Genetic assignment of fisheries bycatch reveals disproportionate mortality among Alaska Northern Fulmar breeding colonies

Global fisheries kill millions of seabirds annually through bycatch, but little is known about population-level impacts, particularly in species that form metapopulations. U.S. North Pacific groundfish fisheries catch thousands of Northern Fulmars (Fulmarus glacialis rodgersii) each year, making fulmars the most frequently caught seabird in federally managed U.S. fisheries. Here, we used genetic stock identification to assign 1,536 fulmars sampled as bycatch to one of four Alaska breeding colonies and quantified the similarity of bycatch locations at sea among colonies. We found disproportionately high bycatch from the Pribilof Islands (6% of metapopulation, 23% of bycatch), and disproportionately low bycatch from Chagulak Island (34% of metapopulation, 14% of bycatch). Overlap between fisheries and colony-specific foraging areas diverge more during the summer breeding season, leading to greater differences in bycatch susceptibility. Contemporary and historical gene flow likely contributes to low genetic differentiation among colonies (F-ST = 0.003-0.01), yet these values may not represent present connectivity. Our findings illustrate how genetic stock identification can link at-sea threats to colonies and inform management to reduce bycatch from impacted colonies.

Automated summary

Global fisheries cause significant harm to seabirds through unintentional bycatch, particularly in species that form metapopulations. This study used genetic stock identification to assign bycatch Northern Fulmars to specific breeding colonies in Alaska and found disproportionate levels of bycatch from different colonies. The overlap between fisheries and colony-specific foraging areas was lower during the summer breeding season, leading to greater differences in bycatch vulnerability. These findings highlight the importance of genetic stock identification in linking at-sea threats to specific colonies and informing management strategies to reduce bycatch.