Aln Estuary Transitional and Coastal Waters Surveys · A survey of fish species was undertaken in...
Transcript of Aln Estuary Transitional and Coastal Waters Surveys · A survey of fish species was undertaken in...
Aln Estuary Transitional and Coastal Waters
Surveys
May and September 2015
Report prepared by: Jon Green Deputy Chief IFCO (environmental)
Northumberland Inshore Fisheries and Conservation Authority
8 Ennerdale Road
Blyth
NE24 4RT
Tel: 01670 797676
Email: [email protected]
Website: www.nifca.gov.uk
Executive Summary
This report presents an assessment of the state of Transitional and Coastal Waters (TrAC)
fish species in the Aln estuary Marine Conservation Zone (MCZ). The main purpose of this
report is to provide information which will be used in future surveys to ascertain changes in
population dynamics within this MCZ.
Fyke nets and seine nets were used to carry out the surveys from May 27th to May 28th and
September 22nd to 23rd september 2015, correlating with late spring and autumn migration
and spawning patterns of fish species. In previous surveys the most common species
included flounder Platichthys flesus, lesser sandeel Ammodytes tobianus, gobies
Pomatoschistus microps & minutus, saithe Pollachius virens and trout Salmo trutta. Other
less common species recorded included pollock Pollachius pollachius, five bearded rockling
Ciliata mustela, viviparous blenny Zoarces viviparous, sea scorpion Myoxocephalus scorpius
and ballan wrasse Labrus bergylta.
The Aln estuary is currently being monitored due to known diffuse water pollution from
agricultural land that surrounds the area as well as the obstructions impeding fish passage.
These ecologically significant issues could be determining what is present or absent from
the estuary. Continuous surveying on a biannual basis will help the Northumberland Inshore
Fisheries and Conservation Authority (NIFCA) gather data that will give an overview of the
estuary and help meet its statutory duties under the Marine and Coastal Access Act 2009.
Introduction
Estuaries are partially enclosed bodies of water which interlink freshwater from rivers and
streams with saltwater from the ocean (Environmental Protection Agency 2012). Estuaries
and estuarine communities are important as they provide various resources, benefits and
services. Species of birds, fish and mammals depend on estuarine environments to live, feed
and reproduce (EPA 2012). Estuaries are frequently used by fish species for the
developmental stages of their life cycle and spawning in particular. Fish species will use the
estuary as a nursery, enabling fish to migrate either upstream to freshwater or downstream
towards a more saline habitat.
A survey of fish species was undertaken in the River Aln, commonly known as the Aln
estuary. The Aln estuary is located beside the town of Alnmouth, Northumberland, and is a
newly designated (2013) Marine Conservation Zone (MCZ). The surveys particularly focused
on juvenile fish species to determine if the estuary acts as a nursery habitat for fish. A
habitat is classed as a nursery if fish occur at high densities and suffer lower rates of
predation or higher rates of growth (Gillanders et al. 2003). It is thought that small fish,
including juveniles are most abundant in shallow areas because these habitats enhance
survivorship and growth (Manderson et al. 2004). Shallow habitats function as refuges for
prey species because large predators are often less abundant in shallow water. This may not
be universal as some predators are not limited to deep water by body size or behaviour
(Manderson et al. 2004; Linehan et al. 2001).
The Aln Estuary is 0.44km2 in area and has a range of habitats including mud, sand,
saltmarsh and estuarine rocky habitats (Net Gain 2012). It was thought that the Aln supports
sprat Sprattus sprattus, flounder Platichthys flesus, sandeels Hyperoplus immaculatus, plaice
Pleuronectes platessa and European eel Anguilla anguilla (Net Gain 2012). Issues that face
the estuary include obstructions that impede upstream migration of important fish species.
There have been 6 fish pass improvements by the Northumbria Rivers Trust,
Northumberland Estates and the Environment Agency in the Aln Estuary to try and restore
the environment for European eel, sea trout Salmo trutta and salmon Salmo salar
(Northumbrian Rivers Trust 2012). The Aln Estuary is surrounded by agricultural land which
has resulted in work being done with Catchment Sensitive Farming to focus on diffuse
pollution and the effects it can have on the estuary. Diffuse pollution is considered a priority
for the Aln in the Rivers Basin Management Plan (RBMP) for the Northumbrian region
(Environment Agency 2009). These harmful disturbances may be used to explain ecological
patterns in the Aln estuary and explain the presence or absence of certain fish species. The
2015 surveys were carried out in May and September to coincide with the spring and
autumn downstream migration of juvenile fish species (Ibbotson et al. 2013).
