Brazilian fishermen follow instructions from wild dolphins to know where to throw their nets, video shows

• A video shows a rare example of wild dolphins collaborating with humans to fish in a small lagoon in Brazil.
• The dolphins learned how to tell the humans exactly when to throw their nets to catch the most fish.
• The dolphins also benefit from the exchange. They catch more fish and stay safer than fishing alone.  

Along the coast of Laguna in southern Brazil, you can hear the buzz of bottlenose dolphins hunting for their prey.

Here, the wild dolphins work hard to herd fish around the lagoons, signaling to local fishermen when it's time for them to throw their nets.

The unusual example of cross-species partnership has been going on for more than a century — and now scientists have finally worked out why.

Researchers at Oregon State University claim the partnership benefits the dolphins, who live longer lives if they work with humans. 

The exchange can be observed in the video below. 

In the video, the dolphins can be seen herding a school of mullet toward the fisherman.

Echolocation clicks can be heard, captured by the study authors using microphones in the water.

When they sense fish are near, they arch their backs and dive, signaling to the humans to throw their round nets.

After the nets are cast, the dolphins will start sounding echolocation clicks. 

The fishers need the dolphins to know when to cast their nets

"The dolphins are really good at herding the mullets," Mauricio Cantor, an assistant professor at Oregon State University's College of Agricultural Sciences and an author of the study, told Insider.

They know how to make the school "really tight and compact" before pushing it toward the fisherman. Without the dolphins, the fisherman would not know when to cast their characteristic round nets into the water. 

"The water is super murky, so you cannot see where the fish are but you can see where the dolphins are," said Cantor. 

The dolphins, on the other hand, can see the fish using echolocation. But mullets are very hard to catch when they are in a school. 

"The nets play a key role, which is breaking apart that mullets school structure," said Cantor.

After the net is cast, the dolphins can catch stray fish or pick a few fish out of the net. It's a much easier hunt for them.

Communicating with humans  

The dolphins have learned very specific queues to tell the humans they should throw their nets. 

"The most common one is this sudden deep dive where they really arched their back," said Cantor. Another queue is if the dolphins use their heads or tails to slap the water. "Then it's pretty obvious," he said. 

As soon as they see this queue, the fishermen only have about seven seconds to cast their nets to be in with a chance of catching the fish, Cantor said.

If the dolphins are satisfied that the net has been cast correctly and it caught a good amount of fish, they let out loud echolocation clicks.

"We can hear it, it sounds like a creaking door," said Cantor. 

"Sometimes you can feel the echolocation, those terminal buzz clicks that they do underwater after the net sinks. If you're close enough, you can even feel it on your legs. It's kind of cool," said Cantor.

A safe haven for the dolphins

There is another advantage for the dolphins: by working with humans, they are protected from other dangers in the open ocean. 

"The other non-cooperative dolphins spend most of the time foraging where they encounter all kinds of other fisheries, including illegal fisheries," he says. Those dolphins are more likely to get tangled in the long dragging nets that kill everything they touch, said Cantor. 

The Laguna dolphins are about 13% more likely to reach old age, per the study. 

And they seem to know how good they have it there. Dolphins of that species tend to migrate a lot, up to 200 miles. 

But the Laguna dolphins, about 50 to 60 individuals, "rarely leave," said Cantor.

This behavior could disappear

This is not the only example of humans and dolphins working together. Throughout human history, dolphins and humans have figured out ways to team up, Cantor said.

"It's one of those examples of convergent evolution, different species trying to find a similar solution for the same problem," he said.

For instance, a very similar species of dolphin learned to fish with aboriginal people in Australia, said Cantor. 

"But then, with the colonization, they pretty much wiped out not only the culture, but the people as well," he said. 

"Once those things are gone, it's pretty much impossible to bring them back.

But naturally-occurring examples of mutual cooperation between wildlife and humans are precious and should be protected, said Cantor. 

The 140-year-long tradition in Laguna is now under threat. Fish are getting scarcer, in part due to illegal fishing. People are also moving away from fishing as their main source of revenue.

More people are taking on the practice as a hobby and losing some of the precision when it comes to timing when to release the nets, said Cantor. Dolphins are clever and will lose interest if they see they don't get the benefit they used to from the collaboration. 

"It's complicated because we need the dolphins, we need the fish, we need the fishers, but we also need that fine-scale knowledge of how to interact," he said. 

"If they're not practicing every day, naturally, they're not as experienced or not as skilled as the others," he said.

The study was published in the peer-reviewed Proceedings of the National Academy of Sciences on January 30.