Dispersal and Diving Adjustments of the Green Turtle Chelonia mydas in Response to Dynamic Environmental Conditions during Post-Nesting Migration

Abstract

International audienceIn response to seasonality and spatial segregation of resources, sea turtles undertake longjourneys between their nesting sites and foraging grounds. While satellite tracking hasmade it possible to outline their migration routes, we still have little knowledge of how theyselect their foraging grounds and adapt their migration to dynamic environmental conditions.Here, we analyzed the trajectories and diving behavior of 19 adult green turtles (Cheloniamydas) during their post-nesting migration from French Guiana and Suriname to theirforaging grounds off the coast of Brazil. First Passage Time analysis was used to identifyforaging areas located off Ceará state of Brazil, where the associated habitat correspondsto favorable conditions for seagrass growth, i.e. clear and shallow waters. The dispersaland diving patterns of the turtles revealed several behavioral adaptations to the stronghydrodynamic processes induced by both the North Brazil current and the Amazon Riverplume. All green turtles migrated south-eastward after the nesting season, confirming thatthey coped with the strong counter North Brazil current by using a tight corridor close to theshore. The time spent within the Amazon plume also altered the location of their feedinghabitats as the longer individuals stayed within the plume, the sooner they initiated foraging.The green turtles performed deeper and shorter dives while crossing the mouth of the Amazon,a strategy which would help turtles avoid the most turbulent upper surface layers of theplume. These adjustments reveal the remarkable plasticity of this green turtle populationwhen reducing energy costs induced by migration