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

While satellite tracking is widely used to identify areas of particular conservation importance, whether there is a need to continue tag deployments across many years is unclear. We show that the destinations of migrating animals from the same breeding population may 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 7 countries used 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 across 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 added information from tracking across multiple years likely extends across sea turtle populations as well as other taxa.

Methods
For further details regarding transmitter attachment and data filtering, see the Methods section in the associated paper "The value of satellite tracking across multiple years to identify key areas for conservation," Stokes et al. (2025).