Trophic ecology of elasmobranchs caught off Gujarat, India, as inferred from stable isotopes

Habitat use and trophic levels were investigated in 13 species of elasmobranch caught off Gujarat, India, through their isotopic composition. Most of the animals were fished commercially and were immature, suggesting that fisheries operate in nursery habitats. All of the sharks analysed except Rhincodon typus had a higher estimated trophic level (>3.8) than rays and guitarfish (<3.8), suggesting a diet of bony fish and cephalopods. The trophic level of Sphyrna lewini and R. typus increased with total length, indicating ontogenetic dietary shifts, but the other species did not follow this trend. According to their delta C-13 values, R. typus, Mobula diabolus, and, surprisingly, Rhina ancylostoma appeared to be the most pelagic species. In comparison, Stegostoma fasciatum, Pristis pectinata, Rhinobatos granulatus, and Aetomylaeus maculatus appeared to be the most demersal, inshore species, and their delta C-13 signatures were significantly different from those of the three aforementioned species.