Aim:The life history of a species is determined by trade-offs between growth, survival and reproduction to maximize fitness in a given environment. Following a theoretical model, we investigate whether the composition of marine fish communities can be understood in terms of a set of lifehistory strategies and whether the prevalence of the strategies follows specific spatial patterns that can be related to the environment.Location: European seas.Time period: 1980-2014.Major taxa studied: Fish.Methods: An extensive set of scientific bottom trawl surveys was collected to obtain the species composition of fish communities across European seas. We complemented these data with species-specific information regarding six life-history traits, reflecting reproductive, growth and feeding modes. We then calculated the optimal number of strategies needed to summarize the information contained in the traits by using archetypal analysis. The proportion of each obtained strategy in the communities and their spatial patterns were explained as a function of the environment and their temporal changes were investigated.Results: The species could be decomposed into a continuum of three life-history strategiesopportunistic, periodic and equilibrium-resulting from trade-offs between traits. The marked spatial patterns of these strategies could be explained by depth, temperature and its seasonality, chlorophyll and fishing effort. In recent years, opportunistic and equilibrium strategies significantly increased, probably due to an increase in temperature and decrease in fishing effort.Main conclusions: Our empirical analysis supports a theoretical framework outlining three lifehistory strategies of fish. The strategies vary predictably in space and time in response to the environment. This highlights the underlying process whereby fitness is optimized through trade-offs between growth, feeding and reproduction under different environmental conditions. Due to their response to the environment, life-history strategies provide a suitable tool for monitoring and understanding community changes in response to natural and anthropogenic stressors, including fishing and climate change. K E Y W O R D S archetypal analysis, community composition, depth, fecundity, life-history strategies, marine fish, offspring survival, size, temperature, trade-off, trait 812 |

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A fundamental challenge in ecology is to understand why species are found where they are and predict where they are likely to occur in the future. Trait-based approaches may provide such understanding, because it is the traits and adaptations of species that determine which environments they can inhabit. It is therefore important to identify key traits that determine species distributions and investigate how these traits relate to the environment. Based on scientific bottom-trawl surveys of marine fish abundances and traits of >1,200 species, we investigate trait-environment relationships and project the trait composition of marine fish communities across the continental shelf seas of the Northern hemisphere. We show that traits related to growth, maturation and lifespan respond most strongly to the environment. This is reflected by a pronounced “fast-slow continuum” of fish life-histories, revealing that traits vary with temperature at large spatial scales, but also with depth and seasonality at more local scales. Our findings provide insight into the structure of marine fish communities and suggest that global warming will favour an expansion of fast-living species. Knowledge of the global and local drivers of trait distributions can thus be used to predict future responses of fish communities to environmental change.

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Marine biota are redistributing at a rapid pace in response to climate change and shifting seascapes. While changes in fish populations and community structure threaten the sustainability of fisheries, our capacity to adapt by tracking and projecting marine species remains a challenge due to data discontinuities in biological observations, lack of data availability, and mismatch between data and real species distributions. To assess the extent of this challenge, we review the global status and accessibility of ongoing scientific bottom trawl surveys. In total, we gathered metadata for 283,925 samples from 95 surveys conducted regularly from 2001 to 2019. We identified that 59% of the metadata collected are not publicly available, highlighting that the availability of data is the most important challenge to assess species redistributions under global climate change. Given that the primary purpose of surveys is to provide independent data to inform stock assessment of commercially important populations, we further highlight that single surveys do not cover the full range of the main commercial demersal fish species. An average of 18 surveys is needed to cover at least 50% of species ranges, demonstrating the importance of combining multiple surveys to evaluate species range shifts. We assess the potential for combining surveys to track transboundary species redistributions and show that differences in sampling schemes and inconsistency in sampling can be overcome with spatio‐temporal modeling to follow species density redistributions. In light of our global assessment, we establish a framework for improving the management and conservation of transboundary and migrating marine demersal species. We provide directions to improve data availability and encourage countries to share survey data, to assess species vulnerabilities, and to support management adaptation in a time of climate‐driven ocean changes.