Dall’s Porpoise, Phocoenoides dalli

Dall’s Porpoise, Phocoenoides dalli. Photograph taken at sea in Prince William Sound, Alaska, August 2011.

Phylogeny:  Dall’s Porpoise, Phocoenoides dalli, is a member of the Phocoenidae Family of Porpoises. The genus Phocoenoides is one of three genera in this family and there is only this species in the genus.  In Mexico this species is known as marsopa de Dall. There are two currently accepted subspecies of Dall’s Porpoise; Phocoenoides dalli dalli and the color morph  Phocoenoides dalli truei of the western Pacific. This species, and many other species, were named in honor of William Healy Dall. Dall was primarily recognized as a malacologist, but he also made many important contributions to the fields of vertebrate biology, paleontology, cartography, ornithology, and anthropology. Much of his work took place in Alaska. Dall was one of the founders of the National Geographic Society.

Morphology:  Dall’s Porpoise have a unique body shape that makes them easily distinguishable from other dolphins. They have very thick bodies and small heads. There  coloration is similar to Orca Whales with the main body being very dark grey to black with very demarcated white patches on the flank and belly. The dorsal fin is tipped in white to light grey and is located just behind the middle of the back. The fluke is also white to light grey in color and curves back towards the body of the animal. Dall’s Porpoise are larger than other porpoises growing up to 2.3 m (7 feet 7 inches) in length and can weigh up to 200 kg (440 Lbs.). They are sexually dimorphic with males being larger than females.

Habitat and Distribution: Dall’s Porpoise prefer environments with cold waters and depths in excess of 183 m (600 feet). They are found over the continental shelf adjacent to the slopes of deep water canyons and in open oceanic waters. They are highly active creatures often seen zig-zaging around at great speed on or just below the water surface, creating a spray called a “rooster tail”. They may appear and disappear quite suddenly. The fastest of all of the small cetaceans, Dall’s Porpoises can swim at up to 55 km per hour, almost as fast as Killer Whales. They rarely put on aerial shows such as breaching and leaping. Dall’s porpoises live in small, fluid groups of two to twelve individuals but they also form loosely associated groups involving tens to hundreds of individuals for feeding. They range through much of the North Pacific and adjacent seas, such as the Bering and Okhotsk Seas and the Sea of Japan. In Mexican waters, they are limited to the northern half of the west coast of the Baja Peninsula; they do enter Scammon’s Lagoon in Central Baja when the water temperatures in the open ocean are unseasonably cold.

Diet:  Dall’s Porpoise consume a variety of cephalopods (squid and octopus) and small fishes. They are occasionally found with krill or other crustaceans in their stomachs, but this is an anomaly.

Predators:  Dall’s Porpoise are preyed upon by Killer Whales and White Sharks.

Reproduction:  As mammals, Dall’s Porpoise are either male or female for life. They reproduce sexually.  They have a polygynous mating system in which males compete for females and when a male finds a female in estrus he will guard her so that he can mate with her. The calving season is in the summer with gestation lasting ten to eleven months, and the lactation period lasting for at least two months. Females in their prime can give birth annually and they have life-spans of fifteen to twenty years.

Ecosystem Interactions:   Dall’s Porpoise play host to several types of internal and external parasites. Most Dall’s Porpoise are infected with helminth worms, including the species Campula oblonga, Halocercus dalli, and Crassicauda sp.

Human Interactions:   The current global population of Dall’s Porpoise is estimated at 1,000,000 individuals. Many are killed each year as a by-catch in fishing nets. Also, the  global ban on whale hunting caused Japanese harpoon fishermen to switch to smaller cetaceans.  Due to public pressure Japan has an annual quota currently set at 16,000 Dall’s Porpoise per year. Historically, Dall’s Porpoise came to worldwide attention in the 1970’s when it was disclosed for the first time to the public that salmon fishing trawls were killing thousands of Dall’s Porpoises and other dolphins and whales each year via accidental net captures. Dall’s Porpoise populations have also been impacted by pollution and overfishing of their food sources. Despite these threats the population remains sufficiently high for Dall’s Porpoise to be considered from a conservation perspective to be of Least Concern.

Synonyms: Synphocaena dalli and Synphocaena truei.