ABSTRACT:

Fisheries constitute a major and dynamic threat to marine biodiversity worldwide. In particular, for wide-ranging megafauna, the risk of individual bycatch in fisheries may vary across seasons and regions because of the movements of both the animals and fishing fleets. To examine the seasonal distribution of the largest western population of black-footed albatrosses Phoebastria nigripes and its spatial overlap with fisheries, we tracked 20 individuals from Torishima, Japan, year-round using geolocators. During the breeding period (November–May), the birds were distributed in neritic waters off the Pacific coast of central Japan, while during the post-breeding period, they moved north-eastward and used neritic waters off northern Japan and the Kuril Islands. They showed the widest distribution in October, predominantly in the northern part of the Sea of Okhotsk. Throughout the nonbreeding period, they did not use the Aleutian Islands, the Gulf of Alaska, or the Bering Sea, which are core nonbreeding areas for the Hawaiian population. Seasonal changes in habitat use also included the selection of productive waters characterized by lower sea surface temperature (SST), higher surface chlorophyll a concentration, shallower seafloor depth with weaker slope, and stronger SST gradients during the nonbreeding period than during the breeding period. Importantly, the birds’ at-sea distribution overlapped more intensively with industrial fishing fleets, including pelagic and demersal longliners and trawlers, during the breeding period than during the nonbreeding period. Our results highlight the importance of assessing the population-specific dynamic patterns of bycatch risk to develop adequate conservation strategies for such wide-ranging marine organisms.