Dall porpoise
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.
The species is named after the American naturalist W.H. Dall. In 1873, this scientist was the first to collect specimen of this animal, today known as Dall's porpoise. Males of this porpoise are larger and more robust than females. As opposed to other porpoise species, Dall's porpoise lacks tubercles or bumps on the front edge of its dorsal fin. The latter is small and triangular, and can angle forward. This agile porpoise is one of the fastest cetaceans: when swimming, the animal leaves behind itself a "rooster tail" of water. The snout of the animal is blunt and the flippers are small. The stocky body is dark gray to black, covered with white spots and exhibiting white markings on the tail and dorsal fin.
Dall's porpoise inhabits offshore, inshore, and nearshore waters of North Pacific Ocean, including the Bering Sea, Sea of Japan as well as Okhotsk Sea. They are distributed across the central North Pacific, the eastern North Pacific (from the Mexico - U.S. border in the south to the Bering Sea in the north) and the western North Pacific (from central Japan to the Okhotsk Sea). The ideal habitat for Dall's porpoise is temperate to "boreal" waters with more than 600 feet (180 m) of depth and with temperatures, varying from 36°F (2°C) to 63°F (17°C).
These animals usually gather in small groups, consisting of 10 - 20 porpoises. However, there have been reported concentrations of more than 200 individuals. Normally, they are not seen in mixed groups with other species, but in the northern part of their range, particularly, in the deep waters off Alaska and in Prince William Sound, Dall's porpoises can occasionally be observed with Harbor porpoises. In addition, they have been seen in a company of Gray whales. Dall's porpoises are known to migrate, travelling north in summer and moving to south by winter. Unlike other porpoise species, Dall's porpoises are not at all shy and secretive: on the contrary, these animals can often be observed bow-riding and charging boats. Being night feeders, they use echolocation to hunt prey, navigate in the ocean and, likely, to communicate with each other. In addition, they use touch as well as a number of sounds, including clicks and whistles, as forms of communication.
Dall’s porpoises are carnivores (piscivores and molluscivores). Their diet consists of lanternfish, Pacific hake, jack mackerel, herring, sardines, crustaceans and cephalopods, including squid.
Dall’s porpoises are polygynous animals. Males of this species mate with multiple females during their life. However, male Dall’s porpoise always guards its mate during pregnancy, which lasts for 10 - 11 months. Dall’s porpoise are likely to mate by the end of each calving season: the animals have two calving seasons a year: one occurs from February to March, the other one lasts from July to August. Females yield a single calf per year. For the first 2 years of its life, the calf is nursed by its mother, while the father usually shows no parental care. Males of this species are sexually mature at 5 - 8 years old, whereas females - earlier - by the age of 3 - 6 years.
Presently, the animal is threatened by pollutants and different contaminants in its marine habitat, found in the blubber of Dall’s porpoise. Accumulating and passing through the marine food web, these contaminants have negative affect on reproduction, being an important toxicity concern. Furthermore, Dall’s porpoises are often incidentally caught in fishing gears, catching groundfish, salmon, and squid in the waters of Canada, Russia, Japan and U.S. (including Alaska). In Japan, particularly, the animals are caught by whalers for their meat.
According to the IUCN Red List, the total population size of the Dall’s porpoise is over 1.2 million individuals, including: 83,400 individuals in Alaska; 35,000 to 134,000 individuals (averaging 86,000 individuals) along the U.S. west coast; 217,000 individuals in the western North Pacific; 226,000 individuals which migrate between the Sea of Japan and the southern Okhotsk Sea as well as 111,000 individuals in the northern Okhotsk Sea. Currently, Dall’s porpoises are classified as Least Concern (LC) on the IUCN Red List.
Hunting on various fish and cephalopods, Dall's porpoises control numbers of these prey species’ populations, thus serving as an important link in the food chain of their habitat.
