Diet composition of sailfish (Istiophorus platypterus) from the southern Gulf of California, Mexico

Diet composition of the sailfish Istiophorus platypterus from the southern Gulf of California was determined using stomach contents of 576 fish. They were sampled from 1989 to 1991 from the sport fishing fleet at six tourist ports of the Mexican Pacific (La Paz, Cabo San Lucas, Mazatlan, Puerto Vallarta, Barra de Navidad, and Manzanillo). A total of 78 different prey taxa was classified and 64 were identified to species. From the diet composition and using the percent of index of relative importance (IRI), three feeding zones were determined by using cluster analysis. The most important prey by zones were in Zone I, La Paz: Dosidicus gigas, Scomber japonicus, and Auxis spp.; Zone II, Cabo San Lucas: Auxis spp., Selar crumenophthalmus, and Lagocephalus lagocephalus; and Zone III, Mazatlan, Puerto Vallarta, Barra de Navidad, and Manzanillo: Argonauta spp., D. gigas, and Auxis spp. We suggest that Sailfish in Mexican Pacific waters are generalist predators feeding mainly on epipelagic species in coastal and oceanic waters, and occasionally diving to Prey on demersal fish. The changes in diet composition among zones seem to be related more to abundance and distribution of the prey than to food preferences.