United Kingdom

Fisheries United Kingdom

Vulnerabilities - Inland fishery

Fishery may decline, limited by low stream flows and increased stream temperatures (1). Fish are unable to control their body heat internally, but do so by swimming to waters that suit their temperature optimum. Fish are particularly sensitive to small changes in temperature, causing changes in distribution at the extremities of their ranges (2).

Risks of climate change for inland fishery are (2):

Fish production will suffer if wetlands and other habitats that serve as nurseries are lost with sea level rise;
In the rivers, higher temperatures and lower oxygen concentration are unfavourable to salmon, sea-trout and trout, and might tip the competitive balance towards less valuable coarse fish, such as pike, allowing both native species and those introduced by anglers to extend their ranges (4);
Increasing pollutants from concentrated river flow during droughts and from leaching of agricultural land during high rainfall may lead to poorer inshore water quality;
The remobilisation of metalliferous mine and industrial wastes due to storms and increased winter rainfall may pollute inshore waters and have potential impacts on fishery (larvae), and shellfish stocks.

Vulnerabilities - Marine fisheries

Analyses of Scottish and English commercial catch data in the North Sea spanning the period 1913–2007 have revealed that the locations where peak catches of target species such as cod, haddock, plaice and sole were obtained have all shifted over the past 100 years, albeit not in a consistent way (13). For example, catches of cod seem to have shifted steadily north-eastward and towards deeper water in the North Sea and this reflects both climatic influences and intensive fishing. Plaice distribution has shifted north-westward towards the central North Sea, again reflecting climatic influences, in particular sea surface temperature as also confirmed.

Impacts on coastal fishery are uncertain, but external pressures on declining fish stocks are likely to exert far greater pressures on the industry (2,3). Traditional species such as cod are migrating north whilst new, more exotic species are now present in southern waters. The other items on the fisherman’s agenda include the recent pronouncements on EU quotas (belatedly designed to control overfishing), and the need to renegotiate the Common Fishing Policy.

Rising global temperatures are likely to reduce the overall productivity of the oceans, affecting species across the entire marine food chain, from plankton, to many fish species and seabirds. Such changes would exacerbate current pressures on fish stocks, and would have serious consequences for fishery in the region, which are important to the local economy. There is recent evidence to demonstrate that fish species are changing in local waters. Fish are unable to control their body heat internally, but do so by swimming to waters that suit their temperature optimum. Fish are particularly sensitive to small changes in temperature, causing changes in distribution at the extremities of their ranges (2).

Trawl data from Scottish research vessels dating from January 1925 show that catches of the warm water pelagic species, anchovy (Engraulis encrasicholus) and sardine (Sardina pilchardus), increased suddenly after 1995. Most were observed in the first quarter of each year, with 1998 and 2003 having the largest numbers, although few data are available for the last quarter. These long-term changes are thought to be due to rising sea temperatures (5).

Many species of plankton and fish have shifted their distribution northward and sub‑tropical species are occurring with increasing frequency in European waters, changing the composition of local and regional marine ecosystems in a major way (6,11). Recent studies have shown that the northward movement of southerly species has caused species richness in the North Sea to increase (7). This may have negative ecological and socio‑economic effects: the three large species that have decreased their range the most in the North Sea are all commercially relevant, while only one of the five most increasing species and less than half of the all the species that expanded their range are of commercial value. A climate change-induced shift from large to smaller species is thus likely to reduce the value of North Sea fisheries (7).

During the past 40 years there has been a northerly movement of warmer‑water plankton by 10° latitude (1100 km) in the north‑east Atlantic and a similar retreat of colder‑water plankton to the north. This northerly movement has continued over the past few years and appears to have accelerated since 2000. Sole and other warm‑water species have become relatively more abundant in northerly areas, while plaice and other cold‑water species have become rare in southerly areas (10). Climate is only one of many factors which affect distribution and abundance, but the consistency of the response of this particular index to temperature, both within particular areas (i.e. time trend) and across all areas (i.e. geographic trend) suggest that the causal relationship is quite strong. Scenario projections of future movements of marine species have not yet been made (8).

