Metapopulation distribution shapes year-round fisheries bycatch risk for a circumpolar seabird

For vulnerable marine megafauna, understanding migratory connectivity and its implications for spatiotemporal overlap with threats is crucial for developing targeted management strategies. Amongst their most severe threats is incidental mortality (bycatch) in fisheries. However, few studies have examined year-round co-occurrence of populations and the implications for bycatch risk. Here, we combine biologging and fisheries datasets to map the global distribution and examine potential bycatch risk of the white-chinned petrel Procellaria aequinoctialis, the most bycaught seabird in the Southern Hemisphere. We tracked year-round movements of 132 adults to determine spatial overlap of seven populations (island groups). Bird distributions were combined with longline and trawl fishing effort from vessel Automatic Information Systems and logbooks to identify risk hotspots and determine time periods and fleets representing the greatest potential risk to each population. Birds from all populations migrated to continental shelf or upwelling zones, concentrating in smaller areas than during breeding. Migratory connectivity and spatial overlap analyses indicated greater mixing within than among genetically distinct Atlantic, Indian and Pacific Ocean population groupings. Overlap with fisheries varied considerably; Indian Ocean populations showed greatest overlap with the pelagic longline fleets of South Africa, Japan, Taiwan (Province of China) and Spain, off southern Africa and in the High Seas, whereas Indian and Atlantic Ocean populations had high overlap with demersal longline and trawl fleets within the areas of national jurisdiction of South Africa, Namibia and Argentina, and with the South Korean demersal longline fleet in the High Seas. Low migratory connectivity among populations from adjacent island groups broadly matched genetic metapopulation structure, and was reflected in fisheries overlap scores, indicating three separate management units. We identified regions and fleets where mitigation efforts should be targeted and the regulatory bodies responsible, showing the value of assessing bycatch risk across the species range for a thorough understanding of population- and species-level impacts.