“Sea otters have some of the thickest fur in the animal world.”
Sea otters live along North Pacific coasts, where dense fur insulates them in cold water and stones help open hard-shelled prey. By controlling sea urchins, they can help kelp forests persist, but several regional populations remain vulnerable or depleted.
By An Nguyen · Published · Updated
Measured against the 176 species profiled on this site. Each figure is converted to one unit system from the published range on the page, so the ranks are computed, not quoted.
| Measure | This species | Rank here | Exceeds |
|---|---|---|---|
| Body mass | 45.4 kg | #68 of 176#50 of 90 Mammalia | 62% |
| Body length | 1.52 m | #67 of 176#44 of 90 Mammalia | 62% |
| Top speed | 9.7 km/h | #72 of 75#46 of 46 Mammalia | 4% |
| Lifespan in the wild | 20 yr | #67 of 169#35 of 85 Mammalia | 59% |
Closest in body mass
Ranks use the upper end of each published adult range, so they compare typical large adults rather than records, and metrics with no published number are left out rather than estimated. The full table is downloadable from the species dataset, and any two species can be put side by side in the comparison tool.
Browse sea otter photographs—from kelp forests and pups to tool use, grooming, and dense insulating fur.
Click any photo to view it larger. 8 images available.
Core article
A closer look at habitat, diet, behavior, reproduction, and conservation.
The sea otter (Enhydra lutris) is a marine mammal that keeps the kelp forests of the North Pacific alive — a keystone species whose appetite for sea urchins protects the kelp that shelters countless other animals. Unlike seals, sea lions, and whales, it has no blubber to keep warm. Instead it survives cold water on three things: the densest fur of any animal, a very high metabolism, and tool use. Much of its life is spent floating on its back at the surface.
With no insulating blubber, the sea otter depends entirely on its coat — the densest fur known, with up to a million hairs per square inch. Long guard hairs over a thick underlayer trap a blanket of air against the skin, and keeping that layer working is a matter of life and death: an otter spends hours a day grooming, and oil or dirt that fouls the fur can cause fatal hypothermia (which is why oil spills are so deadly to them). The body is a mustelid built for the seafloor: dexterous front paws with retractable claws that work almost like hands, big webbed hind feet for propulsion, and a loose pouch of skin under each foreleg used to stash food and a favourite rock while swimming up. It is the largest member of the weasel family yet one of the smallest marine mammals — males 50 to 100 pounds, females smaller.
Sea otters once ringed the North Pacific from northern Japan through Russia, the Aleutians, Alaska, and down the North American coast to Baja California. After the fur trade, their range is now fragmented, with main populations in Russia, Alaska, British Columbia, Washington, and a small isolated group in central California. They are strictly nearshore animals, rarely going into deep open ocean, and are tied above all to giant and bull kelp forests, whose canopy anchors resting otters and teems with the invertebrates they hunt.
To support heat production without blubber, a sea otter eats about 25% to 30% of its body weight each day. It forages on short dives, using whiskers and paws to find sea urchins, crabs, clams, mussels, abalone, snails, and other invertebrates. Some individuals carry a flat rock to the surface and use it as an anvil to open hard-shelled prey. Tool-use methods vary among individuals and can be learned within family lines.
Sea otters are social but segregate by sex, foraging alone yet resting in groups called "rafts" — of males, or of females and pups — that can number from ten to over a hundred. To keep from drifting out to sea or onto rocks while they sleep, they wrap themselves in surface kelp fronds like a mooring line. Grooming is a biological necessity rather than mere tidiness, taking hours each day, and otters stay in vocal contact with whistles, squeals, and coos, especially between mother and pup.
Sea otters can breed year-round, and delayed implantation lets a female time the birth to good conditions. After a true gestation of about four to six months she gives birth to a single pup in the water. The newborn is so buoyant with dense natal fur that it cannot dive, so the mother uses her own chest as a floating cradle, wrapping the pup in kelp to anchor it whenever she must dive to feed, and grooming and provisioning it heavily. Weaning comes at six to eight months, by which time the pup must have learned to dive, use tools, and groom. Wild sea otters live 10 to 20 years.
The sea otter is Endangered. The maritime fur trade cut a population once as high as 300,000 to perhaps 1,000–2,000 by the early 1900s; protection has allowed partial recovery in Alaska and Russia, but the species remains fragile. Lacking blubber, otters are exceptionally vulnerable to oil spills — even a light coating destroys the fur's insulation and they freeze — as the 1989 Exxon Valdez disaster showed, killing thousands. They are also preyed on by orcas in the Aleutians and white sharks in California. Their keystone role is the key point: by eating urchins, otters stop urchins from clear-cutting kelp into barren "urchin barrens," so protecting otters protects the whole coastal ecosystem.
Kingdom
Animalia
Phylum
Chordata
Class
Order
Carnivora
Family
Genus
Enhydra
Species
E. lutris
Sea otters have some of the thickest fur in the animal world.
They sometimes use rocks as tools to crack open shellfish.
Sea otters often wrap themselves in kelp so they do not drift away.
A group of resting sea otters can be called a raft.
They float on their backs while eating.
Sea otters help kelp forests by eating sea urchins that chew on kelp roots.
Select a question to reveal the answer.
Sea otters live in cold coastal waters of the North Pacific, especially near kelp forests and rocky shores.
Sea otters are carnivores that eat shellfish and other marine animals such as sea urchins, crabs, clams, and mussels.
Yes. Sea otters may use rocks to crack open hard shells while floating on their backs.
Instead of thick blubber, sea otters stay warm with extremely dense fur that traps air close to the skin.
Sea otters help keep kelp forests healthy by eating sea urchins that can damage kelp beds.
Some sea otter populations are protected and recovering, but the species still faces threats from oil spills, disease, and changing ocean conditions.
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