Humans and dolphins on the southern coast of Brazil have formed a carefully coordinated ‘dance’ to feed migrating humpback whales in their nets and mouths as much as possible.
Traditional fishermen in Laguna have been working with Lahille’s bottlenose dolphins (Tursiops truncatum gephyreus) fishing for over 140 years.
From above, dolphins can be seen driving schools of mullet along the shore, next to fishermen wading in shallow water. When the fishermen received a signal from the dolphins, they cast their nets.
Researchers have spent more than a decade studying this close relationship, and say it’s a rare example of cooperation, where two species help each other to have a chance at survival.
“We knew that the fishermen were watching the behavior of the dolphins to know when to cast their nets, but we did not know if the dolphins were coordinating their actions with the fishermen,” said marine biologist Mauricio Cantor, from Oregon State University.
“Using drones and underwater photography, we can see the behavior of fishermen and dolphins in unprecedented detail and we found that they catch more fish by working together.”
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The struggle for natural survival is often expressed as such: the struggle for limited resources, friendships, or territories. But collaboration is an important part of the equation that tends to be overlooked.
Teamwork and interspecies activities are common – think of fish swimming in schools or lions hunting in groups – but two species of animals working together are extremely rare.
Humans have always interacted with wild animals for profit. Our ancestors took wild wolves and turned them into domesticated dogs to hunt and protect them. They also welcomed cats into the barn. But often when there is an interaction between different species, only one animal benefits, such as sharks that eat the remains left behind by fishermen.
It’s rare to find a mutually beneficial relationship, but even if two species eat the same meat, lunch doesn’t have to be a zero-sum game.
Co-operative fishing between humans and cetaceans – marine mammals such as dolphins and whales – is a prime example of this.
In the past, human whales have teamed up with orcas to hunt baleen whales off southeastern Australia. Meanwhile, in Eastern Australia, eyewitness accounts and stories from Australian Aborigines indicate that dolphins and humans fished closer together more often than they do today.
The traditional fishermen of Laguna in Brazil are one of the remaining examples of such close cooperation.
The dolphins and local fishermen have learned to read each other’s body language and respond accordingly.
The fishermen, wearing GPS wristbands as they navigated the shallows to be tracked, moved toward the dolphins as the marine animals approached the area. They also throw their nets very high when the dolphins are close.
Apparently, the mammals were a sign that the mullet were nearby. Fishermen who followed their fins were 17 times more likely to catch fish in shallow water. They caught 4 times more, even though they spent the same amount of time casting their nets.
“Dolphins produce a foraging benefit for fishermen and encourage action based on mullet populations that are absent when dolphins are not present,” the authors wrote.
But what do dolphins get? It is very difficult to calculate the number of fish that a mammal eats compared to the number of fish that a fisherman kills. How do dolphins in the presence of humans differ from their dolphins without humans?
Researchers have used a few signals above and below the water to find out. From above, the authors saw dolphins approaching the fishermen and giving them a signal to throw their nets – to sink deep.
Under water, dolphins increase their pulse when fishermen cast their nets. When the nets fall, the dolphins also dive for a long time.
Researchers think that the dolphins are benefiting from the way the nets break up the school of mullet and send people on their own, making it easier to catch them. Underwater footage also shows dolphins catching fish directly from nets, and local fishermen say this is a common occurrence.
Almost all of the local fishermen interviewed by the researchers said they believe that marine animals get extra fish from these activities.
In the end, the authors calculate that only 13 percent of bottlenose dolphins caught with humans survive.
But if anything happens to the dolphins, the mullet, or the people in the area, those benefits could end. There is no genetic difference between these mammals. This character affects everything that is happening, and there is no telling how long the story will last.
“Protecting cultures that benefit humans and wildlife not only encourages coexistence but is also a sign of how preserving ‘culturally important areas’ can help protect ecosystems,” the authors wrote.
The relationship between humans and wildlife is increasing, Cantor says. It is important that we save as much as we can.
This study was published in PNAS.
