Porpoise, the smallest of the toothed whales. It resembles the dolphin, but is smaller—seldom more than six feet (1.8 m) long—and has a blunt muzzle instead of a pointed one. Porpoises have thick bodies, and either one dorsal fin or none. They are warm-blooded and air-breathing, and give birth to live young, which they suckle. Porpoises emit a variety of sounds to communicate with one another. Like other toothed whales, they use echolocation (which is similar in principle to sonar) to avoid obstacles and locate prey.

The porpoiseThe porpoise is the smallest of the toothed whales.

Porpoises inhabit all oceans except the Arctic and Antarctic. They are found near shore and in bays, and occasionally swim up rivers. They travel in schools, feeding on fish and shellfish. The female gives birth to one calf. At birth a calf is about three feet (90 cm) long.

Two species of porpoises are found along the coasts of the United States. The common porpoise, or harbor porpoise, is black on top, pinkish-gray on the sides, and pale gray below. Its dorsal fin is triangular. It is found in the Atlantic and Pacific oceans. Dall's porpoise has a greenish-black back and large white areas on either side of its body. It has a backward-curving dorsal fin. This porpoise is found along the Pacific Coast from Alaska to southern California.

In some places porpoises are eaten by humans, but generally the flesh is not considered palatable. An oil used for lubricating can be obtained from porpoise fat.

A number of small dolphins are sometimes locally called porpoises, especially the bottlenosed dolphin of North America.

Is It a Porpoise or a Dolphin?

All toothed whales have teeth, but the teeth of a porpoise are different from those of a dolphin.

A dolphin has pointy, cone-shaped teeth. But a porpoise has rounded teeth. A porpoise has a smaller head than a dolphin does. And a porpoise has a rounded snout. Most porpoises also have small dorsal fins. The finless porpoise, as you might guess, has no dorsal fin at all.

Some porpoises are quite shy—but not the Dall’s porpoise. The Dall’s porpoise is active all the time, and it seems to like to show off. Dall’s porpoises often approach boats filled with whale watchers. The porpoises swim around the boats and may even ride the waves that the boats make.

Porpoises are cetaceans belonging to the family Phocoenidae. The common porpoise is Phocoena phocoena; Dall's, Phocoenoides dalli.