Dolphins that help humans catch fish are more likely to survive

A 12-year study of unusual fishing partnerships in southern Brazil calculated benefits to both humans and bottlenose dolphins.

To Claire Wilson

By the coastline of Laguna in southern Brazil lies a cemetery with a difference. Each cross represents the life of a dolphin that helped a local fishing community by driving mullet into their nets.

A rare partnership between bottlenose dolphins (Tursiops truncatum) And humans in this region have existed for over a century. Long-term studies now show that dolphins that are engaged have a higher survival rate than dolphins that are not working with humans.

Dolphins practicing this technique appear to catch more fish, but some of the survival advantages arise because dolphins avoid getting caught in the trammel nets used for fishing in other parts of the coast. says Mauricio Cantor of Oregon State University, where the team is studying. 12 years of action with underwater cameras and microphones.

From May to August, dolphins migrate pods of mullet (Mugil Riza) towards the shore where the fishermen are waiting. When the dolphins make their last deep dive to bring the fish closer to shore, the fishermen drop their nets, but if they don’t act at the right time, they’ll miss their chance.

When fishermen see dolphins arching their backs, they know they are about to dive deep. On rare occasions, animals appear to signal humans by tapping the water with their heads or tails. Both fishermen and dolphins need to learn the right techniques to work together, says Cantor. “It’s confusing [to see] For the untrained eye,” he says.

Kanter’s team found that fishermen were 17 times more likely to catch a mullet if they dropped their nets at dolphin signals than if they dropped them at any other time.

Cantor says it’s hard to understand how successful the partnership has been in catching dolphin fish. increase. Nets can also help dolphins by forming a barrier that prevents mullet from escaping.

About 10 out of a group of about 60 dolphins work alongside humans. The research team calculated that dolphins who worked with humans were 13% more likely to survive through the study period than dolphins who didn’t.

Other dolphins may have to catch fish without human assistance. Because there are only a few places near this coast where the technology is possible, says Cantor. But the number of cooperating dolphins used to be higher, between 12 and he 18. This is probably due to the recent decline in mullet numbers.

Fishermen can recognize individual dolphins by their distinctively patterned dorsal fins and their behavior. Last year, the community mourned when a particularly skillful dolphin they called Karoba died, presumably from an infectious disease.

Bruno Diaz López, of the Bottlenose Dolphin Institute in Galicia, Spain, says that dolphins are one of the few animals that exhibit behavior only in certain groups and have a unique culture shared among individuals. . “They need to teach each other this,” he says.

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