A fishing community in southern Brazil has an unusual ally: wild dolphins.
Tales of people and dolphins working together to hunt fish go back millennia, from the days of the Roman Empire near what is now southern France to 19th-century Queensland, Australia. But while historians and storytellers have told the human point of view, it’s been impossible to confirm how the dolphins benefited – or if they were exploited – before sonar and underwater microphones could. follow underwater.
In the seaside town of Laguna, scientists have, for the first time, used drones, underwater sound recordings and other tools to document how local people and dolphins coordinate their actions and benefit from each other’s work. The most successful humans and dolphins are adept at reading each other’s body language. The research has been published Monday in the journal Proceedings of the National Academy of Sciences.
The people of Laguna work with wild bottlenose dolphins to catch schools of migrating silver fish called mullets. It is a locally famous alliance that has been recorded in newspapers dating back 150 years.
“This study clearly shows that dolphins and humans pay attention to each other’s behavior and that dolphins indicate when nets should be cast,” said Stephanie King, a biologist who studies dolphin communication at the University. of Bristol. not involved in research.
“It’s really amazing cooperative behavior,” she added. “By working with dolphins, people catch more fish, “and the dolphins are also more successful at feeding themselves.”
Both dolphins and humans are highly intelligent and long-lived social animals. But when it comes to fishing, they have different abilities.
“The water is really murky here, so people can’t see the schools of fish. But dolphins use sounds to find them, making little clicks,” just like bats use echolocation, said Mauricio Cantor, a marine biologist at Oregon State University and co-author of the study.
As dolphins herd fish to shore, people run through the water holding hand nets.
“They wait for the dolphins to signal exactly where the fish are – the most common signal is what locals call ‘a jump’ or a sudden deep dive,” said Cantor, who is also affiliated with the Federal University of Santa Catarina in Florianópolis, Brazil. .
Researchers used underwater sonar and microphones to track the positions of dolphins and fish, while drones recorded interactions from above and GPS devices strapped to residents’ wrists recorded when they cast their nets.
The more closely people synchronized their net casting with the signals from the dolphins, the more likely they were to trap a big catch.
So what’s in it for the dolphins?
The descending nets startle the fish, which divide into smaller schools, which are easier for the dolphins to hunt. “Dolphins can also take a fish or two from the net – sometimes anglers can feel the dolphin tugging the net a bit,” Cantor said.
Laguna residents categorize individual dolphins as “good,” “bad” or “lazy” — based on their skill at hunting and their affinity for cooperating with humans, Cantor said. People get most excited when they see a “good” dolphin approaching the shore.
“These dolphins and humans have developed a culture of joint foraging that allows them both to do better,” said Boris Worm, a marine ecologist at Dalhousie University in Halifax, Canada, who did not participated in the research.
It’s unclear how the Laguna Co-op came into existence, but it has survived several generations of humans and dolphins – with knowledge passed down from experienced anglers and dolphins to the next generation of each species.
Yet Brazilian researchers fear that the Laguna alliance, possibly one of the last of its kind, is also in danger, as pollution threatens dolphins and artisanal fishing gives way to industrial methods.
“Human-wildlife cooperation is disappearing because we are decimating wildlife populations,” said Janet Mann, a dolphin researcher. at Georgetown University, which was not involved in the study.
Scientists hope that greater awareness of unusual interspecific cooperation can help support its protection. “It’s amazing that it’s been going on for more than a century – can we keep this cultural tradition alive in the midst of so much change?” said Damien Farine, a biologist at the University of Zurich and co-author of the study.
Follow Christina Larson on Twitter at @larsonchristina.
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