Resourceful sea otters use rocks to reach food

Image: Jessica Fujii, Monterey Bay Aquarium

Hungry sea otters regularly use rocks to break open hard shells before eating the contents, a new study has found.

Sea otters are one of the few animals that use rocks and other objects like shells and debris to access their food. Researchers from University of California Santa Cruz (UCSC), the University of Texas at Austin and Monterey Bay Aquarium found that individual sea otters that use tools - most of which are female - can eat larger prey and reduce tooth damage when their favourite food becomes depleted.

In the southern sea otter’s range of coastal central California, prey like large abalone and sea urchins are not difficult to break open. However, these sources dwindle or disappear over time as a result of sea otter predation, leading the marine mammals to broaden their diets to include crabs, clams, mussels and snails - all with hard shells that can damage their teeth as they pry them open.

When an otter’s teeth become too worn or damaged, they could starve. The study found using tools helped otters to meet their calorie needs by reaching valuable food, while reducing the risk of breaking teeth.

"The study shows that, for some animals, tool use is an important behaviour for survival.”

Chris Law, UC Santa Cruz
Image: Anchor Lee, Unsplash

Biologist Chris Law, who led the research at UCSC, said, “Sea otters vary in how often they use tools.

“The females are likely using tools to overcome their smaller body size and weaker biting ability in order to meet their calorie demands. Raising pups takes a lot of energy, and the females need to be efficient in their foraging.

"The study shows that, for some animals, tool use is an important behaviour for survival.”

Law and his team's volunteer otter spotters followed 196 radio-tagged southern sea otters off the coast of California to better understand how the threatened species uses tools in a rapidly changing environment.

Listed as a threatened species under the US Endangered Species Act, southern sea otters number only about 3,000 in California, where they play a critical role in marine ecosystems preying on sea urchins that feed on kelp forests. They have been shown to have positive effects on estuary habitats.