Dall's porpoises, Phocoenoides dalli, are cool water porpoises inhabiting the North Pacific Ocean and adjacent seas. The central Bering Sea marks the northern boundary of their range and, although they prefer colder water, Dall's porpoises are found in the warmer waters of Baja California on the east to southern Japan on the west. They are frequently observed in these lower latitudes during the winter months. There are potentially two subspecies of Dall's porpoises, although they may simply be color morphs, P. dalli dalli and P. dalli truei. Phocoenoides dalli truei is abundant only off the Pacific coast of northern Japan.

Biogeographic Regions: pacific ocean (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: North Pacific: infrequent north of 62 degrees North in Bering Sea; in west, north of Choshi and east-central Honshu, Japan, and in the Sea of Japan and southern Okhotsk Sea; in east, north from about 28 degrees north (usually north of 32 degrees North). TRUEI morph is most abundant off the Pacific coast of northern Japan and off the Kuril Islands.

Dall's porpoises are the largest of the phocoenids. They typically reach a length of 1.8 to 2.0 meters, rarely more than 2.2 meters. At birth, the length is between 0.85 and 1.0 meters. Weight in adults varies from 130 to 220 kilograms. The body is stocky and more powerful than other members of Phocoenidae. The head is small and lacks a beak although there is a sloping forehead. The flippers are small, pointed, and located near the head. The dorsal fin is triangular in shape with a hooked tip.

There are three color patterns observed in the Dall's porpoises. The first is a uniform black or white throughout the entire body. The second pattern consists of intermixed stripes of black and white running along the length of the body. Finally, there is the most common color pattern observed, that of P. dalli dalli. This is defined as having a dorsal area uniformly black with a white ventral side. The white ventral patch begins far behind the flippers. The dorsal fin, flippers, and fluke are black with some white at the tips. The color pattern of P. dalli truei is different only in the distribution of the white ventral patch. The white patch begins ahead of the flippers rather than far behind them, and P. dalli truei is often longer and slimmer than P. dalli dalli.

Range mass: 130 to 220 kg.

Range length: 2.2 (high) m.

Average length: 1.8-2.0 m.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry ; polymorphic

Sexual Dimorphism: sexes alike

Length: 2200 cm

Weight: 220000 grams

• Marine

Generally the colder waters of the North Pacific are home to Dall's porpoises. They are observed inshore and offshore. They are a deep water species, so when they approach the coast they usually follow canyons or deep channels. They are also commonly observed in sounds and inland passages where these meet the open sea.

Habitat Regions: temperate ; polar ; saltwater or marine

Aquatic Biomes: pelagic ; coastal

Habitat Type: Marine

Comments: Sounds, inland passages, nearshore regions (usually in deep water), and the open sea.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Details of migrations are poorly known. Year-round resident thoughout much of range, but generally moves north for summer, south for winter. Migrations into Bering Sea may occur spring though fall. Inshore movements may augment populations off California in winter and spring (Leatherwood and Reeves 1983).

Dall's porpoises apparently feed at night and depend to some degree on the deep scattering layer, that is the fauna which travels upwards each night from the deeper parts of the ocean's water column. Food species as determined from stomach contents include squid and other cephalopods, lanternfish, Pacific hake, jack mackerel, herring, sardines, and crustaceans. Dall's porpoises are thought to be capable of deep diving because mesopelagic, bathypelagic, and deep-water benthic species are represented in the diet.

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore , Molluscivore )

Comments: Eats squid, crustaceans, and various fishes (saury, hake, herring, jack mackeral, and mesopelagic, bathypelagic, and deep-water benthic species) (Leatherwood and Reeves 1983). Feeds mainly on epi- and meso-pelagic squids and small schooling fishes (Jefferson 1988).

Dall's porpoises are important predators of fish and cephalopods in the ecosystems in which they live.

Killer whales and sharks are believed to be the primary natural predators of Dall's porpoises. They largely escape predation through their large body size, agility in the water, and their habit of traveling in groups. Their coloration may make them difficult to see in the water as well.

Anti-predator Adaptations: cryptic

10,000 to >1,000,000 individuals

Comments: Total population estimates range from several hundred thousand to over 2 million, but these figures indicate only the general order of magnitude of the population (IUCN 1991).

Usually travels in groups of 10-20 (also reported as 2-12), though aggregations of at least 200 (or thousands) have been reported. Frequently in association with Pacific white-sided dolphins or pilot whales (Leatherwood and Reeves 1983, Jefferson 1988).

As in most phocoenids, Dall's porpoises use a form of echolocation to navigate, capture prey, and perhaps to communicate with conspecifics. They also use a variety of audible clicks and whistles. They may also use touch for social communication.

Communication Channels: tactile ; acoustic

Perception Channels: visual ; acoustic

Comments: Feeding apparently mainly nocturnal (Jefferson 1988).

The average lifespan of a Dall's Porpoise is 16-17 years.

