The value of satellite tracking across multiple year cohorts to identify key areas for conservation

While satellite tracking is widely used to identify areas of conservation importance, whether there is a need to continue tag deployments across many years is unclear. We show that destinations of migrating animals from the same breeding population can differ significantly across years, and hence we highlight the value of multi-year tracking studies. Between 2012 and 2024, we used Fastloc-GPS Argos and Iridium tags to track 58 green turtles (Chelonia mydas) from their nesting sites in the Chagos Archipelago. If tracking had taken place in a single year, the number of countries used as foraging destinations could have been hugely underestimated (n = 1 country in 2024 versus n = 7 countries across years). Overall, 47% of tracked individuals foraged in the Seychelles, which likely hosts hundreds of thousands of foraging turtles across age classes. Further, the importance of foraging in areas beyond national jurisdiction (ABNJs) was only revealed by tracking over multiple years. Across years, 9% of tracked individuals foraged on the Saya de Malha Bank, a remote ABNJ, equating to likely >1000 adult females and >10 000 green turtles using this foraging area. This cumulative insight from multi-year tracking likely applies broadly to capital breeders where there is environmental variability across the foraging range.