Pilot projects were carried out in 2012 and 2013 to familiarise the Northumberland Inshore
Fisheries and Conservation Authority (IFCA) with surveying methods and with the Aln
estuary. In 2014 Northumberland IFCA conducted 2 surveys of the Aln estuary, one in May
and one in October, a report of these surveys is available on the Northumberland IFCA
website. The Northumberland IFCA have carried out these surveys due to the importance of
the Aln estuary as a recently designated MCZ and the IFCA’s duties under Section 154 of the
Marine and Coastal Access Act 2009 specifically referring to the protection of MCZs. A
Habitats Regulation Assessment and Project Plan were submitted to Natural England and
Northumberland Estates in order to gather the proper consents.
This report will provide an overview of the data collected from the May and September
2015 fish surveys on the Aln estuary, which will be carried forward for analysis against
future surveys at the site.
Methods
Site Description
During the pilot studies in 2012 and 2013, the Officers were given an overview of how to
best use fyke and seine nets. These nets were used for the purposes of this survey. A
desirable fyke net location was identified in the initial pilot project in 2012 and this location
has been used subsequently in 2013, 2014 and now in 2015.The 2012 and 2013 surveys
have allowed through trial and error to
successfully locate three sites where the
seine net can be easily set and fished. The
2015 surveys again used these locations as
will all future surveys. The location of the
fykes is in the deepest portion of the
estuary (which is a designated anchorage,
but is rarely used for this); this allows for
the nets to be fished for 24 hours without
drying out. The seine net locations are at
the mouth of the estuary, below the
anchorage and an upstream location; these
sites will allow for the greatest range of
species to be sampled as the salinity
will vary between sites.
Map 1: Aln estuary with survey locations of fyke nets and seine nets marked.
Position of Fyke nets
Position of Seine nets
Setting of the Fyke net
Equipment
The equipment required to carry out the survey consisted of marker buoys, weights, otter
guards, a boat, floats, life jackets, an estuary Survey Seine Net 43m x 4m deep – 210/12
6.5mm & 14mm and a seven hoop large double dee fyke net 10 & 14mm – 100cm x (2 x
5.3mtrs) – 32ft Leader. Fyke nets are a series of interconnecting nets with one-way entry
that acts to trap fish. They are conical in shape with a D-shaped or circular opening held
open by metal rings (Colclough et al. 2000; Environment Agency. 2013). A series of in-scales
move the fish from the opening of the net into the ‘cod-end’ of the fyke. They are fixed with
weights or anchors parallel to the shore (usually at low water) and allowed to fish over an
entire tidal cycle (Environment Agency. 2013). The opening of the fyke net (mouth) is
attached to a leader, which is a length of net that’s set in such a fashion to gather fish into
the fyke mouth (Encyclopaedia Britannica. 2013). Often fyke nets are ‘paired’, which means
that two nets are attached to one leader. This allows the fyke to fish on both the flood and
ebb tide when placed parallel to the shore (Environment Agency. 2013).
A fyke net
A seine net
Seine nets are composed of a bunt (bag or lose netting) and long wings that are lengthened
with long ropes for towing the seine to the beach (Food and Agriculture Organisation. 2013).
The head rope floats on the surface and the foot rope is in permanent contact with the
bottom therefore allowing the seine net to act as a barrier to prevent fish from escaping
(FAO. 2013; Environment Agency. 2011).
Survey methods
During the surveys Northumberland
IFCA officers, NIFCA members, National
Trust, Northumbria Rivers Trust,
Northumberland County Council,
Students from Newcastle University and
representatives of the Northumberland
Wildlife Trust went to the Aln at mid tide
(10am) to set up the fyke nets.
