May 30, 2024


Swinging on his back in the waters of California‘s Monterey Bay, a sea otter takes a shelled animal and smashes it against a rock sitting on its chest to break open the prey.

This behavior, documented in footage from researcher Chris Law, is seen in relatively few animals and allows the otter to access food without damaging its teeth. A new study, published in the journal Science on Friday, sheds light on the endangered species’ tactics.

Researchers found that when there is a decrease in their preferred food sources, such as abalone and sea urchins, tool-using sea otters can eat larger prey such as crabs and clams and reduce tooth injuries. Most sea otters that do this are female, according to the study. That’s likely because the tools allow them to overcome a smaller body size and weaker biting ability to meet caloric requirements, said Law, a postdoctoral researcher at the University of Texas at Austin, who led the study.

Tall brown otter slides on his back on top of perfectly smooth dark blue water, lifts a rock the size of half a fist and slams it onto a larger rock balanced on his belly. The video is on auto repeat.
Otter using a rock awl to open the shell of a sea creature. Video by Chris Law.

The study looked at sea otters in Monterey Bay on California’s central coast, which is home to the southern sea otter population. The animal once occupied waters from Alaska to Baja California, until the fur trade drove them to near extinction. The US Fish and Wildlife Service has the idea of reimport sea ​​otters along the west coast. The population slowly increased due to conservation efforts in the 1970s, and there are about 3,000 in California today.

Groups such as the Center for Biological Diversity have supported sea otter recovery, citing the important role the animals can play in helping restore the region’s vital, yet depleted, kelp forests.

In central California, sea otters’ preferred prey are sea urchins and abalone, which break open easily, but those species are declining, mainly because the animals eat them, Law said. Therefore, they will more often seek out crabs, mussels and clams as well as marine snails. The hard shells of the snails can damage the otter’s teeth if they try to open them with their mouths, the study points out.

“There is fishing and habitat destruction, so their favorite prey is gone and they have to switch to alternative prey,” Law said. “What we found is that this behavior actually allows them to switch to that prey.”

The study authors and volunteers followed 196 radio-tagged otters for their research.

The sea otters primarily use rocks as hammers, but will also use shells and garbage, and sometimes, boats or docks, said Law, an evolutionary biologist who completed the research as part of his dissertation as a doctoral student at the University of California in Santa. Cruz.

The study determined for the first time that those tools helped reduce dental damage for the otters, which is essential for their survival. If an otter’s teeth develop too much damage, the animal may face starvation.

The research also found that females that used tools were able to eat prey that was up to 35% harder compared to males that used tools. It is not clear whether tool use is increasing among otters, but the behavior is beneficial for the animal.

“This behavior really allows them to eat other prey items and in a depleted environment. It really just shows how important it is to their overall survival,” Law said.

“If there are no urchins and abalone for them to eat and they are faced with other prey species that they cannot open, they cannot survive.”



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