This unique cooperation has been first formally studied by Karen Pryor and her colleagues: Pryor, K.W., Lindbergh, J., Lindbergh, S. & Milano, R. (1990) A dolphin-human fishing cooperative in Brazi...
This unique cooperation has been first formally studied by Karen Pryor and her colleagues: Pryor, K.W., Lindbergh, J., Lindbergh, S. & Milano, R. (1990) A dolphin-human fishing cooperative in Brazil. Marine Mammal Science 6:77--82. Here is how they described it:
"The fishing is highly ritualized and appears to involve learned behavior by both men and Dolphins. The fishermen, each with a circular nylon throw-net rimmed with weights, position themselves in a single line, a net's diameter apart, standing in approximately 1 m of water parallel to the shore. One or two dolphins station themselves several meters outside the line of men, facing seaward, floating or moving slowly at the surface. From time to time a dolphin submerges, usually in moving seaward; the men then brace 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 the net range, 5-7 from the line, thus making the surging roll at the surface, a movement markedly different from normal respiratory surfacings. Men who are in front of the dolphin as it rolls then cast their nets. Successful fishermen return to the beach to harvest their catch, and others replace them on the line. The men rarely cast without a dolphin's cue, and nets were not cast behind a dolphin, or in its general vicinity, or in front of dolphins that had not signaled, but only in front of dolphins performing the correct behavioral sequence indicating the arrival of fish. The cue is quite informative. Timing of roll: fish are present. Direction of dolphin's movement: Location of fish. Vigor of movement: appears to indicate whether the schools is large or small. Episodes which are successful for the fishermen are often followed by bouts of dolphins feeding. For the dolphins, this fishing method provides a reliable, easily located resource. The fishing appears to be initiated and controlled by the dolphinss, not by the men. On 4 occasions, when dolphins moved to another sections of the beach, immediately some or all of the men ran to reform a line in the new site selected by the dolphin. In other parts of the lagoon on several occasions we have seen one or more men waiting to shore in the hope of a dolphin's arrival. Fishing does not begin until a dolphin initiates it. Unlike other parts of the world, here dolphins do not play or socialize. 'At no time did we observe a fisherman call out, signal to, or in any way attempt to affect the behavior of a a dolphin. Fishermen never touch, train, give fish to, dolphins. 25-30 of the dolphins are said to participate in the cooperative fishery. Unlike other accounts, here in Laguna dolphins work individually, and they initiate and control the fishing. Here, as well, used with many prey species, almost year-round. Feeding specializations might be transmitted culturally within long-term associations of related individuals."
As will be described in detail elsewhere, this description beautifully captures the essence of the interaction. One possible minor error is, as can be seen in this and other video clips posted here, that no rolling action is involved. Overall, the action is extremely rapid, so that its details can only be caught and studied on film. On average, during the period that comprises the signal, the dolphin can be seen above water for just 1.4 seconds.
