JWM: To keep sea otters safe, stay away

While some people may find it fun to watch sea otters climb up their kayaks, keeping their distance will better help the population to thrive.

“In California, people and sea otters like the same places to live,” said Heather Barrett, a sea otter biologist and science communications director for Sea Otter Savvy, a research nonprofit that focuses on sea otter conservation, specifically human-sea otter conflicts, such as disturbance. But while people love sea otters, “there’s a cost of cute,” she continued.

On coastlines in California, like Monterey Bay, plenty of different-sized boats come into close proximity to wildlife, including protected species of concern, like the southern sea otter (Enhydra lutris nereis). Barrett and her colleagues wondered what the energetic cost was for sea otters responding to disturbances from vessels that got too close. And how do you define too close?

Sea otters spend most of their time at sea but haul out sometimes to keep warm. They also blow warm air into their fur every time they groom to maintain their insulation. “They basically create an air suit in their fur,” she said.

To maintain a high body temperature, they also burn through calories quickly—sea otters have the highest metabolic rate relative to their size of any marine mammal. They rest a lot to conserve their energy, but they wake up hungry. “Because of the fact that they’re burning through so many calories, they have a voracious appetite,” she said. “They eat over a quarter of their body weight every day.”

Barrett led a study published in the Journal of Wildlife Management as part of her master’s thesis looking at how their human disturbances affected their ability to perform some of these important activities.

To conduct the study, Barrett and her colleagues took a hands-off approach. With help from Sea Otter Savvy community scientists, the team observed southern sea otters at three sites along the coast of California, including Monterey, Moss Landing and Morro Bay, for five years, watching how close vessels got to the animals. They also noted whether the sea otters became active or stayed inactive in response to vessels.

Then, the researchers ran a model to determine at what distances most otters were disturbed as well as how different sizes of boats affected them. They also looked at differences in responses for adult males, females and females with large pups, and then coupled those results with previously recorded sea otter metabolic rates to calculate energetic costs.

In Monterey, overall human disturbance increased sea otters’ energetic costs by 7.2% for adult males and 5.4% for females with or without pups. The Moss Landing site saw 5.8% for males, 4.4% for females and 4.3% for females with pups. Finally, Moro Bay saw energetic costs increase by 5.2%, 4% and 3.9%, respectively.

Barrett said it’s important to note that male values can appear higher as males are larger animals. What’s more, for females with large pups, the values don’t take into account that they live at a 66% higher cost than the energetic baseline of females with no pups. When considering this, the team further calculated the proportional daily increase of a female with a large pup relative to the female with no pup. They estimated an increase of 8.8% in additional energetic costs for a female with a large pup at Cannery Row in Monterey. Additional costs like these can have physical impacts on reproductive females, such as lower body condition and overall health.

The team found that on average, the likelihood of a group of sea otters becoming disturbed was less than 10% when small crafts were more than 100 feet—or eight kayak lengths—away. They started showing evidence of becoming active at 60 feet away. This type of disturbance interferes with the otters’ ability to rest and conserve energy they need for activities like nursing and finding food for pups.

Barrett acknowledged a limitation in her study. For example, if an otter became alert but not active, the team counted that as inactive, which Barrett said could be an area for future study. “Alert is technically an inactive behavior, but that could still have a really big stress response,” Barrett said.

She said it’s not always realistic to give otters wide berth, especially in waterways like rivers or estuaries. “At some places in California, it’s physically impossible to stay 100 feet away,” she said. “We’re dealing with reality and waterways that may be only 80 feet wide.” As a result, Barrett stressed remaining vigilant of sea otters’ behavior and adjusting where your boat is going if you sense disturbance. She recommended following Sea Otter Savvy’s guidelines of staying over five kayak lengths away.

Overall, Barrett said she wants tourists to be excited about sea otters, but distance matters. “Are you capable of respecting them more than you love them?” she asked.

This article features research that was published in a TWS peer-reviewed journal. Individual online access to all TWS journal articles is a benefit of membership.  Join TWS now to read the latest in wildlife research.