Research Finds Dolphins and Humans Benefit by Fishing Together

BRAZIL— According to research published on Jan. 30 in the journal Proceedings of the National Academy of Sciences, a fishing community in southern Brazil has made an unusual ally— wild dolphins.

 

Reports of people and dolphins working together to hunt fish go back millennia. While historians and storytellers have recited the human point of view, it’s been challenging to verify how the dolphins have benefited, or if they’ve been taken advantage of, prior to sonar and underwater microphones could track them. 

 

In the coastal city of Laguna, Santa Catarina, scientists have used drones, underwater sound recordings, and other tools for the first time to document how locals and bottlenose dolphins coordinate activities and benefit from each other’s work to catch a migratory fish called mullet. 

 

According to the University of Bristol biologist Stephanie King (who was not involved in the study), the study shows that humans and dolphins pay equal attention to each other’s behaviors. King also stated that the dolphins provide a cue for when to cast the nets. 

 

In the seaside community, the fisherman waits for the dolphins to signal where the fish are. The most common signal the dolphins give is a jump. 

 

The researchers used sonar and underwater microphones to track the positions of the dolphins and fish. At the same time, 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 to the dolphins’ signals, the more likely they were to trap a large catch.

 

But how does this benefit the dolphins? The nets startle the fish, who then break into smaller schools, making it easier for dolphins to hunt. The dolphins have also been known to remove fish from the nets— the fisherman can feel the dolphins tugging on the net.

 

The Laguna residents rate the individual dolphins as “good,” “bad,” or “lazy” — based on their hunting skills and effort in cooperating with humans. 

 

It’s unclear how the local cooperation between the two mammals first occurred. Still, it has survived numerous human and dolphin generations. Researchers believe that experienced fishers and dolphins pass down knowledge to the next generation of each species.

 

Researchers in Brazil worry that the alliance between the Laguna dolphins and humans, perhaps one of the last of its kind, is in danger as well, as pollution threatens the dolphins, and artisanal fishing succumbs to industrial approaches.

 

Scientists hope bringing awareness of the unique interspecies cooperation can help support and protect it.