Sea Otter (Enhydra lutris)

Sea otter floats on back with its paws
Jeff Foott/Discovery Channel Images/Getty Images

The sea otter (Enhydra lutris) is an easily-recognizable marine mammal that lives in the Pacific Ocean. These furry animals spend most of their lives in the water, although they do sometimes come ashore. Sea otters were hunted to near extinction for their fur - it is thought that their population was as low as 2,000 in the early 1900's, although populations have rebounded significantly in many areas.


Sea otters are the smallest marine mammal by weight. Sea otters weigh 35-90 pounds - females weigh 35-60 pounds, and males weigh up to 90 pounds. Sea otters can grow up to about 4.5 feet in length.

Sea otters have thick fur (which keeps them warm, since they do not have blubber). At about 100 degrees, their body temperatures are very close to ours. The sea otter's coat is made up of the densest fur of any marine mammal - it can contain up to a million hairs per square inch. Their fur consists of two layers - an undercoat with shorter hairs, over the top of which are guard hairs that are about 1.3 inches long.

Sea otters propel themselves using their strong hind feet and tail, and use their tail also for steering. They have strong, agile paws, which have retractable claws. There are pockets of loose skin under their forearms, which the otters use to store food, and its favorite feeding tool - a rock that it uses to crack the shells of its prey.


Keeping Clean

Sea otters spend a generous amount of time each day keeping their fur clean, which involves rubbing their fur, combing it with their claws, and rolling in the water. Grooming allows more air to get into the fur, which is warmed by the otter's body heat, and thus provides insulation.


Sea Otter Senses

Sea otters have a good sense of smell, and good eyesight and hearing.

They can also sense vibrations in the water using their whiskers. They can see well both above and below the water. Similar to a whales' blowholes, a sea otter's nostrils, and ears, close when they are underwater.




  • Kingdom: Animalia
  • Phylum: Chordata
  • Subphylum: Vertebrata
  • Superclass: Gnathostoma
  • Superclass: Tetrapoda
  • Class: Mammalia
  • Subclass: Theria
  • Order: Carnivora
  • Suborder: Caniformia
  • Family: Mustelidae
  • Genus: Enhydra
  • Species: lutris

According to the Alaska Sea Life Center, there a three subspecies of sea otters:

  • Russian northern sea otter (Enhyrda lutris lutris), which lives in the Kuril Islands, Kamchatka Peninsula, and Commander Islands off Russia
  • Northern sea otter (Enhyrda lutris kenyoni), which lives from the Aleutian Islands to Washington state
  • Southern sea otter (Enhyrda lutris nereis), which lives in southern California




Sea otters forage mainly in shallow inshore waters, although they may forage offshore in deeper waters if needed. Feeding dives may last as long as 5 minutes.

Sea otters eat fish, and marine invertebrates such as crustaceans (e.g., crabs), echinoderms (sea stars and sea urchins), gastropods (snails), clams and abalone. Sea otters play an important role in the ecosystem by keeping sea urchin populations in check, which prevents them from over-eating kelp in kelp forest (more information here).

Sea otters eat between 23-33% of their body weight each day. A sea otter's mouth contains sharp incisors that they can use to crack their prey, and flat molars that are used to crush prey. In addition to their teeth, sea otters use tools, such as rocks, to obtain their prey - they may smash a shell against a rock to crack it, and use a rock to dislodge prey such as urchins from rocks. Extra food is kept in the folds of skin underneath the otter's forelimbs.




Females become sexually mature when they are 2-5 years old. Mating occurs in the water, and females may mate with one or more males numerous times during the mating season.

Sea otters give birth in the water, usually to one pup at a time after a gestation period of 4-5 months. Pups weigh 3-5 pounds at birth.

Sea otters can protect and nurse their young by laying them upon their chest.

Mother sea otters and their pups live in groups, while males live in other groups. Pups stay with their mothers for about 8 months. The pups learn to swim at about 4 weeks, and when they are young, they are so buoyant that they cannot dive underwater. The mothers wrap them in kelp to tether them to one spot when they leave the pup to go foraging. Eventually, they learn how, and what, to eat from their mother.


Habitat and Distribution:


Historically, sea otter populations stretched across the Pacific Ocean from Japan up into Russaia, across to the Aleutian Islands, and down through Alaska to Baja California, Mexico. Today, sea otters are found in more fragmented populations in parts of Russia, Alaska, British Columbia, Washington state, and California.

Sea otters may sleep on the water surface, and sometimes wrap kelp or other algae around them to anchor in one spot. They are social animals that live in gender-segregated groups (females and their young in one group, males in another). These groups may be composed of up to 2,000 individuals in some areas.


Communication and Vocalizations:

About 10 different sea otter vocalizations have been identified, and these are thought to be used for short-range communication.



Sea otters are protected by the Endangered Species Act in the U.S. and are listed as endangered on the IUCN Red List.

Sea otters were desired for their fur in the 18th and 19th centuries. The worldwide population of otters in the 1700's was estimated at between 150,000-300,000.

Hunting decimated this population to around 2,000 animals. According to the IUCN Red List, population estimates of sea otters done in 2004-2007 listed 106,822 sea otters worldwide.


Current threats to sea otters:

  • Oil spills: Oil affects sea otters because oil reduces the ability of sea otter fur to absorb air, and the sea otter can't keep warm.
  • Diseases and parasites
  • Entanglement in fishing gear and
  • Boat strikes
  • Other pollutants in their habitat

Natural predators include orcas (killer whales), great white sharks, bald eagles, coyotes and brown bears.


Sources and Further Information: