Marine Mammal Commission

Southern Sea Otter

Sea otters live in shallow coastal waters off the northern Pacific Ocean. Two separate sea otter subspecies occur in the United States, the Southern sea otter and the Northern sea otter. 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.

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 U.S 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 U.S. FWS declared the translocation a failure. The U.S. 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 slowly and now numbers more than 60 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 U.S. 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 U.S. FWS and marine mammal facilities to resolve questions about the placement of non-releasable otters from this population.

Commission Reports and Publications

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

Commission Letters

Letter Date Letter Description
December 1, 2014

Letter to U.S. FWS regarding a research permit

October 6, 2014

Letter to U.S. FWS regarding an incidental harassment authorization

October 28, 2013

Letter to U.S. FWS regarding a research permit on Southern sea otters

September 5, 2013

Letter to U.S. FWS regarding a research permit renewal and amendment on Southern sea otters

September 3, 2013

Letter to U.S. FSW regarding a research permit renewal and amendment on sea otters in California

February 19, 2013

Letter to U.S. FWS regarding a research permit renewal and amendment on samples of sea otters

August 30, 2012

Letter to U.S. FWS regarding a research permit on sea otters

August 3, 2012

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

July 24, 2012

Letter to U.S. FWS requesting a research permit amendment on sea otters

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 one 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. U.S. 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

More from the U.S. FWS on Southern Sea Otters

U.S. FWS Stock Assessment Report

USGS California Sea Otter Surveys and Research page

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