This species inhabits mainly offshore deep waters colder than 18°C (Miyashita and Kasuya 1988), but may also occur in narrow channels and fjords in the western North Pacific (Jefferson 1988, Rice 1998).

Sex-biased dispersal is known to occur in this species, and this may have relevance in assessing the impact of takes on regional populations (Escorza Trevino and Dizon 2000).

Dall's Porpoises are apparently opportunistic feeders, taking a wide range of surface and midwater fish and squid, especially soft-bodied species like lanternfishes (myctophids) and gonatid squids. Krill, decapods, and shrimps found in porpoise stomachs occasionally are not considered normal prey (Houck and Jefferson 1999, Jefferson 2002).

Dall's Porpoises are found only in the northern North Pacific Ocean and the adjacent Bering and Okhotsk seas, and in the Sea of Japan. They inhabit deep waters between about 30° and 62°N (Jefferson 1988. Houck and Jefferson 1999), but occasionally occur as far south as about 28°N off the coast of Baja California (Mexico) during unusually cold-water periods.

The P. d. dalli subspecies is the more widely distributed form, and it occurs throughout the species’ range, from the west coast of North America to Japan, Korea and Russia.

The P. d. truei subspecies is identified by a more extensive lateral white patch, and it inhabits only the western North Pacific. The truei subspecies migrates between wintering grounds off the Pacific coast of northern Japan and summer breeding grounds in the central Okhotsk Sea. It constitutes a single population (IWC 2002).

The species is listed in Appendix II of CITES. Dall’s Porpoise are also protected by generally applicable marine mammal legislation in Canada and the United States. Catches of Dall’s Porpoises in the Japanese salmon driftnet fishery were limited to some extent by quotas set by the U.S. government, because until the early 1990s the fishery took place largely within U.S. Exclusive Economic Zone waters of the Aleutian Islands. There was a large-scale fishery observer program and extensive biological research associated with this fishery in the late 1970s and 1980s (Jones 1984, Ferrero and Walker 1999).

The long period since the last abundance survey (over 15 years) means that reassessment of the status of the two populations hunted in the Japanese hand harpoon fishery is needed. Kasuya (2017) summarized information suggesting that both of those populations have decreased in size from the early 1990s to the late 2000s, though thorough biological reviews and status assessments have not been conducted in recent years. The Japanese government sets quotas for this fishery, but these are based on optimistic assumptions about rates of population increase. As such, they could still result in the depletion of populations (Kasuya 2017).