Washington. A fishing community in southern Brazil has an unusual ally: wild dolphins.
Accounts of people and dolphins working together to hunt fish date back millennia, from the time of the Roman Empire near what is now southern France to 19th century Queensland, Australia. However, while historians and storytellers have recounted the human point of view, it has been impossible to confirm how the dolphins benefited, or if they were taken advantage of, before underwater microphones and sonar could track them underwater.
In the coastal town of Laguna, scientists for the first time used drones, underwater sound recordings and other tools to document how local people and dolphins coordinate actions and benefit from each other’s work.
The most successful humans and dolphins are adept at reading the body language of others. The research was published yesterday in the journal Proceedings, of the United States National Academy of Sciences.
Laguna residents work with wild bottlenose dolphins to catch schools of migratory silver fish called mullets. It is a locally famous alliance that has been recorded in journalistic texts for 150 years.
“This study clearly shows that both dolphins and humans are paying attention to each other’s behavior, and that dolphins provide a clue as to when to cast the nets,” said Stephanie King, a biologist who studies dolphin communication at the University of Bristol and who is not involved in the research.
“This is really incredible cooperative behavior,” he added. “By working with the dolphins,” people catch more fish, “and the dolphins are also more successful in foraging.”
Dolphins and humans are highly intelligent and long-lived social animals, but when it comes to fishing, they have different abilities.
cloudy water
“The water is really cloudy here, so people can’t see the schools of fish, but the 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 into the water with hand nets.
“They wait for the dolphins to tell them exactly where the fish are; the most common sign is what the locals call ‘a jump’ or a sudden deep dive,” added Cantor, also affiliated with the Federal University of Santa Catarina in Florianópolis, Brazil.
The researchers used underwater microphones and sonar to track the positions of the dolphins and fish, while drones recorded interactions from above and GPS devices attached to residents’ wrists recorded when they cast their nets.
The more people synchronized their casting with the signals from the dolphins, the more likely they were to make a big catch.
So what’s in it for the dolphins? The descending nets scare off the fish, which break up into smaller schools that are easier for the dolphins to catch. “Dolphins may also take a fish or two from the net; sometimes the fishermen can feel that the dolphins are pulling the net a bit,” Cantor clarified.
Laguna residents classify individual dolphins as “good, bad or lazy” based on their hunting ability and affinity for cooperating with humans, he added. People get more excited when they see a “good” dolphin coming up to shore.
“These dolphins and humans have developed a culture of co-feeding 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 cooperation came to be, but it has survived multiple generations of humans and dolphins, with knowledge passed down by experienced fishermen and animals to the next generation of each species.
Still, researchers in Brazil worry that the Laguna alliance, perhaps one of the last of its kind, may also be in jeopardy, as pollution threatens dolphins and artisanal fishing gives way to industrial methods.
#Brazilian #fishing #community #maintains #centuryold #alliance #wild #dolphins