Area use and residency behaviour at reproductive and foraging areas of green turtles from the largest rookery in the Atlantic

Abstract

The conservation of migratory marine megavertebrates depends on the protection of different areas during their life cycles. Many populations have recovered following exploitation-driven declines. Green turtles exemplify successful efforts protecting reproductive populations, reducing harvesting, promoting population recoveries globally. Tortuguero, Costa Rica, the second largest rookeries for green turtles worldwide, implemented long-term conservation efforts leading to a population recovery, which is now in decline. This study investigates migratory connectivity of green turtles from Tortuguero across the Caribbean, and the role marine protected areas (MPAs) play in protecting key habitats supporting this population. Over 25 years, we satellite tagged 63 female green turtles to study their internesting and post-nesting foraging movements. Applying a state-space model, we calculated a movement-persistence index, to separate internesting and foraging periods. We calculated turtles' utilization distribution areas for both periods. To assess the protection coverage at each end of the migration, we calculated time spent within and outside MPAs. Tracked turtles spent a median of 42.3 days (SD=18.8, range=12-80) within 30 km offshore before departing the internesting area, spending just 23.0% of time within nearby MPAs. After nesting, turtles migrated to 14 different foraging areas, Miskitos Cays, Nicaragua hosted the most turtles (n=23). Mean transmission time in foraging areas was 175.6 days (SD=126.0; range=13-544). Generally, turtles foraged 58.0% of the time within MPAs boundaries; however, ~32% of tracked turtles foraged outside MPAs. Considering all known stressors, we found this population to be insufficiently protected at either end of their migratory cycle, remaining vulnerable to regional threats.