Harbour is shown in Figure E.2-

Figure E.5. Although the number of sampling stations is limited, these maps indicate that

polychaete abundance is higher in the Ballyrandle Sandflats and in the southern section of the

Whitehouse Bank sandflats, compared to the upper shore zone of the northern section of the

Whitehouse Bank sandflats. There are no samples from the northern section of the lower shore

zone of the Whitehouse Bank sandflats, apart from one sample close to the main tidal channel

with low polychaete abundance; the sandflats in this area were noted during the trestle study to

dry out rapidly when exposed and few birds were recorded in this area.

E.4 Assessment of Bar-tailed Godwit food resources

E.4.1 The sediment data from the two benthic surveys indicate that there are some minor but consistent

differences in sediment composition between the Ballyrandle Sandflats and Whitehouse Bank.

E.4.2 Large polychaetes are likely to be the main food resource for Bar-tailed Godwits in Dungarvan

Harbour. The abundance of large polychaetes was highest in the samples taken along the

Glendine River tidal channel in the Ballyrandle Sandflats. Samples from the northern section of

Whitehouse Bank had low abundances of large polychaetes, while samples from the southern

section had moderate-high abundances. Therefore, the data gives some indication that

abundances of large polychaetes may be generally higher in the Ballyrandle Sandflats compared

to Whitehouse Bank. However, the number of samples is too small and their distribution has

http://species-identification.org/

http://species-identification.org/

http://www.marinespecies.org/

http://www.marlin.ac.uk/


Marine Institute


significant gaps (particularly the northern section of the lower shore zone of Whitehouse Bank) to

allow definitive conclusions to be drawn.

E.5 References

Aquatic Services Unit (2009). A survey of mudflats and sandflats in Ireland: an intertidal soft

sediment survey of Dungarvan Harbour. Unpublished report commissioned by the Marine

Institute.

Duijns, S., Hidayati, N. & Piersma, T. (2013). Bar-tailed Godwits Limosa l. lapponica eat

polychaete worms wherever they winter in Europe. Bird Study, 1–9.

Scheiffarth, G. (2001). The diet of Bar-tailed Godwits Limosa lapponica in the Wadden Sea:

combining visual observations and faeces analyses. Ardea, 89, 481–494.


Marine Institute


Figure E.1 - Sediment composition in the ASU benthic samples from the Outer Sandflats zone of

Dungarvan Harbour.


Dungarvan Harbour (including the ASU dig samples).


Marine Institute



Dungarvan Harbour (including the ASU core samples).


Dungarvan Harbour (including the ASU dig samples).


Marine Institute



Dungarvan Harbour (including the ASU core samples).

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