Sea-Worthy Sea Otters
By Sarah Flaherty
The sea otter, Enhydra lutris, is the only exclusively marine otter species. Growing up to five and a quarter feet long and weighing up to 100 pounds, it is the heaviest and one of the biggest members of the otter family. Unlike other marine mammals, the sea otter is insulated by two layers of dense fur instead of blubber. The inner fur layer is short and fluffy, and traps air bubbles. This creates a pocket of air that keeps the otter’s skin dry. The outer fur layer is made up of longer guard-hairs. This brown coat is waterproof as long as it is clean. If the outer layer gets matted and dirty, as happens in oil spills, the inner layer of fur becomes saturated and can no longer hold air bubbles, and the otter will freeze. Otters have up to one million hairs per square inch, meaning that they have more hair in one square inch than is on an entire human head (which has only about 20,000 total).
Sea otters’ extremely high metabolic rate helps keep them warm, but also requires that they eat up to 30 percent of their body weight each day. This big appetite is sated by urchins, shellfish, crabs, snails, and octopi that the otters hunt in kelp beds and forage for on the ocean floor.
Otters usually dive for 45 to 90 seconds while hunting, but can hold their breath for up to five minutes. Their webbed hind toes propel them through the water, while they use their tails to steer. This frees their dexterous forepaws and semi-retractable claws to snatch prey, or to help pull them through the water.
One of the handful of tool-using mammals, otters use rocks to pry abalone and other shellfish off rocks. They stash their prey out of the way in pockets of skin under their forelegs (effectively their armpits) before surfacing to feast. They eat while lying on their back, using their stomach as a table—or as a counter upon which to smash open their prey with a rock.
For more information, check out the Monterey Bay Aquarium, which runs the world’s only sea otter rehabilitation and breeding program, online at
www.mbayaq.org/atc/atc_so.htm. Also, the Friends of the Sea Otter website, (
www.seaotters.org), offers a wealth of information and photographs.
ZooGoer 28(6) 1999. Copyright 1999 Friends of the National Zoo. All rights reserved.
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