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: nifca@nifca.gov.uk

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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