Historically, sea otters inhabited the North Pacific Rim of the Pacific Ocean, from Hokkaido, Japan, through the Kuril Islands, Kamchatka Peninsula, Commander and Aleutian Islands, Alaska, and south along the west coast of North America down to Baja California, Mexico (Kenyon 1969). In the early 1700s, the worldwide population was estimated to be between 150,000 (Kenyon 1969) and 300,000 individuals (Johnson 1982). An estimate of the southern sea otter population along the California coast historically numbered between 13,000 and 20,000.
Local harvests by indigenous Native Americans appeared to have periodically led to reductions of sea otter populations (Simenstad et al. 1978). The species remained abundant throughout its range until the mid-1700s when Russian explorers arrived in Alaska and a pervasive commercial harvest of sea otters occurred over the next century. Sea otter pelts were highly valued throughout the world due to their thick fur which contributed to the near eradication of the species. Sea otters gained protection under the International Fur Seal Treaty in 1911. At the end of the commercial fur trade, the sea otter population was seriously depleted and believed to be extinct in large parts of the Pacific Rim. In 1911, the world-wide population of sea otters was approximately 2,000 animals that remained in 13 remnant colonies (Kenyon 1969).
Southern Sea Otter
From evidence found in the fossil record, sea otters and their ancestors have been a component of California’s ecosystem for the past five million years but by 1830 sea otters were very rare in California.
Wiped out by the Pacific maritime fur trade, sea otters were believed to be extinct from California by the early 1900s. In 1938, a small, remnant population of sea otters was “discovered” at Bixby Creek on California’s rugged Big Sur Coast. The current sea otter population descended from this small raft of about 50 animals. Since the discovery of this surviving group, the population growth and range of the population has been closely monitored.
Legal protections allowed the population to grow. The California population increased to 2,400 in 1995 before mysteriously beginning to decline. It began to grow again in 1999, and has grown in fits and starts until 2009, when the population entered another decline. Currently, the southern sea otter population is approximately 2,762 animals.
Population growth for the southern sea otter has always been slower than that of other sea otter populations such as Alaskan and Washington populations. The theoretical maximum rate of growth for sea otter populations is 17-20% a year. Other populations have averaged a rate of 9% a year. The California sea otter population increased at a rate of 4-5% a year from the early 1900s until the 1970s. (Riedman and Estes, 1990)