Sea otters, notably females, utilize tools to access their food, according to a recent study. The research found that these tool-using sea otters can consume larger prey and reduce tooth damage when their preferred food sources become scarce.
The study was conducted by researchers who followed 196 radio-tagged southern sea otters off the California coast. Their goal was to understand how this threatened species uses tools in an ever-changing environment. The research team from The University of Texas at Austin, University of California, Santa Cruz, Monterey Bay Aquarium and other institutions monitored how these marine mammals used tools such as rocks, shells and trash to break open prey. They also identified links between tool use and the animals' dietary patterns and dental health.
For the first time, researchers discovered that tool use among both male and female otters led to a reduction in tooth injuries. “Sea otters vary in how often they use tools,” said Chris Law, a postdoctoral researcher and an Early Career Provost Fellow at UT Austin who led the study while a graduate student at UC Santa Cruz. “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 tool use is an important behavior for survival.”
In coastal Central California where southern sea otters reside, some of their preferred prey like large abalone and sea urchins are not difficult to break open. However, these food resources dwindle or disappear in many areas which leads otters to more frequently prey on crabs, clams, mussels and small marine snails whose hard shells can damage the otter’s teeth while prying them open.
Tooth condition is crucial for survival because if an otter’s teeth become too worn or damaged they could starve. Using tools helps individual otters meet their calorie needs by branching out into different types of prey. The study found that female otters had less tooth damage than male otters.
The research indicates that female otters are more likely to use tools, and those that did were able to access harder or larger prey than otters that did not use tools. In fact, females were able to consume prey that were up to 35% harder compared with males that used tools.
This tool-using behavior is also observed in female dolphins, chimps and bonobos who tend to use tools more than their male counterparts, likely for similar reasons. In these species, females are usually the ones raising offspring and passing down tool-use behavior.
Southern sea otters, listed as a threatened species under the U.S. Endangered Species Act, number only about 3,000 in California where they play a critical role in marine ecosystems by preying on sea urchins that feed on kelp forests.
Rita Mehta and Tim Tinker of the University of California, Santa Cruz; Jessica Fujii, Teri Nicholson and Michelle Staedler with the Monterey Bay Aquarium; Joseph Tomoleoni of the U.S. Geological Survey; and Colleen Young of the California Department of Fish and Wildlife also contributed to this paper. Chris Law was previously a postdoctoral scholar with University of Washington.
The research was funded by the U.S. National Science Foundation, Packard Foundation, Coastal Conservancy, U.S. Fish and Wildlife Service, Pacific Gas & Electric and Bureau of Ocean Energy Management.