Animal
Sea otter
The sea otter lives in the ocean and floats on its back. It cracks open shells with a rock. A mother carries her baby on her tummy.
The sea otter is a marine mammal of the North Pacific coast that spends almost its whole life in the water. It has the thickest fur of any animal, floats on its back to eat, and even uses rocks as tools. By eating sea urchins, sea otters help kelp forests stay healthy.
Enhydra lutris, the largest member of the weasel family and the only fully marine otter, keeps warm with the densest fur of any mammal and a high metabolism rather than blubber. A keystone predator of sea urchins in kelp forests, it was hunted almost to extinction for fur and is listed by the IUCN as Endangered.
Photo: "Mike" Michael L. Baird, CC BY 2.0, via Wikimedia Commons
Meet the sea otter
The sea otter is a furry animal that lives in the sea.
It floats on its back like a little boat. It has a round face, long whiskers and very thick fur.
The sea otter is the largest member of the weasel family, and the only otter that lives fully in the ocean. A big male in Alaska can weigh 36 to 45 kilograms, about as much as a ten-year-old child, and grow up to about 1.5 meters long.
Sea otters can spend their whole lives in the water. They eat, sleep, groom and even have their babies while floating. On land they are clumsy, because their back feet are webbed flippers made for swimming, and they rarely go more than a few steps from the water.
Enhydra lutris is the largest mustelid; adult males in Alaska weigh about 36 to 45 kilograms and females 23 to 32, with total lengths up to about 1.5 meters. Of the fourteen otter species, it is the only one that is fully aquatic.
Three subspecies live in separate populations: the southern or California sea otter (E. l. nereis), the northern sea otter (E. l. kenyoni) of Alaska, British Columbia and Washington, and the Russian sea otter (E. l. lutris) off Russia and Japan. Southern sea otters are the smallest, and the Monterey Bay Aquarium describes them as the smallest marine mammal in North America.
Quick facts
- Group
- Mammal
- Length
- 1.2 to 1.5 m
- Weight
- 36 to 45 kg
Where it lives
Sea otters live near the shore in the cold Pacific Ocean.
They like forests of tall seaweed called kelp. They rest on their backs in the kelp, looking like floating lumps of seaweed.
Sea otters live in shallow coastal waters around the North Pacific Ocean: in California, Washington, British Columbia in Canada, Alaska, Russia and northern Japan. They like kelp forests, rocky shores, bays and calm estuaries where rivers meet the sea.
Sea otters do not migrate long distances. Most stay in a home area of a few square kilometers. Long ago they lived along the whole coast from Mexico to Japan, but hunting wiped them out from many places.
The IUCN Red List (2020 assessment) records the species as resident in Canada, Russia and the United States, with occurrences of uncertain seasonality in Japan and Mexico. Its historical range ran from Baja California north to southern Alaska, west along the Aleutians to Kamchatka and south to northern Japan; today it survives in Alaska, Russia, British Columbia, Washington and California.
Sea otters forage in shallow coastal water, kelp forests, estuaries and harbors, and generally keep to home ranges of a few to about 40 square kilometers. The California population occupies only a small part of its former range, roughly from Half Moon Bay to near Point Conception. The map shades the North Pacific and coastal range countries; otters use only a narrow strip of coast.
Continents
Did you know?
A sea otter has more hairs on a tiny patch than you have on your whole head.
A sea otter can have up to about a million hairs per square inch, while you have about 100,000 hairs on your whole head.
At 800,000 to over a million hairs per square inch, sea otter fur is the densest of any mammal.
Where can you find this animal?
- Used to live here · Countries and seas named by a scientific source
- Lives here naturally · Countries and seas named by a scientific source
- Sightings recorded · Records of wild sightings (GBIF)
Used to live here · Countries and seas named by a scientific source
Sea otters once lived along the coast of Baja California, Mexico, before the fur trade devastated them. The IUCN now lists Mexico only as a place where they occur with uncertain seasonality.
Places: Mexico.
