The sea otter, Enhydra lutris, is the heaviest member of the weasel family and one of the smallest marine mammals, and it survives the freezing North Pacific with no blubber. Its fur holds up to 150,000 hairs per square centimeter, with barbed guard hairs and underfur that trap air when groomed. Diving compresses that air layer, so otters run a metabolism two to three times that of a similar land mammal and eat 25 to 38 percent of their body weight daily. They have dense bones, lungs two and a half times larger than expected, and multi lobed kidneys that let them drink seawater. They forage in one to four minute dives across more than a hundred prey species.

Mothers blow air into pups’ fur so they float while she dives, and males grip females by the nose when mating, leaving scars. After Vitus Bering’s shipwrecked crew brought pelts back from the Commander Islands in the 1740s, the soft gold trade cut otters from 150,000 to 300,000 to about 1,000 to 2,000 by the 1911 treaty, while Russian traders forced Aleut men to hunt and the Aleut population fell from about 20,000 to 2,000. Every California otter descends from about 50 found near Bixby Creek Bridge in 1938. As a keystone species they keep urchins from turning kelp forests into barrens.

• They store prey in loose skin pouches under the forelegs, favoring the left one.
• Floating on their backs, they smash shells on a chest rock up to 45 times in 15 seconds.
• Resting rafts wrap themselves in kelp to avoid drifting out to sea.
• By eating crabs in estuaries they help eelgrass bind sediment against erosion.
• Their appetite for abalone, Dungeness crab and clams puts them in conflict with shellfish fisheries.