1. Marine Mammal Research Laboratory, Graduate School of Fisheries Science and Environmental Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
2. Marine Zoology Unit, Cavanilles Institute of Biodiversity and Evolutionary Biology, Science Park, University of Valencia, Catedrático José Beltrán 2, 46980 Paterna, Spain