European continental shelf seas have experienced intense warming over the last 30 33 years 1 . In the North Sea, fishes have been comprehensively monitored throughout 34 this period and resulting data provide a unique record of changes in distribution and 35 abundance in response to climate change 2,3 . We use these data to demonstrate the 36 remarkable power of Generalised Additive Models (GAMs), trained on data earlier in 37 the time-series, to reliably predict trends in distribution and abundance in later years. 38Then, challenging process-based models that predict substantial and ongoing 39 poleward shifts of cold-water species 4,5 , we find that GAMs coupled with climate 40 projections predict future distributions of demersal (bottom-dwelling) fish species 41 over the next 50 years will be strongly constrained by availability of habitat of suitable 42depth. This will lead to pronounced changes in community structure, species 43 interactions and commercial fisheries, unless individual acclimation or population-44 level evolutionary adaptations enable fish to tolerate warmer conditions or move to 45 previously uninhabitable locations. 46 47While the temperature of the world's oceans has gradually risen through the 20 th Century, 48 the northeast Atlantic has experienced particularly intense warming, resulting in the North 49 Sea mean annual sea-surface temperature increasing by 1.3°C over the last 30 years 1 , a 50 rate four times faster than the global average 6 . Predictions for the North Sea suggest a 51 further 1.8°C rise in sea-surface temperatures during the next five decades (Hadley Centre 52 QUMP_ens_00 model, unpublished data supplied by J. Tinker) (Fig. 1). Impacts of recent 53 warming on northeast Atlantic marine ecosystems have been diverse, including 54 reorganisation of the plankton community 7 , modification to the phenology of fish spawning 8,9 , 55 and alterations of ecosystem interactions 10,11 . Due to its longstanding economic importance 56 to fisheries (reported landings in 2007 valued at $1.2 billion 1 ) and other industries, the 57 ecology of the North Sea has been intensively monitored throughout this period of recent 58 warming. 59 60 3 Analyses of North Sea fish surveys have revealed northerly range expansions of warmer-61 water species 12 , population redistributions to higher latitudes 2 and deeper water 13 , and 62 widespread changes in local abundance associated with warming, with impacts on 63 community structure 3 . This substantial modification to fish community composition in the 64 region has had an observable economic impact on fisheries, with landings of cold-adapted 65 species halved but landings of warm-adapted species increasing 2.5 times since the 1980s 3 ; 66 a pattern also identified in other marine ecosystems 14 . With a uniquely rich fish abundance 67 time-series from the period of warming, it is possible to split these data to assess how 68 predictions made using data from earlier years match observations from later years; a 69 validation approach which has been...

Highlights d Global-scale analysis of marine species shows abundance changes linked to warming d Increases at poleward sides of species ranges reflect new ecological opportunities d Declines at equatorward sides show failure to adapt to rapid climate change d Results imply future warming will impact further on abundance of marine species

Populations of fishes provide valuable services for billions of people, but face diverse and interacting threats that jeopardize their sustainability. Human population growth and intensifying resource use for food, water, energy and goods are compromising fish populations through a variety of mechanisms, including overfishing, habitat degradation and declines in water quality. The important challenges raised by these issues have been recognized and have led to considerable advances over past decades in managing and mitigating threats to fishes worldwide. In this review, we identify the major threats faced by fish populations alongside recent advances that are helping to address these issues. There are very significant efforts worldwide directed towards ensuring a sustainable future for the world's fishes and fisheries and those who rely on them. Although considerable challenges remain, by drawing attention to successful mitigation of threats to fish and fisheries we hope to provide the encouragement and direction that will allow these challenges to be overcome in the future.

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.

