Dall’s Porpoise

Dall's porpoises are common in the North Pacific Ocean and can be found off the U.S. West Coast from California to the Bering Sea in Alaska. These porpoises are considered the fastest swimmers among small cetaceans, reaching speeds of 34 miles per hour over short distances. They are named for W.H. Dall, an American naturalist who collected the first specimen of this species.

A special characteristic of Dall’s porpoises is their distinctive color pattern: a black body with a conspicuous white lateral patch on the left, right, and underside. They are often mistaken for baby killer whales, but unlike killer whales, their dorsal fins are triangle-shaped and they do not have eye patches or saddle patches.

Dall’s porpoises, like all marine mammals, are protected under the Marine Mammal Protection Act.

Dall's porpoises have a relatively small, triangular head with little or no beak and a thick, robust body. Their flippers are small, round, and located near the front of the body. The triangular dorsal fin is positioned in the middle of the back, and often angles forward. The tail stock and keel (where the caudal fin attaches to the body) are exaggerated and create a pronounced hump, which is large compared to other marine mammals. Adult males have a thicker tail stock and forward-projecting dorsal fin.

Their coloration is very dark gray or black with contrasting white markings on the dorsal fin and tail that distinguish Dall’s porpoises from other cetaceans. All-black (melanistic) and all-white (albino) forms also exist but are considered rare. Markings and colorations vary by geographic location and life stage, with adults having more distinct colorations. Adults also have a chunkier and more robust body than juveniles.

Dall’s porpoises can dive up to 1,640 feet to feed on small schooling fish (e.g., anchovies, herring, and hake), mid- and deep-water fish (e.g., myctophids and smelts), cephalopods (e.g., squid and octopus), and occasionally crustaceans (e.g., crabs and shrimp). Feeding usually occurs at night when their prey migrates up toward the surface. They have 38 to 56 very small, spade-shaped teeth (about the size of a piece of grain or rice) on each jaw that are useful for grasping.

Dall’s porpoises are usually found in groups averaging between two and 12 individuals, but they have been occasionally seen in larger, loosely associated groups in the hundreds or even thousands of animals. They are known to associate with Pacific white-sided dolphins and short-finned pilot whales but have also been seen swimming alongside large whales. As rapid, social swimmers, Dall’s porpoises are also attracted to fast moving vessels and commonly bowride beside ships. They briskly surface while swimming, creating a "rooster tail" of water spray that is a unique characteristic of the species.

Dall's porpoises emit low-frequency clicks that are presumably used for echolocation.  

Dall’s porpoises prefer temperate to boreal (northern, cold) waters that are more than 600 feet deep and with temperatures between 36° Fahrenheit and 63° Fahrenheit. They can be found in offshore, inshore, and nearshore oceanic waters, between 30° North and 62° North. Dall's porpoises occur throughout the coastal and pelagic waters of the North Pacific Ocean. This species is commonly found in the Gulf of Alaska, Bering Sea, Okhotsk Sea, and Sea of Japan. In the eastern North Pacific Ocean, they can be found from around the U.S./Mexico border (Baja California, 32° North) to the Bering Sea, in the central North Pacific Ocean (above 41° North), and in the western North Pacific from central Japan (35° North) to the Okhotsk Sea. In the Bering Sea, Dall’s porpoises occur in higher abundance near the shelf break. They are commonly seen in inshore waters of Washington, British Columbia, and Alaska. Migration patterns (inshore/offshore and north/south) are based on morphology/type, geography, and seasonality.

Dall's porpoises become sexually mature at 3.5 to 8 years of age and give birth to a single calf after a gestation period of 10 to 12 months, usually between June and September. The calves are generally 3.3 feet long and are nursed by their mother for less than one year. These cetaceans can live up to 22 years, but their lifespan is generally 15 to 20 years.

Hybrids between Dall's porpoises and harbor porpoises are also fairly common in the northeast Pacific but can also occur elsewhere.

Entanglement in Fishing Gear

One of the main threats to Dall’s porpoises is becoming entangled or captured in commercial fishing gear such as drift nets, gillnets, and trawls. This occurs in fisheries targeting groundfish, salmon, and squid in Canadian, Russian, Japanese, Alaskan, and other U.S. waters. Once entangled, porpoises can become anchored or may swim off with the gear attached for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury, which may lead to reduced reproductive success and death.

Hunting

Japanese fisherman hunt Dall’s porpoises in the western North Pacific as a source of meat for human consumption, where approximately 18,000 Dall’s porpoises are taken annually. There are no reports of subsistence take of Dall’s porpoise in Alaska.

Contaminants

Contaminants enter ocean waters and sediments from many sources—such as wastewater treatment plants, sewer outfalls, and pesticide application—and move through the food chain. Pollutants and various contaminants in the marine environment have been found in the blubber of Dall's porpoises. These pollutants can harm their immune and reproductive systems.

Modern pollution controls have reduced but not eliminated many chemical contaminants, which continue to threaten Dall's porpoises. Additionally, some of these contaminants persist in the marine environment for decades and continue to threaten marine life.

Ocean Noise

Underwater noise pollution interrupts the normal behavior of Dall’s porpoises and interferes with their communication.