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Humans and dolphins cooperate in fishing in Brazil


Dolphins work alongside fishermen on the southern Brazilian coast. Both parties benefit from this, but their union is in danger.

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Photo: Stuart Westmorland/Getty Images

A team of man and dolphin does not only exist at Flipper: off the south coast of Brazil, man and animal work together in an extraordinary way away from the television.

Fishermen and dolphins have been fishing here together for over a century.

Biologists have been studying the unique hunting community for 15 years and are now reporting on their observations in the specialist journal »PNAS«.

A special cultural fishing tradition has been cultivated off Laguna, a city in southern Brazil, for more than 140 years: Here people and bottlenose dolphins (Tursiops truncatus gephyreus) hunt together for mullets (Mugiliza).

Both the fishermen and the dolphins pass the practice on from generation to generation.

A video published for the study by the researchers led by Mauricio Cantor from the Universidade Federal de Santa Catarina in Florianópolis shows how the cooperation works: The marine mammals drive schools of fish towards the fishermen who are waiting in the water with cast nets.

Then they give them a signal - usually a distinctive flapping of their fins or they appear briefly.

This is where the fishermen cast their nets.

"Using drones and underwater footage, we were able to observe the behavior of fishermen and dolphins in unprecedented detail," Cantor said, according to a statement from the Max Planck Institute (MPI) for Animal Behavior.

It has been shown that they catch more fish when they work synchronously.

Cooperation is a special feature of this dolphin population.

Four times more fishing

When bottlenose dolphins are present, fishermen are 17 times more likely to catch mullet.

In addition, they would catch almost four times more fish than without animal helpers.

The joint hunt also offers advantages for the dolphins, the fishermen report.

"61 percent said they sense when dolphins pull 'a mullet or two' out of their nets," it says.

The animals also benefit in the long term: according to the study, dolphins that fish cooperatively in this area have a 13 percent higher survival rate.

This is probably due to the fact that, by working together with the net fishermen, they avoid becoming bycatch with other fishing methods.

However, model calculations suggest that this type of fishing is threatened: both dolphins and fishermen depend on a strong and healthy fish population.

But in recent years, the number of mullets in the region has declined.

"Interest in learning the tradition has also fallen," says co-author Fábio Daura-Jorge.

"Our calculations show that if current developments continue, the cooperation could become uninteresting for either the dolphins or the fishermen."

The biologists propose several steps to preserve the common hunt of fishermen and dolphins.

In this way, the causes of the decline in mullet numbers should be determined and measures taken to ensure sustainable fishing.

In addition, traditional practice could be encouraged by setting a higher price for fish caught using this method.


Source: spiegel

All tech articles on 2023-01-31

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