• Excessive fishing pressure has caused fish populations to become more vulnerable to short-term natural climate variability by removing the oldest individuals, and making such populations less able to ‘buffer’ against occasional poor year classes.
• In the short term, climate change will have little influence on fish stock recovery, which depends instead upon reducing fishing effort to allow existing year classes to survive to maturity.
• Climate-related shifts in species distribution, behavior and depth preference may affect the ‘catchability’ of certain stocks to fishing fleets.
• Long-term climate change may affect the overall productivity of fish stocks in a given area. Some species may be adversely affected leading to reductions in sustainable yield whilst others, for example seabass, red mullet and John Dory, may be positively affected leading to enhanced fishing opportunities.

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What is happening now - Medium

What could happen in the future - Medium

For cod, plaice and sole in the North Sea, where there are extensive data and many published analyses, we can say with high confidence that climate change has compromised the ability of the stock to withstand fishing mortality. Fishing mortality rates, which were considered sustainable 30 years ago, are now unsustainable due to negative effects on recruitment. However, at present we are ‘not sure’ of the precise mechanisms by which climate change affects recruitment, beyond that the effects are correlated with sea temperature and to some extent with plankton abundance and composition. For other commercially important species in UK waters (herring, mackerel, haddock, saithe, whiting, monkfish) we have only medium or low confidence in the effects of climate change. This may be partly because a variety of other factors obscure any relationships with temperature, or simply because of a lack of adequate data.

Most of our conclusions regarding the response of fish and fisheries to climate change are assembled from fragmentary information from surveys, fishery landings, anglers and other observers. Despite scientific study we are still not sure exactly why, for example, sea temperature has a negative effect on cod recruitment. However, recent studies using data storage tags, genetics and analyses of otolithA calcified structure used as part of the balance system in bony fishes. The mineral structure changes over time and annual banding can be seen in the otolith allowing scientists to estimate the age of a fish. microstructure and chemistry have begun to unravel the behavioral and physiological processes that dictate the distribution and production of cod in the North Sea. These types of study seem to offer the most promising way of diagnosing the reactions of fish to changing climate conditions in sufficient detail for us to be able to predict responses in the future.

Where data is lacking:

• ‘Real’ information about the linkages between larval fish (their survival and feeding), zooplankton and climate.
• Information for the west of the British Isles; the North Sea has been considered in much greater detail in comparison with western Scotland, the Irish and Celtic Seas.
• Predictive studies, attempting to estimate changes in fish distributions, interactions between fish species as a result of changing distributions, the ecological role of incoming species, prospects for stock recovery and rebuilding.
• Experimental studies relating growth and reproductive output (in species other than cod) to temperature and/or other environmental variables.
• Information on how the behaviour of commercial fish species might be impacted by climatic changes, and thus the impact of climate variability on ‘catchability’ by fishing fleets.

The major commercial impact of climate change on fisheries has been to reduce the maximum sustainable yield of various historically important species, in particular cod, plaice and sole in the North Sea. In the case of cod, climate change has been estimated to have been eroding the maximum sustainable yield at a rate of 32,000 t per decade since 1980. Even if current stock rebuilding measures are effective, it cannot be expected that the fishery could be restored to its past state. Conversely, it seems likely that in the future, significant new fisheries will develop for species, which were not traditionally caught in UK waters, though it is hard to predict what these might be at present.

John K. Pinnegar
Centre for Environment,Fisheries & Aquaculture Science (Cefas), Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk. NR33 0HT, UK.

David W. Sims
Marine Biological Association of the UK (MBA), The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK.

Mike Heath
Fisheries Research Services (FRS), Marine Laboratory, 375 Victoria Road, Aberdeen, AB11 9DB, UK.