Kachemak Bay otters’ behavior seems unaffected by oyster farms

The growing Kachemak Bay mariculture industry and a booming population of local sea otters appear to have a surprisingly uneventful relationship, according to a new University of Alaska ��ˮ����Ƶ study.

The study,, focused on otters around a handful of oyster farms in the area, comparing their actions to otters that were foraging in nearby control areas without farming. During hundreds of hours of observations, otters weren’t seen eating any oysters, and the presence of mariculture operations didn’t appear to have a notable effect on their behavior.

“Broadly speaking, we really found no significant differences,” said Emily Reynolds, the lead author of the study. “They’re doing the same thing whether there’s a farm there or not.”

That result was unexpected, said Reynolds, who conducted the research as a graduate student at UAF’s College of Fisheries and Ocean Sciences. Kachemak Bay has an estimated population of about 6,000 sea otters — more than 6 per square kilometer — who consume as much as a quarter of their body weight in prey each day. The growth of oyster farming in recent decades seemed to provide a rich new ecosystem for foraging.

Reynolds spent the summers of 2022 and 2023 observing otters through a high-powered scope. She noted which foods they consumed and how much time they spent foraging, resting, grooming, and conducting other activities.

Oyster farm infrastructure can potentially offer shelter for sea otters and can support a diverse population of their prey. Otters were seen eating a number of clams, mussels and crabs around both farms and nearby control areas. Their diet didn’t appear to include oysters, which aren’t native to Kachemak Bay. 

The way otters spent their time was similar around oyster farms and in nearby control areas, even though the farms could be more productive areas for finding prey.

Those findings come amid a sometimes-tense relationship between area residents and local otters, said Brenda Konar, a UAF professor of marine biology who contributed to the study.

“Some people really like them because they’re cute and don’t think they do much harm,” she said. “Other people think otters eat everything that people want to eat and are really destructive.”

The results of the study come with a few caveats, Reynolds said. About 40% of prey couldn’t be identified, so the occasional consumption of oysters can’t be entirely ruled out. The cages used for growing oysters are also difficult for otters to access, which could be a key reason they weren’t noted in the survey.

One otter behavior observed in mariculture areas may serve as both a benefit and a potential concern. Otters were seen eating mussels off ropes and buoys, which could pose a challenge to mussel cultivation but help reduce the accumulation of pests on equipment, known as biofouling.

“Biofouling is an incredible nuisance,” Reynolds said. “That would be a benefit to the farm workers, because it’s difficult to keep gear clean.”

ADDITIONAL CONTACTS: Emily Reynolds, ereynolds4@alaska.edu; Brenda Konar, bhkonar@alaska.edu

021-26