Porpoise is a group of sea mammals closely related to dolphins. Porpoises look much like dolphins but are smaller in size. They also differ from dolphins in the shape of the head and teeth. Porpoises have a gently sloping forehead, a rounded snout, and spade-shaped teeth. Dolphins have a steeply sloping forehead, a beaklike snout, and cone-shaped teeth. Porpoises, dolphins, and whales make up a group of mammals known as cetaceans << sih TAY shuhnz >>. Scientists classify porpoises, dolphins, and certain whales as a group of cetaceans called toothed whales.
Porpoises generally roam cool, coastal waters of the Pacific and Atlantic oceans. They can swim at speeds of about 12 miles (20 kilometers) per hour. They eat small fish and squid. Porpoises usually grow from 4 to 7 feet (1.2 to 2.1 meters) in length and weigh from 110 to 220 pounds (50 to 100 kilograms).
There are six species of porpoises. The harbor porpoise or common porpoise and the gulf porpoise or vaquita are dark gray to black on the back and pale gray or white on the sides and belly. The finless porpoise and Burmeister’s porpoise are almost entirely gray or black. The spectacled porpoise and Dall’s porpoise have a striking pattern of black and white. Most porpoises have a thick body and a small dorsal fin (back fin). Only the finless porpoise lacks a dorsal fin.
Human fishing activities have severely reduced the world’s porpoise population. The Gulf of California harbor porpoise, the vaquita, is an endangered species because so many have been trapped and accidentally killed in nets set for fish. There may be fewer than 20 vaquitas left in the wild. Similarly, huge nets called drift nets have killed tens of thousands of Dall’s porpoises (see Fishing industry (Gill nets)). To protect porpoises and other marine life, many countries have agreed to stop using drift nets in ocean waters.
