Dolphins have long been observed helping humans to catch fish. Now scientists believe they know why – the dolphins themselves catch more fish while staying safe.
Researchers studied drone footage, sonar and acoustic recordings from the murky waters off Laguna, Brazil, where dolphins herd vast shoals towards waiting fishermen.
The dolphins dive as a signal to fishermen when to cast their nets, then help themselves to fish that as a result are separated from the main shoal.
Dr Mauricio Cantor of Oregon State University, who led the study, published in the Proceedings of the National Academy of Sciences, said: ‘Dolphins and people have the same goal – to catch fish. They can do it by themselves but have learned they do it better as a team.’
Dolphins have long been observed helping humans to catch fish by diving as a signal to cast their nets
Fishermen were 17 times more likely to catch fish while cooperative dolphins were 13 per cent less likely to die.
Cooperative dolphins off the coast of Brazil signal to fishermen, who can’t see fish below the murky water, when they have dropped off a large catch.
They do this by suddenly diving below the water, at which point the fishermen immediately cast their nets.
Researchers, who watched more than 2,000 interactions, found the tactic worked well, with the dolphins diving and the fishermen rapidly responding in time on about half of occasions.
The clear evidence that dolphins were benefiting came from sonar evidence that they were stealing fish from the nets.
Researchers studied drone footage, sonar and acoustic recordings from the murky waters off Laguna, Brazil, where dolphins herd vast shoals towards waiting fishermen. [File image]
Almost two-thirds of fishermen interviewed said they had felt the creatures making off with a few of their catch.
After herding the fish, which were primarily mullet, and fishermen casting their nets in response, the dolphins spent more time producing fast clicks, so close together they sound like buzzing.
Unlike normal clicks, for navigation, these fast clicks indicate the creatures are homing in on prey.
Dolphins also spent longer beneath the water after working with fishermen.
Both behaviours suggest the creatures were getting more fish than usual from working with the fishermen.
Fishermen certainly benefited, being 17 times more likely to catch fish, and catching almost four times the amount of mullet when they teamed up with dolphins.
When the dolphins worked with the fishermen, they were 13 per cent less likely to die than non-cooperative dolphins.
That is likely because cooperative creatures tend to stay in a smaller area, so are less likely to end up as ‘by-catch’ in the nets of other illegal fishermen.
Dolphins have also been found to work with fishermen in countries including Myanmar and India.
The researchers warn the fascinating behaviour could be lost within 40 to 60 years, however.
That is because fish numbers are declining, and pressure on traditional fishermen could see many give up – losing decades of knowledge on how to work with dolphins.
The 15-year study is published in the journal Proceedings of the National Academy of Sciences.