The Dall’s porpoise is a species of porpoise native to the North Pacific ocean.
Named after the 19th century explorer William Healey Dall, these porpoises are currently listed under the Marine Mammal Protection Act.
Although they are officially a threatened species, their threat category is listed as “least concern.”
Physical Characteristics and Appearance
Dall’s porpoises are among the most distinctive in the porpoise family.
Their bodies are muscular and stocky, and their backs are dark grey or black.
One of their most unique characteristics is the white, oval-shaped paneling on their sides and underbelly.
Their tails are also trimmed with white, and their dorsal fins, which are set slightly back from the center of their body, may be solid black or splashed with white.
Dall’s porpoises have triangular heads, which are relatively small compared to their bodies, end in a small, but powerful beak.
This beak contains up to 46 teeth in their upper jaw and up to 48 teeth in their lower jaw.
Their eyes are also quite distinctive, featuring black or blue irises and blue-green pupils.
Male Dall’s porpoises are usually slightly longer than females, but the average length for both sexes is about 1.8 meters (5.9 feet), with some porpoises growing to 7 – 1/2 ft.
The average weight for both sexes, 123 kilograms (271 pounds), although they can reach weights of over 480 lbs.
Diet and Hunting Methods
Dall’s porpoises are carnivorous, and their diet consists of marine life that are smaller than themselves.
Hunting mostly at night, these animals consume between 7 and 28 pounds of food each day.
Their diet varies depending on their location, but they are most likely to eat small schooling fish and cephalopods.
Common staples of their diet include:
• Anchovies
• Sardines
• Herring
• Mackerel
• Squid
• Octopus
Because Dall’s porpoises are deep divers, some also feed on deep-sea fish such as:
• Deep-sea smelt
• Hake
• Lanternfish
Social Structure and Communication
Dall’s porpoises are social creatures, usually living in groups of between 2 and 12 porpoises, although they may gather in much larger groups of up to 200 when feeding.
They are a very active species and they are among the fastest swimmers in the cetacean family, clocking up to 55 kilometers (34 miles) an hour.
They are known to zigzag just below the surface of the water at high-speed, which creates a distinctive bow wave called a “rooster tail.”
Unlike dolphins, Dall’s porpoises seldom leap from the water.
The normal lifespan of a Dall’s porpoise ranges between 15 and 20 years.
Mating and Reproduction
Dall’s porpoises reach sexual maturity between seven and eight years of age, although females reach this stage slightly faster than males.
Although some populations give birth year-round, most birthing takes place in the summer.
Although a male Dall’s porpoise may mate with many females in his lifetime, the male will always guard the female during the 10-12 months that she is pregnant.
Female Dall’s porpoises give birth to only one calf per year, and nurse this calf for about two years after its birth.
If a female remains in healthy condition, she can give birth to one calf per year for the rest of her life.
Habitat and Migration
Dall’s porpoises are only found in the North Pacific, because they prefer waters whose temperature ranges between 15 degrees Celsius (59 degrees Fahrenheit) and 2 degrees Celsius (35 degrees Fahrenheit).
Their habitat ranges from the coasts of California and Northern Alaska through Japanese waters and into the Bering Sea.
Threats and Predators
Although they are marked in an area of least concern, Dall’s porpoises are still on the MMPA threatened species list.
Some major threats to the Dall’s porpoise population include:
• Hunting by Japanese whalers intending to catch Dall’s porpoises for meat
• Bycatch (i.e. unintentional catch) in fishing nets
• Toxins linked to marine pollution found in the Dall’s porpoises’ blubber
Dall’s porpoises are fascinating and unique creatures that deserve our respect and protection.