Environmental and Biological Drivers of Endangered Leatherback Hatchling (Dermochelys Coriacea) Dispersal from a Costa Rican Nesting Population

Nicole Barbour, University of Maryland Center for Environmental Science, Biology, Solomons, MD, United States, George L Shillinger, Upwell, Monterey, United States; MigraMar, Mexico City, EM, Mexico, Aimee Hoover, University of Maryland Center for Environmental Science, Solomons, MD, United States; Upwell, Monterey, MD, United States, Sean A Williamson, Monash University, School of Biological Sciences, Clayton, VIC, Australia; Upwell, Monterey, CA, United States and Helen R Bailey, Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, MD, United States
Abstract:
Leatherback turtles (Dermochelys coriacea) are vulnerable to extinction and many populations, such as those in Costa Rica, are rapidly declining, despite efforts to protect nests. It is likely that their main source of mortality is at sea, where information on the movement and dispersal of juvenile leatherback turtles is unknown and often termed “The Lost Years”. We conducted a multi-year comparison of hatchling movements during their early movements at sea by performing acoustic tracking of hatchling leatherback turtles (n=94) from the nesting beach region of Pacuare, Costa Rica, in 2016 and 2018. A first passage time analysis was used to determine the spatial scale and where hatchlings spent the most time along their tracks. Comparison with random walk models indicated the hatchlings followed a fixed compass direction offshore. We combined the tracking data with concurrent environmental variables, including tidal state, lunar phase, local wind speed, and current speed, in a generalized additive mixed model to determine the significant predictors of a) the longshore current in this region and b) the true swimming speed of the hatchlings. Our results showed that the alongshore currents in this area have significant spatial and temporal structure that is not driven by the tidal current or local wind speed. Hatchling true swimming speed was significantly related to current speed and increased linearly when currents reached speeds of 0.7 m/s or more. Hatchlings were also significantly larger in 2018 than in 2016 and their swimming speed was significantly related to their body mass. The higher amount of precipitation and storm activity in 2018 likely resulted in stronger current speeds and the larger body sizes of hatchlings, indicating that both environmental and biological factors are important contributors to hatchling dispersal. This has implications for future nest conservation and research efforts in this area, especially in the face of climate change.
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