Relationships among yellowfin and skipjack tuna, their prey-fish and plankton in the Tropical Western Indian Ocean

Stomach contents of yellowfin (#Thunnus albacares$) and skipjack (#Katsuwonus pelamis$) tuna caught by trolling and purse seining in the tropical western Indian Ocean, together with those of the prey-fish found in their stomachs, have been analysed. Epipelagic fish are the main prey of these tunas, whereas no vertically migrating fish, which inhabits subsurface layers at night, have been found in their stomachs. These tunas are thus considered day-feeders. Purse-seine-caught tunas, which belong to large schools, have a much higher number of prey-fish in their stomachs than tunas caught by trolling on small schools. Similarly, prey-fish from purse-seine tunas have a much higher number of planktonic prey in their stomach than those from the troll-caught tunas. Therefore, these tunas adopt a wandering strategy in small schools when they are abundant. (D'après résumé d'auteur