The natural explanation

Natural History, March, 2008 by Erin Espelie

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Sea otters are "aww"-inspiring creatures. Just ask the more than 9 million YouTubers who in the past year have watched an amateur video shot at the Vancouver Aquarium in Canada. In it, two sea otters clasp "hands" as they float on their backs, then (alas) drift apart. In a touching denouement, one otter reaches out to link them up again. The crowd goes wild.

What's the appeal? The marine mammal (Enhydra lutris) belongs to the not-so-cuddly weasel family, the Mustelids. Yet something about a sea otter bobbing on its back, or the adroitness of its sleek little hands, brings out oohs and aahs in people.

The sea otter's forelimbs are indeed unusual. For starters, a special pocket of skin under each arm provides storage for, say, a clam collected on a long dive. And the palms are bare, lacking the dense, waterproof fur that insulates most of the body. To warm up, the animal will often hold its paws out of the water--as the California sea otter on the previous two pages demonstrates.

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When photographer Bruce Lichtenberger spotted this otter, it was with a few companions. But sometimes otters sun themselves in groups, known as "rafts," more than a thousand strong. They will link hands--as the Vancouver duo did--or wrap themselves in giant kelp (Macrocystis pyrifera), as Lichtenberger observed, to keep from drifting apart. The kelp strategy allows an otter to save energy by keeping its hands and head effortlessly above water.

Beyond using the canopy to rest, the sea otters take full advantage of huge kelp forests. Their favorite delicacies are sea urchins, which feed voraciously on kelp. By vacuuming up urchins, the otters protect the kelp, and thus secure food and shelter for a vast array of species--from snails to whales.

The popularity of sea otters (or at least their fur) among humans nearly wiped out the species by the start of the last century. But all three subspecies--the Asian, northern, and California (or southern) sea otters--have been internationally protected since 1911. Their total population reached about 90,000 in 1985, but has declined alarmingly to less than 10,000 since then.

A few rogue killer whale pods may be curbing the northern sea otter population, as their usual prey of seals and sea lions dwindle. But that doesn't explain the stagnant southern otter population, according to U.S. Geological Survey ecologist Tim Tinker, based at the University of California, Santa Cruz. He sees a host of other threats to local otters, including fishnets, guns, pollution, and Toxoplasma gondii, a protozoan from cat waste that can cause brain infections.

Tinker identified the sea otter featured here as a female. "I say female because of the nose scar," he says, which is "a typical wound inflicted by males during mating or attempted mating."

Bruce Lichtenberger is an international wildlife photographer who specializes in polar bears, bald eagles, and Alaskan brown bears. He has published in National Wildlife magazine, among others. Visit www.lichtenbergerphoto.com for more of his photos.