Sea otters belong to the weasel family. All members of this family have very thick fur. They have two layers of fur, an undercoat, as well as longer guard hairs. This traps air next to their skin so that their skin stays dry. Sea otters usually are dark brown, frequently with lighter guard hairs. Their faces are circular and furry, with rounded eyes and ears, short noses, and long whiskers that help with foraging for food. The back legs are long, with broad, flat, webbed paws. The front legs are short, with retractable claws for eating and grooming.
Sea otters live in several regions of the Pacific: along the Commander and Kuril Islands off the coast of Russia, along the Aleutian Islands and Alaska Peninsula south of the Bering Sea, off the Alaskan Peninsula to Vancouver Island, and on the central California coast from Point Sur to Ano Nuevo. They live in temperate coastal waters with soft sediment or rocky ocean bottom. They inhabit offshore giant kelp forests and spend most of their time foraging below the canopy.
Sea otters form groups known as pods or rafts when resting. Females avoid males except during mating. They are long-lived and usually remain for years in the same area. They spend most of their time in the sea, but rest on land during stormy weather or when population density is high. When sleeping or resting, they float on their backs and wrap themselves up in kelp to stop drifting away. They eat, rest, and groom at the water's surface. They are able to dive down to at least 45 meters, but prefer coastal waters less than 30 meters deep. They are diurnal.
Sea otters are carnivorous, eating almost any fish or marine invertebrate from their kelp forest foraging area. They eat sea urchins, sea stars, coast mussels, purple-hinged rock scallops limpets and chitons. They also eat crabs, squid, and octopus. Their prey provides most of their water but they also drink seawater when thirsty. They usually eat 3 to 4 times each day.
Sea otters are polygynous, mating at any time of year. Gestation lasts up to a year, and the mother bears a single pup. Males do not look after their offspring. Pups are weaned when they are about 6 months old but have started eating solid foods soon after birth. Females carry their babies on their bellies while nursing. The mother wraps her pup up in kelp while she is foraging, so that it won't drift away. Pups start diving when they are 2 months old. They are dependent on their mother for 6 to 8 months. Females are sexually mature at 4 years and males at 5-6 years, but they may not mate for some years.
Sea otters were once heavily hunted to the point of near extinction. Their population was reduced from nearly 300,000 individuals in 1700s to only 2,000 individuals at the beginning of 20th century. Commercial harvest of Sea Otters stopped in 1911 when they were afforded protection by the International Fur Seal Treaty. Currently the major threat to sea otters is oil pollution. They are particularly vulnerable, as they rely on their fur to keep warm. Further threats are severe weather and periodic climatic events such as El Niño, expanding predation by killer whales, infectious diseases, net entanglements, and boat strikes.
Population estimates between 2004 and 2012 provide a worldwide total of about 126,000 Sea otters, including 19,000 in the Kurils, 3,500 on the Kamchatka Peninsula, 5,500 on the Commander Islands, 89,000 in Alaska, 4,712 on the Vancouver Island, and about 3000 in California. The ICUN classifies the sea otter as "Endangered", with a decreasing population trend.
Sea otters play a big role in their ecosystem by controlling herbivorous invertebrates. They prey on sea urchins, preventing them from overgrazing the forest of kelp, which supports marine diversity. The variety in their diet supports greater diversity amongst benthic grazers. Their presence is important as part of the kelp forest ecosystems.