People in Laguna proudly refer to their southern Brazilian city as the “national capital of fish-herding dolphins.” For at least 140 years artisanal fishers and bottlenose dolphins have worked together in careful synchrony to catch mullet in a local lagoon. The spectacle of nets flying through the air while dolphins dive into the murky water has become a popular attraction for tourists, and it is recognized by local authorities as an intangible cultural heritage.
In 1998 scientists confirmed that this renowned example of human-wildlife cooperation aids at least one of the parties: the fishers, who enjoy larger catches when they join forces with dolphins. Most believed that the dolphins were reaping rewards, too, but this hypothesis was more difficult to test.
Now researchers have finally documented that the benefits are indeed mutual. An exhaustive new study published in the Proceedings of the National Academy of Sciences USA shows that dolphins that team up with fishers gain more food and have an edge in survival compared with those hunting without human partners.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Laguna’s resident population of up to 60 dolphins uses echolocation to find schools of mullet that humans are unable to detect in the opaque water. Then the cetaceans herd a school toward the fishers, who are typically standing in the shallows just offshore. The dolphins give a cue, such as a sudden deep dive, to let the fishers know when to cast their nets; the net casting in turn breaks up the school of speedy fish, making it easier for dolphins to capture individual mullet.
“Each [species] brings a new skill to the table that increases their mutual success,” says Mauricio Cantor, the study’s lead author and a behavioral ecologist at Oregon State University. The research indicates, however, that these celebrated interspecies hunts are in danger of vanishing. “Our data suggest this interaction is becoming rarer over time,” Cantor says. “If things continue the way they are, these interactions might disappear in the next 50 to 60 years.”
Laguna’s cooperative fishers and dolphins are one of the few remaining examples of a millennia-old tradition across the world. Fossil evidence from Europe indicates that humans and wolves might have collaborated to hunt prey as early as 32,000 years ago. In the first century C.E. Pliny the Elder mentioned fishers working with dolphins in what is now southern France. Since then, seemingly cooperative interactions with people have been recorded in at least 16 species—mostly cetaceans but also some birds—in countries such as Australia, Myanmar, Mauritania and Japan.
Many such collaborations have ended, however. And those left are almost all in decline because of pollution, overfishing and habitat loss, combined with the general disconnection of humans from the natural environment. “Today most interactions we have with wildlife tend to be antagonistic and not mutually beneficial,” Cantor says. “So it’s really important to understand how these things happen and what we can do to safeguard this unique biological phenomenon.”
To analyze Laguna’s human-dolphin cooperation, Cantor and his colleagues collected data using drones, underwater microphones, sonar cameras, GPS and interviews with fishers. The study’s senior author, Fábio Daura-Jorge of the Federal University of Santa Catarina in Brazil, also provided 15 years’ worth of survey responses from fishers, as well as photographs and dolphin behavior records for both individual animals and groups.
After pulling it all together, the researchers found that fishers were 17 times more likely to catch mullet when they worked with dolphins than they were on their own, and dolphins had more success in these partnerships as well (the researchers are still working to quantify the dolphins’ gains). Dolphins that partnered with fishers also experienced a 13 percent boost in survival, most likely because they spent most of their time in the lagoon. In areas nearby, some fishers use illegal drift nets that drown dolphins as bycatch. “By avoiding these encounters, cooperative dolphins have a higher probability of surviving,” Cantor says.
These findings support “the long-standing hypothesis that these dolphins experience a higher prey capture rate when interacting with fishers,” says University of Cape Town behaviorial ecologist Jessica van der Wal, who was not involved in the research. “I applaud the authors for their comprehensive and creative angles to better our understanding of the natural history of [this] complex cooperation.”
The team also built a model to predict how fisher-dolphin interactions might change over time. Fishers have anecdotally reported a decline in joint hunting practices over the past 15 years, and the model suggests that this trend will continue, putting the practice in danger of extinction. The main drivers for that decline, the authors found, are decreasing mullet populations caused by overfishing and climate change, along with livelihood changes in the artisanal fishing community.
The scientists propose some solutions to help prevent this loss: Fishers, for example, could be incentivized to keep working with dolphins if buyers of their catch were willing to pay a premium for their fish. This way, Cantor says, “even if catch declines over time, there will be a higher reward for fishers in monetary terms.”
Protecting dolphins from becoming bycatch would also help. The government could invest in more policing to remove illegal nets and apprehend violators. And raising awareness is key. “Getting people excited about these rare phenomena is a way to add more value to these kinds of cultural practices that seem to be fading away,” Cantor says. “Preserving cultural diversity has been shown to promote the preservation of biological diversity as well.”
The “exemplary” new study is “of huge importance” for showing both how this cooperation is achieved and how it can be conserved, says University of Bristol behavioral biologist Stephanie King, who was not involved in the research. “Humans are renowned for the ways they cooperate,” she says, “but what is even more remarkable is two distantly related species with very different evolutionary histories acting cooperatively to achieve a common goal.”
Editor’s Note (4/13/23): A version of this article entitled “Swim Team” was adapted for inclusion in the May 2023 issue of Scientific American. This text reflects that version, with the addition of some material that was abridged for print.