Feeding ecology of two filter feeding sharks in the northwestern Pacific Ocean

This study examines the feeding information of two filtering shark species, the megamouth shark ( Megachasma pelagios ) and the whale shark ( Rhincodon typus ). Specimens were obtained through the mandatory catch and reporting system in Taiwan, providing stomach composition of M. pelagios and tissue samples for two species. A total of 19 stomachs were examined, with five found to be high digested or empty. Analysis of the remaining 14 stomachs revealed that M. pelagios primarily consumes zooplanktonic prey, including krill (Euphausiacea), jellyfish (Medusozoa), shrimp larvae (Dendrobranchiata), squat lobsters (Anomura), and crab larvae (Brachyura), indicating a low trophic level diet. Stable isotope analysis (SIA) of 91 M. pelagios and 90 R. typus specimens inferred distinct feeding strategies and diet compositions between the two species. M. pelagios is characterized as an inactive feeder employing engulfment feeding, whereas R. typus is an active suction-filter feeder capable of preying on small fish, squid, and displaying ontogenetic changes in diet. Both species are believed born in less productive waters and transition to more nutrient-rich habitats as they mature. Ontogenetic dietary shifts were observed in R. typus , attributed to enhanced swimming abilities and specialized gill-rakers facilitating more active suction feeding. Conversely, no significant diet shift during growth was noted in M. pelagios ; however, differing stable isotope signatures between male and female specimens suggest sexual segregation. Further research involving individuals of various size classes for both M. pelagios and R. typus is needed to corroborate these findings.