Sea otter fur is the densest of all mammalian fur. This, plus its softness and lustre, makes sea otter pelts the most valuable of any mammal. If the animal's hair becomes soiled, such as by oil, the insulating properties are destroyed; if the cold water of this aquatic animal's habitat reaches its skin, the otter could perish of hypothermia.

For its fur the sea otter was hunted almost to extinction during the late 1800s and early 1900s. Its former range - from northern Asia, around the top of the Pacific Ocean and down the North American coast to southern California - was reduced to a few remnant populations and about 1 000 individuals.

Recent transplants from the California are have re-established the species along parts of the Pacific coast where it has been completely wiped out, including the coast of British Columbia. The Asian populations have not recovered to the same extent as the North American populations.