Abstract
Knowledge of the trophic ecology and interactions of marine top predators is funda- mental for understanding community structure and dynamics as well as ecosystem function. We examined the feeding relationships of 4 heavily exploited elasmobranchs caught in coastal arti- sanal shark fisheries in south-western Madagascar in 2009 and 2010— Sphyrna lewini, Loxodon macrorhinus, Carcharhinus falciformis and Rhynchobatus djiddensis—using stable isotope (δ 15 N and δ 13 C) analysis. Relative trophic position (indicated by δ 15 N) and foraging location (indicated by δ 13 C) differed among species. Isotopic niche width was highly variable: more pelagic species, such as S. lewini and C. falciformis, had the broadest isotopic niches while the benthic R. djidden- sis had the narrowest. A high percentage of niche overlap occurred between R. djiddensis and 2 of the species, C. falciformis (93.2%) and L. macrorhinus (73.2%), and to a lesser extent S. lewini (13.3%). Relative trophic position of S. lewini significantly increased with size, suggesting a dietary shift with age. Sex differences in δ 15 N values were observed in L. macrorhinus, suggesting intraspecific niche partitioning. Variation in stable isotope values among these 4 highly exploited elasmobranch species indicates trophic structuring, likely driven by differences in diet and habitat use as well as by size and sex. This study provides the first baseline information on the trophic ecology of elasmobranchs caught in artisanal fisheries from south-western Madagascar.
Highlights
INTRODUCTIONPredicting the community-level consequences of changes in the abundance of a particular species, due to natural or anthropogenic factors, requires an understanding of its trophic interactions and trophic similarity amongst species
Predicting the community-level consequences of changes in the abundance of a particular species, due to natural or anthropogenic factors, requires an understanding of its trophic interactions and trophic similarity amongst species, but there is a paucity of data regarding trophic relationships among species within this predatory guild
The size range of individuals sampled was highly variable among species, with juveniles making up the majority of individuals, especially for S. lewini and R. djiddensis (Table 2, Fig. 2)
Summary
Predicting the community-level consequences of changes in the abundance of a particular species, due to natural or anthropogenic factors, requires an understanding of its trophic interactions and trophic similarity amongst species No baseline ecological data exists for elasmobranchs from this region, but a decline in elasmobranch abundance has been observed for the most exploited species (McVean et al 2006) This decline of elasmobranchs from the coastal waters of south-western Madagascar could have adverse effects on both fishing communities and marine ecosystems. We used stable isotopes to assess trophic relationships, isotopic niche breadth and overlap, as well as ontogenetic variation in trophic interactions among the most commonly caught elasmobranch species in artisanal fisheries operating in the coastal waters off south-western Madagascar (Table 1), including the scalloped hammerhead shark S. lewini, the sliteye shark Loxodon macrorhinus, the giant guitarfish Rhynchobatus djiddensis and the silky shark Carcharhinus falciformis
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
