Panglobal Common Dolphin

The common dolphin is the most abundant cetacean in the world, with an estimated global population of about six million. It is a medium-sized dolphin, 1.9–2.5 m long, weighing 80–235 kg and more commonly 80–150 kg. It has unusual colouring: a dark back and white belly, and on each side an hourglass pattern that is light grey, yellow or gold in front and dirty grey behind (Wikipedia, general species account).

Common dolphins are often seen in groups of several hundred, with subgroups of 20–30, and different groups sometimes come together in mega-pods of over 10,000. Pods may be nursery pods of females and calves, bachelor pods of males, or mixed groups. A calf takes about a year to learn its signature whistle, which then stays stable for life. Its occurrence in Japanese waters is documented by the National Museum of Nature and Science marine-mammal database.