Pros and cons of small-scale native oyster Pros and cons of small-scale native oyster ((Ostrea edulis)Ostrea edulis) restoration programmes: restoration programmes: experiences gained in Strangford Lough experiences gained in Strangford Lough

Northern IrelandNorthern Ireland

Dai Roberts, David SmythDai Roberts, David Smyth& Lynn Browne, Queen’s University, Belfast& Lynn Browne, Queen’s University, Belfast

22

Oysters: component of human diets since prehistoric times

Cultured - in Europe during Roman times

- in Japan during 17th century Complex legislation failed - stocks collapsed in many

parts of the world by the early 1900s due to pollution, disease, over-fishing and habitat loss

Early restoration attempts - introduction of non-native species and the co-transfer of pests and diseases which further exacerbated impacts on native species

1960s, hatchery-based aquaculture (mainly Crassostrea gigas) developed worldwide to meet global demand - now accounts for about 75% of total world production

33

Ostrea edulis:

Natural Range - Norway to Morocco and into the Mediterranean Sea (Alcaraz and Dominguez 1985).

self-sustaining populations due to introductions in Australia (Morton et al. 2003)

Natural beds are now rare in Europe (Gardner & Elliott, 2001).

Listed in UK Biodiversity Action Plan as a species which should be maintained and expanded (Gardner & Elliott, 2001).

is cultivated in many other parts of the world such as Australia, Japan, New Zealand and North America (Hidu and Lavoie, 1991; Gardiner and Elliott 2001).

44

History of exploitation of oysters in Strangford History of exploitation of oysters in Strangford LoughLough

Mesolithic shell middens with large numbers of O. edulis at several locations (McErlean et al. 2002)

Oysters dredged in great numbers from deep water as well as being gathered along the shore (Montgomery, 1683)

Oyster beds commercially exploited with a peak in the 19th century (Brown, 1818).

Oyster fishery collapses about 1903 (government report – Browne, 1903)

Culture of Crassostrea gigas starts in 1970s (Parsons, 1974; Briggs, 1978)

1998 – Ostrea edulis restoration project starts (Kennedy & Roberts, 1999)

55

The present paper reviews :

the historical decline of Ostrea edulis in Strangford Lough

the outcome of restoration attempts

the need to reconcile ecological restoration and sustainable species exploitation

66

Ireland

Figure 1: Study site

4 km

N

Strangford Lough

77

Physical characteristics of Strangford Lough

Catchment Area (km2)

771.5

Length (km) 30.0

Maximum Width (km) 8.0

Surface Area LW (km2)

106.2

Surface Area HW (km2)

182.8

Tidal range (m) 3.5

Max. Depth (m) 60

Volume (106 m3) 1 250

Tidal exchange (106

m3)350350

Coastline (km) 240.0

Salinity range 32-34o/oo

Glacial origin

Substrata: bedrock to fine sediments laid out according to tidal water movement

88

Study site: Strangford Lough, Northern Ireland:

Multi use: over 16 stakeholder organisations represented on Strangford Lough Management Committee [SLMC]

Strangford Lough is currently on the UK designation list as a Special Area of Conservation (SAC) under the European Commission (EC) Habitats Directive (92/43/EEC) the aim of which is to conserve certain habitats and species within the EC.

Approximately 60,000 people live around the lough and a further 1 million are within a one hour’s drive

99

Dredging area 19th century

• Kircubbin

Portaferry

NewtownardsThe Historic Fishery

Oyster landings in Strangford Lough over a 60 year period during the 19th century in comparison with licensed dredgers.