Afterwards they undertook the seining
at the mouth of the estuary where fish
species were identified using the Environment Agency 2009 manual “Key to the marine and
freshwater fishes of Britain and Ireland”. The seine net was deployed from the boat and then
brought into the shore. The seine nets used were
nets that would be operated from the shore
(Seafish. 2005). Handling the equipment requires
a number of individuals to be present to pull the
seine to shore (Seafish. 2005; Environment
Agency. 2011). For successful operation, it is best
that the ground rope reaches the beach first so
that the gear is brought from underneath the fish
(FAO. 2013). Seining was done twice at all three
locations.
On the second day of each survey those
conducting the surveys went to the Aln
estuary for 09:30am to recover the fyke net.
The fyke nets were recovered at mid tide
using the boat and fish caught were
transferred into a bin for
identification by Deputy Chief IFCO
Jon Green and recorded by other
team members. Once both nets
were recovered, the group
proceeded to carry out the second
set of seine netting below the
anchorage before moving upstream
and repeating the process.
Recovering the seine and bunching up to
concentrate fish in small area for capture
Emptying a fyke
Fyke set in position
Summary of results for 2014 & 2015
May-15
Sep-15
May-14
Oct-14
Species
Quantity Range mm Average
Quantity
Range mm Average
Quantity
Range mm Average
Quantity
Range mm Average
Herring
550 30-85 50
75 34-67 49
3 51-53 52
0 0 0
L sandeel
258 80-190 122
13 86-116 96
119 78-164 110
2 148-159 154
Flounder
94 15-315 59
51 38-330 72
41 18-270 57
36 44-318 96
Goby
65 30-70 49
54 35-83 51
42 36-59 45
189 18-82 53
Trout
26 35-147 147
3 315-355 340
5 129-320 173
5 345-720 554
Launce
1 310 310
39 27-285 132
1 253 253
0
Sprat
3 50-60 57
20 55-84 70
0 0 0
40 48-95 74
Saithe
0 0 0
16 125-199 150
64 41-57 49
5 54-172 137
5 Bearded Rockling
0 0 0
5 130-198 177
0 0 0
0 0 0
15 Spined Stickleback
0 0 0
4 84-115 99
0 0 0
0 0 0
Eel
0 0 0
3 350-410 377
0 0 0
0 0 0
Cod
0 0 0
2 80-115 97
0 0 0
1 88 88
Dab
1 102 102
0 0 0
0 0 0
0 0 0
3 Spined Stickleback
1 55 55
0 0 0
0 0 0
1 28 28
V blenny
1 225 225
0 0 0
0 0 0
0 0 0
Scorpion
0 0 0
1 60 60
0 0 0
0 0 0
Plaice
0 0 0
0 0 0
1 85 85
1 82 82
B Wrass
0 0 0
0 0 0 0 0 0
1 80 80
Discussion
Information on the characteristics of the fish species caught has been taken from the
Environment Agency, Key to the Marine and Freshwater Fishes of Britain and Ireland.
During the May survey a total of 550 Herring Clupea harengus were caught, in September a
total of 75 specimens were caught, sizes ranged from 30mm to 85mm in May and 34 to
67mm in September. Herring are an extremely abundant species with significant
commercial value. The spring spawners shed their eggs close inshore, but others spawn in
summer and autumn offshore and on the edges of ocean banks. The eggs are shed close to
the bottom and form a mat, often several eggs deep, over the gravel or shell beds of the
bottom. The young fish form large schools and are particularly common in inshore waters
during their first year.
During the May survey a total of 258 lesser sandeel Ammodytes tobiannus were caught, in
September a total of 13 specimens
were caught. Sizes ranged from 80-
190mm in May and 86mm to 116 in
September; this is typical for this
species which reaches a maximum
length of 20cm. Lesser sandeel are an
extremely common inshore fish in
northern European seas, living in sandy
bays and on beaches from about mid-
tide level to depths of ca 30 m. It is
always found close to clean, fine sand,
in which it burrows with great rapidity,
or swimming over the sand often in a
head-down posture. The mouth of the
Aln estuary consists of cleaner and finer sand which is consistent with the presence of large
amounts of sandeels. No sandeels were caught at the upper site in either May or
September; this area has a muddier substrate and is likely to have a lower salinity.
