Observations on predation of the flatback turtle Natator depressus by the saltwater crocodile Crocodylus porosus at a major rookery in northern Australia

Context We examined predation by the saltwater crocodile (Crocodylus porosus) on the flatback turtle (Natator depressus), an Australian endemic, at Cape Domett, a significant nesting site in Cambridge Gulf, northern Australia, where crocodile populations have recovered since legislative protection was implemented in the 1970s. Aims The investigation aimed to document crocodile predation on flatback turtles across hatchling and adult life stages, assess predation strategies, and evaluate ecological impacts on this genetically distinct turtle stock. Methods Conducted over three Austral winters (2021–2023), the study utilised infrared videography, unmanned aerial vehicles, and beach patrols to observe predation events in a population of ~3250 nesting female flatback turtles. Key results Five predation events were recorded, involving juvenile (<2 m) and large (~5 m) crocodiles. Large crocodiles employed ambushing strategies at the waterline or on land, with tracks, remains, and carcasses indicating an estimated predation rate of one adult turtle per week. Juvenile crocodiles targeted hatchlings during emergence, and scavenging of turtle carcasses was documented. Conclusions The recovery of C. porosus has likely intensified predation pressure on N. depressus. Infrared cameras and drones proved effective in capturing unbiased diurnal and nocturnal predation interactions, contributing to the limited global literature on crocodilian predation of sea turtles. Implications These findings position C. porosus as a significant ecological threat to flatback turtles. Comprehensive assessments, including nest inventories and thermal drone surveys, are recommended to refine predation estimates and enhance population viability models, informing conservation strategies for N. depressus amid increasing crocodile populations.