1. Department of Marine Resources and Energy, Tokyo University of Marine Science and Technology, 4-5-7, Konan, Minato-ku, Tokyo 108-8477, Japan
2. Niigata City Aquarium, Marinepia Nihonkai (Sea of Japan), 5932-445 Nishifunami-cho, Chuo-ku, Niigata 951-8555, Japan
3. Cetacean Research Center, Graduate School of Bioresources, Mie University, 1577, Kurimamachiya-cho, Tsu-shi, Mie 514-8507, Japan
4. Faculty of Human Sciences, Tokiwa University, 1-430-1, Miwa, Mito-shi, Ibaraki 310-8585, Japan