Decadal average annual landings per boat of Ostrea edulis from Strangford Lough 1820-1880

0

20

40

60

80

100

120

140

160

1820s 1830s 1840s 1850s 1860s 1870s

DATE

Kg

(x1

03 )

0

5

10

15

20

25

30

35

40

45

50

No

. o

f li

cen

sed

dre

dg

ers

Landings

No. Dredgers

1111

Cuan Oysters, Strangford Lough, Northern Ireland(http://www.cuanoysters.com/seafood/index/html):

the major producer of oysters in the lough - established 1974

played an important role in the development of oyster aquaculture in the United Kingdom by pioneering culture methods for very small hatchery-reared seed

now one of the main producers in the UK, handling over 400 tonnes of oyster (C. gigas; O. edulis)per annum

1212

Portaferry

Newtownards

Restoration project 1997-1999

Licensed sites [hectares](not to scale)

Boretree IsBoretree Is 113113

Calf rockCalf rock 9494

Chappel IsChappel Is 6565

Mahee IsMahee Is 24.724.7

Connelly IsConnelly Is 22.722.7

Main oyster aquaculture areas 1990s

1313

Restoration 1997-Restoration 1997-9999

• Spreading 70-75 tonnes cultch (mainly C.gigas and scallop shells) to form the basis for new beds

• Concentrating broodstock on new beds

•Seeding with with 250,000 250,000 O. edulisO. edulis

spatspat

1414

SurveysSurveys

• Spat CollectionSpat Collection- 13 collectors - 13 collectors

•IntertidalIntertidal

- - 30 coastal 30 coastal sitessites

-- 8 Island sites 8 Island sites

•Subtidal -Subtidal - 15 dive 15 dive sitessites

• Plankton Plankton samplingsampling -- over tidal fluxover tidal flux

1515

Ballyreagh NewtownardsSailing Club

Mount Stewart

Herring Bay

Kircubbin

Ballyhenry

Marlfield

Grey Abbey

Island Hill

Sites surveyed 2002-2004

Chapel Island

Horse Island

Granagh Bay

Barr Hall Bay

Castleaverry

Castle Espie

Paddy’s Point

Horse Island

NendrumWhiterock

Ringhaddy

Simmy Island

Killyleagh

Nickey’s Point

Castle Island

Castleward BayShore surveys

Spat collectors

Island sites

Newtownards

Portaferry

N

EW

S

1616

The total number of inter-tidal and sub-tidal O.edulis in the North, West, East and South were estimated using the following formula adapted from Gunderson (1993).

h _ P= ∑ ﴾ Ri .F ﴿ C i I=1 a

Where; P= Total population resident in full survey area. Ri= Area of region I in m2 . a= Area sampled within a single sampling unit. F= Correction factor estimating substrate types. _ Ci= Mean number of oysters observed per sampling unit in the region based i on n samples. h= Number of regions composing the survey.

Estimates of standing stocks

1717

Intertidalareas m-2

(x 106)

Substrate Correction factor(Kennedy & Roberts 1999)

Area suitable for settlement m-2 (x106)

Standing stockOysters (x103)

1998 2002 2003 2004

North 19.64 0.056 1.1 102 1,017 1,242 964South 4.701 0.019 0.089 0 0 0.3 0East 4.509 0.236 1.064 0 0.6 0.2 0.1West 5.438 0.027 0.146 8 2.8 1.2 0.5Total 34.29 NANA 3.628 110 1021 1244 965• Proportionally weighted correction factors were applied to

account for the amount of suitable substratum present.• Drop due to unregulated harvesting

Estimates of standing stocks: Intertidal surveys

1818

Subtidal areas m-2

(x 106)

Substrate Correction factor (Kennedy & Roberts 1999)

Area suitable for settlement m-2 (x106)

Standing stockOysters(x103)

1998 2003

North 26.816 0.234 6.274 0 376

South 68.001 0.023 1.564 0 0

East 32.318 0.236 7.627 0 152

West 9.789 0.019 0.185 0 595

Total 136.092 15.650 0 1124 • Proportionally weighted correction factors were applied to Proportionally weighted correction factors were applied to

account for the amount of suitable substratum present.account for the amount of suitable substratum present.

Estimates of standing stocks: Sub-tidal surveys

1919

Kennedy & Roberts 1999 (x103)

2002(x103)

2003(x103)

Intertidalwild stock

110 1021 1244

Subtidal wild stock

0 No data 1124

Commercial oyster mats

125 0 0

Subtidal licensed sites

Not present

No data * 639

TOTALS 235 1021 3007

*Based on known areas of licensed sites and assuming 100% suitable subsratum and sub-tidal density estimates elsewhere

Estimates of total standing stocks

2020

no formal records of the levels of regulated or unregulated shellfish harvesting by hand for Strangford Lough

used the following approximation:

Total removal per month

= nos of collectors X removal rate X nos suitable low tides per month

Estimates based on the approximation above were compared to changes in estimates of standing stocks over Christmas (November - January), the most intense harvesting time when shellfish are at a premium in Europe.

