Tool use helps sea otters survive as ocean changes and food disappears: NPR

In parts of the ocean where sea otters face stiff competition for their favorite food species, some otters get by with tools—such as rocks and even glass bottles—that allow them to break up tougher prey they wouldn’t otherwise. able to eat.

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

Findings published in journal Science, discover how this special set of 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 catch tasty morsels and sometimes rocks that they intend to use as tools. They bring them to the surface and float on their backs, using their bellies as tables as they get to work opening and consuming the snack.

“Their preferred prey is usually urchins and abalones,” says Chris Law, a biologist at the University of Texas and the University of Washington, who notes that urchins and abalones break down relatively easily for otters.

But in places where many otters live together in Monterey Bay, “unfortunately, all of these prey items are dwindling or diminishing,” Law says.

He says there are areas with an excess of urchins – so-called “hedgehogs” where the urchins have eaten all the algae. Since the kelp is gone, these urchins no longer have an adequate food supply and are therefore low in calories. They offer little nutritional value to otters who have no interest in consuming these so-called “zombie hedgehogs”.

“That means otters have to eat alternative foods,” Law says. “A lot of these alternative foods are those super-hard-shelled prey that really require some kind of external force to get into them.”

Snails, for example, are abundant in the bay, but they’re low in calories and “basically like a rock you have to hack into to eat the guts,” Law says.

While sea otters are known to use tools, not all individuals actually wield them. Some otters forego them altogether and simply specialize in eating soft prey. Some otters use tools occasionally, while others use them mostly when foraging.

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

These tagged otters are carefully monitored by volunteer “otter watchers”. This means scientists know what they are eating, how big and hard the prey is, and whether the otter used a tool to get at it.

It turns out that tool users were often able to eat harder and larger prey, according to a journal report Science. This was especially important for female otters, as they are smaller than males and are unable to bite with such force.

“Typically, they wouldn’t be able to penetrate tougher prey,” Law says. “But they use tools more than men, so they’re able to access these new food sources.”

What’s more, tool use protected the otter’s teeth. The researchers were able to obtain dental evaluations of their otters and found that tool users had less damage to their teeth due to the crunch of the hard shells.

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

He explains that some otters learn to specialize in eating hard, low-calorie snails and very often use tools to “basically become really, really, really good at processing lots and lots and lots of snails every day” instead of seeking out high-calorie food , which do not require tools to open, but are in short supply.

“This is such an important document,” says Rob Shumaker, president and CEO of the Indianapolis Zoo and one of the authors of the book titled Behavior of animal tools.

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

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