What is already happening

1. Some fish distributions have moved northwards over the past 30 years by distances ranging from ~50 to 400km with coldwater species such as monkfish Lophius piscatorius and snake blenny Lumpenus lampretaeformis moving the furthest. At the same time some have moved into deeper waters at an average rate of ~3.6m per decade.
2. There have been many occurrences of rare or unusual fish in UK waters in recent years (including seahorses, ocean sunfish, triggerfish, tuna, stingrays etc.), although this does not necessarily reflect the influence of long-term climate change.
3. Warmer temperatures around the UK are correlated with poor conditions for survival of cod larvae and growth, but enhanced growth rates in sole (a warm-water species).
4. Climate and weather are known to influence year class strength (the number of surviving juveniles) in fish, and warmer conditions in recent years have coincided with poor survival of cod larvae.
5. Diadromous species (which spend some of their life in both fresh and marine waters) such as salmon and eel have been shown to be particularly vulnerable to climate change (water temperature and river flow), with impacts on both freshwater and marine phases.
6. Eel recruitment (the number of returning elvers) has declined throughout the UK. One possibility is that climatic changes in the Sargasso Sea are influencing reproduction and larval survival at sea.
7. Sandeels are an important prey resource for seabirds and marine mammals. Poor 'recruitment' of juveniles in recent years is thought to have been related to warmer temperatures, a positive NAO and a lack of availability of certain key planktonic prey items.

What could happen in the future

1. Attempts have been made to predict the future distribution and productivity of fish stocks around the World, but there are few locally-relevant studies for waters around the UK.
2. Climate change may lead to numerous local extinction and invasion events by the year 2050 with pelagic species (such as herring and anchovy) moving pole-ward by up to 600 km and demersal species (such as cod and haddock) by an average of 223 km.
3. Changes to currents may have an impact on the dispersal of fish eggs and larvae. It is anticipated that winter and early spring spawners (such as cod and plaice) will experience poor larval survival and growth, whereas warm-water, later spawning species (such as sprat) may benefit. Ocean acidification may impact food-webs supporting marine fish but there may also be direct physiological consequences for developing fish larvae that will reduce population sustainability overall.
4. Some diadromous fish species which exist in the UK are predicted to benefit from climate change (warmer temperatures and changed river flows) including Twaite shad and Thin-lipped grey mullet, whereas others such as river lamprey and smelt are anticipated to decline.

What is already happening: Medium

In general there is probably more information available about fish than any other component of marine ecosystems, and there have even been specific reviews of likely consequences of climate change for fish species in the British Isles (e.g. Graham & Harrod, 2009).

For cod in particular, there are extensive data and there have been many published analyses. Consequently we can say with high confidence that climate change has compromised the ability of the stock to withstand fishing mortality, but also that fishing mortality has impacted the ability of the stock to withstand variable climate. Fishing mortality rates that were considered sustainable 30 years ago, are now unsustainable due to negative effects of climate 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 (e.g. plaice, herring, mackerel, haddock, sole etc.) we have only medium or low confidence in the effects of climate change. Even less is known about the likely responses of non-commercial species, largely because of a lack of data spanning a sufficiently long time interval to analyse changes. Some species of non-commercial species are known to have increased in recent years (e.g. the boarfish and solenette) but it is unclear how this may relate to climate, or whether such changes have been caused by intensive fishing (van Hal et al., 2009). 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. 

What could happen: Medium

Studies have now been carried out that attempt to predict the likely future distribution or productivity of fish species worldwide, however these have very rarely been 'down-scaled' to the level of the United Kingdom or British Isles. Consequently our knowledge of, and confidence in, future projections remains moderate, although slightly higher than was the case in 2007-2008. More research is needed into the likely consequences of ocean acidification for marine fish, but also predictive studies that can distinguish between the possible influences of drivers such as intensive fishing, habitat degradation as well as climate change.

Research areas where data or knowledge are insufficient:

• '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 (relevant to the UK), attempting to estimate changes in fish distributions, interactions between fish species as a result of changing distributions, the ecological role of incoming species, and prospects for stock recovery and rebuilding.
• We know that abundance and distributional changes have not been consistent in all species, but we do not understand why.
• A key question is how fisheries and climate interact, including whether fisheries remove the ability to buffer against climate change, and whether fisheries (by removal of the largest, oldest and potentially most fecund individuals) prevent species from rapidly benefitting during years with favourable thermal regimes.
• We still know relatively little about how climate has affected the macroecological properties of the UK marine fish assemblage. It would be useful to know if our seas will become more or less productive, whether mean individual body size of the fish assemblage will change, and whether this will impact on other species (including humans).
• There is a significant knowledge gap about climatic influences on the abundance, temporal and spatial distribution of key forage fish species of importance to seabirds and marine mammals. In the UK we do not collect the spatially and temporally-explicit data required to investigate how forage fish abundance affects the distributions, migrations and breeding success of these high profile marine organisms.
• The potential implications of ocean acidification for fin-fish; both indirect consequences through the marine food web, but also direct physiological effects.
• Predictive and experimental studies aimed at elucidating the possible consequences of climate change for diadromous species, and most notably eels and salmon in the UK. It remains very unclear whether climatic influences during the marine phase are having negative consequences for 'recruitment' of elvers or retuning adults to some UK catchments.
• The impact of climate change on non-commercial species, but also fishes in the deep sea and open ocean.
• The ability of fish to 'adapt' (both physiologically and behaviorally) to long-term climate change.
• The potential impact that incoming non-native species or marine pathogens might have on 'native' fish populations, if they were to become established as a result of warmer waters or changing transmission routes (e.g. via an ice-free Arctic).

A detailed review of possible consequences of climate change for commercial fisheries (fin-fish and shellfish) is provided in a separate MCCIP report. The main conclusions of this report are:

• The location where high catches of cod, haddock, plaice and sole occur, as reported by UK commercial fishing vessels, seems to have shifted over the past 80-90 years. However, it remains unclear whether this has been due to long-term climate change or other factors.
• Climate change may be having an impact on the effectiveness of marine protected areas and on the apportionment of fishery resources between neighbouring countries.
• New fisheries have developed for a number of warmer-water species including seabass, red mullet, anchovy and squid. The biomass of seabass in the Channel has quadrupled since 1985.
• Ocean acidification may pose a significant threat to the UK shellfish industry, but the implications are poorly understood.
• The UK as a whole is expected to benefit from slightly enhanced fishery yields (by ~1-2%) over the next 50 years, although there will be regions where overall fishery yields may be reduced (e.g. the Irish Sea and Channel).
• Simulations suggest that cod stocks in the Celtic and Irish Seas are expected to disappear altogether by 2100, while those in the North Sea will decline. Climate change has been 'eroding' the maximum sustainable yield of cod in the North Sea by ~32,000t per decade.

Very little work has been carried out on the social and economic implications of climate change for the UK fishing industry, however calculations suggest that consequences will be significant only for fishery-dependent communities in the North of Scotland and in the SW of England.

Pinnegar, J.K., and M. Heath (2010) Fish in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 23pp. www.mccip.org.uk/arc