The kinds of fish which are available for human consumption are not necessarily affected by the distribution changes shown above, because fish are often transported long distances from where they are caught to where they are marketed, but the prices of fish may change if certain species that are common today become less common. People eating locally caught fish may notice changes in the species they catch or buy. Changes in distribution may affect the management of fisheries. Fisheries regulations in the EU include allocations of quotas based on historic catch patterns, and these may need to be revised (8). In general it is not possible to predict whether northward shifts in distribution will have a positive or a negative effect on total fisheries production (9).

Risks of climate change for marine fishery are (2):

fish production will suffer if wetlands and other habitats that serve as nurseries are lost with sea level rise;
stocks of more northerly species such as cod, sprat and plaice may decrease;
increasing sea levels and storm events could damage harbours and quays;
estuaries may become silted up leading to permanent dredging to ensure access;
climate change impacts are likely to exacerbate existing stresses on fish stocks – notably overfishing and pollution.

In addition, ocean acidification may pose a major threat to commercial fisheries, especially those for calcifying shellfish species (14).

The major issue faced by both freshwater and marine fishery is the decline in fish stocks. In recent years salmon and sea-trout numbers have fallen, particularly in the rivers of the west coast of Scotland (4). The stocks of most of the commercially exploited species of sea fish are close to, or out with, safe biological limits. There are many possible causes, which include over-fishing, pollution, eutrophication (enrichment of water with nutrients from, for example, agricultural runoff or sewage sludge), acidic runoff from forestry and changes in predator numbers. Another possible cause that has come to light recently is changes in ocean currents: these can affect the amount of food available to adult fish, and disrupt the normal pattern of dispersal of larval fish to the main fishing areas. Over-fishing is generally considered to be the major cause of the decline in the sea fishery.

Scientists state that there is convincing evidence that changes in ocean currents are occurring and that these might be contributing to the decline in wild salmon by reducing their survival at sea (4). In the rivers, higher temperatures and lower oxygen concentration are unfavourable to salmon, sea-trout and trout, and might tip the competitive balance towards less valuable coarse fish, such as pike, allowing both native species and those introduced by anglers to extend their ranges.

The East of England has several inshore fisheries of note, such as Oyster beds in the Blackwater Estuary. These may be affected by sea level rise and flood defence decisions. For example, the fishery in the Blackwater Estuary may be affected by the largest coastal realignment project in Europe at Abbots Hall Farm in Essex. Here Essex Wildlife Trust has converted 84 hectares of arable farmland into saltmarsh and grassland as part of a nationwide initiative to restore the UK’s rapidly declining coastal wetlands (3).

Adaptation strategy

Adaptation strategies include (12):

Travelling further to fish for current species, if stocks move away from existing ports.
Diversifying the livelihoods of port communities, this may include recreational fishing where popular angling species become locally more abundant (e.g. seabass).
Increasing vessel capacity if stocks of currently fished species increase.
Changing gear to fish for different species, if new or more profitable opportunities to fish different species are available.
Developing routes to export markets to match the changes in catch supplied. These routes may be to locations (such as southern Europe), which currently eat the fish stocks which may move into northern waters.
Stimulating domestic demand for a broader range of species, through joined-up retailer and media campaigns.

It is recommended that artificial reefs should be developed to capitalize on the appearance of exotic species for diving and recreational fishery (2). This will result in immediate benefits to the industry regardless of the pace of climate change as it is known that exotic species are already appearing regularly in South West waters.

The aquaculture industry could benefit from higher growth rates caused by increased water temperature, though this might also favour pests and diseases (4). Farming of different species requiring warmer water might become possible. Increased summer rainfall might allow salmon to enter the rivers more quickly, avoiding netsmen and predators.

Future change requires better management of river catchments and river bank habitat for salmon. A closed season in spring for salmon fishing with rods or mandatory catch and release regulations could be introduced. At sea, switching the fishing effort to new (warmer water) fish species is possible. The fishing industry is inherently adaptable, but there can be significant costs associated with re-equipping boats to catch different species (4).

References

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