Standard Talk (15 mins) Australian Society for Fish Biology Conference 2022

Spatio-temporal distribution and trophic niche of Australian cownose rays (Rhinoptera neglecta) off eastern Australia (#85)

Alysha Chan 1 , Jane Williamson 1 , Victor Peddemors 2 , Fabrice Jaine 1 3
  1. School of Natural Sciences, Macquarie University, North Ryde, NSW, Australia
  2. New South Wales Department of Primary Industries, Fisheries Research, Sydney Institute of Marine Science, Mosman, NSW, Australia
  3. Sydney Institute of Marine Science, Mosman, NSW, Australia

Pelagic myliobatiform rays are important mesopredators within marine ecosystems, yet major knowledge gaps currently exist regarding the biology and ecology of some species within this group. The Data Deficient Australian cownose ray (Rhinoptera neglecta) commonly occurs along the coast of eastern Australia, however, its distributions and trophic ecology remain unresolved. In this study, over 1300 sightings of cownose rays, collected during systematic aerial surveys, were analysed using a generalised additive modelling framework to identify trends and drivers of the species’ occurrence and estimated group size in the New South Wales (NSW) region. Latitude and sea temperature had the largest effect on cownose ray presence/absence and group size, with the species occurring most frequently and in the largest groups in northern NSW, when sea temperatures were warmer. Additionally, stable isotope analyses of cownose ray fin clips (n = 29) were conducted to estimate the species’ isotopic niche and compare to that of co-occurring whitespotted eagle rays (Aetobatus ocellatus; n = 21). Species was identified as the main factor contributing to variation among δ15N (p <0.01) and δ34S values (p <0.01), whilst disc width influenced δ13C (p <0.05), indicating these species may be foraging in similar areas but are likely using different prey sources. The isotopic niches of these species overlapped substantially (57 to 75%), with the trophic niche of cownose rays being smaller and more constrained. Results from this study provide first insights into the distribution, relative abundance, and trophic ecology of Australian cownose rays at their southernmost distribution range and contributes important baseline information that will facilitate further research efforts and aid future population assessments.