Dall’s porpoises are “high strung,” fast swimming members of the porpoise family and are common in the North Pacific Ocean. They can reach a maximum length of just under 8 feet (2.4 m) and weigh up to 480 pounds (220 kg). Males are slightly larger and thicker than females, which reach lengths of just under 7 feet (2.1 m) long. Animals in the eastern Pacific are smaller than those in the western Pacific and waters around Japan.
Dall’s porpoises have a relatively small, triangular head with little or no beak and a thick, robust body. The flippers are small, round, and located forward on the body. The dorsal fin is positioned in the middle of the back, triangular in shape, and often cant, or angles, forward. The tail stock and “keel” (otherwise known as the “caudal peduncle”) 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. The body is very dark gray or black in coloration with variable contrasting white “thoracic” panels and white “frosting” on the dorsal fin and tail that distinguish it from other cetacean species. These markings and colorations vary with geographic location and life stage, with adults having more distinct coloration.
Taxonomically, Dall’s porpoises are separated into two major morphs/ types/ subspecies: the truei-type and the dalli-type.
The truei-type (P. d. truie) is common in the Western Pacific Ocean (between 35°N and 54°N), and thedalli-type (P. d. dalli) is common throughout the North Pacific Ocean. The two types can be distinguished by the location and size of the white thoracic panels. All black (melanistic) and all white (albino) forms also exist, but are considered rare. Hybrids between Dall’s porpoises and harbor porpoises are also fairly common in the Northeast Pacific, but can also occur elsewhere.
These porpoises are usually found in groups averaging between 2-20 individuals, but 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 bowriding on large rorquals (whales in the Balaenopteridae family). As rapid, gregarious swimmers, they are also attracted to fast moving vessels and commonly bowride.
They 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 crabs and shrimp. Feeding usually occurs at night when their prey vertically migrate up toward the surface. Dall’s porpoises are capable of diving up to 1640 feet (500 m) in order to reach their prey. They have 38-56 very small spade-shaped teeth on each jaw that are useful for grasping. Their brisk surfacing while swimming creates a “rooster tail” of water spray that is a unique characteristic of the species.
Dall’s porpoises become sexually mature at 3.5-8 years of age and give birth to a single calf after 10-12 months, usually between June and September. The calves are generally 3.3 feet (1 m) long. Calves are typically nursed by their mother for less than one year. These cetaceans can live up to 22 years, but their lifespan is generally 15-20 years
|up to 480 pounds (220 kg)|
|up to 7-8 feet (2-2.4 m)|
|relatively small, triangular head with little or no beak and a thick, robust dark gray or black body, with variable contrasting white panels|
|about 15-20 years|
|anchovies, herring, hake, smelts, squid, octopus, and occasionally crabs and shrimp|
|usually found in groups averaging between 2-20 individuals; they also associate with Pacific white-sided dolphins and short-finned pilot whales|
RELATIVE SPECIES: Harbor porpoise
NEIGHBORING SPECIES: Pacific white-sided dolphins, Harbor porpoise
PREDATORS: Humans, Killer whales
THREATS: Trapped in fishing nets, attacked by killer whales.
DIET: Small schooling fish such as herring, pilchards and hake. Squid.
MANNER OF FEEDING: Possibly waits for the evening when its prey comes to the surface. They have to eat often in order to maintain a high metabolic rate because their layer of blubber is relatively thin.
BEHAVIOR: Small groups of 2-12. Often seen in large groups while feeding. Creates a large splash while surfacing called “rooster tail”. Known or bow riding. Mothers with calves will avoid vessels.
REPRODUCTION: Gestation is 10-11 months. Females give birth annually. Males will compete to mate with the females. Lactation lasts at least 2 months.
LIFE SPAN: 15-22 years
This species prefers temperate to “boreal” waters that are more than 600 feet (180 m) deep and with temperatures between 36°F (2°C) and 63°F (17°C). They can be found in offshore, inshore, and nearshore oceanic waters.
Dall’s porpoises occur throughout the North Pacific Ocean. This species is also found in the adjacent Bering Sea, Sea of Japan, and Okhotsk Sea. In the eastern North Pacific, they occur from around the U.S./Mexico border (Baja California) (28-32°N) to the Bering Sea (65°N); in the central North Pacific (above 41°N); and in the western North Pacific from central Japan (35°N) to the Okhotsk Sea. In the Bering Sea, they occur in higher abundance near the shelf break. There are some migration patterns, inshore/offshore and north/south, based on morph/type, geography, and seasonality.
For management purposes, Dall’s porpoises inhabiting U.S. waters have been divided into two stocks: the Alaska Stock and the California/Oregon/Washington Stock. For both stocks, there are insufficient data available on current population trends. However, Dall’s porpoises are considered reasonably abundant. The most recent stock assessment reports with population estimates are available on our website.
In the western North Pacific, there are an estimated 100,000 off of Japan and several hundreds of thousands of Dall’s porpoises in the Okhotsk Sea (Shirihai and Jarrett, 2006).
- incidental catch/ bycatch in fishing gear, such as those targeting groundfish, salmon, and squid in Canadian, Russian, Japanese, Alaskan, and other U.S. waters
- drift nets
- Japanese hunting in the western North Pacific as a source of meat for human consumption (about 18,000 are currently taken each year)
- pollutants and various contaminants in the marine environment, which have been found in this species’ blubber. These contaminants could present a major toxicity problem, especially to reproduction, as they accumulate and pass through the marine food chain.
The IUCN Red List of Threatened Species considers this species to be “Lower Risk/Conservation Dependent.”
This species is protected under the Marine Mammal Protection Act of 1972 as amended.
- Dall’s porpoises are considered the fastest swimmers among small cetaceans. They are capable of reaching speeds of 30 knots (34 miles per hour [55 km/h]) over short distances.
- Dall’s porpoises are named for W.H. Dall, an American naturalist who collected the first specimen of this species (Reeves et al. 2002).
- Unlike dolphins that have conical-shaped teeth, porpoises have spade-shaped teeth.
- Occasionally mates with Harbor porpoises, these offspring look like Harbor porpoises but act like Dall’s porpoise.
- Flukes change shape and color as they mature.