Shift in trophic role of northern fur seals in the northwestern Pacific Ocean

摘要

Northern fur seals (Callorhinus ursinus, NFS) are the most abundant otariid species with recent population estimates reaching approximately 1.2 million (Angliss and Lodge, 2004). NFS are widely distributed in the subarctic zone of the North Pacific Ocean, with the northwestern Pacific Ocean (particularly the area off the Tohoku region of Japan) providing a major wintering and foraging area for NFS. Approximately 100,000 of fur seals, primarily adult females and juveniles, migrate to this area where they remain from the winter to early spring. Thus, NFS are important apex predators in the area, which corresponds to one of the most productive fishing grounds in the world due to mixing of the Kuroshio and Oyashio currents.