(Phocoenoides dalli)

Morphology

Dall's Porpoise is slightly larger than the Harbor Porpoise. This length of this species is typcially 1.8 to 2.0 meters, though a maximum length of 2.2 meters recorded. The weight range is approximately 130 to 220 kilograms. The body of Dall's Porpoise is stockier and more powerful than other members of the family Phocoenidae. The head of this porpoise is small and lacks a beak. There is, however, a sloping forehead present. A large ridge runs both above and below the tail stock. Similarly, this species possesses a pronounced keel.

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Color

There are three color patters observed in this species. The first type of Dall's Porpoise is uniform black or uniform white throughout the body and flanks. The second color pattern observed in this species is intermixed stripes of black and white running along the length of the body. The final, and most frequently observed, type of Dall's Porpoise displays a solid black dorsal portion, while the underside is white. In this variet of the species, the white ventral patch begins far behind the flippers, and the flippers, dorsal fin, and fluke are black with a fringe of white at the tips. In addition, this porpoise has one subspecies, Truei's Porpoise, whose color pattern is very similar to the third type of Dall's Porpoise. The primary distinguishing characteristic between Dall's Porpoise and Truei's Porpoise is the distribution of the white ventral patch. In Truei's Porpoise, the white coloring begins just ahead of the flippers, rather than behind the flippers, as is seen in the third variety of Dall's Porpoise. Also, Truei's Porpoise is typically longer and slimmer than Dall's Porpoise.

Fins

The flippers of Dall's Porpoise, which are small and pointed, are located near the head. The dorsal fin is triangular in shape with a hooked tip. A slight notch is present on the fluke. The fluke in this species is unique as it supports a backward appearance.

Behavior

The personality of Dall's Porpoise seems to be unique from other members of this family, as this porpoise does not exhibit the typical shy and secretive behavior. Dall's Porpoises are often seen in groups of 10 to 20 individuals. Groups of up to 200 feeding Dall's Porpoises have also been viewed on occasion. Another unique characteristic of this group is their affinity for boats. This species, unlike other members of the family Phocoenidae, are frequently seen charging boats and bow-riding enthusiastically.

Swimming Style

Dall's Porpoises are the fastest of the phocoenids, reaching speeds of 35mph. This porpoise is said to appear hyperactive, as they frequently swim in a zig-zag pattern with fast, jerky, steep angled turns. This quick darting movement makes them very difficult to spot when surfacing to breath.

Three different surfacing behaviors have been documented for this species. Dall's Porpoises may surface with a slow roll, a fast rool, or a rooster-tailing roll. The third surfacing behavior can be a useful tool in the identification of this species in the wild. With this surfacing movement, Dall's Porpoises kid up a "rooster tail" of spray. This tail of spray is a cone of water coming off of the head as the porpoise surfaces. It is a result of the quick speed and steep angels at which they surface.

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Life History

Calving season for Dall's Porpoise takes place during the summer, from June to September. Gestation is believed to last for approximately 11 months. Mothers tend to nurse thier young for roughly 2 years. Sexual maturity in males is reached at 7.9 years, while females reach sexual maturity at 6.8 years.

Diet

The diet of Dall's Porpoise is very similar to the diet of the Harbor Porpoise. The preferred foods of this species include fishes, squid, and crustaceans.

Distribution/Population

Dall's Porpoises are found in coastal to deep waters of the northern North Pacific and Bering Sea. In North America, they are seen inshore and offshore from southern California to Alaska. Sine it is a deep water species, which is an additional unique trait of this group, this porpoise usually approaches the coast following canyons or deep channels.

Dall's Porpoises are also observed in sounds and inland passages, usually where they meet the open sea. The Truei's form of this species is abundant only off the Pacific coast of northern Japan and the Kuril Islands. The estimated population of this species is between .79 and 1.738 million individuals

Harms

Over 30,000 members of this species have been reported killed annually by Japanese fisherman. These deaths result either from direct hunting for porpoise meat or incidental catch in gill nets. Killer whales are believed to be the primary natural predator of Dall's Porpoise, though sharks are also a likely predator.