Abstract
i. In December 2003 the UK Government announced that it was to promote a second round of offshore wind-farm development. After consultation with the wind-energy industry, the Department of Trade and Industry (DTI) identified three strategic areas in which Round 2 developments would take place: the Thames Estuary, the Greater Wash, and the North West - an area of the eastern Irish Sea extending from North Wales to south-west Scotland east of 4º W. Developments on this scale are subject to the provisions of the EU Directive 2001/42/EC on the assessment of the effects of certain plans and programmes on the environment, commonly known as the Strategic Environmental Assessment (SEA) Directive. An assessment of the fish and shellfish stocks in the eastern Irish Sea has been undertaken to meet the requirements of this directive.
ii. The report is presented in three parts:
- a review of the fish and shellfish resources in the eastern Irish Sea, describing their distribution and biology;
- a summary of the current status of fish and shellfish stocks exploited in the eastern Irish Sea);
- an initial consideration of the potential effects that developing wind farms may have on fish and shellfish during the pre-construction, construction, operation and decommissioning of wind farms in the eastern Irish Sea.
iii. The report was prepared as a desk study which drew on information provided by the Department of Environment, Food & Rural Affairs (DEFRA) Fisheries Statistical Unit (FSU), research survey data provided by the Centre for Environment, Fisheries & Aquaculture Science (CEFAS), advice from officers of the North Western & North Wales Sea Fisheries Committee (NWNW SFC), published literature, the internet, and the author’s personal knowledge of the fish and shellfish resources of the eastern Irish Sea.
iv. Approximately 70 species of marine fish and commercially exploited shellfish are indigenous to the eastern Irish Sea in addition to salmon, sea trout, eels and a variety of fish of nature conservation interests: basking sharks, allis and twaite shad, common and sand goby, sea and river lamprey, and smelt. The five most abundant species taken in a CEFAS beam-trawl survey were dab, solenette, plaice, common dragonet and Dover sole, but the greatest quantities of fish caught by UK-registered fishing vessels in the eastern Irish Sea were king and queen scallops, nephrops, plaice, cod and whiting. There are also major intertidal fisheries for cockles and mussels centred on, but not limited to, Morecambe Bay.
v. The intertidal shellfisheries are assessed and managed by the North Western and North Wales Sea Fisheries Committee but the finfish stocks are assessed by the International Council for the Exploration of the Sea (ICES) and managed through the European Common Fisheries Policy (CFP). All of the shellfish stocks are currently judged to be in robust condition but most of the commercially important finfish stocks are giving cause for concern and are subject to highly restrictive catch limitations. Salmon, sea trout and eel stocks that run through the eastern Irish Sea to their freshwater spawning or feeding grounds appear to be suffering a prolonged, long-term decline in abundance.
vi. The exact status of the fish of nature conservation interest is not known but there are UK Biodiversity Action Plans in place to safeguard basking shark, shads and lampreys in UK waters. There is no such plan for salmon-related smelt or the gobies; although the smelt is not as numerous as was once the case both goby species are ubiquitous to shallow sandy areas of inshore UK waters.
vii. The greatest single effect that wind farms are likely to have on fish is the change in habitat. Natural habitat will be lost as turbine foundations are put in place and new habitat created by the surface area of wind-farm structures. Although many of the species upon which fish feed live in or on the seabed, only a trivial proportion (
viii. The wind-farm structures, and any transmission cables that are surface laid and rock armoured, will create artificial reefs or act as fish aggregation devices. In addition to the new feeding areas that these reef structures offer, they can affect the behaviour and local abundance of fish by causing them to aggregate within the boundary of each wind farm. This localised aggregation will, inevitably, be countered by a drop in local abundance in the area around each wind farm from which the fish are drawn. It is concluded, however, that the physical presence of wind farms in the eastern Irish Sea will not have an adverse effect on fish.
ix. During the construction and cable-laying phase of developing wind farms it is anticipated that there will be increases in the suspended sediment concentrations locally. As the eastern Irish Sea is naturally a relatively turbid environment it is not anticipated that any construction-related increases in turbidity will affect fish adversely with the possible exception of salmon and sea trout. While they too can accommodate high suspended sediment concentrations a persistent plume of suspended sediment in the vicinity of a salmon river-mouth could be sufficient to deter these fish from entering the rivers to spawn. These concerns will need to be considered when scheduling construction or cable-laying activities in sensitive areas.
x. Similar sensitivities will also need to be addressed with respect to certain shellfish species, particularly if modelling indicates that there may be higher than natural settlement rates of resuspended sediments. Intertidal species such as cockles are adapted to the rigours of a highly dynamic environment and mobile habitat but a sustained daily sediment settlement rate of ~5 mm or more may exceed their adaptive capabilities and smother them. For recently settled juvenile cockles the figure could be as low as 1 mm per day. These concerns will be of greatest relevance around Morecambe Bay, the Ribble Estuary and the Dee Estuary. The gills of nephrops (‘scampi’), a species that is found between Cumbria and the Isle of Man, may also be susceptible to clogging from high suspended sediment concentrations.
xi. The preliminary evidence of fish aggregating around North Hoyle suggests that fish are not adversely affected by the noise of an operational wind farm but there may be greater disturbance during the construction phase. At this stage the noises generated are likely to be more variable and allow the fish less time to adapt. The greatest potential concern, however, is during pile-driving when fatal damage could be sustained by fish within 1-2 m of the foundation. This potential risk can be minimised by ‘tapping’ with the pile-driver to drive fish away from the immediate vicinity before commencing full-force operations.
xii. There remains a degree of uncertainty about the potential effects that electromagnetic fields (EMF) along cable routes may have on fish, particularly elasmobranchs such as dogfish and rays. It is highly unlikely that salmon or sea trout will be affected as their use of EMF is for oceanic migration; in coastal waters they rely on olfaction to detect and recognise their natal river. The elasmobranchs, however, utilise micro-variations in local EMF to detect their prey and any anomaly associated with transmission cables may affect their feeding behaviour or access to preferred spawning grounds. This concern is subject to on-going research.
xiii. At the decommissioning stage the primary concerns would, once more, be with respect to increased suspended sediment concentrations and the loss of habitat as structures, including cable rock-armouring, were removed and the original habitat became re-established.