The Wild Dolphins That Tell Fishermen When to Cast

In the shallow, muddy waters off Laguna, a small fishing town on Brazil's southern coast, a fisherman stands waist-deep with a cast net folded over his shoulder. He is not watching the water for fish. He is watching for a dolphin.

A Signal With No Instructions

Wild bottlenose dolphins in Laguna drive schools of mullet toward the shore, where fishers wait in a line. As the fish scatter into the murky shallows, a dolphin gives a distinct cue, usually a sudden deep dive or a sharp slap of its head or tail on the surface. That cue tells the fishers exactly when and where to throw. Cast too early or too late and the net comes up empty. Cast on the signal and it often comes up full.

Nobody trained these dolphins to do this. There are no treats, no hand signals, no marine park routine behind it. It is a wild, spontaneous behavior that some of Laguna's dolphins do and others, in the very same waters, do not.

A Partnership Documented for Well Over a Century

Written accounts of fishers and dolphins working together in Laguna go back to the 1800s, making this one of the longest continuously documented cases of wild animals and humans coordinating a hunt anywhere on Earth. Generations of local fishing families have passed down where to stand, how to read the water, and which dolphins tend to show up.

Proving It With Drones and Hydrophones

For 15 years, researchers led by Mauricio Cantor of Oregon State University, with Fabio Daura-Jorge of the Federal University of Santa Catarina and Damien Farine of the Australian National University, tracked the partnership from every angle. They flew drones overhead, dropped underwater microphones to record dolphin clicks, and fitted more than 170 fishers with GPS wristbands to log exactly where and when each cast landed.

Their study, published in the Proceedings of the National Academy of Sciences in January 2023, confirmed both sides come out ahead. Fishers who cast in sync with the dolphins' cue catch more mullet, and bigger ones. The dolphins, in turn, close in on the fish that scatter loose and disoriented from the nets, an easier meal than chasing mullet through open, murky water alone.

The Part Scientists Still Cannot Explain

What nobody has pinned down is how the behavior spreads. It appears to be a local tradition rather than something built into bottlenose dolphin genetics, since dolphins in other parts of the world that interact with fishers do not cue net casts this way. Whether young Laguna dolphins pick it up by watching others, or work it out fish by fish on their own, remains an open question the research team is still trying to answer.

For now, the fishers of Laguna do not need an explanation. They just need to keep watching the water for the next dive.