Insights into diet and niche separation in the context of prey availability between two sympatric whiprays in a tropical intertidal estuary

Abstract

Increasing evidence supports associations between various elasmobranch species and estuarine habitats, particularly during early life stages. However, with substantial knowledge gaps surrounding spatial habitat use and trophic ecology of estuary‐associated species in Australia, we cannot reliably assess the functional importance of these areas or identify relevant drivers of resource partitioning in estuarine food webs. Here, we compared the diets and trophic niches of two sympatric dasyatid species, the Australian whipray Himantura australis and brown whipray Maculabatis toshi, in a tropical estuary in North Queensland. Stomach contents were collected from juvenile specimens in 2022–2025 using gastric lavage, muscle tissue samples were analysed for stable isotopes (δ ¹³ C, δ ¹⁵ N) and invertebrate communities were surveyed to contextualise prey availability in the intertidal zone. Dietary composition differed significantly between species, with H. australis showing a stronger reliance on burrowing crustaceans (e.g., Callianassidae and Mictyridae), while M. toshi consumed more epibenthic crustaceans (e.g., Ogyrididae, Penaeidae, Portunidae). Himantura australis occupied a larger isotopic niche space than M. toshi , and there was no trophic overlap of larger size classes of H. australis (>50 cm disc width) with M. toshi or with smaller conspecifics (<50 cm disc width). Prey availability was spatially variable and indicated that while both species target locally abundant crustacean taxa, resources may be partitioned across different sediment layers. These findings highlight the importance of estuaries as feeding grounds for juvenile rays and suggest that morphological and behavioural adaptations may drive dietary variability between similar species.