Dall's Porpoise - Ecology and Lifestyle

Ecology and Lifestyle

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 been recorded to dive to 94m. Dall’s porpoise are prey to killer whales and white sharks. They also are susceptible to certain parasites. The trematode fluke Nastitrema, an internal parasite, is known to cause death and stranding of the porpoises. External parasites of the porpoise are whale lice.

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. They will also "snout ride" on waves made by the heads of large whales. They may also do more calm behaviors, such as subdued rolls at the surface. They rarely leap from the water.

Dall’s porpoises live in small, fluid groups of two to 12. However they can gather in the hundreds when feeding. 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.

One study determined through DNA sequencing that a fetus found in British Columbia was an intergeneric hybrid of a Dall's porpoise and a harbour porpoise. This hybrid may not be rare— it may describe the origins of some atypically coloured individuals that otherwise appear to be Dall's porpoises spotted off the coast of Vancouver Island.