Humans and dolphins on Brazil’s south coast have created a carefully timed “dance” to direct as many migrating mullets into nets and mouths as possible.
Traditional fishermen in Laguna City have been working with Lahill bottlenose dolphins (Tursiops truncatus gephyreus) for over 140 years.
From above, it looks like dolphins are leading flocks of mullets to the shore, next to fishermen roaming the shallow water. And only after receiving a signal from the dolphins, the fishermen cast their nets.
Researchers have spent more than a decade studying this close relationship and say it’s a rare example of mutualism, where two species help each other improve their chances of survival.
“We knew that fishermen were watching dolphin behavior to determine when to cast their nets, but we didn’t know if dolphins were coordinating their behavior with fishermen,” says marine biologist Mauricio Cantor of Oregon State University. drones and underwater photography, we can observe their behavior as fishermen and dolphins in unprecedented detail, finding them catching more fish by working together in sync.
The struggle for survival in nature is often portrayed as abstract: a battle for limited resources, companions, or territories. But collaboration is also an important part of the equation that we tend to overlook.
Teamwork and simultaneous activity within the same species is common—think of fish swimming in unison or lions hunting in packs—but collaboration between two different species is rare.
Humans always interact with wildlife for their own benefit. Our ancestors took wild wolves and turned them into domestic dogs for hunting and protection. They also welcomed the cats in the barn. But often in cases of interspecies interaction, only one species of animals wins.
Cooperative hunting between humans and cetaceans—aquatic mammals such as dolphins and whales—is a great example of this.
In the past, whalers have teamed up with killer whales to hunt baleen whales in southeast Australia. Meanwhile, in eastern Australia, eyewitness accounts and Australian Aboriginal stories suggest that dolphins and humans hunted together more often than they do today. The traditional fishermen of the Laguna in Brazil are one of the few surviving examples of this close and collaborative association.
Both dolphins and local fishermen have learned to read body language and respond accordingly.
The fishermen, who wore GPS bracelets, moved by wading through shallow water so that they could be tracked towards the dolphins as the marine mammals arrived on the scene. They also cast their nets at a faster rate when dolphins were present.
Obviously, the mammals were evidence that there was a mullet nearby. Anglers who followed its fins were 17 times more likely to fish in shallow water.
“It is clear that dolphins benefit fishermen in their search for food and elicit beneficial actions in response to increased mullet availability, which would not be the case when dolphins are absent,” the researchers write.
It is very difficult to calculate the amount of fish swallowed by a mammal compared to how many a fisherman catches. How is hunting dolphins with people different from hunting dolphins without people?
The researchers used some clues above and below the water to figure it out. From above, the researchers observed how the dolphins get very close to the fishermen, giving them a signal to cast their nets – a deep dive.
Meanwhile, underwater, the dolphins amplify their echolocation clicks as fishermen cast their nets. When the nets fall, the dolphins also dive for longer periods.
The researchers suspect that the dolphins are taking advantage of the fact that the nets break up the swarm and send individuals out singly, thus making it easier for them to get stuck. Underwater footage also shows individual dolphins catching fish directly from their nets, and local fishermen report that this happens frequently.
Nearly all of the local fishermen interviewed by the researchers said they thought marine mammals would catch more fish in this situation.
Ultimately, the researchers calculated that bottlenose dolphins that hunt together have a 13 percent increased chance of survival.
But if something happens to the dolphins, mullets, or people in the area, those benefits could be gone. These mammals do not have any genetic differences.
“Protecting behaviors that benefit both humans and wildlife not only promotes their coexistence, but is also symbolic of how the conservation of ‘important units’ in biodiversity conservation can be improved,” the researchers write.
The study is published in PNAS.
Source: Science Alert
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