Understanding population size and ecology is crucial for conservation, but for rare, cryptic species in remote habitats, data collection is challenging. Female sea turtles provide accessible nesting data, while juveniles can be studied through in-water surveys. This research in the Chagos Archipelago combined traditional surveys with modern tools (UAVs, camera traps) to assess population size and threats to reproduction. Nesting ecology, incubation conditions, hatching success, and predation risks were key focuses. Findings validated UAVs and mark-recapture for estimating immature turtle densities and recorded sand temperatures suitable for both male- and female-biased clutches. Global meta-analyses revealed the largest known immature hawksbill population and first documented cases of coconut crab and invasive rat predation on turtle eggs. This work highlights the Chagos Archipelago’s importance for sea turtles and demonstrates novel monitoring tools for endangered species in remote locations.