Cephalopods eaten by pelagic fishes in the tropical east Pacific, with special reference to the feeding habitat of pelegic fish

Abstract

Cephalopods removed from stomachs of pelagic fish in tropical East Pacific were examined. From 131 stomachs of 14 pelagic fish species, more than 40 cephalopod species of 20 families were identified. 30% of prey cephalopods were occupied by the onychoteuthids consisting by at least 3 species followed by the Ommastrcphidae (14%), and tho Bolitaenidae (7.0%). Predominant prey species for Xiphias gladius was epipelagic octopus, Tremoctopus violaceus, which shared 17% in number. There were some differences between prey species composition between two species of tunas, Thunnus obesus and T. albacares. T. obesus fed on more deeply distributed. mesopelagic species than T. albacares. A coincidence in time and depth was detected between predatory fish and prey cephalopods. Small onychoteuthid species, Onykia rancureli was most abundant in number among prey cephalopods (21%). 1t shared 29% of prey cephalopods for Thunnus obesus. From frequency of occurrences in fish stomach contents, 0. rancureli seems to live in epipelagic or upper mesopelagic waters, abundant around the bottom of mixing layer, and thus plays an important role among food of T. obesus and T. albacares. From the species composition of eaten cephalopods, the major large pelagic fish discrete feeding depth with minor overlaps, such as, surface layer for bill- and swordfish, around bottom of mixing layer for tunas, and mid water for rnidwater scornbrids. Only Alepisaurus ferox seems to be a vertical wonderer