Stomach Contents of Pygmy Sperm Whales (Kogia breviceps) Stranded in Hokkaido, Japan

Abstract

Pygmy sperm whale Kogia breviceps is found in temperate to tropical areas throughout the world. In Japan, it is often reported to have stranded ashore on the Pacific side of Honshu Island, but only six individuals have been reported in Hokkaido. Its feeding habits in the waters surrounding Japan have not been reported. In this study, the stomach contents of three pygmy sperm whale individuals stranded on the Pacific coast of Hokkaido from 2011 to 2014 were investigated. As a result, ten species of cephalopods from 8 families and one species of fish were found. All individuals fed on cephalopod of the family Gonatidae and Watasenia scintillans, Gonatus pyros, and Chiroteuthis calyx appeared from two out of three individuals. The largest percentage (73.0%) of the total number of prey species belonged to the family Gonatidae spp., followed by Watasenia scintillans (6.2%) and Chiroteuthis calyx (3.4%). Only one individual fed on fish, which were identified as Gadus chalcogrammus. The size composition of the prey showed that the smallest prey was Chiroteuthis calyx with a dorsal mantle length of 29.4 mm and the largest prey was the Galiteuthis phyllura with a dorsal mantle length of 420.2 mm. These results indicate that the pygmy sperm whale use mainly mesopelagic cephalopods off the coast of Hokkaido.