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
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
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.
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
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 )
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 )
Dall's porpoises are important predators of fish and cephalopods in the ecosystems in which they live.
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
Dall's porpoises have no negative effects on humans.
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
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 ; tactile ; acoustic ; chemical
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); sexual ; 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
Dall's porpoise (Phocoenoides dalli) is a species of porpoise endemic to the North Pacific. It is the largest of porpoises and the only member of the genus Phocoenoides. The species is named after American naturalist W. H. Dall.
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Dall’s porpoise is the only member of the genus Phocoenoides. The dalli- and truei-types were initially described as separate species in 1911, but later studies determined that the available evidence only supported the existence of one species.[4][5] Currently, these two color morphs are recognized as distinct subspecies, Dall's porpoise (Phocoenoides dalli dalli) and True's porpoise (Phocoenoides dalli truei).[2]
Dall's porpoises can be easily distinguished from other porpoises and cetacean species within their range. They have a wide, robust body, a comparatively tiny head, and no distinguished beak. Their flippers are positioned at the front of the body and a triangular dorsal fin sits mid-body. Patterns of coloration are highly variable, but Dall’s porpoises are mostly black, have white to grey patches on the flank and belly, and frosting on the dorsal fin and trailing-edge of the fluke.[6][7]
They are the largest porpoise species, growing up to 7.5 ft (2.3 m) in length and weighing between 370 and 490 lbs (130 and 220 kg).[7] Sexual dimorphism is apparent in body size and shape, with mature males being larger, developing a deeper caudal peduncle, and having a dorsal fin that’s significantly angled forward in comparison to a female’s.[6] Dall’s porpoise calves have a greyish coloration with no frosting on flippers and flukes. Calves measure about 100 cm at birth.[8] Growth rates are similar at first, but at about 2 years old males begin to grow faster than females.[8] Externally, maturity is measured by length which is usually attained at 3 – 5 years old.[9] Sizes vary between populations, but on average females reach a maximum size of 210 cm and males grow to about 220 cm, except in the southern Okhotsk Sea where males can grow as long as 239 cm.[8]
Two colormorphs have been identified: the dalli-type and truei-type. The truei-type, found only in the western Pacific, has a white belly patch that extends farther forward across the body than that of the dalli-type.[6][4][10]
Dall’s porpoises are limited to the North Pacific: in the east from California to the Bering Sea and Okhotsk Sea, and in the west down to the Sea of Japan.[11] They have been sighted as far south as Scammon’s Lagoon in Baja California when water temperature was unseasonably cold.[11]
Dall’s porpoises generally prefer cold waters less than 64 °F (18 °C).[7] Although mostly an offshore species, they do occur in deeper coastal waters, near submarine canyons or in fjords.[7][11]
Dall’s porpoises are opportunistic, hunting a variety of surface and mid-water species. Common prey are mesopelgic fish, such as myctophids, and gonatid squid.[6][11][2] Stomach content analyses have also found cases of crustacean consumption, including krill and shrimp, but this is abnormal and likely not an important part of their diet.[11] A previous study revealed that tagged Dall’s porpoises spent most of their time within 10 m of the surface,[12] but have been recorded diving to depths of up to 94 m.[13]
Dall's porpoises live in small, fluid groups of 2 – 10 individuals,[7] but aggregations of hundreds have been reported.[11] They have a polygynous mating system in which males compete for females.[14] During the mating season, a male will select a fertile female and guard her to ensure paternity.[14] While guarding, males may sacrifice opportunities to forage on deep dives.[14] Births usually take place in the summer after a gestation period of 11 – 12 months.[11] Females generally give birth every 3 years, depending on their condition.[7] Life expectancy is about 15 – 20 years, but a lot about their mortality is unknown.[15]
Dall’s porpoises are prey to transient killer whales.[16] They have, however, been observed in association with resident killer whales, engaging in apparent play behaviors with their calves, and swimming with them.[17] One recognizable Dall’s porpoise was observed travelling with the AB pod of resident orca from May through October 1984.[17] Great White Sharks are also a known predator, with at least one documented case on the eastern North Pacific Ocean.[18]
Dall’s porpoises are highly active swimmers. Rapid swimming at the surface creates a characteristic spray called a "rooster tail". They are commonly seen approaching boats to bowride, and they will also ride on the waves formed at the heads of larger swimming whales.[7][11]
Abundance throughout their range and is estimated to be over 1 million, but current population trends are unknown.[2]
Surveys along the coasts of California, Oregon, and Washington between 2008 and 2014 estimated a population abundance of 25,800.[19][20] Alaska’s population is estimated to be 83,400.[21][22] Abundance in coastal British Columbia is nearly 5,000 individuals.[23]
Populations in the western North Pacific are divided by both subspecies and migratory patterns. Abundance of the offshore dalli-type is about 162,000.[24] It is estimated that there are about 173,000 dalli-type that travel between Japan and the southern Okhotsk Sea.[24][25] The dalli-type that migrates to the Okhotsk Sea in the summer is estimated at 111,000.[25] The population of truei-type porpoises migrating between Japan and the central Okhotsk Sea number about 178,000.[24]
Dall’s porpoises are vulnerable to fisheries bycatch. Thousands were killed in commercial driftnet fisheries until the United Nations issued a moratorium in the 1990s.[2][26] Before the moratorium went into effect, 8,000 Dall’s porpoises are estimated to have been bycaught in one year alone (1989-1990).[27] Smaller numbers, from several hundred to a few thousand, are estimated to have been bycaught in Japanese salmon fisheries in US waters and in the Bering Sea from 1981 to 1987.[28] Driftnet and trawl fisheries still operate in some areas throughout their range,[2] with particularly high levels of bycatch in Russian waters.[29]
The Dall's porpoise is still harvested for meat in Japan. The number of individuals taken each year increased following the 1980s moratorium on whaling of larger cetacean species.[30] In 1988, more than 45,000 Dall’s porpoises were harpooned.[30] In 1990, after international attention was drawn to the issue, the Japanese government introduced a reduction on take. A quota of over 17,000 a year is in effect today (9,000 dalli-type in the Japan-southern Okhotsk Sea population; 8,700 from the truei-type population that migrates into the central Okhotsk Sea)[2] making it the largest direct hunt of any cetacean species in the world.[31] The hunt of Dall’s porpoises has been criticized by scientific committees which question the sustainability of large quotas on regional populations.[32][33] Assessments are outdated for these targeted populations, and given the level of annual reported take, there may be regional declines in abundance.[30][24]
Environmental contaminants, including dichlorodiphenyldichloroethylene (DDE) and polychlorinated biphenyls (PCBs), are another threat to Dall’s porpoises. Pollutants accumulate in the blubber layer, and in high concentrations can reduce hormone levels, affect the reproductive system,[34] and result in calf death.[35]
Dall’s porpoise is listed as Least Concern on the IUCN Red List.[2] Levels of both bycatch and commercial hunting are likely underestimates because they account only for reported data; however, there is no evidence for a range-wide decline of the species.[2]
The species is also listed on Appendix II[36] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS), and, like all other marine mammal species, is protected in the United States under the Marine Mammal Protection Act (MMPA).[37]
Dall's porpoise (Phocoenoides dalli) is a species of porpoise endemic to the North Pacific. It is the largest of porpoises and the only member of the genus Phocoenoides. The species is named after American naturalist W. H. Dall.
William Healey Dall's 1873 field notes on Phocoenoides from the Smithsonian Institution's Field Books collection
