New study shares intimate details of sea otter surrogacy, confirms its effectiveness in rehabilitating orphaned pups

The Monterey Bay Aquarium provides information on best practices for releasing orphaned sea otter pups into the wild in a new study. The study confirms the effectiveness of the Aquarium’s innovative sea otter breeding methods and finds that the main factors affecting individual sea otters’ abilities to reacclimate to the wild occurred after release.

Published today in the magazine Biological Conservationthe paper, “Advancing Surrogate-rearing Methods to Enhance Southern Sea Otter Recovery,” examines the Aquarium’s surrogate-rearing recovery and release program and identifies key components that contribute most to a sea otter’s release success.

The Monterey Bay Aquarium developed and pioneered the sea otter surrogacy program, which pairs young orphaned otters with non-releasable adult female otters who bond and care for the pups as their own. Aquarium researchers began the study to optimize the program’s methods and contribute to the recovery of this endangered species.

“These findings describe the daily life-threatening challenges faced by sea otter pups and help us identify the optimal conditions for returning orphaned otters to the wild, where they can benefit population and ecosystem recovery,” said lead author Teri Nicholson, Senior Research Biologist for Monterey. Bay Aquarium’s Sea Otter Program. “Due to the strong foraging behavior of our surrogate females, three-quarters of the orphaned pups in our program are re-acclimated to the wild after release. What we learn from this study will increase that success.”

Nicholson and her colleagues examined 20 years of surrogate rearing methods for 64 sea otter hatchlings that washed ashore along the California coast and then were released as juveniles. The team tracked 34 key elements of restoration and release to determine which modifications would do the most to improve successful outcomes in the wild. These results will inform decisions about when and where sea otters can be released within the species’ historic range to maximize their chances of survival.

“By sharing more details about the sea otters in our program and our shared challenges, we hope to inspire stronger connections to these wildlife populations and stewardship of our shared ocean environment,” Nicholson said.

This study also provides the basis for expanding the surrogacy program to other aquariums, including the Aquarium of the Pacific in Long Beach, California. The Aquarium of the Pacific joined the surrogacy program in 2020 and has built a specialized area for mating stranded sea otter with surrogate mothers.

The study highlights the following key findings:

• Surrogacy derives from the natural behavior and adaptability of sea otters, resulting in a 75% success rate in reacclimating orphans to the wild, regardless of their age, origin, early development, temperaments of the surrogate mother, weaning age and pre-release preparation.
• Release conditions—such as favorable seas and mild weather—represented the strongest drivers of model success.
• Low daily swimming distances by released individuals and less competitive local population dynamics were additional factors contributing to success.
• Comparable success rates among a variety of sites and habitats, such as estuarine seagrass meadows and openshore kelp forests, demonstrate the potential for broader application of these methods throughout California where release conditions are favorable.

The results of this study may also have broader applications for the recovery of other endangered and threatened species and provide a blueprint for nature-based solutions that enhance ecosystem resilience in the face of increasing impacts from climate change.

“Our surrogacy program is effective and the results of this study build our confidence that we will be able to increase the number of animals we can return to the wild through key partnerships,” said Jess Fujii, Monterey Bay Sea Otter Program Director Aquarium. “The study also provides valuable information about when and where we can release rescued otters with the best chance of success.”