Porpoises

Relatives of dolphins and toothed whales, porpoises are small, shy sea mammals that swim fast in the sea. Many porpoises are threatened by human activities, such as fishing and pollution.

Porpoises and dolphins both evolved from a common ancestor around ten million years ago. Both animals have a sleek, streamlined body, a dorsal fin, flippers, and a blowhole on the top of their head. However, porpoises have a short, rounded snout, instead of the dolphin’s long, beaklike snout. Porpoises also have flat, spade-shaped teeth, while dolphins have cone-shaped teeth. Both dolphins and porpoises feed mainly on fish and use their teeth to hold their preyrather than for cutting or chewing their food. Porpoises do not seem to help each other catch food, as do many species of dolphins. Harbor porpoises can

dive deeper than 650 feet in search of prey.

Social Life and Conservation

Living alone or in small groups, most porpoises are hard to see or follow, and much of their social life remains a mystery. The only lasting links among porpoises is between a mother porpoise and her calf. Some older calves may stay with their mother for a short time after they stop drinking her milk.

The coastal waters where many porpoises live are also used by large numbers of people. Porpoises are badly affected by pollution, the noise of boat engines, and people digging deep channels for ships near the coast. However, the greatest danger occurs when many thousands of porpoises are trapped accidentally in fishing nets. Porpoises die if they cannot breathe air.