Tracking the Return of Sea Otters to Southeast Alaska

The Southeast Alaska stock of northern sea otters (Enhydra lutris kenyoni) ranges from Cape Yakataga in the north to the Dixon Entrance in the south. A U.S. Geological Survey fact sheet explains how scientists have followed the population's recovery.

Northern sea otter stock regions — southwest, southcentral and southeast — within the 100-meter depth contour, as managed by the U.S. Fish and Wildlife Service in Alaska. Map: U.S. Geological Survey.

Gone, then brought back

During the maritime fur trade, sea otters in southeast Alaska were hunted for their pelts to near extinction, and they were not expected to return on their own. While they were absent, their prey — clams, sea urchins, crabs and others — grew larger and more plentiful, setting the stage for rapid growth if otters came back.

A sea otter nursing her small pup. Photo: Nicole LaRoche, U.S. Geological Survey.

From 1965 to 1969, the Alaska Department of Fish and Game and the U.S. Atomic Energy Commission reintroduced 413 sea otters, taken from Amchitka Island and Prince William Sound, to seven sites along southeast Alaska's outer coast.

The Southeast Alaska stock region, with sea otters' estimated 2022 occupancy probability and the reintroduction sites. Map: U.S. Geological Survey, adapted from Schuette and others (2023).

Counting otters

Since then, surveys by boat and aircraft have tracked the otters' numbers and spreading range:

• Early surveys (1975–1994) gave minimum counts or rough estimates, because no one knew how many otters were missed — for example, while diving.
• Recent surveys (2002–2022) added extra search effort to estimate the share of otters not seen, making abundance estimates more accurate.
• Since 1993, the USGS and National Park Service have regularly surveyed Glacier Bay from the air; the results suggest about one-third of all sea otters in southeast Alaska may live in the bay.

Statistical methods for turning survey counts into population estimates have steadily improved, so re-analyzing historical data can give different answers depending on methods and data. Many older estimates used a single year of data; newer methods can use many or all years. A 2023 study used all aerial survey data through 2022 and the latest methods to give an updated picture of how the population has changed since reintroduction.

Estimated sea otter abundance in Southeast Alaska: current estimates (small black circles) and earlier published estimates (large grey circles), with the estimated carrying capacity and its credible interval from the 2019 and 2023 studies. Chart: U.S. Geological Survey, adapted from Schuette and others (2023).

Next steps

Ongoing and planned research aims to:

• improve statistical models, including using harvest data directly and adding boat and, eventually, drone survey data;
• bring in biological data on the predator-prey relationship between shellfish and sea otters to improve estimates and monitoring;
• adapt monitoring to more frequent local surveys by coastal communities, agency and academic partners, and Alaska Native Tribes;
• find faster ways to update abundance estimates as those local surveys come in.

Sources

• U.S. Geological Survey, Alaska Science Center: "Understanding sea otter population change in southeast Alaska," Fact Sheet 2024–3007.
• Studies it cites include Kenyon (1969); Burris and McKnight (1973); Jameson and others (1982); Williams and others (2017, 2019); Tinker and others (2019); Lu and others (2020); Eisaguirre and others (2021, 2023); and Schuette and others (2023). The map, chart and photograph are reproduced from the fact sheet.