• Abundances of warm-water fish species (e.g. red mullet, john dory, triggerfish) have increased in UK waters during recent decades, while many coldwater species have experienced declines.
• There has been a massive influx of snake pipefish to UK waters since 2004, but unusual fish occurrences or sudden proliferations of species cannot definitively be attributed to climate change.
• A number of commercial and non-commercial fish species are suggested to have exhibited shifts in mean latitude over the past 25 years.
• Poor 'recruitment' in traditional fishery target species such as cod, plaice and herring may be related to a shift in the composition of zooplanktonPlanktonic marine animals. Click for link to the SAHFOS Marine Climate Change Encyclopaedia, which are a key prey for developing larvae.
• In some parts of the southern North Sea, cold-water species, such as cod and eelpout, have been shown to experience metabolic stress during warm years, as evidenced by slower growth rates and difficulties in supplying oxygen to body tissues.
• Climate change will have far-reaching impacts on the dynamics of fish populations, however knowledge of underlying mechanisms is rather limited, especially in non-commercial species.

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What is happening now - Medium

What could happen in the future - Low

Little is known regarding the likely responses of non-commercial species to marine climate change, largely because of the lack of data spanning sufficient time interval to analyse changes. Nevertheless, we can say with high confidence that since 1980 the distribution of many warm water northeast Atlantic fish species has shifted northwards to occupy latitudes at which they were previously unobserved or rare.

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.

For commercial impacts on fisheries see the fisheries topic under the commercially productive seas section.

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.