Phocoenoides dalli | Dall’s Porpoise

The Dall’s Porpoise

The fastest small cetacean

A black-and-white porpoise races across the cold North Pacific. Its wake fans out like a rooster tail. White patches flash along the flanks.

The dorsal fin is small and hooked. Speed is the whole point here. Few cetaceans swim faster, of course.

Small fish and squid are the prey. Groups travel together and bow-ride boats. Because the animal moves so fast, it can chase prey at depths and speeds that most of its rivals cannot match at all.

Family tree

Phocoenidae, the porpoises

The species belongs to the family Phocoenidae. Frederick True named it in 1885. Only one species now sits in the genus Phocoenoides.

The name honours the naturalist W. H. Dall, in short.

The humpback whale belongs to the baleen whales, not to this family. Both animals live in the North Pacific, yet one filters tiny prey and the other chases fast fish by echolocation.

Black body, white flanks

How to tell one

Body length runs 1.8 to 2.4 m. Weight falls between 80 and 220 kg. Its body is thick and blunt-nosed.

Black skin covers most of it. A white patch runs up each flank. That tail stock is deep and muscular.

A small dorsal fin sits mid-back. In addition, teeth are small and spade-shaped. Nothing about the shape is slow, and the whole animal is built for one short burst of speed after another.

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Cold North Pacific shelf edge

Where it lives

Cold North Pacific water is the only home. The Bering Sea holds many animals. Coastal waters off Alaska are prime ground.

Sightings run from Japan to Baja California. Deep water near the shelf edge is favoured. Shallow bays are used at times.

Ice edge water is avoided, however. Because the porpoise hunts at 200 to 300 m, it needs deep water close to shore and never strays into shallow warm seas.

Schooling fish and squid

What it eats

Small schooling fish are the staple. Pacific herring is a favourite. Saury and lanternfish follow.

Squid are taken as well. Even so, deep-water prey dominates the list. Dives last a few minutes at a time.

Echolocation finds prey in dark water. Because the porpoise burns energy so fast, it must feed often, and a day without fish shows up quickly in its body condition.

One calf after 11 months

The breeding cycle

Groups hold 2 to 12 animals. Bigger groups form where prey is thick, though. Mating seems to peak in late summer.

Calves are born after about 11 months. A single calf is the rule. Newborns measure about 1 m.

Calves stay at the mother’s side. Milk is rich and fat, in fact. Because the calf must keep up with a fast group from the start, it grows quickly and stays close to its mother for more than a year.

Least Concern

Conservation

The IUCN rates the species as Least Concern. Its population is large and wide. No range-wide decline has been shown.

Drift nets killed huge numbers in the past, however. Japanese hunts still take some animals each year. Ship strikes are a growing risk.

Unlike the narwhal, which lives only in Arctic ice, this porpoise ranges over a huge stretch of open ocean. That wide range helps, since losses in one small fishing area do not threaten the whole species at once.

Side by side

How It Compares

Common misreadings

What People Get Wrong

• Porpoises are all slow. Dall’s is among the fastest cetaceans.
• The white patches are always the same. Two colour forms differ.
• The rooster tail is spray from the blow. It comes from the fast wake.

Going further

Sources and Further Reading

• Wikipedia, Dall’s porpoise
• IUCN Red List, Phocoenoides dalli. The IUCN Red List of Threatened Species.
• Animal Diversity Web, University of Michigan. Phocoenoides dalli.
• Jefferson, T. A. 2015. Dall’s Porpoise. Encyclopedia of Marine Mammals.

Quick hits

Five things to remember

• Top speed can pass 55 km per hour.
• The spray it throws is called a rooster tail.
• Bow-riding boats is a common habit.
• White flank patches differ between two colour forms.
• Wild animals usually live 16 to 22 years.