It is said that tuna aggregate under floating objects, such as lengths of old rope, pieces of wood, or even large marine mammals. And so the purse-seine fishery operators take advantage of the associated concentrations of fish. The fishermen cast off floating rafts equipped with buoys which act as FADs. It was first observed in 1990s that the tuna catches from under these FADs showed sudden growth in the size.
It is said that the flesh from floating-object associated tuna was less plump than that of specimens caught from free schools. An IRD research team probe whether or not the practice of drifting FAD fishing could set up an ecological trap for the tropical tuna species. To check if the large-scale deployment of drifting FADs could present an ecological trap for these species, a range of biological (fish plumpness, growth rate, stomach fullness) and ecological (migration pattern and distance) indices were determined on yellowfin and skipjack captured under FADs in the Atlantic and Indian Oceans.
The result was that 74 percent of drifting FAD-associated skipjack had empty stomachs at the moment of capture compared with only 13 percent for those fished from free schools. For yellowfin tuna 49 percent caught on drifting FADs and 7 percent from free schools. It shows that tuna caught under the FADs fed less well than those fished from free schools.
According to the research team the drifting FADs appeared to act as super-stimuli, like strong magnets exerting a binding attraction that leads the tuna towards ecologically inappropriate waters with scarcer food supplies. Nevertheless, the biological effects observed indicated that it would be more reasonable to preclude deployment of drifting FADs near coasts where tuna juveniles aggregate.
