DNA Metabarcoding Reveals the Trophic Ecology of Critically Endangered Juvenile Green Sawfish (Pristis zijsron) and Sympatric Predators

North-western Australia is home to many of Australia’s rare and threatened elasmobranchs. Basic ecological data is still lacking for many of these species, including empirical dietary information. DNA metabarcoding was performed on cloacal swabs to obtain the first empirical insights into the trophic ecology of the IUCN Critically Endangered green sawfish ( Pristis zijsron ). Additionally, qualitative insights were gained into the piscivorous diet of sicklefin lemon sharks ( Negaprion acutidens ), nervous sharks ( Carcharhinus cautus ), and blacktip sharks ( Carcharhinus tilstoni/C. limbatus ). A total of 20 teleosts were identified as prey for green sawfish, with sampling effort covering an estimated 77.9% of their total piscivorous diet. An ontogenetic dietary shift in green sawfish diet was identified, shifting from glassfish ( Ambassis sp.) to hairback herring ( Nematalosa come ) and sharksuckers ( Echeneis naucrates ) as individuals grew from ∼800 to 2,500 mm total length. Of all co-occurring predators, green sawfish had the greatest piscivorous dietary overlap with sicklefin lemon sharks, and the most common prey among sampled elasmobranch species were hairback herring and giant trevally ( Caranx ignobilis ). This research vastly expands our understanding of the trophic ecology of green sawfish in Australia, particularly at the critical juvenile age class. The results highlight how the complex intraspecific and interspecific dietary interactions of green sawfish require holistic, ecosystem-based approaches to effectively conserve this highly threatened species.