Humans and Dolphins Make a Great Fishing Team

A bottlenose dolphin, similar to the ones that aid fishermen in Brazil. (Source: Australian Geographic)

For generations in a small coastal community in southern Brazil, local fishermen have used dolphins to aid in catching fish. Or maybe it’s the dolphins that have been using the fishermen, it’s difficult to say. In this cooperative arrangement, both groups have benefited greatly. The bottlenose dolphins will herd schools of mullet toward the fishermen and then dive underwater, a signal the fishermen use to cast their nets. This isn’t just the dolphins being altruists, the dolphins use the disorientation from the nets to pick off extra mullets.

This dolphin-human cooperation isn’t unique to Laguna, but the Brazilian case is the most famous, with the local dolphins being closely monitored by scientists since 2007. A recent article published in Proceedings of the National Academy of Sciences studied the Laguna case extensively, finding a complex web of interactions between the two groups of predators. It also clarified what the dolphins get out of the bargain. Beyond using the fishermen to catch fish, dolphins in this cooperative arrangement live 13% longer than those who hunt solo.

A dolphin and fisherman hard at work in Laguna. (Source: Federal University of Santa Catarina)

The study found that the fishermen and dolphins don’t merely respond to each other’s behaviors, but directly modify it. The dolphins do this by displaying a cue by diving underwater when the fishermen should cast their nets, then emitting a specific echolocation when the cast is successful, which the fishermen can feel in the water. This is not simply two predators hunting side-by-side, but small scale communication between two different species. Everyone wins: the fishermen take home more fish, and the dolphins have a reliable food source.

The study conducted its research by tracking the movements of the three parties involved in the hunting: the humans, the dolphins, and the mullet. By breaking down the animals involved into data points, one can see just how intermingled their behavior is. For example, the number of fishermen spikes whenever a dolphin presence is high, regardless of the number of mullet. The results speak for themselves. When fishing with dolphins, the fishermen are 17 times more likely to catch fish, and their yield increases four times over.

Another human-dolphin fishing team in Myanmar. (Source: Wildlife Conservation Society)

There is a reason that such arrangements as the Laguna case are a rarity. Overhunting and climate disruptions have weakened the amount of mullet in these waters. As the available catch has fallen, so too has the amount of cooperation, as each side vies for their piece of the action. Such human and animal cooperation, already a rarity, is at risk of disappearing entirely unless drastic changes are made to curb illegal fishing. The Laguna case could potentially be a model for protecting other human-animal cooperation cases in other parts of the world.