Sea Otter Facts

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 fuel the heat production that replaces blubber, a sea otter eats an enormous 25% to 30% of its body weight every day. It is a carnivore that forages the bottom on short one-to-two-minute dives, using sensitive whiskers and nimble paws to find over 100 kinds of invertebrate — sea urchins, crabs, clams, mussels, abalone, snails. Its famous trick handles armoured prey: the otter carries up a flat rock, rolls onto its back at the surface, sets the rock on its chest as an anvil, and smashes the shell against it until it breaks. This inherited, routine tool use is rare in the animal world and central to how the otter makes a living.

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.

• IUCN Red List of Threatened Species: Enhydra lutris
• Monterey Bay Aquarium: Sea Otter
• National Geographic: Sea Otter
• Marine Mammal Center: Sea Otter Facts