- Without any formal training from humans, certain bottlenose dolphins in Brazil are helping fishermen with their catches.

- The dolphins round up the fish and alert fishermen with signals as to when and where nets should be thrown.

- The dolphins that help the fishermen have high cooperation and social skills.

Certain bottlenose dolphins in Laguna, southern Brazil, have apparently taught themselves to work as a team with artisanal fishermen, creating a win-win for both the marine mammals and humans.

A study on the dolphins, published in the latest Royal Society Biology Letters, has found that the most helpful ones also turn out to be particularly cooperative and social with each other, perhaps explaining why some wild dolphins decide of their own free will to work with humans, while others do not.

"Through highly synchronized behavior with humans, cooperative dolphins in Laguna drive mullet schools towards a line of fishermen and 'signal,' via stereotyped head slaps or tail slaps, when and where fishermen should throw their nets," wrote lead author Fabio Daura-Jorge of the Federal University of Santa Catarina.with colleagues.

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The effort is not entirely charitable on the part of the dolphins. Fish that escape the nets often swim right into the mouths of the dolphins, which have learned to wait for that fulfilling moment.

Daura-Jorge and his team conducted boat surveys over a two-year period, collecting photo identification data and other information on the dolphins. Any that teamed up with humans for fishing was classified as "cooperative." The others were classified as "non-cooperative."

The researchers next used computer modeling to identify social relationships among the dolphins. "Cooperative" dolphins turned out to spend more time together, even when not assisting humans. They appeared to have their own social network within the larger local population of bottlenose dolphins.

The scientists suspect that "ecology, genetics and social learning" could be driving and maintaining the wild dolphin subset's unique relationship with humans. Interestingly, the phenomenon seems to mirror how the Brazilian fishermen learn their trade.

"The human side of this dolphin-fishermen interaction is maintained through inter-generational information transfer, that is, teaching by elders, and it is likely that a similar process is used to transmit complex behavioral traits between generations of dolphins, as found in other localized behaviors, such as 'sponging' in Shark Bay, Western Australia," they wrote.

Dolphins and fishermen work together in Laguna, Brazil, to catch fish.Fábio Daura-Jorge

"Sponging" refers to how some bottlenose dolphins tear off pieces of marine sponges and wear them on their snouts during foraging to protect them from scrapes and other damage.

Dolphin smarts help to explain some of these complex behaviors.

Lori Marino, a senior lecturer in the Department of Psychology at Emory University, told Discovery News, "If we use relative brain size as a metric of 'intelligence' then one would have to conclude that dolphins are second in intelligence to modern humans."

Cooperation also appears to be a key component of advanced learning among all animals, and not just dolphins.

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Luke McNally of the Theoretical Ecology Research Group at Trinity College Dublin explained, "The idea that the demands of complex social interactions could have driven the evolution of intelligence has been around since the mid 70's. Most work on this hypothesis since then has utilized data from the primates to show that various social characteristics, such as group size, group stability and deception, correlate with brain size."

Intelligence and cooperation go hand in hand, he said, with the former facilitating the latter. Cooperation alone is not necessarily very brainy, since some of the world's "least cognitively complex" organisms, such as bacteria, are very cooperative. "Selection for cooperation," McNally said, "drives the evolution of intelligence."

Daura-Jorge and his team are now testing that idea out, by studying the genetics of the Laguna dolphins. It could be that certain dolphins are inheriting their human teamwork skills, with teaching mothers reinforcing the behaviors.