Northeast Atlantic elasmobranch community on the move: Functional reorganization in response to climate change

While spatial distribution shifts have been documented in many marine fishes under global change, the responses of elasmobranchs have rarely been studied, which may have led to an underestimation of their potential additional threats. Given their irreplaceable role in ecosystems and their high extinction risk, we used a 24-year time series (1997-2020) of scientific bottom trawl surveys to examine the effects of climate change on the spatial distribution of nine elasmobranch species within Northeast Atlantic waters. Using a hierarchical modeling of species communities, belonging to the joint species distribution models, we found that suitable habitats for four species increased on average by a factor of 1.6 and, for six species, shifted north-eastwards and/or to deeper waters over the past two decades. By integrating species traits, we showed changes in habitat suitability led to changes in the elasmobranchs trait composition. Moreover, communities shifted to deeper waters and their mean trophic level decreased. We also note an increase in the mean community size at maturity concurrent with a decrease in fecundity. Because skates and sharks are functionally unique and dangerously vulnerable to both climate change and fishing, we advocate for urgent considerations of species traits in management measures. Their use would make it better to identify species whose loss could have irreversible impacts in face of the myriad of anthropogenic threats. Elasmobranchs are experiencing habitat shifts in the Northeast Atlantic, as evidenced from 1997 to 2020 data. Suitable areas for six species expanded by 1.6 times, and/or shifted towards the northeast and deeper waters. These shifts altered the community structure, notably reducing average trophic levels and affecting reproductive patterns. Given their critical ecological roles and heightened vulnerability, there's an urgent need for tailored conservation strategies, recognizing the unique traits of these species to mitigate potential irreversible consequences.image