California is home to two distinct types of otters: the Southern Sea Otter, thriving in the Pacific Ocean, and the North American River Otter, inhabiting inland freshwater ecosystems. Both species are members of the weasel family (Mustelidae) but are adapted to dramatically different environments. The marine species occupies a limited stretch of the central coast, while the freshwater species is widely distributed across the state’s river systems and wetlands.
Southern Sea Otters Marine Habitats
The Southern Sea Otter (Enhydra lutris nereis) is an iconic marine mammal found in California’s near-shore coastal waters. This subspecies inhabits the shallow continental shelf, strongly associated with kelp forest and rocky habitats. Their primary range extends along the central California coastline, roughly from San Mateo County down to Santa Barbara County, including a separate population at San Nicolas Island.
Sea otters lack insulating blubber, relying instead on the densest fur in the animal kingdom. To maintain their high body temperature, they must consume 20 to 30 percent of their body weight daily. Their diet consists mainly of bottom-dwelling invertebrates like sea urchins, crabs, clams, and snails. This foraging behavior is important to the kelp forest ecosystem, as the otters act as a keystone species by controlling sea urchin populations.
North American River Otters Inland Habitats
The North American River Otter (Lontra canadensis) is adapted to freshwater and estuarine environments. These otters are smaller than their marine relatives, typically weighing between 11 and 31 pounds, and are found across a broader geographic area. Their habitat includes rivers, streams, lakes, wetlands, and the brackish water of estuaries.
River otters are present in the North Coast river drainages, the Sacramento-San Joaquin Delta, and the aquatic habitats of the Klamath, Cascade, and Sierra Nevada Ranges. They are highly versatile, spending about 70 percent of their time on land and establishing dens in burrows, hollow logs, or under river banks. Their diet focuses on aquatic organisms, including fish, crayfish, amphibians, and occasionally small turtles and birds. Populations in the San Francisco Bay Area have shown recovery and are actively expanding their range.
Current Population Status and Conservation
Both otter populations faced near-extinction due to the extensive fur trade between the 18th and early 20th centuries. The Southern Sea Otter population was decimated, surviving only as a remnant group of about 50 individuals near Big Sur. Following protection under the Endangered Species Act in 1977, their numbers have slowly recovered, but the population has fluctuated around 3,000 individuals. This slow recovery is partly due to increased shark attacks and the susceptibility of the narrow coastal population to oil spills and disease.
The North American River Otter was also severely impacted by historical trapping, which was banned in California in 1961. Their population is considered stable or recovering and is not listed as threatened or endangered at the federal level. However, river otters remain sensitive to environmental changes and face ongoing threats from habitat loss, watershed development, and water pollution. Conservation efforts for both species focus on mitigating human-caused mortality, such as entanglement in fishing gear and vehicle strikes, and protecting their aquatic habitats.