1. Laboratory of Cetacean Biology Tokyo University of Marine Science and Technology Minato‐ku, Tokyo Japan
2. School of Life Science and Technology, Tokyo Institute of Technology Meguro‐ku, Tokyo Japan
3. Tsurumi University Tsurumi‐ku, Yokohama City Kanagawa Japan
4. Kamogawa Sea World Higashi‐cho, Kamogawa, Chiba Japan
5. Institute of Cetacean Research Chuo‐ku, Tokyo Japan