SCIENCE / MEDICINE : Fishermen Take Cues From Dolphins in Rare Partnership

In what may be a unique swapping of roles, a group of dolphins in a lagoon near the southern tip of Brazil seem to be leading the local fishermen in a highly successful cooperative fishing operation.

Historical accounts, going back to Pliny the Elder (AD 23-79), offer repeated examples of joint dolphin-human efforts to trap mullet against beaches. In these accounts, ranging from the Mediterranean to North Africa to Australia, men on shore observe mullet traveling along the coast, too far to reach from land. If dolphins happen to be passing, the men shout, whistle or slap the water to attract the dolphins. If the dolphins then move toward shore, the mullet are trapped, and men scoop or spear them in the shallows.

But these events, recorded centuries and continents apart, appear to have been sporadic, opportunistic and seasonal examples of joint predation, associated with the inshore movement of breeding mullet.

Not so in the 143-year-old dolphin-human fishery at Laguna. A complex choreography has evolved in which the fishing is initiated and controlled by the dolphins. And as such, the behavior may be unique.

The water at Laguna is extremely murky; visibility is less than a foot. The fishermen cannot see the fish and must depend on the dolphin’s behavior to know when to cast their nets. The dolphins detect fish, round them up and deliver them to waiting fishermen near the shore.

The fishing at Laguna occurs primarily on the shores of an inlet that extends from the ocean to a brackish lagoon near the center of town. Fishermen and townspeople said the fishing takes place all day, every day, except during bad weather, and all year except in the Southern Hemisphere winter months of July and August.

According to town records, the unusual arrangement began in 1847. Some fishermen said their fathers and grandfathers fished with the dolphins, sometimes with the same individual animals, many of them recognizable by marks and scars. In at least one “family” of dolphins, three generations of recognized animals are now working in the fishery.

While mullet are the main catch, other species taken include the Brazilian croaker and the black drum. The catch is sold in nearby markets, and the dolphin-associated fishery appears to be the primary source of income for about 100 families.

But this is strictly a business relationship. Like many joint ventures, there is mutual respect but no obvious friendship between the partners.

Here’s how the enterprise usually works:

The fishermen, each with a circular nylon throw-net rimmed with weights, position themselves in a single line, a net’s diameter apart, in knee-deep water parallel to the shore. One or two dolphins station themselves several yards outside the line of men, facing seaward, floating or moving slowly at the surface. From time to time a dolphin submerges, usually moving seaward, and the men ready themselves.

The dolphin reappears, usually in a few seconds, traveling toward the line of men. It comes to an abrupt halt and dives just out of net range, 15 or 20 feet from the line, making a surging roll at the surface that is quite different from normal respiratory surfacings.

The men wait for the dolphin’s signal and then cast their nets. Successful fishermen return to the beach to harvest their catch, and others replace them on the line.

The timing and placement of the net cast are crucial because refolding the nets takes time and may cause a fisherman to miss a better opportunity.

Cues by the dolphins give the fishermen vital information. The timing of the roll indicates that fish are present; the direction of the dolphin’s movement indicates the location of the fish, and the vigor of the movement appears to tell whether the school is large or small.

And what’s in this partnership for the dolphin? When the nets fall, the fish schools lose their rhythm and cohesion and become easy prey. Individual dolphins, including females with calves and at least one dolphin the fishermen said was more than 70 years old, can catch mullet with minimal effort.

Successful fishing episodes are often followed by bouts of the dolphins’ feeding behavior. They dart about rapidly under water, wave their flukes in the air and thrust their heads out of water, fish clenched in their jaws.

Meanwhile, the human partners are profiting. In half an hour, a single dolphin can bring fish to the line six times. In a typical dolphin fish delivery, one or more fishermen will catch fish, typically 10 or more weighing up to 4 1/2 pounds each. One man in a boat, working with a single dolphin, can catch more than 220 pounds of mullet in about two hours.

The fishing appears to be initiated and controlled by the dolphins. Fishermen and their families often wait along the shore in hope of a dolphin’s arrival, and the process does not begin until a dolphin decides to start work.

Sometimes a working dolphin leaves the line of men and moves to another section of beach; immediately the men run through the water to re-form a line in the new site selected by the dolphin. One young male dolphin sometimes makes the men move repeatedly, apparently for sport.

The fishermen do not call out, signal or attempt to affect the dolphins’ behavior, which sets this activity apart from the informal man-dolphin interaction in other parts of the world where dolphins have been known to play or socialize with swimmers and boaters.

The Laguna fishermen do not think they train the dolphins. They never give them a fish. They do not attempt to touch them. Several fishermen said it is important not to distract the dolphins from their work.

The participating animals have been named and recognized by many fishermen. Even animals without obvious marks or scars can be identified by fishermen at a distance of 160 feet or more.

Dolphins that are not in the partnership are called “bad” dolphins ( ruim in Portuguese). The ruim may occasionally interfere with the fishing, typically by dispersing fish and by damaging nets. Dolphins in the partnership were reported by fishermen to be aggressive in defending the fishery. And the fishermen said they believe the “good” dolphins stay close to their work, being mostly resident in the lagoon.

Although the human-dolphin cooperative fishing has long been part of daily life in Laguna, the situation is fragile. Tourism and increasing industry in the state of Santa Catarina are luring fishermen’s sons into construction work and taxi-driving.

Working dolphins have been drowned in commercial fishing nets offshore, and attempts to widen or deepen the lagoon entrance, to accommodate vessel traffic, might destroy the principal fishing beaches. Scientists hope to work with Brazilian environmental organizations to protect this unique example of human and animal cooperation.