Now, scientists have discovered just how these dolphins learn to catch their prey in this extraordinary way — using their beaks to bring the shells to the surface and then shake the fish into their mouths — similar to how we humans get at those last few chips at the bottom of a packet.
“Our study shows that the foraging behavior ‘shelling’ — where dolphins trap fish inside empty seashells — spreads through social learning among close associates,” said Sonja Wild, who conducted this research for her doctorate at the University of Leeds.
“This is surprising, as dolphins and other toothed whales tend to follow a ‘do-as-mother-does’ strategy for learning foraging behavior,” she said in a press statement. Dolphin mothers and calves typically form very tight bonds, staying close to one another for at least two years learning social behaviors and feeding techniques.
The findings provided more evidence of similarities between dolphins and great apes — chimpanzees, gorillas and humans — who have also shown a range of socially learned foraging behavior, the study, which published Thursday in Current Biology, said.
“Despite their divergent evolutionary histories and the fact they occupy such different environments: Both dolphins and great apes are long-lived, large-brained mammals with high capacities for innovation and the cultural transmission of behaviors,” said Michael Krützen, director of the department of anthropology at the University of Zurich and senior author on the study.
Using boats, the international team of researchers conducted surveys in the western gulf of Shark Bay, Australia, between 2007 and 2018 to evaluate how shelling behavior spread across the population.
In 5,278 encounters with dolphins during that time, the scientists identified 1,035 different Indo-Pacific bottlenose dolphins (Tursiops aduncus). They spotted 19 dolphins in the act of shelling 42 times.
Although shelling appears quite rare, both the number of shelling events and the number of individual “shellers” is likely to be an underestimate, according to the study, as the shell-shaking only lasts a few seconds, and is therefore hard to observe.
“Some dolphins use shells quite regularly during foraging, while others have only ever been seen with a shell once,” said Wild. “So, while there may be other explanations, it’s possible that some dolphins have mastered the skill more than others.”
The social network
To find out how this way of foraging had spread from one dolphin to the next, the researchers looked at the influence of environmental factors, genetic predisposition and the dolphin’s social network.
The model they developed showed that dolphins learn shelling from associates within their social group and they concluded that using the shells spreads primarily within — rather than between — generations, providing the first evidence that dolphins are also capable of learning from their peers, not just their mothers.
Shelling is only the second reported case of tool use in dolphins. Dolphins in the same area are also known to use marine sponges as foraging tools to help them catch prey, according to the researchers.
Wild said that a marine heat wave in 2011 wiped out Shark Bay’s critical seagrass habitat and triggered a die-off of fish and invertebrates, including the gastropods — sea snails — that live in the giant shells. She said it was possible that the resulting abundance of dead giant gastropod shells may have made it easier for the dolphins to learn this behavior.
“Our results show that dolphins are definitely capable, and in the case of shelling, also motivated to learn new foraging tactics outside the mother-calf bond,” Wild said.
“Learning from others allows for a rapid spread of novel behaviors across populations, and it has been suggested that species with the capacity for learning from others in this way may be better able to survive,” she said.