Seasonal and Spatial Occurrence of Northern Fur Seals Callorhinus ursinus Around Northern Japan

Abstract. Northern fur seals (Callorhinus ursinus) disperse to broad areas and overwinter in the North Pacific Ocean during the non-breeding season. Fur seals breeding on islands off Russia mainly overwinter in the Sea of Japan and the off Pacific side of Japan in this season. Although the distribution of fur seals seems to vary with sexes and growth stages in this season, there is little information around Japan. We analysed data on stranding and collecting records of fur seals in the non-breeding season around northern Japan during 2005–2014 for investigating their intra-seasonal and spatial occurrence. The sex and growth stage composition differed between sampling areas. Adult males were dominant in the Sea of Japan, while juveniles and adult females were dominant in the Pacific coast of northern Japan. Compared with previous researches, our results can provide important information for elucidating migration pattern and habitat selection of each sex and growth stage around northern Japan.