Sea Otters Are the Party Animals of the Sea

Sea otters (Enhydra lutris) are in the weasel family, native to the North Pacific Ocean, from California, north along the Pacific coasts and islands of Alaska, and down the eastern edge of the Kamchatka Peninsula of Russia. Since they spend most of their lives bobbing around in chilly waters, using rocks and things to break shellfish open on their bellies, and they don't have a bunch of blubber to keep them warm as seals and walruses do, sea otters possess the densest fur in the animal kingdom: While you probably have fewer than 100,000 hairs on your entire head, that many hairs can be found on a single square inch (6.5 square cm) of a sea otter's body. But what keeps them cozy can be a liability in some cases.

"The problem with a sea otter's unique fur is it cannot get dirty, so they spend a lot of time grooming it to keep it clean," says Terri Williams, professor in the Department of Ecology and Evolutionary Biology at the University of California, Santa Cruz. "The Exxon Valdez oil spill of 1989 killed more than 1,000 sea otters in Prince William Sound because their fur was contaminated with oil. Our team spent months cleaning them — the bottom line, though, is oil and otters don't mix."

Aside from the fact that sea otter fur needs to be kept clean and fluffable or else it stops insulating them and they freeze to death, humans have unfortunately noticed how luxurious their coats are. And don't tell us about anything good unless you want it to be hunted to extinction or otherwise entirely ruined. Between the 18th and 19th centuries, the European fur trade decimated sea otter populations throughout their range.

By the early 1900s, about 50 California sea otters (Enhydra lutris nereis) — the subspecies living along the southern coast of California — remained in the wild. Thanks to the International Fur Seal Treaty of 1911, the Marine Mammal Protection Act and Endangered Species Act of the 1970s, California sea otters were able to make a partial comeback — about 3,000 live on the California coast today.

"In California, sea otters have reached carrying capacity in Monterey Bay — in other words, there is just enough food for the sea otters currently living there," says Williams. "For the population to grow, it would need to move to a new area. However, white sharks are believed to be keeping the otters from moving. In Alaska, killer whales have taken out large numbers — 90 percent of the population! — of sea otters along the Aleutian Islands. The picture is happier in the Cordova area, where sea otters seem to be booming."

Thanks to that nosedive in sea otter populations, it's easy to see that these fuzzy marine goofballs are actually extremely important to the ecology of the North Pacific seashore. For starters, their populations make for healthy kelp forests — the dense underwater jungles of tall algal strands that make coastal marine ecosystems in the North Pacific what they are. Sea otters service every part of these kelp forests; because they have to eat a quarter to a third of their body weight daily — and spend between 10 and 12 hours each day finding food — individuals within a population naturally sort themselves into specialized eating groups, or "dietary guilds," the preferences for which are passed on from mother to pup.

Which guild an otter occupies has to do with the depth at which it likes to find food. Some otters dive deep and end up nabbing things like sea urchins and Dungeness crabs off the seafloor, while others find their favorite foods at mid-range depths of about 40 feet (12 meters), collecting small shellfish and worms. A third group prefers to forage around in shallow waters for snails. In this way, a population of sea otters can really work the kelp forest at every level, helping it to stay healthy and resilient in the way only a top predator can.

One way scientists have helped sea otters make a comeback in California is by pairing orphaned otter babies with captive surrogate moms that can't be released into the wild. For the past 30 years, the Monterey Bay Aquarium has been pairing stranded babies with females in the aquarium's Sea Otter Program, and the experiment has been wildly successful — it turns out, female sea otters are more than happy to raise a baby that's not their own. Since it started in 1984, more than 700 adults and pups have moved through the Sea Otter Program.

"In our latest study we showed that surrogate-reared otters and their offspring account for over half of the population growth in Elkhorn Slough," says Kyle Van Houtan, chief scientist at the Monterey Bay Aquarium. "We're just starting to see the extensive and positive impacts associated with a growing and healthy otter population. Today, many of our state's ecologically degraded estuaries could benefit from sea otters' return. So, while we knew this was a great program and a feel-good story — now we know it's also great science."

There may come a time when you'll see more sea otters frolicking in the waves off the coast of California, but don't get too close:

"Sea otters have been nicknamed 'chainsaws in a burlap bag,'" says Williams. "They have enormously powerful jaws — perfect for cracking the shells of clams and easily breaking fingers. So, as cute as otters look, they can be unpredictable and can deliver a really nasty bite. Give them wide space in the wild."