For years, resident bottlenose dolphins in Laguna, Brazil, have helped local fishermen catch schools of fish. Like marine sheepdogs, the Laguna dolphins herd fish toward the shore where the fishermen wait, and then slap their heads or tails against the surf when the fish are close enough to be caught by fishing nets. This unique behavior has attracted the attention of tourists, as well as biologists Simon Ingram, from Plymouth University in the United Kingdom, and Fábian Daura-Jorge, from the Federal University of Santa Catarina in Brazil, who have recently published a report online in Biology Letters about the phenomenon and their observations of the dolphin’s behavior.
The lagoon is home to about 50 dolphins, although only some of them take part in the fishing tradition. Ingram and Daura-Jorge were curious about this fact, and decided to observe the dolphins in order to discover why only one-third of the dolphins engaged with the fishermen, while the rest kept their distance. The researchers watched the dolphins by boat and took photos as they swam together in order to record how the animals interacted. They discovered that the dolphins that helped local fishermen also tended to cluster with each other, while the dolphins that didn’t help the fishermen stayed more isolated.
Daura-Jorge believes this behavior may suggest that learning is involved, as dolphins with closer bonds may copy each other’s behavior. It is too soon however, to rule out the possibility that these specific dolphins may also have a genetic predisposition to hunt in this manner. For now the focus will remain on aiding the dolphins, as many fishermen’s livelihoods depend on the marine mammals: “If we lose the cooperative dolphins,” Daura-Jorge explains, “we lose this traditional way of life.”