Sea otter conservation began in the early 20th century, when the sea otter was nearly extinct due to large-scale commercial hunting. The sea otter was once abundant in a wide arc across the North Pacific ocean, from northern Japan to Alaska to Mexico. By 1911, hunting for the animal's luxurious fur had reduced the sea otter population to fewer than 2000 individuals in the most remote and inaccessible parts of its range. The IUCN lists the sea otter as an endangered species. Threats to sea otters include oil spills, and a major spill can rapidly kill thousands of the animals. During the 20th century, sea otter populations recovered from remnant populations in the far east of Russia, western Alaska, and California. Beginning in the 1960s, efforts to translocate sea otters to previously populated areas were also successful in restoring sea otters to other parts of the west coast of North America. Populations in some areas are now thriving, and the recovery of the sea otter is considered one of the greatest successes in marine conservation. In three important parts of its range, however, sea otter populations have recently declined or have plateaued at depressed levels. In the Aleutian Islands, a massive and unexpected disappearance of sea otters has occurred since the 1980s. The cause of the decline is not known, although the observed pattern of disappearances is consistent with a rise in orca predation. In Russia, the sea otter population has declined precipitously, with illegal poaching suspected as a possible cause. In the 1990s, California's sea otter population stopped growing for reasons that are probably different from the difficulties facing Alaska's otters. A high prevalence of infectious disease in juveniles and adults has been found to cause many sea otter deaths. A parasite, which is often fatal to sea otters, is carried in the feces of wild and domestic cats. Oil spills are also threatening to sea otters, both for the toxins released into the water and potential for hypothermia resulting from a degradation of the insulating layer of the otters' fur.
Background
The sea otter (Enhydra lutris) is a marine mammal living near the shores of the North Pacific, from northern Japan, the Kuril Islands and Kamchatka east across the Aleutian Islands and along the North American coast to Mexico. It has the thickest fur in the animal kingdom. Between 1741 and 1911, a period of extensive hunting for sea otter pelts, known as "the Great Hunt", brought the world population to 1,000 – 2,000 individuals in a fraction of the species' historic range. Since then, most commercial hunting of the species has been banned, although a limited amount of hunting by indigenous peoples has been permitted. The sea otter preys mostly upon invertebrates such as sea urchins, diverse mollusks and crustaceans, and some species of fish. In most of its range, it is a keystone species, with a stabilizing effect on its local ecosystem that is disproportionate to its size and abundance. Sea otters control sea urchin populations which, left unchecked, can destroy kelp forests and harm the species relying on these ecosystems. Because of the sea otter's crucial ecological role, as well as the animal's aesthetic and cultural value, particular efforts have been made to protect the species and to expand its range. Conservation of the sea otter is complicated by the fact that some of its preferred prey species, such as some species of abalone, crabs, and clams, are also eaten by humans. Because of the species' reputation for depleting shellfish resources, advocates for commercial, recreational, and subsistence shellfish harvesting have often opposed allowing the sea otter's range to increase, and there have even been instances of fishermen and others illegally killing them. The sea otter's range is currently discontinuous. It is absent from about a third of its former range, including all of Oregon and northern California, and it has only recently begun to reappear in Mexico and northern Japan. Sea otters can do well in captivity, and are featured in over 40 public aquaria and zoos. The southern sea otter (E. l. nereis), whose range historically spanned from Baja, California up to the shorelines of Oregon and Washington, now only occurs from Southern California to just north of Half Moon Bay, California. What was historically a vast population now numbers just over 3000 as of 2006 census. The largest extant population of sea otters can be found in the waters surrounding Alaska. While population numbers of the northern sea otter (E. l. kenyoni) located in this region have still declined, the population hasn't been affected nearly as drastically as southern sea otters.
Conservation issues Research conducted by the U.S. Geological Survey suggests that food availability is the major determinant in sea otter population growth. The IUCN describes the significant threats to sea otters as oil pollution, predation by orcas, poaching, and conflicts with fisheries. Sea otters can drown if entangled in fishing gear. They can also be stressed by well-meaning human watchers who approach too closely. The most significant threat to sea otters is oil spills. Unlike most other marine mammals, sea otters have very little subcutaneous fat. Otters rely primarily on their fur to be clean, dense, and water resistant in order to be insulted from the cold. When their fur is soaked with oil, it loses its ability to retain air, which can lead to hypothermia. The liver, kidneys, and lungs of sea otters also become damaged after they inhale oil or ingest it when grooming. The small geographic ranges of the sea otter populations in California, Washington, and British Columbia mean that a single major spill could be catastrophic for that state or province. Prevention of oil spills, and preparation for the rescue of otters in the event one occurs, are major areas of focus for conservation efforts. Increasing the size and the range of sea otter populations will also mitigate the species-level effects of catastrophic oil spills. Sea otters must maintain a high level of internal heat production in order to compensate for a lack of blubber. Because of this, sea otters need to consume food equal to 25% of their body mass every day to satisfy their high energetic requirements. Consequently, depending on the habitat, reproductive status, and per capita prey presence, hunting for food can cost sea otters between 20 and 50% of the day foraging.
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