Dall's Porpoise

Description

Dall’s porpoise is a robust, powerful porpoise species and one of the fastest of all small cetaceans. Adults measure 5.5 to 7.5 feet in length and weigh between 270 and 490 pounds, making them the largest of the porpoise family. Their body is thick and muscular, with a remarkably stocky build that is wider at the midsection than typical for cetaceans of their length. The coloration is dramatic and distinctive: the body is predominantly black with a large, conspicuous white patch on the flanks and belly that extends from roughly the midsection to the tail. The dorsal fin is small and triangular, often with a frosted white or light gray tip, and the tail flukes are small with white or light gray trailing edges. The head is small and rounded with no discernible beak, and the mouth is small with 38 to 56 very small, spade-shaped teeth in each jaw. A key identification feature at sea is their unique “rooster tail” splash pattern created when they swim rapidly at the surface, producing a cone-shaped spray of water that is unlike the surface disturbance produced by any other cetacean species.

Habitat & Range

Dall’s porpoises are found exclusively in the North Pacific Ocean and adjacent seas, ranging from Japan and the Sea of Okhotsk across to Alaska, British Columbia, and southward along the west coast of the United States to approximately Southern California. They are primarily a cold-water species, preferring sea surface temperatures below 64 degrees Fahrenheit, and are most abundant in waters between 36 and 54 degrees Fahrenheit. In the eastern North Pacific, they are common from Alaska to central California, with their abundance declining in the warmer waters of Southern California. Dall’s porpoises are occasionally observed in the waters off Orange County, particularly during cooler water periods associated with La Nina conditions or during winter and spring when sea surface temperatures drop. They are a deep-water species that prefers offshore waters over the continental slope and in deep ocean basins, typically at depths greater than 600 feet, though they may come closer to shore where deep submarine canyons approach the coast. The California-Oregon-Washington stock is estimated at approximately 25,000 to 30,000 individuals.

Diet

Dall’s porpoises feed primarily on small schooling fish and cephalopods found in mid-water and deep-water environments. Their diet includes lanternfish (myctophids), Pacific hake, capelin, jack mackerel, sardines, herring, and a variety of squid species including market squid and deep-water squid. They are opportunistic feeders that forage both during the day and at night, often targeting organisms associated with the deep scattering layer as it migrates vertically through the water column. Dall’s porpoises are capable divers, reaching depths of at least 500 meters in pursuit of prey, though most foraging dives are in the range of 100 to 300 meters. Their echolocation system operates at high frequencies similar to other porpoises, allowing them to detect and track small prey items in dark, deep waters. An adult Dall’s porpoise consumes approximately 12 to 20 pounds of food per day. Their high metabolic rate, necessitated by their cold-water habitat and active swimming lifestyle, requires frequent and efficient foraging.

Behavior

Dall’s porpoises are energetic and fast-moving animals, capable of swimming at speeds up to 34 miles per hour, making them one of the fastest of all cetaceans. Their characteristic “rooster tail” spray, created by rapid surface swimming, is often the first sign of their presence and can be spotted from considerable distances. Unlike the shy harbor porpoise, Dall’s porpoises are often attracted to boats and are enthusiastic bow-riders, racing toward vessels and riding the pressure wave at the bow, often zigzagging back and forth in front of the boat in an apparent display of speed and agility. They are typically found in small groups of 2 to 20 individuals, though aggregations of up to several hundred may occur in productive feeding areas. Dall’s porpoises rarely breach or engage in the aerial behaviors common in dolphins, but their high-speed surface swimming is highly energetic and visually distinctive. They are relatively quiet for a cetacean, producing fewer whistles than dolphins, with their vocalizations consisting primarily of high-frequency echolocation clicks. Females give birth to a single calf after a gestation period of approximately 11 to 12 months. The calving interval is about three years. Dall’s porpoises have an estimated lifespan of approximately 15 to 20 years.

Conservation Status

Dall’s porpoise is listed as Least Concern on the IUCN Red List, with a total population in the North Pacific estimated at over one million individuals, making them one of the most abundant small cetaceans in the region. In the United States, they are protected under the Marine Mammal Protection Act. Historically, Dall’s porpoises suffered enormous bycatch mortality in the high-seas drift-net fisheries of the North Pacific, with estimates of over 10,000 to 15,000 killed annually during the peak of these fisheries in the 1980s. The United Nations moratorium on high-seas drift-net fishing, which took effect in 1993, dramatically reduced this source of mortality. Japan continues a direct hunt of Dall’s porpoises, with several thousand harvested annually under a government quota, making it the largest deliberate kill of any cetacean species worldwide. Other threats include entanglement in coastal fishing gear, ocean pollution, habitat degradation, and potential competition with commercial fisheries for prey species. In the eastern North Pacific, the population appears stable, though continued monitoring is necessary. The effects of ocean warming associated with climate change could shift their range northward, potentially reducing their occurrence in Southern California waters over time.