Feeding Ecology of Elasmobranch Species along the Visakhapatnam Coast, India

Abstract

Overfishing is a major threat to Indian elasmobranch populations. The reduction in their numbers leads to significant top-down ecological consequences, disrupting marine ecosystems. Therefore, understanding the marine food web dynamics is essential. This study investigates the feeding ecology and trophic interactions of elasmobranchs, including bigeye houndsharks (Iago omanensis), longtail butterfly rays (Gymnura poecilura), stripenose guitarfish (Acroteriobatus variegatus), whitespotted whiprays (Maculabatis gerrardi) and mobulid rays along the Visakhapatnam coast. We used stomach content analysis (SCA) and stable isotope analysis (SIA) to investigate: (i) the effect of habitat on diet, and (ii) dietary differences between species. G. poecilura and I. omanensis exhibited piscivorous diets, with I. omanensis showing greater prey diversity. In contrast, A. variegatus and M. gerrardi majorly consisted of crustaceans, indicating lower dependence on teleosts. Overall, benthic species (A. variegatus, G. poecilura, and M. gerrardi ) showed distinct diet differences from pelagic species (I. omanensis), minimizing niche overlap. Similarly, SIA revealed the benthic species, G. poecilura and M. gerrardi, were enriched in 13 C while the pelagic species, mobulids and I. omanensis, were depleted in 13 C, consistent with their expectations based on their feeding habitats. δ 15 N values highlighted significant differences in trophic levels: mobulids had low δ 15 N values, aligning with their planktivorous diet, whereas G. poecilura had high δ 15 N values, indicating its role as a predator. This study valuable insights into the feeding ecology of elasmobranchs and their role in the western Bay of Bengal. Further research on temporal variation, resource partitioning, and ecological roles are required to support conservation and management efforts.