When sea otters lose their favorite foods, they can use tools to search for new foods

A sea otter in Monterey Bay with a rock anvil on its belly and a scallop in its front legs.

Jessica Fujii


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Jessica Fujii


A sea otter in Monterey Bay with a rock anvil on its belly and a scallop in its front legs.

Jessica Fujii

In parts of the ocean where sea otters face fierce competition for their favorite types of food, some otters survive by using tools – such as rocks and even glass bottles – that allow them to smash open tougher prey that they otherwise wouldn’t have. can eat.

That’s according to a new study of sea otters in Monterey Bay, California, which looked at the tool use of individual otters to see how it affected their health and nutrition.

The findings, published in the journal Science, reveal how these special skills can increase their chances of survival in an uncertain world.

Sea otters are large marine mammals that spend their days foraging in kelp forests. They dive to the bottom to grab tasty morsels, and sometimes stones to use as tools. They bring these to the surface and float on their backs, using their bellies as a table as they get to work opening and eating their snacks.

A female sea otter floats in Monterey Bay, off the coast of California, with an anvil-like stone on her belly that she will use to help open the mussel she is holding in her forelimbs.

Jessica Fujii


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Jessica Fujii


A female sea otter floats in Monterey Bay, off the coast of California, with an anvil-like stone on her belly that she will use to help open the mussel she is holding in her forelimbs.

Jessica Fujii

“Their favorite prey tends to be sea urchins and abalone,” says Chris Law, a biologist at the University of Texas and the University of Washington, who notes that otters and sea urchins can break up with relative ease.

But in places where otters coexist in Monterey Bay, “all those prey species have unfortunately declined or even declined,” Law says.

He says there are areas with an abundance of sea urchins – so-called ‘urchin barrens’, where the sea urchins have eaten all the kelp. However, because the kelp has disappeared, these sea urchins no longer have a good food supply and are therefore low in calories. They provide little nutritional value to otters, who are not interested in consuming these so-called ‘zombie urchins’.

“So that means that otters have to eat alternative foods,” says Law. “A lot of those alternative foods are super-hard-shelled prey that really require some kind of external force to break in.”

Snails, for example, are plentiful in the bay, but they are low in calories and “basically look like a rock that you have to break into to eat the inside,” says Law.

Although sea otters are known for using tools, not all individuals actually wield them. Some otters forgo them completely and simply specialize in eating soft prey. Some otters use tools occasionally, while others use them mostly while foraging for food.

“We were interested in this variation in tool use,” says Law, so he and some colleagues analyzed data on 196 otters in California.

These tagged otters are closely monitored by volunteer ‘otter spotters’. This means that researchers know what they eat, how big and hard the prey is and whether the otter used a tool to eat it.

It turns out that frequent tool users were able to eat harder and larger prey, according to a report in the journal Science. This was especially important for female otters, as they are smaller than males and cannot bite with as much force.

“Normally they wouldn’t be able to break into tougher prey,” says Law. “But they use more resources than men, so they can access these new sources of food products.”

In addition, the use of tools protected the otters’ teeth. The researchers were able to obtain dental assessments from their otters and found that tool users suffered less tooth damage from grinding on hard shells.

“Without their teeth, they obviously can’t eat anything. So then they die. What we’re suggesting is that this behavior really allowed them to continue living despite not having their favorite prey,” says Law.

He explains that some otters learn to specialize in eating hard, low-calorie snails, using tools very often to “basically become very, very, very good at processing a lot of snails in a day,” rather than to look for snails with a high calorie content. high-calorie foods that require no tools to open but are in short supply.

“This is such an important article,” said Rob Shumaker, president and CEO of the Indianapolis Zoo and one of the authors of a book called Animal tool behavior.

He says scientists have spent decades documenting tool use in dozens of species; For example, tool use in sea otters has been recognized since the 1960s. But now studies like this show that this field of research is starting to shift.

“It’s no longer about describing actual tool use or tool production,” says Shumaker. “It describes the impact it has on that animal’s life.”

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