Composition of piscine prey in the diet of large pelagic fish in the eastern tropical Pacific Ocean

Abstract

We examined the stomach contents of seven pelagic fish species collected by longline in the eastern tropical Pacific Ocean: yellowfin tuna Thunnus albacares, bigeye tuna T. obesus, swordfish Xiphias gladius, striped marlin Tetrapturus audax, dolphinfish Coryphaena hippurus, lancetfish Alepisaurus ferox, and pelagic thresher Alopias pelagicus. Fifty fish species from 31 families were identified in 222 stomachs examined. The choice of prey fish was very similar between bigeye tuna and swordfish, yellowfin tuna and swordfish, yellowfin tuna and dolphinfish, and big eye tuna and pelagic thresher. In contrast, similarity was low between striped marlin and lancetfish, dolphinfish and pelagic thresher, and lancetfish and pelagic thresher. According to the habitat depth range of prey fish, the seven predator species were divided into three groups: (i) wide range feeders from surface to midwater (yellowfin tuna and striped marlin); (ii) epipelagic feeders (dolphinfish); and (iii) midwater (mesopelagic) feeders (bigeye tuna, swordfish, lancetfish, and pelagic thresher). The most important prey fish belonged to the following families: Sternoptychidae, Phosichthyidae, Paralepididae, Omosudidae, Myctophidae, Exocoetidae, Hemiramphidae, Bramidae, Gempylidae, and Scombridae. Although pelagic fish predators extensively use these prey families, different dominant families and feeding depths of each predator are considered to reduce trophic competition among pelagic fish in the eastern equatorial Pacific.