Source: https://www.adfg.alaska.gov/index.cfm?adfg=seaotter.main · checked October 2026
Lives here naturally · Countries and seas named by a scientific source
A narrow strip of shallow coastal water around the North Pacific: California, Washington, British Columbia, Alaska, Russia's Pacific coast and northern Japan. Sea otters live only close to shore, not in the open ocean or inland.
Places: Pacific Ocean, United States, Canada, Russia and Japan.
Source: iucn-red-list · checked October 2026
Sightings recorded · Records of wild sightings (GBIF)
Counts of GBIF records of wild observations (human and machine) and preserved specimens. Records include introduced populations, vagrants, escaped or released animals and misidentifications, so a country with records is not necessarily part of the native range.
Wild sightings have been recorded in United States, Canada, Russia, Japan, Mexico, Germany, UK, Norway and 6 more places.
Source: gbif · checked October 2026
Range maps show where scientists say an animal lives, often country by country. An animal may live in only part of a country shown, and sightings records can include animals that wandered far from home.
Dinner on the water
Sea otters dive to the sea floor to find food.
They eat sea urchins, crabs, clams and mussels. They float on their backs and use their tummies as a table.
Sea otters dive to the seafloor to catch sea urchins, crabs, clams, mussels, snails, abalone and octopus, and some northern otters eat fish. Most dives last only a minute or two.
They always come back up to eat. Floating on its back, an otter uses its chest as a table. To open a hard shell, it may bang it against a rock balanced on its chest. Sea otters even have 'pockets', loose skin under each front leg, where they stash food and a favorite rock during a dive.
The diet is mainly benthic invertebrates, sea urchins, crabs, clams, mussels, snails, abalone and octopus, with fish taken by northern sea otters. Most dives last one to two minutes, though otters can hold their breath for more than five; the Monterey Bay Aquarium cites dives to 183 meters, while the Alaska Department of Fish and Game gives a usual range of about 1.5 to 76 meters.
Prey is eaten at the surface on the chest. Sea otters are tool users, cracking shells with rocks they carry in loose skin pouches under the forelimbs, and their teeth are adapted for crushing hard-shelled prey. To fuel their metabolism they eat about a quarter of their body weight every day.
The thickest fur on Earth
A sea otter has the thickest fur of any animal.
It has no thick fat to keep warm, so its fur does the job. It brushes and fluffs its fur many times a day.
Whales and seals keep warm with blubber, but sea otters don't have it. Instead they have the densest fur of any mammal: up to about a million hairs on a patch of skin the size of a postage stamp. You have only about 100,000 hairs on your whole head!
The fur traps a layer of air that keeps cold water away from the skin. To keep it working, otters spend hours a day grooming, rubbing in natural oils and fluffing in air bubbles. They also burn food fast to stay warm, eating about a quarter of their weight every day.
Lacking blubber, sea otters rely on fur and metabolism. The two-layer coat, dense underfur under longer guard hairs, holds about 800,000 to more than a million hairs per square inch, the densest of any mammal. Air trapped in the fur and warmed by the body provides, according to the Alaska Department of Fish and Game, about four times the insulation of the same thickness of fat, and adds buoyancy.
Grooming, which takes hours each day, removes salt and excess oil, spreads skin oils and works air back into the fur. A high metabolic rate, fueled by eating about 25 percent of body weight daily, maintains a body temperature near 38 degrees Celsius. Webbed hind feet propel swimming; the short, stiff forepaws handle food and tools.
A floating nursery
A mother sea otter has one baby at a time.
The baby is called a pup. It rides on its mother's tummy while she floats. Its fluffy fur keeps it floating like a cork.
A mother sea otter has one pup at a time, and in Alaska most are born in late spring. A newborn weighs about 1.4 to 2.3 kilograms and is born with its eyes open and a special fluffy coat that makes it float, even before it can swim.
The pup rides on its mother's chest as she swims on her back. She leaves it only to dive for food. After three to six months the pup stops drinking milk. By then it weighs about 14 kilograms and looks almost as big as its mother.
Sea otters breed year-round, though in Alaska most pups are born in late spring. A single pup weighing about 1.4 to 2.3 kilograms is born, unusually among otters, with its eyes open and a buoyant natal coat. It rides on the mother's chest and is left alone only while she dives.
