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Floating on his back in the waters of CaliforniaIn Monterey Bay, a sea otter takes a shelled animal and strikes it against a rock resting on its chest to break open the prey.
This behavior, documented in footage by researcher Chris Lowe, is seen in relatively few animals and allows the otter to access food without damaging its teeth. A new study, to be published in the journal Science on Friday, sheds light on the endangered species’ tactics.
The researchers found that when there was a decline in their preferred food sources, such as snails and sea urchins, tool-using sea otters were able to consume 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 smaller body size and a weaker biting ability to meet caloric needs, said Lowe, a postdoctoral fellow at the University of Texas at Austin who led the study.
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 inhabited waters from Alaska to Baja California until the fur trade drove them to near extinction. The US Fish and Wildlife Service has explored the idea of re-entry sea otters along the west coast. The population slowly increased due to conservation efforts in the 1970s, and today there are about 3,000 in California.
Groups such as the Center for Biological Diversity have supported the restoration of sea otters, citing the important role the animals could play in helping to restore the region’s important, yet decimated kelp forests.
In central California, sea otters’ preferred prey are sea urchins and snails, which are easy to open, but those species are declining, mainly because the animals eat them, Lo said. Because of this, they will more often seek out crabs, clams and mussels, as well as sea snails. The hard shells of the snails can damage the otters’ teeth if they try to open them with their mouths, the study said.
“There’s fishing and habitat destruction, so their favorite prey is gone and they have to switch to alternative prey,” Lo said. “What we found is that this behavior actually allows them to move on to that prey.”
The study authors and volunteers tracked 196 otters that were fitted with radio tags for their study.
Sea otters primarily use rocks as hammers, but will also use shells and trash, and sometimes boats or docks, said Lowe, an evolutionary biologist who completed the study as part of his doctoral dissertation at UC Santa Cruz.
The study found for the first time that these tools helped reduce damage to the otters’ teeth, which is essential for their survival. If the otter’s teeth become too damaged, the animal can starve to death.
The research also found that women who used tools were able to consume prey that was up to 35% harder than men who used tools. It is unclear whether tool use is increasing among otters, but the behavior is beneficial to the animal.
“This behavior does allow them to eat other prey items and in an environment where that is depleted. It really just goes to show how important it is to their overall survival,” Lo said.
“If there are no hedgehogs and snails to eat, and they’re faced with other prey species that they can’t open, they can’t survive.”
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