Dolphins, humans both benefit from fishing collaboration
A fishing community in southern Brazil has an unusual ally: wild dolphins.
Stories of humans and dolphins working together to hunt fish stretch back millennia, from the time of the Roman Empire near what is now southern France to 19th century Queensland, Australia. But while historians and storytellers told the human point of view, it was impossible to confirm how the dolphins benefited — or if they benefited — until sonar and underwater microphones could track them underwater.
In the coastal city of Laguna, scientists used drones, underwater sound recordings and other tools for the first time to document how local people and dolphins coordinate actions and benefit from each other’s labor. The most successful humans and dolphins are adept at reading each other’s body language. The research was published Monday in the journal Proceedings of the National Academy of Sciences.
The Laguna residents work with wild bottlenose dolphins to catch schools of migrating silver fish called mullet. It is a locally known alliance recorded in newspaper records going back 150 years.
“This study clearly shows that both dolphins and humans pay attention to each other’s behavior, and that dolphins signal when the nets should be thrown,” said Stephanie King, a biologist who studies dolphin communication at the University of Bristol and was not involved in the research.
“It’s really incredibly cooperative behavior,” she added. “By working with the dolphins,” the people catch more fish, “and the dolphins are also more successful in looking for food.”
Dolphins and humans are both highly intelligent and long-lived social animals. But when it comes to fishing, they have different abilities.
“Here the water is very cloudy, so the people cannot see the schools of fish. But the dolphins use sounds to find them, sending out little clicks,” just like bats use echolocation, said Mauricio Cantor, a marine biologist at Oregon State University and co-author of the study.
While the dolphins chase the fish to the shore, the people run into the water with hand nets.
“They wait for dolphins to indicate exactly where fish are – the most common signal is what locals call a ‘jump’ or a sudden deep dive,” says Cantor, who is also affiliated with the Federal University of Santa Catarina in Florianópolis, Brazil. .
The researchers used sonar and underwater microphones to track the positions of the dolphins and fish, while drones recorded the interactions from above, and GPS devices attached to residents’ wrists recorded when they cast their nets.
The more closely the people synchronized their net casting with the dolphins’ signals, the more likely they were to catch a big catch.
So what are the dolphins up to?
The lowering nets startle the fish, which break into smaller schools that are easier for dolphins to hunt. “The dolphins can also take one or two fish out of the net – sometimes fishermen can feel the dolphin tugging on the net a little bit,” Cantor said.
The Laguna residents categorize the individual dolphins as “good,” “bad” or “lazy” — based on their skill in hunting and affinity for cooperation with humans, Cantor said. The people get most excited when they see a “good” dolphin approaching.
“These dolphins and humans have developed a joint foraging culture that allows them both to do better,” said Boris Worm, a marine ecologist at Dalhousie University in Halifax, Canada, who was not involved in the research.
It is not clear how the Laguna collaboration first came about, but it has survived several generations of humans and dolphins – with knowledge passed down to the next generation of each species by experienced fishermen and dolphins.
Yet the researchers in Brazil worry that the Laguna Alliance, perhaps one of the last of its kind, may also be at risk as pollution threatens the dolphins and artificial fishing gives way to industrial methods.
“Human-wildlife cooperation is disappearing because we are destroying wildlife populations,” said Janet Mann, a dolphin researcher at Georgetown University who was not involved in the study.
Scientists hope that greater awareness of the unusual interspecies cooperation can help boost support to protect it. “It is amazing that it has lasted for more than a century – can we keep this cultural tradition alive in the midst of many changes?” said Damien Farine, a biologist from the University of Zurich and co-author of the study.
The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.
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