Ontogenetic Dietary Shift in Megabenthic Predatory Elasmobranchs of a Tropical Estuarine Bay

Abstract

Elasmobranchs play a significant role in structuring the marine food webs in many marine habitats.Estuaries provide an essential habitat primarily as nurseries for elasmobranchs.The present study investigates the feeding preferences of megabenthic predatory elasmobranchs from Caranzalem Bay, Goa.The elasmobranchs in this habitat were represented by guitarfishes, Glaucostegus granulatus and Glaucostegus obtusus; rays, Brevitrygon walga, Pastinachus sephen, Neotrygon kuhlii, and Maculabatis gerrardi; and bamboo sharks, Chiloscyllium griseum and Chiloscyllium spp.Crustaceans were the major prey of these predators followed by teleosts and cephalopods.The bamboo shark was an opportunistic predator while rays and guitarfish were specialised feeders on penaeid shrimps.Indices suggest that bamboo sharks occupy the highest trophic level in this benthic food chain while guitarfishes and rays function as mesopredators.Ontogenetic dietary changes were observed in all predators, indicating the feeding niche segregation among size classes.Low resource overlap was observed between and within species probably due to high prey availability in the bay.These elasmobranch species frequently occur in bycatch, which can negatively affect their populations and thereby impact the lower trophic strata resulting in large-scale ecological repercussions.