Quantities of flounder Platichthys flesus were caught during both surveys, with 94 fish being
caught in May (15-315mm) and 51 in September (38-330mm). No flounder were present in
the mouth of the Aln in either survey. Flounder is a widespread European fish living from
the tide line to 55m, and also penetrating into fresh water so that it is found in rivers and
lakes in communication with the sea where the water is entirely fresh. The flounder
penetrates further into fresh water in more northern, cooler conditions than in the south. It
lives on sandy and muddy bottoms. It breeds in spring at depths of 25-40 m, the eggs, larvae
Lesser sandeel
and post-larvae live at the surface. The flounder lives on the sea bed from a length of 1.5-3
cm. The earliest stages live close inshore and, at about the size of a postage stamp, are very
abundant in rivers estuaries
Two species of gobies, the common goby Pomatoschistus microps and the sand goby
Pomatoschistus minutus, were caught in large number during both surveys. Due to the
difficulties of identifying the closely related species in the field they have been grouped
together. A total of 65 fish were caught in May with sizes ranging from 30mm to 70mm. In
September 54 fish were caught with sizes ranging from 35mm to 83 mm. The common goby
is a small goby which is found close inshore in intertidal pools, estuaries, and in slightly
brackish drainage ditches and rivers. It is particularly common on muddy, marshy shores,
but is also found in high shore pools on sand. In winter most migrate into deeper water. It
spawns from April to August, the eggs being laid on the hollow surface of an overturned
bivalve shell such as a cockle or a clam. Several broods of eggs are produced by each female,
each guarded within the shell by the male. The sand goby is an extremely common goby on
inshore sandy grounds from about mid-tide level to 20 m. It is possibly most common in
depths of 30 cm below low tide level down to 10 m, and is caught in great quantity by
shrimp nets and trawls. It enters the mouths of estuaries, but is rarely found in low salinity
water. It moves into deeper water in winter. After hatching, the young are pelagic until they
reach a length of ca 17 mm. It is likely that the majority of the gobies caught at the upper
sites were the common goby as it is able to tolerate lower levels of salinity, while larger
individuals are likely to be sand gobies.
During the May surveys a total of 3 sprat Sprattus sprattus were caught, sizes ranged from
50mm to 60 mm. In September 20 fish were caught, sizes ranging from 55mm to 84 mm.
Juvenile and mature Flounder
The sprat is an extremely abundant, small
pelagic fish in northern European waters. It
is particularly common in inshore coastal
waters, the young especially being found in
estuaries and arms of the sea. In summer,
sprats are found in depths of 10-50 m, but
go deeper in winter. In all seasons they rise
towards the surface at night. The sprat
spawns in spring and summer, the eggs and
early larvae are planktonic, and the latter
drift inshore as they develop.
During both surveys trout Salmo trutta were caught. In May 26 fish were captured ranging
in size from 35mm to 320mm, while in September 3 fish were captured ranging from
315mm to 355mm. Many of the trout caught during the May survey were parr, with only
one fish over 20mm being caught. The September fish were clearly mature adults returning
to the river to spawn. The brown trout shares many of the biological features of its close
relative, the Atlantic salmon, but forms two basic ecotypes: migratory (sea trout) and non-
migratory (brown trout); there is no justification for regarding them as subspecies. Trout
spawn in winter from October to January, the eggs being shed in redds cut by the female in
river gravel, usually in upstream reaches (although many spawn in the gravel below weirs).
The eggs hatch in 6-8 weeks, depending on the water temperature, and the fry remain in
the gravel for a further 4-6 weeks before beginning to feed.
In May no saithe Pollachius virens were caught, while only sixteen were caught in
September. For those caught in September the size range was between 125-199mm. Saithe
is widely distributed in the North Atlantic, living in large schools near the surface and in
midwater at depths of 200-250 m. From Scotland northwards the young fish are particularly
abundant in inshore waters; in their first year they may be found in intertidal pools and
A selection of sprats
Trout parr and mature trout
close to the shoreline in their second year. Saithe spawn from January to April in depths of
100-200 m. The eggs and larvae drift near the surface and are carried from the deep-water
spawning grounds to the shallower nursery areas.
