Dolphins and Humans Cooperate To Catch Fish

The state of the universe.
Jan. 31 2013 1:41 PM

Fishing With Dolphins

An astonishing cooperative venture in which every species wins but the fish.

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No matter how pedestrian, cynical, or out-there the goals were, the transactions were largely performed in captivity, with dead fish as currency. Some researchers may have considered dolphins capable of conversation, dreaming of the day when the animals could visit and leave the labs as they wished, but in practice the relationship differed little from that of people and their dogs or any other clever domestic animal.

Here on the small beaches of Laguna, no fish are exchanged directly. The dolphins work on their own time: The fishermen often stand idly onshore when the botos are not around. “There is no schedule here,” a fisherman told me. “Sem botos, não da.” (Without dolphins, it’s not worth it.)       

Beyond Brazil, such symbiotic interactions, in which both humans and a wild species benefit, are rare. Most appear to be what biologists call commensal relationships: One side benefits, the other neither gains nor loses. (Dolphins feeding on fisheries discards is a good example of commensalism.) When dolphins feed directly off of a fishing line, it’s known as parasitism, or kleptoparasitism, and it often fuels tensions between fisheries and cetaceans. But in Burma, the Irrawaddy dolphins appear to cooperate with a cast-net fishery, and there are accounts of Australian aborigines fishing with dolphins and orcas in eastern Australia. In Mauritania, dolphins help strand mullet on the beach, in what has been described as a “great melee.”

Simões-Lopes believes that a similar process occurs in the relaxed atmosphere of Laguna. The techniques and rewards of cooperative feeding are passed from generation to generation—by the fishermen, as well as the dolphins. “When the kids come, they learn,” a fisherman told me, talking about the juvenile dolphins. Mother dolphins train their offspring by escorting them toward the nets and then letting the young give chase.

Daura-Jorge describes the social structure of the good dolphins as “fission-fusion:” a fluid social network dominated by short-term associations that often form around the fishermen, then break apart.

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That night, I stopped by a restaurant across the street from my lodgings (the Flipper Hotel, of course). The place was nearly empty. The menu was long, but there it was: grilled tainha. Mullet isn’t my favorite fish, but I couldn’t find a good excuse not to order it.

A tainha the length of my forearm arrived, sizzling on a hotplate. It was moist, fresh, and delicious. This being Brazil, it was accompanied by french fries, rice, a salad, and pirão, a thick orange fish sauce. When the waiter returned with a beer, I asked him where the fish was from. “Tesoura.” Mine was a dolphin-assisted meal.

Tesoura seems like a throwback in time, before fishing became industrial, from some time in our distant past, if it ever existed, when there was a pervading sense of harmony. The fishermen have a tradition of cooperation with the dolphins and among themselves: Simões-Lopes has recorded a “shift rotation system” that prevents one fisherman from taking more than his fair share. At Tesoura, when a man catches two mullets, he has to leave his place in the water, which is taken by the next one in line. Elsewhere in Laguna, the person who gets a fish big enough to feed his family has to yield his place to the next.

That morning, the men fed small fish to the cats. They pet the stray dogs. They tossed the occasional fish to the herons waiting patiently on the edge of the riprap. They told me a story about an endangered right whale that swam up the channel with its newborn calf a couple of years ago. The pair became disoriented in the lagoon, and after showing signs of distress, the whales were joined by a few dolphins. Though much smaller even than the newborn whale, the dolphins escorted the mother and calf out of the channel to the safety of the open sea. Or so the fishermen say.

As the sun goes down, Laguna can feel dreamlike, almost Edenic. But I’m from a family of worriers, so I worry. As I sat on the shore, I started to think about the risks of disease transmission. Most of the dog and cat feces must wash into the sea. Toxoplasma, a parasitic protozoan carried by cats, has been found in seals and sea otters, giardia in whales.

The fishermen look out for the dolphins. Daura-Jorge told me that he couldn’t biopsy them, which required taking a piece of skin and blubber the size of a pencil eraser, within sight of Tesoura. The fishermen got too upset. But bigger risks waited up in the lagoon. Dolphins occasionally swim into gill nets stretched along the Tubarão River that flows into the lagoon; they get entangled and often die. (The “good” dolphins have a slightly higher mortality rate.)

Changes in the fishery may be putting the relationship between fishermen and dolphins at risk. The last season has been pretty bad for the mullet fishermen of Santa Catarina. Some locals blame fishermen from Uruguay for endangering the fish population by targeting gravid females for the roe. (When I looked, mullet roe, or bottarga, was available on-line from Uruguay and Brazil in 50-pound cartons. External markets, whether in Japan, Europe, or elsewhere, can tilt the balance of local fisheries away from sustainability.) Daura-Jorge isn’t so sure the pressure is external: 2011 was one of the best years that anyone could remember for cooperative hunting, and 2012 was one of the worst. The bad year could be a blip, or something more worrisome. Natural resource managers use the term “killer spike,” to describe a pattern of rising catches, followed by a steep decline.

Given the ravages that we have imposed on the ocean, I admit to feeling reluctant to celebrate any aid in removing fish from the sea. Are these dolphins helping build a sustainable coastal economy, or are they helping destroy it?

There is resilience to this dolphin population. Cooperative fishing survived the 1940s construction of the kilometer-long jetty that points out into the South Atlantic. The jetty changed the hydrology of the region—the lagoon, once only intermittently connected to the ocean, is now permanently linked by a channel. Still, the inlet is rarely used. During the few windy days I stayed in Laguna, I never saw a boat head out to sea. The waters at the mouth are often too rough for navigation.

The dolphins have no such troubles. When most of the men started packing up for the day, a mother-calf pair left Laguna, headed east to the open ocean. I followed the dolphins out to the point. These are wild animals, at home in the rough sea, which almost lapped against the pink ceramic lighthouse. If the snarling whitecaps bothered the mother-calf pair, I couldn't see it. They seemed to be enjoying the breakers, intentionally choosing the roughest patches to surf, swimming to the back of the wave, and then breaking through the crest.

A wave heaved up over the jetty, soaking my pants. As I hustled back to town, I noticed that a fisherman had returned to Tesoura. A dark triangle slowly approached him from the water. It was getting oddly close and wasn’t submerging like a dolphin. I wondered if it was a shark, or perhaps a dog.

But no. It was another “enemy” of the fisherman, the sea lion. In many parts of the world, a fisherman would shoot a pinniped on sight (or out of sight, if the animal was protected by law). The seal paused, nose in the air, head slightly tilted, then approached the fisherman, who slapped his thigh, as if calling in a new tradition.

Joe Roman is a conservation biologist at the University of Vermont and a fellow at the Gund Institute for Ecological Economics. He is the author of Listed: Dispatches from America's Endangered Species Act, winner of the 2011 Rachel Carson Environment Book Award. His website is www.joeroman.com. This article was written while he was a Fulbright Scholar in Brazil.