Marine Mammal Commission

Southern Sea Otter

Sea otters live in shallow coastal waters in the northern Pacific Ocean. Two sea otter subspecies occur in the United States, the southern sea otter (Enhydra lutris nereis) and the northern sea otter (E.l. kenyoni). Southern sea otters, also known as California sea otters, live in the waters along the central California coastline. Historically, sea otters numbered in the hundreds of thousands in the North Pacific Ocean. But due to the fur trade, their numbers plummeted in the early 1900s. The threat to the southern sea otter posed by oil spills prompted its listing as a threatened species in 1977.

Sea otter. (U.S. FWS)

Species Status

Before commercial hunting began in the mid-1700s, an estimated 150,000 to 300,000 sea otters occurred in coastal waters throughout the rim of the North Pacific Ocean from northern Japan to Baja California, Mexico. In 1911, hunting was prohibited under the terms of an international treaty for the protection of North Pacific fur seals and sea otters signed by the United States, Japan, Great Britain (for Canada), and Russia. By then, only a few thousand otters remained, including a small colony of about 50 otters along the remote Big Sur coast of central California. By the time the Marine Mammal Protection Act (MMPA) was enacted in 1972, the California population had grown from as few as 50 to more than 1,000 individuals (an average annual growth rate of about 5 percent) and had recolonized more than 200 miles (370 kilometers) of the California coast. Today, its range is principally along the central California coast from Monterey Bay to Point Conception.

The U.S. Fish and Wildlife Service (FWS) listed the southern sea otter population as threatened under the Endangered Species Act (ESA) in 1977 and adopted a recovery plan for the population 1982, which was updated in 2003. The recovery plan specifies that the species should be considered for delisting when the average population level over a three-year period exceeds 3,090 animals. The FWS estimated southern sea otter abundance in 2016 at 3,272 individuals, a record high since 1972. The 2017 count declined somewhat, to 3,186 otters, but still exceeded the potential delisting threshold for a second straight year. The three percent decline reflects lower numbers of otters observed along the mainland California coast, offset somewhat by continued growth of the translocated population at San Nicolas Island. The lower mainland count in 2017 could be due to poorer sighting conditions, but also might be attributable to increased mortality from shark bites and other causes such as harmful algal blooms and disease. Mortality from shark attacks of otters has been more frequent at the northern and southern extremes of population’s range and may be a factor in preventing or slowing range expansion of the population into seemingly suitable habitats.

One of the primary threats to the southern sea otter is the risk of an oil spill. To reduce the risk of a large oil spill contacting otters throughout all or much of the species’ range, the FWS in the late 1980s attempted to establish a separate population at San Nicolas Island through a translocation of otters from the parent range. The population never grew as expected and in 2012, the FWS declared the translocation a failure. The FWS determined that moving the otters that remained on San Nicolas Island would likely result in several deaths to the animals and decided to allow the otters to remain at the island. Despite the translocation having been declared a failure, the population on San Nicolas Island continues to increase. The population has grown by about 10 percent per year over the past decade and now numbers about 80 animals. Also as a result of the failure finding, there no longer is a legal obligation to try to prevent expansion of the parent population’s range south of Point Conception.

What the Commission Is Doing

The Commission continues to follow closely ongoing research into the status and trends of this population, both for the coastal “parent” population and the translocated population on San Nicolas Island. Although the FWS declared the translocation a failure, it is quite possible that otter numbers at San Nicolas will continue to grow.

The Commission also consults periodically with the FWS and marine mammal facilities to resolve questions about the placement of non-releasable otters from this population.

Most recently, the Commission commented on proposed revisions to the southern sea otter stock assessment report. The draft report identified the potential for sea otters to become trapped in gear used to catch crab, lobster, and finfish. The Commission identified a need to establish an observer program with sufficient coverage to obtain reliable information on the rate and circumstances surrounding the entrapment of sea otters in such gear. The Commission also recommended that, as a precautionary measure, gear modifications to reduce entrapment of sea otters be adopted for crab and lobster traps, similar to those that have been in place for finfish traps since 2002. In addition, the Commission noted the need to update the southern sea otter stock assessment report more frequently.

The FWS published a notice of availability of the revised stock assessment report on 28 August 2017, in which it addressed the comments submitted by the Commission and others.

Commission Reports and Publications

For more information on southern sea otters, see the Commission’s 2012 annual report.

Commission Letters

Letter Date Letter Description
March 13, 2017

Letter to FWS with comments on the 2016 draft stock assessment report for the southern sea otter

January 25, 2017

Letter to FWS regarding an Application from California Department of Fish and Wildlife-Central Region to take southern sea otters incidental to construction activities in association with a tidal marsh restoration project in Elkhorn Slough, California

August 3, 2012

Letter to FWS regarding revised stock assessment report for the Southern sea otter

Learn More


While sea otters are vulnerable to natural predators such as sharks, the population also faces risks from other factors such as disease, contaminants, availability of prey, and entanglement in commercial fishing gear. In addition, the risk of oil spills remains an ongoing concern.

Current Conservation Efforts

Current effects center on monitoring the status, trends, distribution, and causes of mortality of otters in this population. A key indicator of recovery of the population is its ability to expand its range along the California Coast. Currently, it appears that shark predation is an important factor limiting range expansion, particularly in the north end of the range.

The Future/Next Steps

Future actions to promote the conservation and recovery of the southern sea otter will depend on the results of ongoing research, particularly if needed to respond to human-caused sources of mortality. FWS, U.S. Geological Survey (USGS), and their partners are expected to continue to conduct annual abundance surveys and respond to strandings, including conducting necropsies to identify the causes of death for retrieved carcasses.

Additional Resources

U.S. FWS Southern Sea Otter Species Page

U.S. FWS Stock Assessment Report

USGS California Sea Otter Surveys and Research page

International Union for Conservation of Nature (IUCN) Sea Otter page