Enhydra lutris

(Linnaeus, 1758) - Sea otter

Distinctive Characteristics

The sea otter is the most derived of the otters. The muzzle has a set of thick vibrissae. The large head has a blunt snout, and is connected to the body by a short, stocky neck. The forelimbs are short and similar to those of other otters, with a loose flap of skin under each that is used to store food. The hind-limbs are large and flattened like flippers; they are oriented backwards. Although the short tail is not noticeably tapered, it is flattened top to bottom into a paddle-like structure. Three subspecies are currently recognized (described below).

The pelage of sea otters is the densest of any mammal (more than 100,000 hairs/cm2). A layer of sparse guard hairs overlays the dense underfur. Sea otters are completely covered with fur, except for the nose pad, inside of the ear flaps, and the pads on the bottom of the feet. The colour of the fur is dark brown to reddish brown. Older individuals become grizzled, with the fur around the head, neck, and shoulders becoming almost white.

The dental formula is I 3/2, C 1/1, PM 3/3, M 1/2.

Can be confused with

The sea otter is the only truly marine otter in its range, although North American river otters (Lutra canadensis) are often found in marine waters along the northwest coast of North America. River otters are smaller and more slender than sea otters, with longer tails. Also, river otters generally swim belly down even at the surface, while sea otters usually move along the surface on their backs.


Male sea otters reach lengths of 148 cm and weights of 45 kg. Females can be up to 140 cm and 32.5 kg. Newborns weigh about 1.8 to 1.9 kg.

Geographical Distribution

Sea otters are found in shallow, nearshore waters of the North Pacific Rim, from the southern Kurile Islands, north along the Aleutian Islands, and thence south to southern California. Originally, their distribution was nearly continuous from Hokkaido, Japan, to central Baja California, Mexico. However, there are now 4 disjunct remnants: Kurile Islands to southeast Kamchatka Peninsula (classified as E. l. gracilis); Commander Islands; Aleutian Islands to Prince William Sound, Alaska (these 2 groups are classified as E. l. lutris); and central California (classified as E. l. nereis). In addition, there have been several reintroduction attempts (some successful, others not) along the west coast of North America.

Biology and Behaviour

Sea otters can be seen singly or in groups (most often resting groups called rafts). Rafts in California rarely exceed 50 individuals, but those in Alaska can contain up to 2000 otters.

Sea otters are polygynous; males tend to defend large territories that encompass the ranges of several females. Pupping occurs throughout the year, but peaks in May to June in Alaska, and in December to February in California. During mating, the male bites the nose of the female to position himself; thus, females often have nose scars (these are useful to researchers in identification of individuals).

Sea otters feed on or near the bottom in shallow waters (often in kelp beds). Major prey items are benthic invertebrates such as abalones, sea urchins, and rock crabs. However, sea otters also eat other shellfishes, cephalopods, and sluggish near-bottom fishes.


Sea otters have been commercially hunted since the 1700s, mostly for their pelts. All 3 subspecies were significantly reduced. Protection was finally afforded in some areas near the turn of this century. Oil spills and catches in net are the major remaining threats.

IUCN Status

Not listed.