Seasonal, sex and ontogenetic trophic shifts of striped <scp>M</scp> arlin ( <i>Kajikia audax</i> ) in <scp>C</scp> abo <scp>S</scp> an <scp>L</scp> ucas, <scp>B</scp> aja <scp>C</scp> alifornia <scp>S</scp> ur, <scp>M</scp> éxico

Abstract The striped marlin ( Kajikia audax ) is an important target species for the sportfishing industry of Cabo San Lucas, Baja California Sur. This study evaluated intraspecific variations in feeding ecology using stomach content and stable isotope analyses across sex (males vs. females), ontogenetic stage (juvenile vs. adult) and season (cold vs. warm). Between 2019 and 2022 a total of 251 stomachs containing identifiable prey items and 80 muscle tissue samples were collected. Diet was dominated by pelagic fishes and cephalopods, with jumbo squid ( Dosidicus gigas ), paper nautilus ( Argonauta spp.), Pacific mackerel ( Scomber japonicus ) and finescale triggerfish ( Balistes polylepis ) among the most important prey. Stomach content analysis revealed significant seasonal variation in diet composition, whereas no differences were detected between sexes or ontogenetic stages. Stable isotopes analysis showed no significant differences in δ 13 C or δ 15 N values among seasons, sexes or ontogenetic stages. However, mixing model results indicated a seasonal shift in resource use: planktivorous fish ( Sardinops sagax, Lagocephalus and Decapterus macrosoma ) contributed more during warm season, while piscivorous fishes ( S. japonicus, B. polylepis, Caranx caballus, Auxis spp. and Fistularia spp.) dominated across sexes, ontogenetic stages and during the cool season. Overall, these results suggest that striped marlin exhibit flexible, seasonally driven trophic behaviour likely mediated by changes in prey availability, whereas sex and ontogeny have limited influence on dietary patterns in this population.