Fishing in tandem brings benefits for people and dolphins

Dolphins and net fishermen in Brazil catch more fish by working together, a new study by an international team of researchers has shown.

According to the authors, this is a rare example of an interaction by two top predators that is beneficial to both parties.

The study was led by Assistant Professor Mauricio Cantor of Oregon State University. The research team also included Associate Professor Damien Farine from The Australian National University (ANU) and University of Zurich, and Dr Fabio Daura-Jorge from the Federal University of Santa Catarina in Brazil.

“We knew the fishermen were observing the dolphins’ behavior to determine when to throw out their nets, but we didn’t know if the dolphins were actively coordinating their behavior with the fishermen,” Assistant Professor Cantor said.

“Using the latest techniques, combining drones and underwater imaging, we were able to observe the behavior of fishermen and dolphins in unprecedented detail and found that they catch more fish by working together.”

This cooperation between the Lahille’s bottlenose dolphins and traditional net fishermen, which is considered a cultural tradition, can be observed in the city of Laguna on Brazil’s south coast. It has been passed down through generations of fishermen and dolphins for over 140 years. But it could be at risk if populations of mullet – the type of fish sought by both parties – continue to decline, or if future generations of anglers lose interest in learning the art.

“The practice is unlikely to continue if either the dolphins or the fishermen no longer benefit from it, or something major happens to disrupt it,” Associate Professor Farine said.

“We’ve seen similar interactions disappear in other parts of the world – there’s even evidence that indigenous communities here in Australia cooperated with bottlenose dolphins to catch mullet until the 19th century.”

The study found that teamwork not only greatly increases the probability of catching fish and the number of fish caught, but that cooperation causes a 13 percent increase in dolphin survival rates and better socio-economic well-being for the fishermen.

“What makes this interaction so unusual is the fact that it is mutually beneficial rather than competitive,” Associate Professor Farine said.

“This makes it of substantial scientific interest, as it can help us understand under what conditions cooperation can develop and – of growing importance in our rapidly changing world – under what conditions it can die out, such as the historical cases of Australia and elsewhere.”

The findings were published in the Proceedings of the National Academy of Sciences.