For over 150 years in southern Brazil, humans and wild dolphins have fished side by side, dolphins driving mullet toward the shore, fishers casting nets on a flick of the fin. A new 2025 study reveals the science behind this extraordinary partnership, synchrony measured in frames of drone footage, hauls over three times larger and dolphins gaining a survival boost. Yet this fragile alliance is now in decline, threatened by overfishing, gillnets, and cultural loss.
The light over the Laguna estuary comes up as fishers stand waist deep in the shallows, nets coiled over their shoulders. Nobody speaks. Everyone stares at the same dark seam of water.
A fin cuts through the surface, then another. Bottlenose dolphins circle the shoal of mullet with small, precise turns. One dolphin rolls, flicks its head toward the beach, and slaps its tail against the surface with a sound like a whip crack. Nets arc through the air. The water erupts silver. Fishers haul heavy mesh to their chests while dolphins slice in to catch their share.
For a few moments, humans and dolphins move like parts of the same machine.
Local families say their grandparents did the same. Newspaper reports confirm the practice has been observed for more than 150 years. But for the first time, science is not only confirming it, it is warning us how fragile it is.
A new study in People and Nature (May 2025) frames Laguna’s fishery as a linked system, where dolphins, people and fish are bound together. Dolphins and fishers are not just sharing fish. They are co-creating a relationship, bound by reciprocity. When the “users” of the system change, when mullet runs falter, when young fishers turn to gillnets, when dolphins stop signalling, the partnership itself begins to fray.
When Data Meets Folklore
Between 2007 and 2018, researchers recorded over 1,600 cooperative fishing events at Laguna. That is not folklore. That is data.
When the team analysed it, the advantages leapt out:
17 times more likely to catch fish when casting on a dolphin cue
Over 3 times larger hauls on average when synchronised with dolphins
Around 13% higher survival for cooperative dolphins compared with non-cooperators
The impact for fishers was staggering: 86% of all 4,955 mullets caught during the study period came from synchronous interactions. In interviews, 98% of experienced fishers confirmed that dolphins gain clear foraging benefits too.
Synchrony is razor sharp. The window between success and failure is often measured in frames of drone footage, not minutes. Cast too early and the net encloses water. Cast too late and the school has scattered. Cast within seconds of the cue, and both predators profit.
Sonar in the Shallows
The water of the estuary is cloudy, stirred by sand and silt. Humans cannot see the fish clearly enough to time their nets. Dolphins solve this with echolocation.
Think of them as carrying portable sonar. Each click sends out a sound pulse; each echo paints a picture. Where humans see murk, dolphins hear maps.
When fishers cast in synchrony, dolphins shift into a “terminal buzz”, a rapid-fire burst of clicks they use only when closing in on prey. It is the sound of precision, of dolphins locking their sonar on the shoal just as the net lands.
Once the school is driven toward the beach, a dolphin gives a cue, a roll, a flick, a tail slap. It is a signal as clear as a whistle. Nets thrown on that beat are many times more successful, and the chaos they cause sends extra fish straight into dolphin mouths.
The payoff is not only in food. Cooperative dolphins spend less time overlapping with hazardous gear. A 13% survival edge might sound small, but for a wild population it is enormous, enough to determine whether a community grows, holds steady, or slides toward extinction.
If you’ve read this far, you know dolphins are not just performers of clever tricks, they are cultural partners, carrying sonar in their skulls and teaching humans when to cast. The next part of this piece dives deeper: how only 20 dolphins sustain 200 families, the names and stories of Scooby and Caroba, and why scientists warn this alliance could vanish within 50 years.
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