The sea otter (Enhydra lutris) measures up to 4 ft (1.3 m) long with a 12 in (30.5 cm) tail. Sea otters are common on rocky coastlines and islands on both sides of the North Pacific Ocean, from Japan north to the Aleutian Islands and south to the coast of California.
Sea otters spend almost all of their lives at sea and are the only mustelids able to do so. While they are in the water, they usually lie on their back, grooming themselves, feeding their young, resting, or eating. Sea otters come to land only to breed or when the weather is bad, for while they are skilled swimmers, they are slow and clumsy on land. When sea otters swim, they use their tail and hind feet, tucking their front feet under their chest. Their webbed hind feet, resembling those of sea lions, are much bigger than the hind feet of other otters. The tail is shorter than that of other otters, as are the fingers, which have small, rectractile claws.
The thick reddish to black fur, which is soft and silky in texture, serves to insulate sea otters from the cool water. Sea otters do not have an excess layer of fat for insulation, like many other aquatic mammals. They rely on a layer of air in their fur to protect them from the cold, and they keep their fur aerated by rubbing it with their feet to squeeze the water out. They contort themselves and wriggle around until the fur on even the most hard-to-reach parts of their body is aerated. Also, sea otters tend to blow on their coats to increase the amount of trapped air.
Sea otters feed on clams, mussels, and other crustaceans. To break open these hard shells, they use rocks, which they bring up from the sea bed, as tools. As a sea otter lies on its back, it places the stone on its chest and beats the prey against it, thereby cracking the shell and exposing the meat inside. At twilight, sea otters move into kelp beds to sleep, tangling themselves in the vegetation so that they do not drift out to sea.
Sea otters breed every two years. The female bears one pup after a gestation period of eight to nine months. The newborn pup is well developed, having all of its teeth and open eyes. The mother carries and nurses her offspring on her stomach while swimming on her back.
Sea otters were once relentlessly hunted for their dense, lustrous pelage, and were taken to the brink of extinction. In fact, it was considered extinct until the 1930s, when remnant populations were discovered in the Aleutian Islands and off the coast of northern California. These animals were protected, and the sea otter has since increased greatly in abundance and has repopulated much of its original range. Their total population now exceeds 100,000 animals.