84 Marine Mammals, Extinctions of otters for pelts began soon after In California the harvest was pursued by hunters from Russia, often utilizing enslaved Aleut hunters, and from Spain, Mexico, and the US All commercial hunts for sea otters were terminated with approval of the Treaty for the Preservation and Protection of Fur Seals (37 Stat 1542, T.S No 542) by Japan, Russia, Great Britain (on behalf of Canada), and the US The Treaty was proclaimed in 1911 and ratified in 1912 Article V of the Treaty afforded protection to sea otters from further hunting Protection of sea otters from hunting in US waters was extended by Presidential Proclamation in 1913 by US President Wilson, and by Executive Order in 1929 by President Coolidge The State of California enacted regulations to prohibit hunting of sea otters in 1913 However, in California and Mexico the sea otter populations had been depleted commercially by the 1860s By 1900 only two small populations survived One was along the Big Sur coast south of the Monterey Peninsula, numbering approximately 50–100 animals The second, of unknown size off the Islas San Benitos, Mexico, was extinct by the 1920s The Big Sur population grew at a rate of approximately 5% per year through much of the twentieth century and now numbers approximately 2800 animals, ranging from near Half Moon Bay in San Mateo County southward to the vicinity of Cojo Anchorage in Santa Barbara County The observed rate of growth in California is currently approximately 3% per year, much lower than rates commonly observed in more northerly populations with protection from harvest and available adjacent vacant habitat In the late 1980s a new colony was established by translocation at San Nicolas Island (SNI) off southern California The SNI colony now numbers approximately 50 animals, shows consistent local pup production, and is growing slowly in number, fostering increasing optimism for long-term persistence, Reeves et al (2002) to the contrary notwithstanding The California sea otter population is listed as ‘‘threatened’’ as per ESA and is designated ‘‘endangered’’ by RLTS Several risk factors are known for sea otters in California Near-shore set-net fisheries were responsible for significant rates of incidental take in the late twentieth century Changes in fishery regulations have reduced but not eliminated incidental take Sea otters are known to compete with near-shore marine shellfish fisheries in California, particularly for abalones, sea urchins, clams, and crabs Concern about interactions of sea otters and shellfisheries is significant, often leading to controversy among scientists, managers, and stakeholders There is long-standing concern about illegal killing of sea otters to protect shellfisheries, but little solid evidence of a significant problem Since the 1980s shark attack has been recognized as a significant source of sea otter mortality, particularly in the northern portion of the current range, where great white sharks are relatively common In the recent decades new concerns have emerged regarding a range of diseases and parasitic infestations that may be highly significant sources of sea otter mortality In some cases, diseases may have been introduced to sea otters by way of anthropogenic infrastructure such as domestic sewage outfalls, whereas others may have dispersed naturally from terrestrial mammal populations Increased occurrence of exotic intestinal parasites from unknown sources, particularly a species of acanthocephalan not previously known in sea otters, has been associated with significant rates of fatal peritonitis in the population The California sea otter population is also regarded to be at high risk of potential damage from oil spills, associated with significant tankship traffic and marine petroleum development, both implemented and proposed, in coastal marine habitats either occupied or suitable for occupation by sea otters Oiling mats the pelage and eliminates the thermoregulatory function of sea otters, leading rapidly to chilling and death Oiling is also known to cause other pathologies The Exxon Valdez oil spill of 1989 in Prince William Sound and adjacent waters, Alaska, killed hundreds of sea otters and provided extensive opportunities for detailed insights into pathologies resulting from oiling of animals The event validated concerns about potential population-scale damage to sea otter populations wherever they overlap in space with marine petroleum extraction, transportation, or processing activities A clear consensus on the cause or causes of relatively low growth rates of the California sea otter population has not emerged Primary risk factors are thought to be ongoing incidental taking in fishing nets, effects of contaminants, mortalities from diseases and exotic parasites, and shark attacks There is a perception that sea otters in California are more susceptible to disease impacts as compared with other sea otter populations The long-term survival of the sea otter population in California will likely require ongoing research to more effectively characterize current risk factors, and the development of strategies to minimize associated mortalities The large and growing human population in California is a major underlying cause of the jeopardy status of sea otters, and broad popular support, including economic compromise by shellfishery and marine oil interests, likely will be required if recovery is to be successful Northern Sea Otter: E Lutris Kenyoni Wilson, 1991 The original geographic range of the northern sea otter extended from Attu Island, at the western extreme of the Aleutian Archipelago, Alaska, eastward and southward along the coasts of Alaska, British Columbia, Washington, and Oregon Sea otters currently dwelling in waters off Washington, British Columbia, and southeastern Alaska are descended from animals reintroduced in the 1960s and 1970s Source populations in all cases were northern sea otters moved from either Amchitka Island or Prince William Sound As noted in Section ‘‘California Sea Otter: E lutris nereis (Merriam, 1904)’’, largescale commercial hunting of sea otters for pelts began in 1741 It is estimated that between 500,000 and 900,000 northern sea otter pelts were taken during the commercial harvest period When legal hunting ended in 1911, the number of surviving northern sea otters was probably between 1000 and 2000 individuals, scattered among seven isolated remnant populations from the Queen Charlotte Islands, Canada, to the Rat Island group of the Aleutian Archipelago The Queen Charlotte population was extinct by 1920 The northern sea otter has been subject to ongoing subsistence harvest by native peoples for meat and pelts, probably for many centuries Populations from Prince William Sound westward largely recovered from effects of the fur harvest period without assistance, other than prohibition of harvest, during the twentieth century Observed annual population growth rates were as high as 10–15% in some cases The translocation projects