Ecology of sea turtles in the Chagos Archipelago, Indian Ocean

Understanding population size, distribution and reproductive success is vital for management and conservation planning. For rare and elusive species in remote island habitats, this information is difficult to obtain. As female sea turtles come ashore to nest, data can be collected relatively simply from the nesting population. Although other life stages are largely understudied, juveniles tend to forage at coastal sites and so in-water surveys can be conducted to estimate populations and study space use. To investigate aspects of sea turtle ecology in the remote islands of the Chagos Archipelago, Western Indian Ocean, I used a combination of traditional surveys and modern technology (remote and in situ sensing) to answer key questions relating to population size and threats to reproductive success. Most of my research focussed on nesting ecology including clutch incubation conditions, nesting behaviour, hatching success, and predation risk. To assess population size in remote areas, I experimented with in situ sensing (e.g., UAVs, camera traps) and validated results with traditional methods (e.g., foot patrols, in-water capture) to assess nesting and foraging populations. The findings demonstrate the novel approach of camera traps to successfully count turtle tracks and how the combination of UAV surveys, mark-recapture, and satellite tracking can effectively estimate immature turtle population densities. A wide range of sand temperatures were recorded spatially and temporally across the archipelago providing conditions for both male and female-biased clutches. To place my findings within a broader context, I conducted global meta-analyses and literature reviews, reporting the largest immature population of the critically endangered hawksbill turtle, and the first observations of coconut crab and invasive rat predation on sea turtle eggs. These results address several knowledge gaps about sea turtle ecology in the Western Indian Ocean, highlighting the importance of the Chagos Archipelago for all life stages and demonstrating complimentary tools for monitoring endangered species at remote locations.