Marine Mammal Commission

Northern Sea Otter

Sea otters live in shallow coastal waters off the northern Pacific. In the U.S., there are two distinct sea otter subspecies, the Northern sea otter and the Southern (or California) sea otter. Northern sea otters live in the waters off southcoastal Alaska, British Columbia, and Washington State.

Sea otters

Sea otters. Photo taken under U.S. FWS permit #MA-043219. (Ryan Wolt)

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. The survivors were scattered among small colonies in remote areas of Russia, Alaska, British Columbia, and central California.

Since the prohibition on commercial hunting in 1911, sea otters have recolonized or have been reintroduced into much of their historic range. By the time the Marine Mammal Protection Act (MMPA) was enacted in 1972, remnant groups in Alaska had grown considerably and, in the late 1960s and early 1970s, several hundred otters were moved from Amchitka Island and Prince William Sound to try to reestablish populations in southeast Alaska and the outer coasts of Washington and Oregon. Since the 1980s, most northern sea otter populations have continued to recover. Populations in south-central and southeast Alaska continue to grow or have stabilized. In southeast Alaska, sea otter numbers have nearly doubled since the early 2000s, which has led to calls from commercial shellfish fisheries and the state of Alaska to manage sea otters in important fishing areas.

In Alaska there are three stocks of northern sea otters—the Southwest stock, the Southcentral stock, and the Southeast stock. The Southwest stock, which includes otters in the Aleutian Archipelago, the Alaska Peninsula, and Kodiak Island, is listed as threatened under the Endangered Species Act (ESA). The Southcentral and Southeast Alaska stocks continue to grow or have stabilized and are not listed under the ESA. All three stocks in Alaska are protected under the MMPA.

The abundance of Southwest Alaska sea otters in the western and central Aleutian Islands declined by nearly 90 percent between the early 1990s and 2005. A less precipitous decline occurred over that same period in the eastern Aleutian Islands. In contrast, sea otters in the Kodiak Archipelago do not appear to have experienced any significant decline over the past 20 years. One theory for the observed population declines is an increase in predation by killer whales. Other theories suggest that the observed declines are attributable to oceanographic changes or fisheries effects. The U.S. Fish and Wildlife Service (FWS) listed the Southwest Alaska stock as threatened in 2005 and designated critical habitat for the population in 2009. That designation includes waters out to either 100 meters from shore or out to the 20 fathom isobaths in most areas within the population’s range. FWS finalized a recovery plan for the Southwest Alaska sea otter in 2013.

In contrast to the Southwest Alaska stock, the numbers of otters in the Southcentral and Southeast Alaska stocks have increased or stabilized despite thousands of sea otters from the Southcentral Alaska stock having died in Prince William Sound as a result of the 1989 Exxon Valdez oil spill. Rebuilding the population took about 25 years. The U.S. Geological Survey (USGS) published a 2014 report concluding that the population had recovered to pre-spill levels. Population levels in the Southcentral stock have now stabilized and are estimated to be around 15,000 animals.

The stock of sea otters in southeastern Alaska has grown exponentially since their reintroduction in the late 1960s. This growth, coupled with concern that sea otters are competing with commercial fisheries for sea urchins, sea cucumbers, crabs, and clams has led to calls from Alaska State officials and some fisheries groups for a cull of the population. Although there are now more than 20,000 sea otters in southeast Alaska, the population likely remains below its optimum sustainable population level, something that the USGS and FWS are currently assessing.

What the Commission Is Doing

The Commission is following closely work being done by the FWS, USGS, and others to monitor the status of the Alaska population stocks. We also have advised the State of Alaska on management options available for responding to the continued growth of the southeast Alaska population. The Commission expects to review updated stock assessment reports for the three northern sea otter stocks in 2018.

Commission Reports and Publications

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

Commission Letters

Letter Date Letter Description
June 13, 2016

Letter to FWS regarding an incidental take authorization for oil and gas activities in Cook Inlet

September 29, 2014

Letter to FWS regarding an incidental take authorization for oil and gas activities in Cook Inlet

July 17, 2013

Letter to FWS regarding a draft stock assessment report for three stocks of Northern sea otters in Alaska

May 17, 2013

Letter to FWS regarding request for comments on the interpretation of specific terms as they pertain to Alaska natives’ taking of sea otters

Learn More

Threats

Northern sea otters face a variety of threats throughout their range. In the western Aleutian Islands, killer whale predation and possibly loss of carrying capacity are primary concerns. Elsewhere in Alaska, competition with commercial shellfish fisheries, entanglement in commercial fishing gear, oil spills, disease outbreaks, contaminants, and subsistence harvests are the primary threats.

Current Conservation Efforts

Ongoing conservation efforts are directed at monitoring changes in abundance and distribution of northern sea otters and trying to ascertain the causes of declines in southwestern Alaska.

The Future/Next Steps

Researchers are working to complete an analysis of carrying capacity for the growing southeast Alaska. The results of this study are expected to inform a determination of the stock’s status relative to its optimum sustainable population level, which in turn will dictate what management options might be available under the MMPA. Future actions to conserve the threatened southwest Alaska sea otter population will depend on the results of planned abundance surveys and additional research into the cause or causes of observed declines.

Additional Resources

U.S. FWS Northern Sea Otter species page

U.S. FWS Stock Assessment Reports – Sea Otters

U.S. FWS Sea Otter management

USGS Nearshore Marine Ecosystem Research Program

Alaska Department of Fish and Game Northern Sea Otter species page

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