Dolphins are teaching each other how to use shells to catch and eat fish

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The first time Sonja Wild saw a dolphin using an empty seashell to scoop an unwitting fish into its mouth, she got so excited she almost forgot to photograph it.

This rare and unique hunting technique is called "shelling" or "conching." A hungry dolphin will chase a hard-to-catch fish into an empty seashell, then ferry the shell to the surface where the dolphin uses its beak to jostle the prey into its mouth. 

"Seeing it for the first time was just a 'wow' moment because you do not expect a shell popping up right next to the boat that is being carried by a dolphin. You kind of, like, drop everything," said Wild, a behavioural ecologist at the University of Konstanz and the Max Planck Institute of Animal Behavior in Germany.

"I was definitely mind-blown," she told As It Happens guest host Duncan McCue.

Wild is the lead author of a new study in the journal Current Biology that documents how conching has spread through dolphin populations as the clever creatures teach each other how to do it.

Scientists have observed instances of conching going back at least 10 years, though it has always been a rare sight. 

Wild says there was a major uptick in sightings in Shark Bay, off the coast of Western Australia, after a 2011 marine heat wave killed off a large number of sea snails, leaving their shells ripe for the picking.

Wild and her colleagues have been observing the Shark Bay dolphins for years, mapping their social and genetic relationships. Between 2007 and 2018, they identified 1,000 individual dolphins and saw 19 of them engage in conching 42 times.

While conching still appears to be quite rare, Wild says all the dolphins who do it know each other. 

While analyzing their population data, the researchers found that conching spreads horizontally within dolphin generations, meaning from peer to peer, as opposed to vertically, from mother to calf.

"That is indeed quite special because dolphins normally rely very much on their mothers for foraging behaviour," Wild said.

"And we're now showing for the first time that they are, indeed, capable of learning foraging behaviour outside of the mother-calf bond."

Janet Mann, a dolphin researcher at Georgetown University who wasn't involved in the study, told the New York Times it's impossible to say definitively that peer imitation is the only way dolphins learn about conching, noting we've "barely scratched the water's surface" when it comes to understanding the behaviour.

Wild agrees. 

"It is very much possible that some dolphins may have learned this by themselves, by just interacting with their shells and then by accident kind of lifting them above the surface," she said.

She says it's possible, too, that some dolphins are passing the skill down to their young. But her team's models "clearly show that the majority have learned from their peers."

Why do they do it?

Wild says she's not sure why dolphins use shells to trap and eat fish.

She says they are very playful creatures, and it could be as simple as "just a little bit of fun to get your meal in a different way than usual."

But whatever their motivation, it proves they can adapt to a changing environment and pick up new skills — an ability that could help them survive as climate change alters ocean populations and makes food more scarce, she said.

"Learning from your mother is very useful in kind of stable environments that don't change, because the parental behaviour is tested and stable and adapted to the environment. But as soon as the environment changes, the behaviour may become outdated or inefficient or even maladaptive," Wild said.

"And in that case, it's beneficial if you start looking around to see what other dolphins are doing."

'Humans are not the only ones with culture'

Picking up new tricks from friends is rare in the animal kingdom, Wild said. It's a form of learning that's usually only observed in primates, including apes, chimpanzees and, of course, humans.

"It certainly helps to understand their intelligence by knowing that they are capable of innovating such remarkable behaviour, but it also helps us to understand that dolphin societies are maybe not that different from us humans," Wild said.

"They have very complex social relationships. They use tools. They are able to learn to use tools from one another. So it kind of helps our understanding that humans are not the only ones with culture."

Written by Sheena Goodyear. Interview produced by Katie Geleff and Jeanne Armstrong.