Sea Otter Sea Otter
Sea Otter

Scientific Classification

Common Name
sea otter
Genus Species
Enhydra lutris

Fast Facts

In appearance, sea otters are stouter and have larger rib cages, smaller tails and blunter muzzles than other species of otters. Yet, sea otters do possess the fine, dense fur coats characteristic of the Mustelidae. Their forefeet are small and dexterous with retractile claws and the flipper-like hind feet are broad and webbed. Juvenile sea otters tend to be a uniform dark-cinnamon brown while adults develop lighter gray or buff coloration on their heads.
Male:  In general, mature male sea otters tend to be slightly larger than females of their respective subspecies.
Alaskan sea otters are slightly larger than California sea otters
Female: Female Alaskan sea otters measure up to 140 cm (55 in.) in length
Male: Mature male Alaskan sea otters weigh up to 39 kg (85 lbs.), while California sea otters average 29 kg (64 lbs.)
Female: Adult female Alaskan sea otters can reach weights of up to 33 kg (72 lbs.), and female California sea otters weigh on average 20 kg (44 lbs.)
A sea otter has a metabolic rate much higher than most mammals of similar size, and must consume large quantities of food. Adult sea otters may eat as much as 9 kg (20 lbs.) of food each day. Among their food preferences are sea urchins, crabs, abalone, clams, mussels, octopus, and fishes. Most sea otters specialize in only a few types of the available food items.
Approximately 4 to 9 months with an average of 6 months; probably includes a 2 to 3 month period of delayed implantation
Estral Period
The reproductive cycle in California sea otters is about 12 months. If a female's pup doesn't survive, she may experience postpartum estrus.
Nursing Duration
Approximately 6 to 8 months (wean)
Sexual Maturity
Male: Approximately 5 to 6 years; usually don't actively breed for several more years
Female: Approximately 4 years
Life Span
On average, 10 to 15 years with some individuals living more than 20 years in zoological parks
In coastal regions throughout the eastern North Pacific Ocean. Alaskan sea otters inhabit the coast of Alaska, including the Aleutian and Commander Islands. California sea otters are found off the coast of central California, from Half Moon Bay to Pt. Conception.
Typically found in coastal waters no further away than 1 km (0.6 mi.) from shore. The Alaskan sea otter has a greater tendency to haul out (come to shore) than the California sea otter.
Regional: The California population is still small, roughly 2,200 to 2,800 sea otters
IUCN: Endangered
CITES: Appendix II (California subspecies is listed as Appendix I)
USFWS: Overall, listed as threatened. The population south of Pt. Conception, CA is listed as Experimental Population/Non-essential

Fun Facts

  1. The sea otter's dark brown fur is the finest and densest of any animal fur. On an adult animal, there are an estimated 650,000 hairs per square inch. A sea otter relies on its fur to keep warm because it doesn't have an insulating layer of blubber as other marine mammals do. Natural oils in a sea otter's fur repel water and trap tiny air bubbles, providing a layer of warm air between the otter's skin and the harsh elements of its environment. Sea otters may spend as much as 48% of the daylight hours grooming their fur.
  2. Sea otters sleep, rest, and usually swim by paddling with their hind flippers on their backs. California sea otters spend almost all of their time in the water, while Alaska sea otters often sleep, groom, and nurse their young on land.
  3. Tool use is an unusual behavioral trait seen only in sea otters and a few other types of animals. An otter may remove an abalone by repeatedly hitting it with a rock. It also may use a flat rock to break open the shells of crustaceans and mollusks. While holding the rock on its chest, the otter pounds the animal on the rock until it breaks or opens.
  4. For more information on otters, explore the Otters Infobook.

Ecology and Conservation

Sea otters once were abundant along most of the coastal North Pacific Ocean. That was before fur traders hunted them for their thick, luxurious pelts. By the year 1900, sea otters were nearly extinct. Protected since 1911, Alaska sea otters have made a comeback.

Because they rely on their dense fur for insulation from the chilly ocean water, sea otters are particularly vulnerable to the detrimental effects of an oil spill. If a sea otter swims into an oil spill, its fur becomes soiled and loses its insulating qualities, allowing water to penetrate to its skin, causing hypothermia and ultimately, death.


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Reeves, R. R., Stewart, B.S., Clapman, P.J., and J.A. Powell (Peter Folkens illustrator). National Audubon Society: Guide to Marine Mammals of the World. New York: Random House, 2002.

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