The results of the analysis, conducted by Mauricio Cantor, a behavioral ecologist at Oregon State University, Corvallis, were published Monday in the Proceedings of the National Academy of Sciences.
The research was based on 5,000 fishing excursions and 177 interviews with anglers in the small coastal city of Laguna -- where the gentle sea creatures are believed to have first teamed up with fishermen about 140 years ago.
Data was collected from 2018 to 2019, and for the first time researchers delved into whether dolphins also benefited from what appears to be a naturally-occurring partnership with humans.
The dolphins are known to swim up a narrow lagoon from the Atlantic Ocean, guiding small fish to the shallow waters where they can be easily netted.
Scientists also observed the animals flailing in the water at certain times, which serves to alert the fishermen to the exact location of the catch.
"We knew the fishers were observing the dolphins to determine when to throw their nets," Cantor told Science. "But we didn't know if the dolphins were coordinating their behaviors with the fishers."
The human subjects of the study were also asked what specific qualities made a dolphin suitable for fishing, and most said they looked for a cooperative attitude in the animal as well as its reliability to help them regularly catch food.
At the same time, scientists also noticed that dolphins were observing the fishermen as they eagerly cast their nets out into the murky waters. The coordinated effort seemed to be timed up perfectly and often led to a bonanza for both man and beast.
"The dolphins are almost like teachers," Cantor noted.
The research found that 86% of catches made came as a result of "synchronous interactions" with dolphins. The study also showed that fishermen were 17 times more likely to score a big catch of mullet when dolphins were present in the lagoon.
Not every expedition was successful as sometimes communication mixups would occur between the dolphins and fishers. Still, about half of the recorded fishing attempts were considered major bounties for the region.
Simon Ingram, a marine biologist at the University of Plymouth, who has conducted separate studies on human interaction with aquatic animals, says the new research proves animals like dolphins play a more critical role in human adaptation and survival than previously thought. This was demonstrated by dolphin behavior that tells fishers "where to stand and when to get ready to throw their nets."
"It's almost as if the dolphins are training the humans," Ingram said.
The study "shows convincingly that when both species get their timing right, the fishers catch more mullet, and the dolphins emit more terminal buzzes," said Claire Spottiswoode, a behavioral ecologist at the University of Cambridge.
Stephanie King, another behavioral ecologist at the University of Bristol, theorizes that the relationship between Laguna dolphins and humans evolved over time as both species cogently recognized the opportunity to benefit each other.
Similar human-dolphin interactivity has been recorded in eastern Australia, Mauritania, and Southeast Asia, but native fishing practices like these are becoming increasingly obsolete in the modern world.
Overfishing also threatens to impact the Brazilian fishing industry as mullet numbers have fallen dramatically over the past decade.
"Without mullet, this partnership will end," said Cantor.
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