A MOTHER'S LOVE MAKES A DIFFERENCE
Sea otter life isn't always about splashing in the waves and lounging in the kelp.
“These animals are so much like us,” said Teri Nicholson, a research biologist at the Monterey Bay Aquarium. ”They're just out there trying to find a safe home, make a living, raise their kids.”
But storms and rough sea conditions make it hard to forage, groom and rest, especially for otter moms with pups that can't do much on their own yet. Sometimes moms and pups get separated. And pups under eight weeks old have little chance of surviving on their own.
Since 2001, the Monterey Bay Aquarium has rescued stranded otter babies — more than half of them under two weeks old — and rehabilitated them through their otter surrogacy program. Instead of “hand rearing,” or raising the pups themselves, the humans pair a pup with a surrogate mom, then back off and let the otter mom teach the pup the ropes of otter life. Once the pup is weaned from the mom, has medical clearance and can dive, forage, groom and be social on their own, the team gives them a shot at returning to the wild.
Jessica Fujii, the aquarium's sea otter program manager, said the group is the only sea otter rescue facility that actively runs a surrogacy program. “We're the ones that developed it and started testing it,” she said.
The team recently evaluated two decades of work and reported that the program is working — 75 percent of pups reacclimate to the wild — in a paper published March 9 in the journal Biological Conservation. According to the study, any pup that goes through the program has a strong chance of success in the wild, regardless of the mom they're paired with or their individual development. But environmental conditions at release time can impact the pup's success — poor conditions may lead to a failed release. The results will help the team to improve releases and to expand the surrogacy program, which could be a key part of reestablishing southern sea otter populations along California's northern coast.
“Surrogacy kind of trumps it all,” said Nicholson, the lead author of the study. “But we do have to be careful about when and where we release these animals. And by focusing more on that, now we can actually build on the success that we already have.”
Leaving the nest
When someone reports a stranded otter pup, the Monterey Bay Aquarium, California Department of Fish and Wildlife and the Marine Mammal Center all coordinate to investigate. They attempt to reunite pups with their mothers whenever possible, but it happens less than 10 percent of the time. If the team can't find a mom, they transport the pup to the aquarium.
Pups over nine weeks old tend to do OK on their own and are released as soon as they're healthy. The younger ones get paired up with a surrogate mom — a female otter that's non-releasable because of medical issues or other factors preventing their success in the wild. The aquarium has had about 10 surrogate moms over the past two decades.
The team releases otters that have completed the surrogacy program at sites in Elkhorn Slough, Monterey Bay or Morro Bay, then
monitors them closely for the first two weeks, observing them from land, from boats and even from the air if needed. They watch how far released otters swim, make sure they're foraging and look for weight loss or injuries from interactions with other otters.
If an otter makes it two weeks and is stable, the release is considered successful. “After that point in time, they have comparable survival and eventually reproductive rates as the wild population,” said Nicholson.
But sometimes the transition is hard on the little juveniles. They go “from a small rehabilitation pool to the big ocean where they've probably really not seen a harbor seal before or a sea lion or, you know, all these other species and weather,” said Nicholson. “So it's a big shock I think, those first couple weeks.”
If the juvenile disappears, dies, restrands or is recaptured in poor health, the release is considered to be a failure. But they get another chance, or even two or three more chances.
“The peak in success is generally between the second and the third release and then by the fourth, you're kind of done,” said Nicholson. “By the fourth release, you're handling them too much and they're also getting kind of desensitized. …You really want them to go out on their first time and be fine.”
Using machine learning
Nicholson and her team wanted to know what factors most impacted the success or failure of release so they could fine-tune the program.
“What we were really trying to do with this study was to look more closely at the specific components of the program, so that we can kind of understand what we could modify as we move forward to really improve success, especially if we're trying to kind of increase our capacity and potentially expand the program and develop it as a potential recovery strategy for sea otter populations,” said Nicholson.
They used Random Forest, a machine learning algorithm, to sort out data from 115 releases — some successes, some failures — of 64 otters over the past 20 years. They looked at 34 different parameters: factors from the program itself — like the pup's origin, age at first successful foraging dive, surrogate mom and weaning age — as well as factors at release — like the location, month, sea and wind conditions, and information about local otter populations.
The results showed that environmental conditions, like sea conditions, weather and having some local otters around (but not too many) had the most impact on success — a single poor condition could cause failure.
But Nicholson emphasized the results also showed that any pup who makes it through the surrogacy program to the point of release has a good chance at success.
“The most important factor is kind of reestablishing that natural motherpup bond, because it's likely the key actually to the pups' long-term survival,” said Nicholson. “It's like that crucial relationship kind of reinforces the pup's social identity, creates a strong foundation for them to learn life skills from wild otters after release.”
“It's a pretty impressive analysis,” said Tim Tinker, an adjunct professor at UC Santa Cruz who studies sea otter populations and was not involved in the study. “There are some actionable conclusions,” he said, like choosing a good geographical location and timing the release right.
Surrogacy as a conservation tactic
Releasing sea otters back into the wild can serve multiple purposes. One is to give these wild animals another chance at life. Another is to potentially establish new populations or deepen the genetic pool in areas where otter populations are small or stagnant.
Sea otters are recognized as a keystone species with critical roles in marine ecosystems. But fur traders drove them to the brink of extinction from the 1700s to the 1900s. The international Fur Seal Treaty of 1911 protected the species and they have rebounded in some areas along the Pacific coast — especially in Alaska which has over 90,000 otters. But otters are still listed as a threatened species. Fewer than 3,000 live along California's coast.
In 2020, the U.S. Fish and Wildlife Service performed a feasibility study for reestablishing sea otters on the Pacific Coast of the contiguous United States, specifically in northern California and Oregon. They determined that it is feasible and noted surrogacy programs as a potential option for establishing populations in those places.
The report, published in 2022, did not recommend whether or not reintroductions should take place — officials are still conducting socioeconomic studies and hosting public meetings to consider, among other things, the impacts reintroductions would have on shellfish fisheries, a concern for many in the area.
But the report did recommend pilot studies and small-scale experimental reintroductions of surrogate-reared pups to see if it's a viable option for establishing new populations. Pups from the Monterey Bay Aquarium's surrogacy program could potentially be released along the coast in areas that were historically part of their range. And the results from this study would help researchers to pinpoint good release sites and ensure the conditions are just right for success.
Tinker said the new study also builds on previous work showing that it's better to release pups in areas that have some otters, but not too many. He said the insight into social context deserves further study as scientists consider “taking these results on the road” and introducing otters to new areas.
“It does raise questions about, what if you're releasing them to an area where it's open habitat but there are no otters at all, where it doesn't have the necessary social context that pups can fit into like they did at Elkhorn Slough or at Monterey or Morro Bay?” he said.
As a broader impact, the study could also help researchers to select optimal sites for another way to establish new population: translocations — moving wild otters from one place to another.
“I think that this informs more than just the right conditions for the surrogate animals,” said Shawn Larson, who is the curator of conservation research at the Seattle Aquarium and co-editor of the book Sea Otter Conservation and was also not involved in the study. “I think that that this information will help inform the best environmental conditions for even wild translocated animals.”
The study may also help to establish additional surrogacy programs. According to the Monterey Bay Aquarium, the Aquarium of the Pacific in Long Beach, joined the surrogacy program in 2020 and is establishing their own facility and program. This study could help guide their expansion.
For now, Nicholson hopes the study will bolster the program's message of conservation and stewardship of our environment.
“This is all happening right in our backyard,” said Nicholson. “aren't foreign to us. They're our neighbors. We share this Peninsula with them.”