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Southern sea otter

The southern sea otter (Entydra lutris nereis) is found in shallow waters along the coast of central and southern California from Half Moon Bay to Point Conception [1]. A century ago otters were abundant, but by 1914 hunting by fur traders had reduced the population to only 50 animals [1]. Passage of the International Fur Seal Treaty in 1911 protected remaining sea otters from further hunting, but their distribution had become highly fragmented [2].

As a result this protection, the southern sea otter population increased to 1,789 animals by 1976 [1]. The sea southern sea otter was placed on the endangered species list in 1977 and in 1982, a standardized method to survey sea otters was developed and put into use in 1982 [3]. Southern sea otter numbers declined between 1976 and 1984, increased through 1996, and then experienced a decline until 1999 [1, 4]. Since then numbers have resumed a slow increase reaching the highest levels seen in a hundred years in 2004 and 2005 [1, 4].

The reasons for the periodic declines are not well understood and appear to be associated with altered age-specific mortality rates [2]. In addition, while recent increases are encouraging, the increases have been mainly in the number of male otters and it is unclear what this means for the recovery of the southern sea otter population [2] The otters still face threats from disease and parasites, possibly linked to coastal pollution that can weaken otter immune systems and an oil spill could be devastating to the population [2]. Many programs, however, are working to rescue and rehabilitate the otters and to better understand what can be done to help the species recover.

[1] USFWS. 2003. Final Revised Recovery Plan for the Southern Sea Otter (Enhydra lutris nereis). U.S. Fish and Wildlife Service, Portland, Oregon. Xi+pp.
[2] U.S. Geological Survey. 2004. Sea Otter Studies Fact Sheet. Available at <http://www.werc.usgs.gov/otters/pdfs/seaotter.pdf>.
[3] U.S. Geological Survey. Southern Sea Otter Surveys. <http://www.werc.usgs.gov/otters/ca-surveys.html>.
[4] USGS. 2005. Spring counts of southern sea otters, 1983-2005. U.S. Geological Survey, Western Ecological Research Center. Available at < www.werc.usgs.gov/otters/ca-surveydata.html>.

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