Every summer, in the waters off the coast of the town of Laguna, in the southeast corner of Brazil, fishermen wade through estuary channels to cast their nets in hopes of catching migratory mullets. The water is cloudy and the fish are hard to spot. However, the fishermen have help from an unexpected source: bottlenose dolphins that push their prey into the nets.
“The experience of fishing with dolphins is unique,” said Wilson F. Dos Santos, a Laguna fisherman who has cast nets with dolphins for 50 years.
In research published last month in the Proceedings of the National Academy of Science, a team of Brazilian scientists reported that dolphins could benefit from cooperation just as much as fishermen. Those that fish with humans seem to live longer than other dolphins in the area.
“Human-wildlife cooperation in general is a rare phenomenon on a global scale,” said Mauricio Cantor, a biologist at Oregon State University and an author on the paper. “Usually, humans get the benefit and nature pays the price. But this interaction has been going on for more than 150 years.”
The practice has also been observed in Mauritania, Myanmar and India, but the Laguna dolphins are the most famous. The local population of about five dozen cooperative dolphins has been monitored since 2007, said Fábio G. Daura-Jorge, a biologist at the Federal University of Santa Catarina in Brazil and an author on the paper. In 2017, the team began tracking fish and dolphins with GPS, drones, and sonar.
The team found that the dolphins gave a signal—usually a sudden, deep plunge—to signal that they had brought their prey within reach of the fishermen’s nets.
Eighty-six percent of the successful catches during the study period came from anglers who read the dolphins’ behavior, Cantor said.
Dolphins also time their foraging carefully. When a fisherman made a successful cast, the dolphins would head for the disoriented mullets or pull some fish out of the net. When the fishermen missed the timing of the cast or did not respond to the dolphins’ cues, the dolphins did not act.
“The dolphins know what they are doing,” Daura-Jorge said. “They are taking advantage of the actions of the fishermen to actively feed themselves.”
The fishermen identified the clicking noises of the dolphins and told the researchers that they felt the echolocation buzz in their legs when the dolphins “scream.”
The strategy has clear benefits for dolphins, Cantor said: Those who hunted with humans were 13 percent more likely to survive to adulthood.
While this dumbbell helps both parties, the practice has been on the decline for the past decade, Cantor said. Commercial operations overexploit mullet populations in southern Brazil. As the number of fish decreases, individual dolphins and fishermen hunt less together.
“Safeguarding the cultural tradition of the fishermen and the dolphins is essential for them to continue cooperating and it is also important to conserve the dolphin population,” said Daura-Jorge.
By: ASHER ELBEIN
BBC-NEWS-SRC: http://www.nytsyn.com/subscribed/stories/6561903, IMPORTING DATE: 2023-02-08 00:00:07
#Brazil #humans #catch #fish #dolphins