Weaning comes at three to six months, when the pup weighs about 14 kilograms. Females mature at 2 to 5 years and males at 4 to 6. With one pup at a time and a long period of care, reproduction is slow, which is why the Alaska Department of Fish and Game notes sea otters are vulnerable to overharvest.
Rafts and kelp forests
Sea otters often rest together in big groups.
A group of floating otters is called a raft. By eating sea urchins, otters help the kelp forest grow.
Sea otters are social. They often rest together in floating groups called rafts, and more than 1,000 have been seen in one place. Breeding males guard areas where females gather.
Sea otters are a keystone species, which means they have a huge effect on their home. Sea urchins eat kelp. Without otters, urchins can multiply and munch whole kelp forests down to bare rock, called urchin barrens. By eating urchins, otters keep the kelp forest healthy for fish and many other animals.
Sea otters often rest in groups called rafts, sometimes of more than 1,000 animals. Breeding males defend territories where females concentrate, while nonbreeding males form separate groups nearby.
They are a classic keystone species. By preying on sea urchins they prevent urchins from overgrazing giant kelp; where otters are absent, urchin populations can explode and leave 'urchin barrens'. In Elkhorn Slough, an estuary on Monterey Bay, otters eating crabs allow sea slugs to thrive, which eat algae that would otherwise smother eelgrass, a nursery for fish. Changes in otter health are therefore a useful indicator of the coastal ecosystem's condition.
Did you know?
Sea otters have pockets under their arms.
Sea otters have a pocket of loose skin under each front leg where they keep food and a favorite rock while diving.
Loose skin pouches under the forelimbs carry prey and stone tools during dives, leaving the paws free to keep foraging.
Back from the brink
Long ago, people hunted sea otters for their fur.
Almost all of them were gone. Now laws protect them and there are more again. They still need our help.
In the 1700s and 1800s, people hunted sea otters for their thick fur until they were almost extinct. In 1911 an international treaty stopped the hunting. In California, only about 50 otters were found in 1938, off the Big Sur coast, and today's California otters, about 3,000, come from that small group.
Sea otters are still endangered. Oil spills are a big danger, because oil ruins their fur. Shark bites, disease and lost habitat are problems too. Aquariums rescue stranded pups and raise them to return to the wild.
The maritime fur trade from the 1700s reduced sea otters to near extinction by the early 1900s. Protection under the 1911 Fur Seal Treaty allowed a dramatic rebound in many areas, and California's population, rediscovered as about 50 animals off Big Sur in 1938, has grown to around 3,000. It is listed as threatened under the U.S. Endangered Species Act, and the southwest Alaska stock is also threatened.
The IUCN lists the species as Endangered (criteria A2abe, 2020) with a decreasing trend. Threats include oil spills, which destroy the insulating value of fur, shark bites that limit the California range, killer whale predation in the Aleutians, disease and fishery interactions. Surrogate-mother programs have released rescued pups that boosted local populations.
IUCN Red List
How is the sea otter doing in the wild?
- Least Concern
- Near Threatened
- Vulnerable
- Endangered (this animal)
- Critically Endangered
- Extinct in the Wild
- Extinct
Endangered
At very high risk of disappearing from the wild.
See the IUCN Red List assessment · The IUCN Red List of Threatened Species 2022.2
Amazing facts
-
Sea otters have pockets under their arms.
Sea otters have a pocket of loose skin under each front leg where they keep food and a favorite rock while diving.
Loose skin pouches under the forelimbs carry prey and stone tools during dives, leaving the paws free to keep foraging.
-
A sea otter has more hairs on a tiny patch than you have on your whole head.
A sea otter can have up to about a million hairs per square inch, while you have about 100,000 hairs on your whole head.
At 800,000 to over a million hairs per square inch, sea otter fur is the densest of any mammal.
-
More than 1,000 sea otters have been seen floating together.
Sea otters rest in groups called rafts, and more than 1,000 have been seen floating together in one area.