During the May survey a single greater sandeel Hyperoplus lanceolatus was caught,
measuring 310mm. In September 39 greater sandeel were caught with sizes ranging
between 27mm to 285mm (all were caught in the mouth of the estuary). This inshore
sandeel is found from the low-tide level (young specimens) down to ca. 150 m, on sandy
bottoms. It breeds during spring and summer at depths of 20-100 m, shedding its eggs in
sand. The larvae and post-larvae are pelagic.
During the 2015 survey no plaice Pleuronectes platessa were caught and with only one
plaice being caught in 2014 it is unlikely that the Aln is a nursery area for this species. The
plaice is a bottom-living fish, most abundant on sandy bottoms, but also found on muddy
bottoms and gravel in depths of 0-200 m. It is most common in 10-50 m. Young fish, even
newly metamorphosed plaice of ca 2 cm, live in the shallower depths from the shoreline to
10 m. It is not uncommon to find them in sandy intertidal shore-pools. Large fish also come
into the tidal zone to feed at high tide on sand and mud flats. The plaice spawns mainly
between January and March throughout its range, but tending to be concentrated on
certain areas in depths of 20-40 m. The eggs float at the surface initially, hatching after 10-
20 days depending on the temperature. The larvae and postlarvae are also surface-living for
between 4 and 6 weeks, after which, with the eye now migrated to the right side and other
internal changes completed, it becomes bottom-living at a length of 10- 17 mm. By this time
the young fish have usually drifted into shallow inshore water.
A single three-spined stickleback Gasterosteus aculeatus, measuring 55m was caught at the
upper site during the May survey. Three-spined stickleback is a very widely-distributed
species throughout northern Europe, often abundant in lakes, rivers and coastal waters. In
fresh water its normal habitat is in shallows of 0-1 m usually in open areas but with cover
nearby. In estuaries it usually lives close to the river bank, and in the sea it is common in
coastal waters in tidal pools, but usually among marine algae. It is only common in fully
marine habitats from Scotland northwards. This stickleback breeds in spring and early
summer, the male constructing a nest of plant fibres in a hollow on the bottom in both fresh
and salt water habitats. Eggs are laid within the nest where the male aerates them and
removes infertile eggs. The nest is central to the male’s territory, which is strongly defended
by the brightly-coloured fish.
No ballan wrasse Labrus bergylta were caught during either survey but have been during
past surveys although generally these have been single fish. Probably the most abundant
large wrasse in the eastern North Atlantic, ballan wrasse is common close to rocks and
around reefs from 2-3 m to about 20 m, while the young are often found in shore pools
(provided there is abundant algae and rock). The adults are usually solitary or form small
schools. Like several other wrasses it builds a nest of fine algae, wedged into a crevice, in
which the eggs are laid in summer. After hatching, the larvae are pelagic for a short while
before drifting into shallow inshore waters.
During the September survey one scorpion fish Myoxocephalus scorpius measuring 60mm
was caught. This is a common fish on rocky shores. It lays its eggs in clumps among algae
after which they are guarded by an adult. After hatching they swim in mid water offshore
before returning to the coast.
During the May survey one dab Limanda limada measuring between 80mm and 115mm.
Dabs are an abundant flatfish found in shallow waters and are most common over sandy
bottoms. They spawn offshore in the spring and summer and the eggs and young fish are
pelagic, when they become 20mm they inshore and are bottom living.
During the September survey 4 fifteen-spined stickleback Spinachia spinachia were caught
measuring in size from 84mm-115mm. These fish are abundant in shallow water and are
occasionally found in estuaries but is most common in tidal pools or among eelgrass.
Spawning takes place in spring and up to 200 eggs are laid into a nest made and guarded by
the male.
During the May survey one viviparous blenny
Zoarces viviparous measuring 225mm was also
caught. The viviparous blenny is a long bodied
almost eel like fish. It is bottom living, most
commonly buried in mud or amongst rocks on
rocky shores and is often common in estuaries. It
is a live bearing fish, mating taking place in the
summer. The eggs develop and hatch within the
female and the young are born over the winter.
During the September survey 5 five bearded rockling Ciliata mustela ranging in size from
130mm to 198mm. Five bearded rockling is another eel like fish mostly found on rocky
shores. It spawns in winter and the early young are pelagic before moving into inshore
waters.
