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 (δ13C, δ15N and δ34S) 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 δ15N and δ34S values, and disc width for δ13C. 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 δ13C were similar between species, variation in isotopic niches were due to differences in δ15N and δ34S 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.

Visitation patterns of two ray mesopredators at shellfish aquaculture leases in the Indian River Lagoon, Florida

“…These contrasting visit patterns may be a result of interspecific competition due to their shared semipelagic nature and likely comparable trophic levels confirmed via overlapping isotopic niches observed in Australian cownose rays ( Rhinoptera neglecta ) and spotted eagle rays ( A . ocellatus ) [ 66 ] and similar diet compositions [ 6 – 9 , 11 ].…”

Isotopic niche overlap among foraging marine turtle species in the Gulf of Mexico

“…However, it is worth noting that while the δ 15 N values differed among species, there may not be a substantial ecological significance as the observed maximum difference (1.5‰) did not exceed the general discrimination factor of 3.4‰ for δ 15 N (Post, 2002 , but see Hussey et al., 2014 ). Samples from green turtles also had the widest ranges for δ 13 C, δ 15 N, and δ 34 S (Table 1 ), which may suggest that they use a wider range of resources and exhibit higher variability in diet and habitat type, and thus may be more generalists (Chan et al., 2022 ). This is further supported by their larger niche size estimate compared with the other species.…”

“…Most of the studies to date that use bulk isotope ratios to characterize marine turtle niches focus on carbon (δ 13 C) and nitrogen (δ 15 N) (Haywood et al., 2019 ). However, the addition of a third isotopic marker, sulfur (δ 34 S), can provide additional insights since δ 34 S isotope ratios exhibit limited trophic fractionation and can be used to determine differences between benthic and pelagic productivity pathways in coastal systems (Chan et al., 2022 ; García‐Vernet et al., 2021 ; Peterson & Fry, 1987 ). This is because primary producers that use different sources of sulfur will have different δ 34 S values (Connolly et al., 2004 ).…”

Recent expansion of the Atlantic cownose ray (Rhinoptera bonasus) into Bermudian waters

“…However, recent dietary data suggest the two species exhibit only modest niche overlap (37). A recent isotopic study suggested Aetobatus is less trophically constrained than Rhinoptera, possibly due to its larger size, gape, and buccal morphology, allowing it to exploit a wider range of prey (38). In Florida's Indian River Lagoon, the two genera occupy similar spaces, although visitation patterns to the same habitats are asynchronous (26).…”