The State of California's Sea Otters

Southern sea otter
Southern sea otter in Monterey County. Photo by Dr. Lloyd Glenn Ingles © California Academy of Sciences.

Adorable sea otter souvenirs—sweatshirts, posters, plush toys—abound in central and Northern California. There’s even an otter on the bag of coffee beans in my kitchen. They’re local icons, and with a face like that, it’s easy to see why. But sea otters themselves are not so plentiful. In honor of Sea Otter Awareness Week at the end of September, I’m taking a closer look at what’s behind that furry façade.

Most southern sea otters (Enhydra lutris nereis) live along the 150 miles of coastline between Santa Cruz and Pismo Beach, and are federally classified as threatened. They are considered a keystone species in kelp ecosystems like those in Monterey Bay because they prey on invertebrates like urchins, which, left unchecked, could decimate the kelp beds many fish depend on for habitat. However, not all otters eat the same thing.

Sea otter skull
Otters that specialize in purple sea urchins accumulate purple pigment in their teeth and bones over time, as seen here. The older the animal, the more pronounced the color. Photo by Lovell and Libby Langstroth © California Academy of Sciences.

At San Nicolas Island in southern California, where a small population of otters was reintroduced in the late 1980s, otter diets are very consistent across individuals. But among central California sea otters, where the population is denser and food is scarcer, otters tend to specialize in a particular food source like snails, crabs, or purple urchins. One of the questions ecologists hope to answer, now that they understand this differentiation, is whether there is a link between specialized diets and infectious disease.

The U.S. Geological Survey just issued its spring census report, which shows that the population of southern sea otters has increased about two percent since 2010, reaching 2,792. For a species that was presumed extinct in California until a group of less than fifty was rediscovered in the 1930s, this is certainly progress. But their population growth seems to have reached a plateau, and the contributing factors are a complex puzzle.

While the otter population did increase slightly, so did the mortality rate. In 2011, scientists documented a record high of 335 stranded sea otters, and made an effort to examine each one to determine what led to their injuries or deaths. One of the most surprising findings was that “tasting” bites from sharks accounted for 30 percent of sea otter deaths, up from 8 percent in the 1980s and ‘90s. Other otters, ironically, perish while mating. (Male otters are very aggressive, and have been known to inflict fatal wounds or drown their mates in the throes of passion.) Additional causes of death seen year over year, including infectious diseases, parasites and harmful algae blooms, can be attributed to human activity.


Availability of food ultimately dictates how large a population can grow in one area, and there is growing evidence that the central coast population is reaching a point of saturation. If the otters were to spread out into new territory, that pressure could be reduced, but scientists have not observed that happening as of yet. In order to be “delisted” as threatened, the southern sea otter population would need to exceed 3,090 for three consecutive years.

Data about local sea otter populations doesn’t collect itself. Scientists and volunteers use shore-based spotting scopes and aircraft to conduct annual surveys. And organizations including the California Academy of Sciences, Marine Mammal Center, Monterey Bay Aquarium, and U.S. Geological Survey coordinate to respond to reports of stranded or dead marine mammals, collecting data and samples that will help them answer critical questions now and for decades to come.

If you are curious to learn more about these fascinating creatures’ behaviors, check out some of the local activities planned in celebration of Sea Otter Awareness Week:

September 22 – 30
Sea otter specimens and family-friendly activities at the California Academy of Sciences

The California Academy of Sciences is home to the world’s largest collection of skulls, skeletons, and other preserved samples of the southern sea otter. Throughout the week, stop by the Project Lab to see select specimens on display, and check out sea otter-themed resources and games in the Naturalist Center and Early Explorers Cove. Finally, view sea otter skulls being prepared in the Project Lab and talk to biologists at a special sea otter table during NightLife on September 27 (6:00-10:00 pm for ages 21+).

Sunday, September 23, from 9:00 am – 4:30 pm
Sea Otter Awareness Kayak and Movie at Elkhorn Slough

Kick off Sea Otter Awareness Week face to face with the otters of Elkhorn Slough. Start with a kayak tour from Kirby Park to Moss Landing, followed by lunch, Q&A, and a special screening of the film Otter 501.

Thursday, September 27 at 7pm
Free sea otter talks at Long Marine Lab’s Seymour Center in Santa Cruz

Topics include If I Only Had A Hammer: Tool Use by Sea Otters, and The Land Sea Connection: What Southern Sea Otters Can Tell Us about Coastal Health.

Visit the national calendar of events for the 10th Annual Sea Otter Awareness Week for more.