Concentrations of more than 1,000 sea otters have been seen floating together in a single area.
-
Baby sea otters float like corks.
A sea otter pup's fluffy coat holds so much air that it floats, even before it can swim.
The air-filled natal coat makes pups buoyant, so they can be left floating while the mother dives.
Words to know
- marine mammal
- a mammal that lives in or depends on the sea
- kelp
- a very large brown seaweed that can grow into underwater forests
- keystone species
- a species that has a huge effect on its whole ecosystem
- raft
- a group of sea otters floating together
- tool
- an object an animal uses to help it do a job
- blubber
- a thick layer of fat under the skin of whales and seals
Discovery challenge
-
How does a sea otter keep warm?
How do sea otters keep warm without blubber?
Which two features keep a sea otter warm?
- Very thick fur
- A woolly hat
- Sitting in the sun all day
Show the answer
Very thick fur
Its very thick fur keeps it warm.
Super-dense fur traps air, and eating lots of food keeps the body warm.
The densest fur of any mammal, trapping insulating air, and a high metabolism fueled by eating about 25 percent of body weight daily.
-
What does a sea otter use to open shells?
What tool do sea otters use?
Where do sea otters carry their stone tools?
- A rock
- A spoon
- A stick of kelp
Show the answer
A rock
It bangs shells on a rock.
It cracks hard shells open with a rock.
In loose skin pouches under the forelimbs.
-
Where does a baby sea otter ride?
Where does a sea otter pup spend its first months?
Why can a pup be left floating while its mother dives?
- On its mother's chest
- In a tree
- In a burrow on land
Show the answer
On its mother's chest
It rides on its mom's tummy.
On its mother's chest as she floats on her back.
Its air-filled natal coat makes it buoyant.
-
How do sea otters help kelp forests?
Why are sea otters called a keystone species?
What can happen to a kelp forest without sea otters?
- They eat the sea urchins that eat kelp
- They plant kelp seeds
- They water the kelp
Show the answer
They eat the sea urchins that eat kelp
They eat urchins, so the kelp can grow.
By eating urchins, they stop urchins from eating the kelp forest.
Urchins can overgraze it into an 'urchin barren' of bare rock.
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For parents & teachers
What children will learn
- Explain how sea otters stay warm without blubber.
- Describe how sea otters find, carry and open their food, including tool use.
- Explain what a keystone species is, using sea otters, urchins and kelp.
- Describe how hunting nearly wiped out sea otters and how laws helped them recover.
Recommended ages: 3 to 17 · About 15 minutes
Talk about it
- What might happen to the fish in a kelp forest if the sea otters disappeared?
- Why do you think oil spills are so dangerous for animals that rely on fur?
- Sea otters use rocks as tools. What other animals can you think of that use tools?
Try at home or in class
- Fur and oil test: dip a cotton ball in water and see how it absorbs water, then rub a little cooking oil into another and compare. Talk about why clean, fluffy fur matters.
- Make a food web on paper with kelp, sea urchins and sea otters, then remove the otters and draw what happens.
Key vocabulary: marine mammal, kelp, keystone species, raft, tool, blubber
Where these facts come from
- The IUCN Red List of Threatened Species , International Union for Conservation of Nature (IUCN terms of use (no redistribution of Red List data or range maps))
- GBIF Backbone Taxonomy and GBIF Occurrence Search , Global Biodiversity Information Facility (CC0 1.0 (backbone); occurrence counts are facts derived from records under CC0, CC BY and CC BY-NC)
- Sea otter , Monterey Bay Aquarium
- Northern Sea Otter Species Profile , Alaska Department of Fish and Game
- Otter , San Diego Zoo Wildlife Alliance
- Enhydra lutris (Sea Otter), 2020 assessment , IUCN Red List of Threatened Species
- Wikidata , Wikimedia Foundation (CC0 1.0)
- Wikimedia Commons , Wikimedia Foundation (Per file: Public domain, CC0, CC BY or CC BY-SA only (credited on each page))
Checked, not yet human-reviewed. Last updated October 24, 2026. Spotted a mistake? Tell us.