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 (δ13 C, δ15 N and δ34 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 δ15 N and δ34 S values, and disc width for δ13 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 δ13 C were similar between species, variation in isotopic niches were due to differences in δ15 N and δ34 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.
Keywords: Myliobatiformes; batoid; foraging ecology; isotopic niche; stable isotopes; tissue storage.
© 2022 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.