Otter-preneurs: Female sea otters lead the way in tool use for survival


In California’s Monterey Bay, where the vast Pacific Ocean meets lush kelp forests, sea otters, especially the females, are becoming more resourceful. These charismatic marine mammals, known for their playful nature and voracious appetites, are facing new challenges and using tools to overcome them.

For generations, southern sea otters (Enhydra lutris nereis) have relied on the abundant urchins and abalone that populate the kelp forests as their primary food sources. These preferred prey items are relatively easy for otters to crack open and provide a rich source of nutrients. However, as the pressures of climate change, overfishing and other environmental factors have taken their toll, these once-plentiful food sources have begun to dwindle.

A sea otter uses rock anvil to feed on a sea animal. Image courtesy of Monterey Bay Aquarium
A sea otter uses rock anvil to feed on a sea animal. Image courtesy of Monterey Bay Aquarium

Faced with this new reality, some sea otters have turned to alternative prey items, such as hard-shelled snails, clams and mussels. While these creatures are abundant, they present a unique challenge for the otters. Their tough exteriors require a significant amount of force to break open, making them difficult for otters to access without the help of tools.

Enter the innovative southern sea otters. Armed with rocks, shells and even trash and discarded glass bottles, these otters have developed a remarkable set of skills. By using these tools as hammers and anvils, they can crack open even the most stubborn of shells, accessing the nutritious meat inside.

For a new study published in the journal Science, researchers followed 196 tagged sea otters over several years. With the help of dedicated volunteer “otter spotters,” the researchers tracked the feeding habits, tool use and overall health of these individuals.

Otters that frequently used tools could consume prey up to 35% harder than what non-tool users could access. This was particularly true for female otters, who are smaller than their male counterparts and have a weaker bite force.

“Female otters are likely using tools to overcome their smaller body size and weaker biting ability in order to meet their calorie demands,” said Chris Law, a postdoctoral researcher at University of Texas, Austin, who led the study while a graduate student at the University of California, Santa Cruz.

“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,” he added. Female bonobos, chimps and dolphins also use tools more than the males of their respective species, likely for similar reasons.

The benefits of tool use extended beyond just accessing harder prey. The researchers also found that tool users had significantly less tooth damage than non-tool users. By using tools to crack open shells, otters can avoid the wear and tear on their teeth that comes from constantly biting down on hard surfaces.

This is crucial for the long-term health and survival of sea otters. “Without their teeth, they clearly can’t eat anything. So then they die,” Law told NPR. “What we’re suggesting is that this behavior really allowed them to continue living on despite not having their preferred prey.”

A southern sea otter uses a rock anvil to feed on a clam. Image courtesy of Monterey Bay Aquarium.
A southern sea otter uses a rock anvil to feed on a clam. Image courtesy of Monterey Bay Aquarium.

The study also revealed the remarkable adaptability of some otters, which have become specialized snail eaters. These individuals use tools frequently to process large quantities of these low-calorie foods. While snails may not provide the same nutritional value as urchins or abalone, they are abundant and can sustain otters in areas where the preferred prey is scarce.

“This is such an important paper,” Rob Shumaker, president and CEO of Indianapolis Zoo and co-author of Animal Tool Behavior, who was not involved in the study, told local media. This study represents a shift in the field of animal tool use research, he said: Rather than simply describing the use of tools by animals, scientists are now focusing on the broader ecological and evolutionary implications of this behavior.

As a threatened species under the Endangered Species Act, southern sea otters number only around 3,000 individuals in California. They play a crucial role in maintaining the balance of coastal ecosystems by preying on sea urchins, which, if left unchecked, can decimate kelp forests. Kelp forests, in turn, provide habitat for numerous marine species and help to sequester carbon dioxide from the atmosphere, mitigating some of the impacts of climate change.

Researchers say understanding how sea otters adapt to changing environmental conditions can better inform conservation efforts and management strategies. The insights gained from this study highlight the importance of behavioral flexibility in the face of ecological challenges and underscore the need to protect not just the animals themselves but also the habitats and resources they depend on.

Liz Kimbrough is a staff writer for Mongabay and holds a Ph.D. in ecology and evolutionary biology from Tulane University, where she studied the microbiomes of trees.

Citation:

Law, C. J., Tinker, M. T., Fujii, J. A., Nicholson, T., Staedler, M., Tomoleoni, J. A., … Mehta, R. S. (2024). Tool use increases mechanical foraging success and tooth health in southern sea otters (Enhydra lutris nereis). Science, 384(6697), 798-802. doi:10.1126/science.adj6608

This article by Liz Kimbrough was first published by Mongabay.com on 24 May 2024. Lead Image: Southern sea otter feeding on sea animal. Photo courtesy of Chris Law.

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