Sea temperature is the primary driver of recent and predicted fish community structure across Northeast Atlantic shelf seas.

Climate change has strongly influenced the distribution and abundance of marine fish species, leading to concern about effects of future climate on commercially harvested stocks. Understanding the key drivers of large-scale spatial variation across present-day marine assemblages enables predictions of future change. Here we present a unique analysis of standardised abundance data for 198 marine fish species from across the Northeast Atlantic collected by 23 surveys and 31,502 sampling events between 2005 and 2018. Our analyses of the spatially comprehensive standardised data identified temperature as the key driver of fish community structure across the region, followed by salinity and depth. We employed these key environmental variables to model how climate change will affect both the distributions of individual species and local community structure for the years 2050 and 2100 under multiple emissions scenarios. Our results consistently indicate that projected climate change will lead to shifts in species communities across the entire region. Overall, the greatest community-level changes are predicted at locations with greater warming, with the most pronounced effects at higher latitudes. Based on these results, we suggest that future climate-driven warming will lead to widespread changes in opportunities for commercial fisheries across the region.

Can we project changes in fish abundance and distribution in response to climate?

Large-scale and long-term changes in fish abundance and distribution in response to climate change have been simulated using both statistical and process-based models. However, national and regional fisheries management requires also shorter term projections on smaller spatial scales, and these need to be validated against fisheries data. A 26-year time series of fish surveys with high spatial resolution in the North-East Atlantic provides a unique opportunity to assess the ability of models to correctly simulate the changes in fish distribution and abundance that occurred in response to climate variability and change. We use a dynamic bioclimate envelope model forced by physical-biogeochemical output from eight ocean models to simulate changes in fish abundance and distribution at scales down to a spatial resolution of 0.5°. When comparing with these simulations with annual fish survey data, we found the largest differences at the 0.5° scale. Differences between fishery model runs driven by different biogeochemical models decrease dramatically when results are aggregated to larger scales (e.g. the whole North Sea), to total catches rather than individual species or when the ensemble mean instead of individual simulations are used. Recent improvements in the fidelity of biogeochemical models translate into lower error rates in the fisheries simulations. However, predictions based on different biogeochemical models are often more similar to each other than they are to the survey data, except for some pelagic species. We conclude that model results can be used to guide fisheries management at larger spatial scales, but more caution is needed at smaller scales.

Climate Change Drives Poleward Increases and Equatorward Declines in Marine Species.

Marine environments have increased in temperature by an average of 1°C since pre-industrial (1850) times [1]. Given that species ranges are closely allied to physiological thermal tolerances in marine organisms [2], it may therefore be expected that ocean warming would lead to abundance increases at poleward side of ranges and abundance declines toward the equator [3]. Here, we report a global analysis of abundance trends of 304 widely distributed marine species over the last century, across a range of taxonomic groups from phytoplankton to fish and marine mammals. Specifically, using a literature database, we investigate the extent that the direction and strength of long-term species abundance changes depend on the sampled location within the latitudinal range of species. Our results show that abundance increases have been most prominent where sampling has taken place at the poleward side of species ranges, and abundance declines have been most prominent where sampling has taken place at the equatorward side of species ranges. These data provide evidence of omnipresent large-scale changes in abundance of marine species consistent with warming over the last century and suggest that adaptation has not provided a buffer against the negative effects of warmer conditions at the equatorward extent of species ranges. On the basis of these results, we suggest that projected sea temperature increases of up to 1.5°C over pre-industrial levels by 2050 [4] will continue to drive latitudinal abundance shifts in marine species, including those of importance for coastal livelihoods.