by A new study has found that sea otters on the West Coast are using tools to exploit richer prey and gain a leg up on the competition.
In Monterey Bay, their favorite prey has become scarce due to an incredible rebound in water dog populations — and it has pushed them to pursue tougher options, according to findings published Thursday in Science.
“Historically, [otters] they preferred sea pole and sea pole – prey items that do not require tools to break open,” said lead author Chris Law, a researcher at the University of Texas at Austin.
“But those populations have declined dramatically. And a lot of it has to do with the otters eating them all.”
That reduction is beneficial to coastal ecosystems. Seaweeds are voracious consumers of kelp, undersea algae “forests” that serve a similar function in the sea to tree-based forests on land.
Otters are “extremely efficient predators, eating three times more per pound of body mass than a typical mammal of their size,” said ecologist and co-author Tim Tinker of the University of California, Santa Cruz.
By eating their favorite marine algae that graze on kelp and coastal marshes, otters helped facilitate the recovery of both ecosystems, according to findings published in Nature in January.
That’s the result of a major conservation success, Tinker noted. To survive in the cold waters of the North Pacific, sea otters have the densest coats of any mammal: up to a million hairs per square inch, which is fifty times more than chinchilla hair – or a thousand times more than human hair .
This dense fur fueled a two-century commercial hunting spree in which traps killed hundreds of thousands of otters—creating corporate giants like the Hudson’s Bay Company and eventually driving the otter population in Central California down to a remote colony of 50 individuals.
As scientists now understand, otters are a “keystone species,” meaning they influence ecosystems far beyond what their numbers would normally suggest. Their decline over the past century triggered an “escapade” when the hungry sea heron, freed from its main predator, ate through kelp forests.
As a result, the coastal ecosystem “went through a phase change from kelp forests to deforested seagrass beds,” a 2009 paper found. As the kelp forests disappeared, the number of mussels declined. and the guineas that were feeding filters, as were the populations of fish such as greens. The bald eagle switched from a balanced diet to one consisting of seabirds such as gulls; gulls, in turn, changed from eating fish to eating invertebrates.
Sea otters swim near shore at Elkhorn Slough in Moss Landing, California on April 12, 2018. Marine biologists from the Monterey Bay Aquarium noted that rehabilitating and releasing sea otters into Elkhorn Slough helped restore eelgrass beds and the ecosystem . (Photo by Paul Chinn/The San Francisco Chronicle via Getty Images)
Verge of extinction
In 1911, with otters on the verge of extinction, Congress banned the fur trade, and by the time it passed the Marine Mammal Protection Act in 1972, the local population was back to 1,000.
Now they are closer to 3,000 – putting them somewhere close to “balance” with their local prey resources, Tinker said.
Their increasingly specialized diets – an exclusive focus on snails or clams – “and an increase in tool use are some of the interesting types of behavior associated with this process” of recovery, Tinker said.
The tools involved are, in human terms, very simple: rocks, glass bottles, shells or the sides of boats or docks.
But these make an excellent anvil on which a hungry otter can open a clam (rare but highly nutritious) or a sea snail (low in calories, but very common) and extract the tasty meat inside.
These tools allowed the emerging otter populations to do something little reported during the years when the otter had a bounty of sea urchins they could eat: specialize in hard-shelled molluscs.
No one knows if this specialization – or tool use – is really new to sea otters. “Their tools don’t really fossilize,” Law said. “So in terms of when their tools first appeared – no idea.”
“It would be really cool to find out,” he said.
The sea otter split from its freshwater relatives about 5 million years ago — about as far back as humans split from the other great apes.
Nor is it clear whether it is a new option to specialize on a particular prey — as sea otters now do. The last time sea otters were this high was during the height of the fur trade, and there was no modern study of marine ecology.
In other words, no one has ever seen Monterey Bay alive when it was close to its carrying capacity for otters — at least, until now.
One thing, however, is clear from the research: whether it’s a new behavior or not, an aquatic dog’s ability to exploit new resources can mean the difference between life and death as competition increases for their -favorite resources.
Female sea otters are prone to tool use
That’s especially true for female sea otters — which scientists have found to be particularly prone to tool use.
“Females have a weaker biting ability, so they are not able to open harder or larger prey items,” Law said.
Using tools “really allows them to access these larger, harder prey items that they might not be able to access otherwise by sticking alone.”
That’s important because sea otter women are the ones who have to carry, nurse and raise the next generation.
This is a long and energetically demanding process that only comes to an end when the cubs have learned to forage for themselves – which often includes adopting whatever tool-use strategy their mother uses.
“Anything that increases feeding efficiency will help these otters survive as well as raise pups until they’re ready to leave,” Law said.
This gender difference in tool use is not unique to otters. Female chimpanzees, chimps and dolphins tend to use tools more often than their male counterparts.
Sea otters are seen together along the Elkhorn Slough in Moss Landing, California on March 26, 2018. (AP Photo/Eric Risberg)
By using tools, female otters were able to break open prey that was twice as hard as they would otherwise be able to break, the researchers found.
For males, tool use does not necessarily open up new resources: their hard jaws can unaidedly break open snails or clams.
But it saves their teeth. Both male and female water dogs caused less tooth damage when they used rocks, boats or bottles as anvils to open their clams or crabs – which meant fewer cracked teeth and ultimately a longer life.
This adds otters to a “growing list of exemplar species” that use tools to minimize injury when hunting – such as birds that drop prey with hard shells from a height to break it, or dolphins that use sponges as gloves to protect their hunting. chunks as he pulled bottom-dwelling fish out of the sand.
In broad terms, Tinker said, the water dogs’ recovery, and their surprising changes in behavior, may have lessons for the vast stretches of coast in California and Oregon where they have not yet recovered.
In those areas, “their ecosystem functions are still absent,” Tinker said.
“But as we look at future environmental change and the need to build resilience in coastal ecosystems – we think sea otters can be an important part of that.”
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