Sea otters have inhabited the northern coasts of the Pacific Ocean since the Pleistocene, about 1 to 3 million years ago.  The historical range of the sea otter extended from central Baja California northward along the coast of North America to Alaska, westward through the Aleutian, Pribilof, and Commander islands to the coast of Kamchatka, Russia, and south through the Kuril Islands to southern Sakhalin Island, Russia, and northern Japan.  In the mid-1700s, between 100,000 and 300,000 sea otters lived along the North Pacific coast

In 1741, Vitus Bering and his expedition sailed from Russia to explore and map the coastlines of the North Pacific.  Also on board the ship was the naturalist Georg Steller, who studied and documented the flora and fauna, including the sea otter, which was encountered in the Aleutian and Commander islands.  The first scientific description of the sea otter was later published in 1751 in Steller’s book De Bestiis Marinis (The Beasts of the Sea).

Intensive commercial exploitation of sea otters began with their discovery by Bering’s expedition and continued through the early 1900s.  Historically, Native Americans along the Pacific coast hunted sea otters, but the abundant numbers encountered by the early Russian hunters indicate that sea otters were not widely overhunted before contact with Europeans.  Between 1741 and 1900, Russian and American fur traders harvested the sea otter almost to extinction in order to profit from its luxurious fur.  Sea otter fur is extraordinarily dense, providing excellent insulation to sea otters in cold ocean waters and to humans in their fine fur coats.  Sea otter fur has up to 1 million hairs per square inch, more than any other mammal, and is considered some of the finest fur in the world.

By the early 1900s commercial harvest had essentially ceased, for the simple reason that it was difficult to locate a sea otter.  Their numbers had been reduced to 13 tiny remnant colonies, scattered across their former range and totaling no more than a few hundred sea otters each.  In 1911, the International Fur Seal Treaty was signed by the U.S., Russia, Great Britain, and Japan, halting commercial hunting of sea otters.  Once commercial harvest ceased, sea otter numbers rebounded and they re-colonized much of their former range between Prince William Sound, Alaska, and west to the Kuril Islands, Russia.  However, by the 1950s they had disappeared from the Pacific coast from Prince William Sound south to Baja California, with the exception of one remnant population in California.

During the 1960s and 1970s, the Alaska Department of Fish and Game reintroduced sea otters into former habitat in Alaska, Canada, Washington and Oregon in collaboration with other State and Provincial wildlife management agencies.  In 1987, otters were reintroduced to San Nicholas Island in southern California.  Due to these efforts, sea otter numbers in southeast Alaska, British Columbia and Washington are currently stable or increasing, and sea otter range has expanded correspondingly.

Human activity, especially coastal development and marine pollution, is one of the most significant threats to sea otters.  A striking example is the Exxon Valdez oil spill.  The oil tanker Exxon Valdez struck Bligh Reef on March 24, 1989, spilling 11 tons of crude oil into Prince William Sound, Alaska.  Over the next two months, the oil spread to the southwest along the coast, fouling beaches and marine waters as far as 500 miles from the source of the spill.

According to surveys conducted by the U.S. Fish and Wildlife Service, the spill killed approximately 3,905 sea otters (range 1,904-11,257).  At present, abundance of sea otters in some oiled areas of Prince William Sound remains below pre-spill estimates, and evidence from ongoing studies suggests that sea otters and the nearshore ecosystem have not fully recovered from the spill.  For more information on the Exxon Valdez oil spill and its effect on sea otters, see Sea Otter Reports.

Recent precipitous declines in sea otter numbers in southwest Alaska, from Kodiak Island through the western Aleutian Islands, constitute the most significant conservation issue for northern sea otters since commercial fur trades.  Once containing more than half of the world’s sea otters, this population segment has undergone an overall population decline of at least 55–67 percent since the mid-1980s.  In some areas within southwest Alaska, the population has declined by over 90 percent during this time period.  The cause of the overall decline is not known with certainty, but the weight of evidence points to increased predation by the killer whale (Orcinus orca), as the most likely cause.  In 2005, the U.S. Fish and Wildlife Service listed this distinct population segment as Threatened under the Endangered Species Act.

Other recent human threats to sea otters include contamination from pollutants such as heavy metals or PCBs; pollutants from log transfer sites and harbors; disturbance from recreational and industrial activity; entanglement in fishing equipment, such as set nets or gill nets; competition from commercial fishing for food; and fish offal dumped into marine waters by seafood processing plants.