During the September survey two cod Gadus morhua were also caught; with sizes from 80 –
115mm. Cod is an extremely important commercial species which in the past has been
overly exploited. It is widely distributed in a variety of habitats from the shoreline to depths
of 600m on the continental shelf. To the south of its range it is found in shallow water only
during the winter, and there, as elsewhere, it is the younger, smaller fish which live close
inshore. It usually schools at least 30-80 m off the bottom, although it forages for food on
the sea bed and in mid-water.
Viviparous blenny
For the first time since NIFCA began the surveys on the Aln estuary 3 European eels Anguilla
anguilla ranging in size from 350-410mm were caught during the September survey. This is a
species that historically was a targeted species using Fyke nets; it was a common species in
the Aln but has recently been in decline (pers coms. Les Weller). Eels have a relatively
strange life history, beginning with being born in the Sargasso Sea and the juveniles then
take 3 years to drift across the
North Atlantic. They enter river
at which time they are known as
elvers, they then develop into
true eels and spend a significant
period of up to 30 years in
freshwater. Upon full maturity
they undergo a further
metamorphosis as they become
silver eels at which time they
swim back to the Sargasso to
breed.
Historically the River Aln has had obstructions that would impede migration movements for
sea trout, salmon and European eel. Records of European eel in the River Aln date back to
1966, but no records have been made since (Environment Agency. 2001). Fish passage has
improved on the Aln estuary which has increased opportunities for fish species to migrate
(Northumberland Rivers Trust. 2012).
The current ecological quality of the estuary is moderate with the overall area being
probably at risk (Environment Agency. 2012). The Aln estuary is addressed in the
Northumbrian Rivers Basin Management Plan stating that diffuse water pollution from
agriculture is a problem for the area (Environment Agency. 2009). The levels of diffuse water
pollution may be affecting the presence and absence of certain fish species. Water quality
information such as dissolved oxygen, salinity and temperature were not recorded during
the May survey.
During the September survey the following data was recorded;
At site at mouth Temperature 12.3, Salinity 34.6, DO 89.5 and pH 8.08
At site below anchorage Temperature 12, Salinity 34.7, DO 86 and pH 8.01
At upper site, Temperature 11.5, Salinity 12.35, DO 74.9 and pH 7.77
At Fykes, Temperature 12.1, Salinity 31.55, DO74.9 and pH 7.84
All the above were recorded prior to the hauling of each net.
European eel
Conclusions
These surveys along with those carried out in 2014 provided an initial assessment as to what
can be found in the estuary and where. The next survey will take place in April/May (spring)
2016 to correlate with the migration and spawning patterns of other fish species. The 2012
Net Gain report developed by the North Sea Marine Conservation Zone Project indicated
that the Aln estuary supports sprat, flounder, sandeels, plaice and European eel. While small
numbers of plaice (2 individuals in each of the 2014 surveys) the Aln estuary does not
appear as a regularly used area for this species, which is common in the inshore waters
locally (NIFCA Druridge bay surveys 2015). While only during the September 2015 have any
eels been caught (3 individuals) it is still believed that the Aln is likely to be locally important
for this species which will migrate to sea through the estuary often at night and in the
autumn.
The surveys have demonstrated the importance of the Aln estuary for the other 3/4 species
(sprat, flounder and sandeels – lesser and greater) noted in the report. They also indicates
that for several other species that the estuary is important, most notably herring, common
goby, and sand goby. While to a lesser degree the estuary has some significance for saithe
although this may be seasonal in nature. The estuary has some importance for the trout
particularly the upper site where numbers of parr have been caught; the larger trout were
probably intercepted while moving to breeding grounds further up river. Some of the other
species caught are probably resident to the area, particularly the sticklebacks, rockling,
blennies and scorpion fish. While the likes of the cod, dab and wrasse may have been
carried in on the tide.
Acknowledgements
Thank you for those who took time to help with the survey, NIFCA Committee Members
Northumberland Wildlife Trust officers, National Trust Wardens, Representatives of the
Northumbrian River Trust and Marine Students from Newcastle University.
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