There are 19 species of earless seals, 9 species of sea lions, 5 species of fur seals, and 1 species of walrus.
Of the earless seals, some of the more familiar are the harbor seals that are found in the North Atlantic and Pacific Oceans. These seals position themselves on rocks or sandbars uncovered by low tides, swimming only when the high tide reaches them and threatens their perch. The seals that both entertain and annoy residents of San Francisco Bay with their loud barks and enormous appetites are harbor seals.
Another earless seal is the elephant seal, which can weigh up to four tons. The largest of all pinnipeds, the male elephant seal has a characteristic inflatable proboscis (nose) reminiscent of an elephant's trunk.
The harp seal was at one time one of the most endangered of the earless seals, since the pure white coat of the harp seal pup was prized by the fur industry. Harp seals are migratory animals and are found in the Arctic Atlantic.
Among the eared seals, the long-tusked walrus is one of the most familiar. Walruses use their tusks to lever themselves out of the water; at one time it was thought that they also used them to dig up food. Walruses can weigh up to two tons, feeding on mollusks, which they delicately suck out of the shell before spitting it out. Like all eared seals, walruses have front flippers that can be rotated forward, allowing them to walk and run on land, walk backward, and rest upright on their front flippers.
Sea lions are eared seals, commonly seen performing tricks in zoological parks. They lack the thick underfur seen in the earless seals, and so have not been hunted heavily for their pelts. In contrast, the fur seals are eared seals that have almost vanished completely due to intense hunting but are now protected: in 1972, the United States passed the Marine Mammal Protection Act, which outlaws the killing of seals for their fur and other products and restricts the selling of these products within the United States.
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Science EncyclopediaScience & Philosophy: Jean-Paul Sartre Biography to Seminiferous tubulesSeals - The Body, Reproduction, Diversity - Seals are mammals, General characteristics of seals, Diving and reproduction