Trophic niche of Australian cownose rays ( Rhinoptera neglecta ) and whitespotted eagle rays ( Aetobatus ocellatus ) along the east coast of Australia

Abstract

Australian cownose rays ( Rhinoptera neglecta ) and whitespotted eagle rays ( Aetobatus ocellatus ) are large myliobatiform rays that co‐occur off temperate eastern Australia. Here, we performed stable‐isotope analyses (δ 13 C, δ 15 N and δ 34 S) on fin clips of both species to gain insights into their trophic interactions and isotopic niches, and assess the effect of preservation (ethanol‐stored versus frozen) on isotopic values of fin‐clip tissue of R. neglecta . Linear mixed models identified species as the main factor contributing to variation among δ 15 N and δ 34 S values, and disc width for δ 13 C. Bayesian ecological niche modelling indicated a 57.4% to 74.5% overlap of trophic niches, with the niche of R. neglecta being smaller and more constrained. Because values of δ 13 C were similar between species, variation in isotopic niches were due to differences in δ 15 N and δ 34 S values. Linear mixed models failed to detect differences in isotopic values of ethanol‐stored and frozen fin tissue of R. neglecta . This study provides the first examination of the trophic ecology of R. neglecta and the comparison of isotopic niche with A. ocellatus , which will facilitate future research into the trophic interactions of these species and aid better resource management.

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