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Modern efforts in sea otter conservation began in the early 19th 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. 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.〔VanBlaricom, p. 53〕 In two 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 in recent decades. The cause of the decline is not known, although the observed pattern of disappearances is consistent with a rise in orca predation. Sea otters give live birth. 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, however it is not known why California sea otters would be more vulnerable to disease than populations elsewhere. Other threats to sea otters are well-known. In particular, sea otters are highly vulnerable to oil spills, and a major spill can rapidly kill thousands of the animals. The IUCN lists the sea otter as an endangered species. ==Background== (詳細は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. Specifically, sea otters control sea urchin populations, which would otherwise inflict extensive damage to the kelp forest ecosystems that provide crucial habitat and food for other marine organisms and help contain coastal erosion. 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. However, 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.〔Nickerson, pp. 47-48〕 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. 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.〔VanBlaricom p. 69〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sea otter conservation」の詳細全文を読む スポンサード リンク
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