Phocoenoides dalli
Dall's porpoise

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. (Genther, 2000; Klinowska, 1991; Reeves and Leatherwood, 1994)

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. (Klinowska, 1991; Reeves and Leatherwood, 1994)

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. (Genther, 2000; Klinowska, 1991; Reeves and Leatherwood, 1994)

The average lifespan of a Dall's Porpoise is 16-17 years. (Klinowska, 1991)

Dall's porpoises usually occur in small groups of 10 to 20 individuals, although aggregations of at least 200 have been reported. They occur only rarely in groups of mixed species, although further north they are sometimes seen in the company of harbor porpoises, especially in the deep waters off Alaska and in Prince William Sound. They have also been spotted with gray whales. Migration north in summer and south in winter has been reported.

Dall's porpoises do not exhibit the typical shy and secretive behavior of most other porpoises. They are frequently seen charging boats and bow-riding. They are the fastest of the phocoenids and reach speeds of up to 35 mph. They frequently swim in a zig-zag pattern with fast, jerky, steep angled turns. Dall's porpoises may surface with a slow roll, a fast roll, or a rooster-tailing roll. The rooster-tailing roll is often used to identify the species in the wild. The spray resulting from this roll is a cone of water coming off the head of the porpoise which looks like a "rooster tail" due to the quick speed and steep angles at which the species surfaces. (Klinowska, 1991)

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.

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. (Klinowska, 1991; Reeves and Leatherwood, 1994)

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.

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

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. (Reeves and Leatherwood, 1994)

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. (Klinowska, 1991; Reeves and Leatherwood, 1994)