The sea otter is a marine mammal of the North Pacific coast and one of the smallest marine mammals. Adults typically weigh 14–45 kilograms. Unlike most marine mammals, sea otters lack a thick blubber layer; instead, they rely on the densest fur of any animal—up to a million hairs per square inch—to stay warm in cold water.
They inhabit coastal waters with kelp forests, rocky reefs, and soft-bottom habitats from California to Alaska and across to Russia and Japan.
Diet, tools, and ecology
Sea otters are tool users. They often carry a rock in a pouch under the forearm and use it to crack open hard-shelled prey such as sea urchins, crabs, and mollusks while floating on their backs. Their diet has a major ecological effect: by controlling sea urchin populations, they help maintain healthy kelp forests, which in turn support many other species. This makes them a classic keystone species.
They spend much of their time floating, grooming, and feeding. Grooming is essential to keep the fur waterproof and insulating.
Conservation
Sea otters were hunted nearly to extinction for their fur in the 18th and 19th centuries. Legal protection and reintroduction efforts have allowed recovery in parts of their range, though numbers remain well below historical levels in many areas. The species is listed as Endangered. Current threats include oil spills, entanglement in fishing gear, predation by sharks in some regions, and disease.
Their recovery continues to benefit coastal ecosystems, particularly kelp forests.