Isotopic niches of four commercially important pelagic elasmobranch species captured by the small-scale driftnet fishery of northern Peru

Abstract

Despite the high landings of elasmobranch in Peru, little is known about some aspects of their basic biology, including their trophic ecology. The present study aims to provide basic information regarding the isotopic niche and trophic interactions of four pelagic elasmobranchs of commercial importance in northern Peru (Alopias spp., Galeorhinus galeus, Sphyrna zygaena, and Mobula japanica). One hundred and twenty-four samples were collected from fishing activities between January and December 2015 and processed for stable isotopes analysis (δ13C and δ15N), using Bayesian statistics to describe their isotopic niche. Differences between species were assessed using PERMANOVA and PERMDISP, allowing testing length, sex, and latitude as covariates. These combined results suggest trophic redundancy among sharks. However, unique areas of no overlap in the SEA<inf>C</inf> of all species could evidence a broad niche with a low interaction between these sharks. M. japanica had no overlap with any shark species, which indicates a trophic niche that is distinct from other elasmobranch top predators. Increasing sample size and including temporal covariates should help define these isotopic niches better, either by merging or splitting the studied elasmobranchs into more specific groupings. Further complementary studies are required to better understand trophic interactions within the pelagic community ecosystems.