Dall's porpoise ranges through much of the North Pacific and nearby seas, such as the Bering and Okhotsk Seas and the Sea of Japan.
Dall's porpoise (Phocoenoides dalli) is a species of porpoise found only in the North Pacific. It came to worldwide attention in the 1970s when it was disclosed for the first time to the public that salmon fishing trawls were killing thousands of Dall's porpoises and other cetaceans each year by accidentally capturing them in their nets. Dall's porpoise is the only member of the genus Phocoenoides. It was named after American naturalist W. H. Dall.
The unique body shape of Dall's porpoise makes it easily distinguishable from other cetaceanspecies.
The animal has a very thick body and a small head. The colouration is rather like that of a killer whale; the main body of the porpoise is very dark grey to black, with very demarcated white patches on the flank and belly. The dorsal fin is set just back from the middle of the back and sits up erect. The upper part of the dorsal fin has a white to light grey "frosting".
The fluke has a similar frosting. The adult fluke curves back towards the body of the animal, which is another distinguishing feature. It is larger than other porpoises, growing up to 2.3 m (7.5 ft) in length and weighing between 130 and 220 kg (290 and 490 lb). There is also sexual dimorphism in the species, with males being larger, having a deeper caudal peduncle and a pronounced hump behind the anus.
Dall's porpoises primarily eat small fishes (of numerous species) and cephalopods. Schooling fish, such as herrings, anchovies, pilchards, mackerels, hake and sauries are favored prey, as well as mesopelagic fish such as myctophids and deep sea smelts. They may also consume krill, but these are probably not important in their diet. Dall's porpoise are also deep divers.
They have a polygynous mating system in which males will guard females in estrus. During the mating season, a male will select a fertile female and guard her to ensure that he will sire her calf. While guarding, males may sacrifice opportunities to forage in deep dives. Births usually take place in the summer. Porpoise gestation lasts 10 to 11 months, and the lactation period lasts at least two months. Depending on their condition, females can give birth up to every year. Dall's porpoises live for up to 15 years.
Dall’s porpoises live in small, fluid groups of two to 12. However they can gather in the hundreds when feeding. Dall's porpoises are highly active creatures. They will often zigzag around at great speed on or just below the water surface, creating a spray called a "rooster tail". They may appear and disappear quite suddenly. The fastest of all small cetaceans, Dall's porpoises can swim at up to 55 km/h, almost as fast as the killer whale. The porpoises will approach boats and will bow- and stern-ride, but may lose interest, unless the boat is travelling quickly.