Estimates of unregulated harvesting

2121

no formal records of the levels of either regulated or unregulated shellfish harvesting by hand for Strangford Lough

used the following approximation:

Total removal per month = 12 X (nos) 92k X 8

= 8,832 kg

= 17,664 kg (November – January)

Estimated change in standing stocks

November – January = 278x103 (24,464 kg)

September – April = 1112x103 (97,856 kg)

Impacts of unregulated harvesting on standing stocks

2222

Ballyreagh 2002

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm 40-50mm 70-80mm 100-110mm

Nos

m2

Ballyreagh 2003

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm 40-50mm 70-80mm 100-110mm

Ballyreagh 2004

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm 40-50mm 70-80mm 100-110mm

NSC 2002

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm 40-50mm 70-80mm 100-110mm

Nos

m2

NSC 2003

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm 40-50mm 70-80mm 100-110mm

NSC 2004

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm 40-50mm 70-80mm 100-110mm

Impacts of unregulated harvesting on coastal populations

UNFISHED

FISHED

2323

Impacts of unregulated harvesting on island populations

Dougherty Rock 2002

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm

30-40mm

50-60mm

70-80mm

90-100mm

110-120mm

Nos m-2

Dougherty Rock 2003

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm

30-40mm

50-60mm

70-80mm

90-100mm

110-120mm

Dougherty Rock 2004

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm

30-40mm

50-60mm

70-80mm

90-100mm

110-120mm

Nos m-2

Sheelahs Island 2003

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm

30-40mm

50-60mm

70-80mm

90-100mm

110-120mm

Sheelahs Island 2004

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm

30-40mm

50-60mm

70-80mm

90-100mm

110-120mm

Sheelahs Island 2002

0

0.1

0.2

0.3

0.4

0.5

0.6

10-20mm

30-40mm

50-60mm

70-80mm

90-100mm

110-120mm

Nos m-2

ND

ND

FISHED

FISHED

2424

Further consequences of harvestingFurther consequences of harvesting

• Decrease in suitable cultch for larval settlement

•Decrease in broodstock assemblage and therefore larval swarms

•Anthropogenic disturbance of intertidal habitats within a SAC•Decrease in the oyster shell as a habitat (Korringa 1945 listed 68 sp. on O. edulis) (Mistakidis 1951 listed 121 sp. on Essex oyster grounds)

2525

>95% Increases in the densities of native oysters in Strangford Lough between 1998 and 2003 in Northern basin

due to over-summering of commercial oysters initially, hydrographical conditions and restoration efforts

Restoration of O. edulis will increase biodiversity within Strangford Lough,

is unlikely to be due to recruitment from wild stock

SummarySummary

2626

Increase in standing stocks since 1998 has resulted in the first significant harvests from Strangford Lough for over 100 years.

However, harvests have resulted in the removal of an estimated 25% of the total intertidal oyster population and are unregulated

Dredging is currently banned

Until these issues are resolved, the very promising recovery of oysters in Strangford Lough with the tangible potential to reconcile ecological and harvest goals of restoration will not be realised.

Annual removal estimated at 97 tonnes which is nearly twice the levels at which the fishery collapsed (52 tonnes) in the 19th century and is unlikely to be sustainable

SummarySummary

2727

Should restoration of Ostrea edulis be continued in Strangford Lough?

• the restoration of O. edulis assemblages have the potential to increase biodiversity within Strangford Lough.

Yes- because:

• the Lough has suitable regions where local circulation will promote larval retention (Kennedy & Roberts,1999)

• Strangford Lough oysters largely disease free

2828

Acknowledgements

The Worshipful Company of Fishmongers Strangford Lough Fishermen’s Co-

operative Department of Agriculture and Rural

Development for Northern Ireland Richard Kennedy