Average lifespan

Status: wild: 16-17 years.

Average lifespan

Status: wild: 22.0 years.

Average lifespan

Status: wild: 17.0 years.

Little is known about mating in cetaceans, especially in species which occur primarily offshore. Mating systems in Dall's porpoises are unknown.

Little is known about the reproductive biology of Dall's porpoises. Two calving periods have been reported for portions of the eastern North Pacific, one in winter, from February through March, and the other in summer, from July through August. Some segregation of animals seems to occur with juveniles found closer to shore and larger adults well offshore. In offshore areas, females in late pregnancy or lactation seem to be distributed in northern areas, and southern areas are mainly occupied by males and females not accompanied with calves. This seems to indicate that not all females become pregnant every year. Females usually reach sexual maturity between the age of 3 to 6 years, whereas males reach sexual maturity between the ages of 5 to 8 years. Gestation is believed to last about 11 months, and lactation periods are usually about 2 years.

Phocoenoides dalli dalli appear to have three major breeding grounds. Two occur in the North Pacific north of 45 degree latitude, and another breeding site occurs in the central Bering Sea. Phocoenoides dalli truei may breed off the northern coast of Japan.

Breeding interval: Individual females probably do not breed every year. Breeding intervals may be as long as 3 to 4 years because of the length of dependence of calves.

Breeding season: Mating is likely to occur after the calving seasons each year which occur in winter, from February to March, and in summer, from July to August.

Average gestation period: 11 months.

Average weaning age: 24 months.

Range age at sexual or reproductive maturity (female): 3 to 6 years.

Range age at sexual or reproductive maturity (male): 5 to 8 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average gestation period: 347 days.

Average number of offspring: 1.

Females feed and care for their offspring for extended periods of time. It is likely that some form of extended learning occurs during this period as well. Male parents do not contribute parental care.

Parental Investment: no parental involvement; precocial ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); extended period of juvenile learning

Single calf is born mainly late June-September, though births may occur year-round in the eastern North Pacific. Gestation estimates: 7-9 months, 11.4 months. Calves nurse for a few months. Not all adult females become pregnant every year; nonbreeders may segregate from breeders. Males are sexually mature at 5-8 years, females at 3-7 years, depending on location. Most live less than 13 years.

Dall's porpoises are not directly exploited in the eastern Pacific, but serious conservation problems are centered in the western Pacific where, during the 1980's, Dall's porpoises were intensely hunted. Estimates suggested 40,367 Dall's porpoises were killed in 1989 from the Japanese hand-harpoon fishery alone. In recent years these numbers have declined because of the Japanese government's effort to regulate the hand-harpooning of these animals. In 1992 11,403 were killed. This species is often killed accidentally in the Japanese seas and off of North America by drift nets set for salmon. It has been estimated that up to 20,000 porpoises are entangled and drowned in these nets off of Japan and up to about 4,100 off of North America annually. Due to international negotiations between Japan and the United States, along with new fishing gear and techniques, the incidental take has been reduced drastically. However, the conservation of Dall's porpoises remains a major issue.

US Federal List: no special status

CITES: appendix ii

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N4 - Apparently Secure

United States

Rounded National Status Rank: NU - Unrankable

Rounded Global Status Rank: G4 - Apparently Secure

Comments: Thousands were killed annually in the 1970s and 1980s in the Japanese salmon fishery. Unknown number are taken incidently in squid gillnet fisheries in the western North Pacific. During 1986-1989, in excess of 110,000 were taken directly in Japanese harpoon fishery (IUCN 1991).

Dall's porpoises have no negative effects on humans.

The only direct commercial harvest of Dall's porpoises is a traditional coastal harpoon fishery in Japan which accounts for annual harvests of about 6,000 animals to compensate for the shortage of whale meat. Dall's porpoises contribute to marine ecotourism through their gregariousness and their aquatic antics.

Positive Impacts: food ; ecotourism

Comments: Through at least the late 1980s, tens of thousands were harpooned annually for human consumption in Japan (IUCN 1991).

Comments: The taxonomic status of the two morphologically distinct forms of Dall's porpoises, Phocoenoides dalli (dalli- and truei-type), has been uncertain. A neighbor-joining tree of mtDNA haplotypes presented by Escorza-Trevino et al. (2004) showed 2 distinctive clades, each containing individuals from both types. According to Escorza-Trevino et al., "This suggests that truei- and dalli-types are forms of the same species. However, at the population level, statistically significant genetic differentiation was found between truei-type and sympatric dalli-type populations. These results argue that differentiation between truei- and dalli-types is at the population level, much in the same way that dalli-type populations differ among each other."

Rice (1998) and Mead and Brownell (in Wilson and Reeder 2005) recognized dalli and truei as subspecies.

See Winans and Jones (1988) for information on genetic relationships among populations in the North Pacific and Bering Sea. Based on calving grounds, there may be at least six stocks of dalli-type and one stock of truei-type in the North Pacific (see IUCN 1991).