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Sea otters in Elkhorn Slough


Our Surrogate-Raised Sea Otters are Helping to Restore a Wetland



Surprising new research has revealed that the transformation of Elkhorn Slough from a sludgy marsh into a thriving habitat is due largely to sea otters raised as pups in our Sea Otter Program. Those rescued pups and their offspring now make up the majority of sea otters in the slough, where these ecosystem engineers have helped restore this vital wetland.

Our Sea Otter Program rescues stranded pups, eventually introducing them to one of our non-releasable exhibit sea otters, which serve as surrogate mothers behind the scenes. They teach pups the skills they need to survive in the wild, like grooming and foraging. When the pup is ready, our biologists release it into Elkhorn Slough—California's largest tract of tidal salt marsh outside San Francisco Bay.

Aquarium scientists diligently track these surrogate-reared animals for years, collecting data on how long they live and how many offspring they have. What they've learned is encouraging.

"These young animals survive as well as wild-reared otters, and they retain their wariness of people," says Animal Care Coordinator Karl Mayer. "Even better, the females mature, give birth and raise pups."

By 2016, we asked a very important question: Has the Aquarium's sea otter surrogacy program made a significant contribution to the slough's otter population?

The answer: A resounding yes. Almost 60% of the 140 or so sea otters living in Elkhorn Slough today are there as a result of our sea otter surrogacy program.

Considering the southern sea otter population as a whole—which, according to the latest figures, is about 3,200—the release of a few animals each year from our program doesn't make a big difference. But this new research shows it can have a huge impact on local and regional populations, like the otter population in Elkhorn Slough.

In kelp forests, sea otters are well-known keystone predators. They keep sea urchin populations in check, which allows kelp to flourish and provides rich habitat for a host of other species.

The slough's food web is a little more complex than in the kelp forests. Otters eat crabs, which otherwise eat invertebrate grazers that clean algae off seagrass and allow it to thrive. Large, healthy seagrass beds offer essential habitat for numerous fish and invertebrate species.

In the years since the Aquarium began releasing otters into Elkhorn Slough, the seagrass beds in the slough have rapidly expanded—evidence of the power of sea otters to restore wetland ecosystems.

We're now exploring the potential benefits of surrogate-reared otter releases in other areas that were part of the otters' historical range before the fur trade decimated their population.

Our Sea Otter Program is only possible because of donations we receive from our members and donors—thank you for supporting this critical work! To learn more, check out our Conservation and Science blog.