1. Fisheries Management Department, Hokkaido National Fisheries Research InstituteJapan Fisheries Research and Education Agency116 Katsurakoi Kushiro Hokkaido 085‐0802 Japan
2. Division of Marine Bio‐resource and Environmental ScienceGraduate School of Fisheries Sciences, Hokkaido University3‐1‐1 Minato‐Cho Hakodate Hokkaido 041‐8611 Japan
3. Marine Mammal LaboratoryAlaska Fisheries Science Center/National Oceanic and Atmospheric AdministrationSeattle WA 98115 USA
4. Kamchatka Branch of the Pacific Geographical InstituteFar East Branch of Russian Academy of Sciences6 Partizanskaya Street Petropavlovsk‐Kamchatsky 683000 Russia