Risso's Dolphin

Risso's dolphin is the only member of its genus, and at 300–500 kg the largest species called a dolphin. It grows to about 3 m, sometimes 4 m, and is identified by heavy white scarring. The front of the body and dorsal fin are relatively large and the rear tapers to a narrow tail. Infants are grey to brown above and cream below; older animals become mostly white as they age (Wikipedia, general species account).

It is found nearly worldwide, from cold and temperate to tropical waters, and is most often seen along continental shelves. It feeds almost exclusively on squid, mostly at night, and can dive to about 600 m after them. Gestation is an estimated 13–14 months, with calving about every 2.4 years, and the oldest specimen reached nearly 40 years. Its occurrence in Japanese waters is documented by the National Museum of Nature and Science marine-mammal database.