1. Projecting the future effects of climate change on marine fished populations can help prepare the fishing industry and management systems for resulting ecological, social and economic changes. Generating projections using multiple climate scenarios can provide valuable insights for fisheries stakeholders regarding uncertainty arising from future climate data. 2. Using a range of climate projections based on the Intergovernmental Panel on Climate Change A1B, RCP4.5 and RCP8.5 climate scenarios, we modelled abundance of eight commercially important bottom dwelling fish species across the Celtic Sea, English Channel and southern North Sea through the 21st century. This region spans a faunal boundary between cooler northern waters and warmer southern waters, where mean sea surface temperatures are projected to rise by 2 to 4°C by 2098. 3. For each species, Generalized Additive Models were trained on spatially explicit abundance data from six surveys between 2001 and 2010. Annual and seasonal temperatures were key drivers of species abundance patterns. Models were used to project species abundance for each decade through to 2090. 4. Projections suggest important future changes in the availability and catchability of fish species, with projected increases in abundance of red mullet Mullus surmuletus L., Dover sole Solea solea L., John dory Zeus faber L. and lemon sole Microstomus kitt L. and decreases in abundance of Atlantic cod Gadus morhua L., anglerfish Lophius piscatorius L. and megrim Lepidorhombus whiffiagonis L. European plaice Pleuronectes platessa L. appeared less affected by projected temperature changes. Most projected abundance responses were comparable among climate projections, but uncertainty in the rate and magnitude of changes often increased substantially beyond 2040. 5. Synthesis and applications. These results indicate potential risks as well as some opportunities for demersal fisheries under climate change. These changes will challenge current management systems, with implications for decisions on target fishing mortality rates, fishing effort and allowable catches. Increasingly flexible This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Over the last century, climate change has substantially affected the physical and chemical properties of the global ocean. The most spatially pervasive stressor on marine life is warming, and the global average ocean temperature has increased by 1°C between 1850 and 2018 (Kennedy et al., 2019). Warming has strongly impacted multiple components of marine ecosystems, including reorganisation of the plankton community (

Small and intermediate-size pelagic fisheries are highly impacted by environmental variability and climate change. Their wide geographical distribution and high mobility makes them more likely to shift their distribution under climate change. Here, we explore the potential impact of different climate change scenarios on the four main commercial pelagic species in the North-East Atlantic (NEA): Atlantic mackerel (Scomber scombrus), European sprat (Sprattus sprattus), Atlantic herring (Clupea harengus) and blue whiting (Micromesistius poutassou).We used a process-based fisheries model (SS-DBEM), where all the target species were exploited at their maximum sustainable yield (MSY), to project future potential catches under a high and low future greenhouse gas scenario (RCP 2.6 and 8.5, respectively). Two ocean biogeochemical models (GDFL and MEDUSA) were used to force the environmental conditions. Mackerel and sprat are projected to have increases in a potential catch under both scenarios. Herring and blue whiting are projected to increase under the RCP2.6, but future projections under RCP8.5 show mixed responses with decreases or no changes forecasted.Overall, the potential catch is projected to increase in the northern area of the NEA but is projected to decrease in the southern area. These projected changes are mainly driven by changes in temperature and primary production. Shifts in the distribution of pelagic resources may destabilize existing international agreements on sharing of straddling resources as exemplified by the dispute in sharing of quota for Atlantic mackerel. Novel climate-ready policy approaches considering full species distribution are needed to complement current stock-based approaches.

Using analysis of field survey size-at-age data, we examine responses of European plaice (Pleuronectes platessa) to spatial differences in environmental variables in the North Sea. Using available samples of plaice aged 1–7, northern and southern migrating groups of males and females grew differently. However, length-at-age growth patterns were not corroborated by complementary otolith-based estimates. Southern females and males were smaller than their northern counterparts until age 3. Southern males remained smaller up to age 7; by contrast southern and northern females reached similar size-at-age by year 4. Due to covariation, the influence of spatially variable environmental conditions was equivocal. However, temperature, depth, fishing pressure, phosphate levels, distance from shore, and conspecific density were all significant predictors of size for plaice aged 1–7. Our results suggest that fishing impacts on age structure limit the potential to examine the role of environmental variation on body size. For fish that rarely reach their full potential age and size, expected metabolic responses to warming may remain unexpressed, challenging predictions in a changing climate.