The Real Survivors

Supplementary article not published in the printed edition of The Scientist. Sea otters once cavorted all along the rim of the Northern Pacific, from Japan across the Arctic and down to Baja California, and their total population was estimated as high as 300,000. Today, only small populations of sea otters remain along the Pacific shorelines from central California to Alaska, and along the coasts of Russia. A member of the weasel family (Mustelidae), the sea otter (Enhydra lutris) averages about 3.5 feet in length (its tail extends as long as a foot) and weighs about 70-80 pounds. There are actually three subspecies of sea otter. In addition to the California sea otter (Enhydra lutris nereis), also known as the Southern sea otter, there are two other subspecies: Russian (Enhydra lutris lutris) and Alaskan (Enhydra lutris kenyoni). Sea otters spend most of their lives in the ocean. These furry marine mammals-who live in loose-knit groups called rafts-eat and sleep floating on their backs. They also mate and have their pups in the water. (Only on rare occasions will females come ashore to rest after mating, and an ill or injured otter may beach itself.) Rafts often sleep side by side, wrapped up in strands of kelp, to keep them from drifting too far apart. Intriguingly, males and females usually live in separate groups, with females commanding small home territories, although they and their pups may gather in large groups. Mature males tend to protect large territories, encompassing the small home regions of several females. On the outskirts of those ranges are rafts of bachelor males, too young or too old to hold their own territories. Sea otters' normal body temperature is about 100° F, while the ocean is a nippy 35° to 60° F. Their fur, the densest fur of any mammal-up to a million hairs per square inch, helps keeps them warm. In addition, they meticulously groom their fur to trap a layer of insulating air bubbles between their warm skin and the cold water. Even so, sea otters have to stay active when they're not sleeping to stay warm. Sea otters can dive as deep as 330 feet and stay under as long as five minutes. Interestingly, sea otters are one of the few known tool-using animals. They take their prey-primarily shellfish, such as oysters, clams and mussels-and place a rock on their chest to use as a sort of anvil, then break the shells to get to the meat inside. Right now, however, the California sea otter is headed back to the Endangered Species List. It won't be the first time. In fact, this species seems to have been confronting extinction for a couple of centuries now. Their pelts of fine, silky brown fur became highly desirable in the 1700s and 1800s, and they were hunted then nearly out of existence. The International Fur Seal Treaty-which only incidentally covered otters because the California sea otter was already believed to be extinct by 1900-banned all hunting of fur seals and sea otters. In 1915, however, a group of biologists found about 50 otters that had somehow survived in a remote cove in Big Sur. To protect these survivors, the scientists kept them a secret until 1938. That's when people began to see the otters as the construction of Highway 1 granted easy public access to that area of the coast. (All of today's California sea otters descend from the tiny Big Sur colony.) "Their numbers then slowly increased pretty steadily at about 5 percent a year, on average, from about 1940 to 1977," informs David A. Jessup, senior wildlife veterinarian for the California Department of Fish and Game (CDFG) and supervisor of the Marine Wildlife Veterinary Care and Research Center in Santa Cruz. In the late 1970s, however, large numbers of sea otters were getting caught in gill nets used by the fishing industry. This problem, combined with the increasing threat of a major oil spill that could cover much of their range-because of increased tanker traffic from the Alaska pipeline trade-resulted in the U.S. Fish And Wildlife Service listing them as Threatened on the Endangered Species List. "The CDFG in 1982-'83 changed fisheries management practices so activity was further offshore and pretty much out of the sea otters' range. "That allowed the population to make another comeback, increasing at about 5 or 6 percent a year until 1995," Jessup explains. Since then, however, sea otter numbers have declined from a high of just under 2,400 to about 2,000, Jessup continues. That drop is "considerable," he adds. A loss of about 200 more will put them back on the Endangered List. -A.J.S. Rayl For more information: www.montereybayaquarium.org

The Real Survivors

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