Skip to content

The Geographic Range of Sea Otters and The Future of Populations Along the California Coast

Blog by: Annette Lee, Development and Communications Intern 

Featured Image: Morgan Rector

Brief Overview of the Sea Otter   

Sea otters (Enhydra lutris) are a charismatic marine species that are among some of the smallest marine mammals but have a larger body size when compared to their fresh-water dwelling relatives, the river otters. Sea otters are known for their incredibly dense layer of fur, allowing for survival in cold water environments. Their success in these harsh conditions is also made possible by their large consumption of food and high metabolism. In fact, sea otters eat roughly one-fourth of their body weight every day!  

Otters play a significant role in their representative habitats, which include giant kelp forests and rocky shorelines. They are considered a keystone species which essentially means that they help maintain biodiversity. Their typical diets include a variety of invertebrates such as urchins, crabs, and abalone, which are all organisms that feed on kelp and algae. When there is an absence of otters, these grazing organisms will deplete the environment of these essential marine producers and as a result, the ecosystem becomes less biodiverse—and consequently less healthy. 

Photo by Joe Tomoleoni 

Origin of Otters and History in California 

The geographic range of sea otters has fluctuated over the last 300 years. At the largest, the range spanned the entire northern Pacific Rim from Southern California to areas of Japan. This abundant population lasted until the early 1700s when the hunting of otters for their pelts began to popularize. Russian fur traders worked their way down the western coast from  Alaska to California, and for a short period of time Russians had a permanent settlement at Fort Ross on the Sonoma Coast. This hunting pressure extinguished the sea otter population throughout most of the southern section of its historic range, from Oregon through California. 

In 1911, the Fur Seal Treaty protected the remaining sea otters from hunting, with roughly 13 colonies remaining. Sea otters were considered locally extinct in California until a small remnant population was found floating together in the Bixby Bridge area of Big Sur in 1938. During this time, many habitats which otters previously inhabited, such as kelp forests, were slowly becoming barren landscapes with dwindling biodiversity and stability. Even now, in places where sea otters have not yet made a comeback, many of California’s kelp ecosystems are at risk without a major keystone predator to maintain the balance.  

In the late 1970s, the sea otter was listed as a Threatened Species under the Endangered Species Act. In the 1980s, researchers from the US Fish and Wildlife service translocated otters from surviving Central California populations down to San Nicolas Island. Although many otters were lost during those years and quite a few swam back to their home coastline, there is currently a small persisting population out at that Channel Island.  

Photo by Morgan Rector

Southern Sea Otter Population Today  

Today the southern sea otter population remains small. Still, it ranges along the California coastline from near Point Conception in Santa Barbara County up to the Año Nuevo area of Santa Cruz County. Although wayward individual otters may be spotted above that point, no permanent populations currently exist in the San Francisco Bay area or Northern California. 

Sonoma State University professor Dr. Brent Hughes was an algae biologist researching eelgrass ecology in the Monterey Bay area during the opportune time to watch the sea otter expand its population into the Elkhorn Slough. He was able to document how quickly the eelgrass community grew and flourished as the population of otters in the estuary dramatically increased. 

Much like the dynamics at work in a kelp forest, the sea otter plays a critical role in contributing to the health of an eelgrass-dominated community. When sea otters are present in an estuary, they eat the animals that would otherwise prey on smaller animals that graze on algae. Without the predatory pressure of those consumers, herbivore populations like crabs and sea slugs can expand and keep a check on the algae that foul the health of eel grasses. An area without sea otters is heavily infested with algae. Conversely, an area with sea otters can develop into a healthy and biodiverse eelgrass community. 

Future of the southern sea otter

Sea otters were undoubtedly once in San Francisco Bay and could be again. Why haven’t they moved north from Santa Cruz County? Lack of suitable habitat? Lack of protection from white sharks? San Mateo County is, after all, the southern tip of the so-called ‘white triangle.’  

Studies like that of Dr. Hughes suggests that sea otters could find suitable habitat not only in San Francisco Bay, but also in Drakes Bay, Tomales Bay, and Bodega Bay. He has estimated that the southern sea otter population in California could triple if they expanded into San Francisco Bay alone.  

While there are a variety of factors that complicate the expansion of sea otter populations along the California coast, the future is hopeful with research like Dr. Hughes’ which works to not only gain a greater understanding of sea otter communities but also broaden our perception of their special role in ecosystems as a whole. 

Intrigued by the future of sea otters in Northern California? Tune in to our webinar to ask questions and learn more from Dr. Hughes, alongside Heather Barrett from the nonprofit Sea Otter Savvy, and Dr. Lance Morgan, president of Marine Conservation Institute. The webinar will be held on September 22 at 5 pm pacific time.  


Cannon, John C. “The Legacy of the Fur Trade.”, 

Meadows, Robin. “Sea Otters Used to Live in the Bay – Should We Bring Them Back?” Bay Area Monitor, Bay Area Monitor, 1 June 2020, 

“Natural History.” Center for Biological Diversity, 

Nystrom, Siera. “Celebrate a Conservation Success Story during Sea Otter Awareness Week!” Celebrate A Conservation Success Story During Sea Otter Awareness Week!, Blogger, 2 Oct. 2017, 

Oregon History Project, 

“Sea Otter Natural History.”, 

“We Were Here.” Sea Otter Savvy,