Arklow Dredge Spoil Disposal – Fish Migration Review 10WW02

Arklow Harbour Dredge Spoil Disposal

Fish Migration

Impact Assessment

1st November 2010

All maps produced under licence from Ordnance Survey Ireland Licence No. EN 0020010© Ordnance Survey Ireland Government of Ireland

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1. Introduction

The following figure shows the distribution of shore angling on the east coast from Wicklow Head to Raven Point. It was produced by the then Central Regional Fisheries Board now Inland Fisheries Ireland and presents the various sea fish available to catch by rod and is representative of the main fish stocks in the Irish Sea including; Cod, Mackerel, Whiting, Dogfish, Plaice, Sea Bass etc.

Figure 1. Showing the distribution of shore angling locations in the vicinity of Arklow.

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Sea fish most associated with migration include Cod, Bass and Mackerel. The following paragraphs outline the migratory period of each lifecycle. Cod, Bass and Mackerel are oceanodromous fish in that they migrate within salt water only, whereas eel are catadromous fish living in fresh water, and breeding in the ocean. Salmon and Sea Trout are anadromous fish that live in the ocean mostly, and breed in fresh water.

2. Migration Patterns

Cod (Gadus morhua) Adult cod form spawning aggregations from late winter to spring1. In general, fish larvae diet consists of copepod nauplii, copepodites, mollusc veligers, and protozoa (e.g. tintinnids and dinoflagellates). Hard- bodied protozoa, such as tintinnids and armoured dinoflagellates have frequently been found in fish larvae guts2. Thus their diet is linked with primary production and the spring production cycle.

Sea Bass (Dicentrarchus labrax) Adult Sea Bass manifest demersal behaviour and inhabit coastal waters down to about 100m depth but more common in shallow waters. They are found in the littoral zone on various kinds of bottoms on estuaries, lagoons and occasionally rivers. They enter coastal waters and river mouths in summer, but migrate offshore in colder weather and occur in deep water during winter in the northern range3. In the Republic of Ireland, there are strict laws regarding bass, all commercial fishing for the species is banned and there are several restrictions in place for anglers i.e. a closed season May 15- June 15 inclusive every year, minimum sizes of 400mm and a bag limit of 2 fish per angler in a 24 hour period.

Atlantic mackerel (Scomber scombrus) The Atlantic mackerel is a pelagic schooling species of mackerel found on both sides of the North Atlantic Ocean. It is extremely common in huge shoals migrating towards the coast to feed on small fish and prawns during the summer. Abundant in cold and temperate shelf areas, it forms large schools near the surface. They overwinter in deeper waters but move closer to shore in spring when water temperatures range between 11° and 14°C. The most familiar movement of mackerel in Irish waters takes place from late summer until late autumn.

1 K. M. Brander. 1994. The location and timing of cod spawning around the British Isles. ICES Journal of Marine Science 51 (1): 71– 89. 2 G.M. Figueiredo, D.J.S. Montagnes and R.D.M. Nash. 2004. The importance of protozoan prey in the diet of larval fish in coastal areas of the Irish Sea. Physiology of Fish Eggs and Larvae, Symposium Proceedings, International Congress on the Biology of Fish, Brazil, August 2004. 3 http://www.fishbase.org/Summary/SpeciesSummary.php?id=63

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Salmon, sea-trout and eels belong to the group of fish which live for part of their lives in freshwater and part in the ocean. In the case of salmon and sea trout, these fish migrate from the seas where they have been feeding and return to spawn in the rivers in which they themselves were spawned. In contrast, eels spawn in the ocean, returning to rivers and lakes to feed and grow.

European Eel (Anguila anguila) The larvae of European Eel travel with the Gulf Stream across the ocean and, after one to three years, their leptocephali reach a size of 75 – 90 mm before they reach the coasts of Europe. The common name for this recruiment stage of eels is glass eel, based on the transparency of the body. Once they recruit to coastal areas they migrate up rivers and streams, overcoming all sorts of natural challenges. They can move themselves over wet grass and dig through wet sand to reach upstream headwaters and ponds. In freshwater they develop pigmentation, turn into elvers (young eels) and feed on creatures like small crustaceans, worms and insects. They grow up in 10 or 14 years to a length of 60 to 80 cm. In this stage they are now called yellow eels because of their golden pigmentation. Individuals mature and some migrate back towards the sea in July, crossing even wet grasslands at night to reach rivers that lead to the sea. Eel migration out of their freshwater growth habitats from various parts of Europe have been the basis of traditional fisheries with characteristic trapnets. However, there is at present a moratorium on catching eels in Irish waters in order to conserve the species.

Salmon (Salmo salar) In spring, large numbers of smolts leave Irish rivers to migrate north along the slope current into the rich feeding grounds of the Norwegian Sea and the greater expanse of the North Atlantic Ocean. Some Irish salmon, called grilse will reach maturity after one year at sea and return to their river in summertime weighing from 1 to 4kg. If it takes two or more years to mature, the salmon will return considerably earlier in the year and larger at 3 to 15kg - becoming a highly prized fish but also a very rare one.

Sea Trout (Salmo trutta) Both sexes usually survive spawning and anadromous trout migrate back to sea or lake in autumn or overwinter in rivers and migrate in spring. Smolts start to migrate downstream in April-May when temperature increases from low winter level, reaching beyond 5-11°C; migration peaks at rising water levels with increased turbidity.

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2. Discussion

From the migration patterns outlined above, there is a clear pattern in terms of timing however varied the species in terms of its biological cycle. In the case of oceanodromous fish, the greatest movements are associated with the spring bloom in the case of cod and the movement of bass into inshore waters during summer and the shoaling of mackerel in late summer. Salmonids migrate in spring and summer and Eels migrate in summer.

In terms of avoiding impacts from dredge spoil loading and disposal on migrating fish, the preferred time of works would be during the late summer/early autumn months. This corresponds with guidance from Inland Fisheries Ireland (previously the Eastern Regional Fisheries Board).

Any avoidance mitigation measures should be observed in tandem with those measures proposed for adjacent conservation areas, e.g. the timing of spoil disposal outside times of extended high velocity south easterly winds.

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