Bycatch-threatened seabirds disproportionally contribute to community trait composition across the world

Human pressures in the ocean are restructuring biological communities, driving non-random extinctions, and disrupting marine ecosystem functioning. In particular, fisheries bycatch, the incidental mortality of non-target species, is a major threat to seabirds worldwide. Direct bycatch data are often scarce. Instead, leveraging trait-based analyses with fine-scale fisheries data could answer fundamental questions about spatial patterns of bycatch-threatened species and facilitate targeted conservation strategies. Here, we combine a dataset of species' traits and distribution ranges for 361 seabird and sea duck species with spatially resolved fishing effort data for gillnet, longline, trawl, and purse seine gears. First, we quantify geographic patterns of seabird community traits. Second, we describe how community traits could shift under local extinction scenarios in areas where bycatch-threatened seabirds spatially overlap with fishing activities. These objectives allow us to highlight the collective contribution of species currently threatened from bycatch to ecosystem functioning. We reveal distinct spatial variation in the community weighted mean of five seabird traits (body mass, generation length, clutch size, diet guild, and foraging guild) are evident. Moreover, our results show that fisheries bycatch is selectively removing a distinct suite of traits from the community within particular oceanic regions. Specifically, fisheries bycatch is threatening species with larger body masses, slower reproductive speeds (smaller clutch sizes and longer generation lengths), and specialised diet and foraging guilds. The spatial non-uniformity of the community trait shifts suggests that within specific marine regions, communities have limited redundancy and therefore may have less insurance to buffer against declines in ecosystem functioning. Our extinction scenario warns that seabirds currently threatened from fisheries bycatch substantially contribute to community functional composition. Management actions that incorporate species’ traits and fine-scale fisheries datasets as tools for marine spatial planning will add an important dimension when evaluating the success of conservation initiatives.