Abstract
In response to seasonality and spatial segregation of resources, sea turtles undertake long journeys between their nesting sites and foraging grounds. While satellite tracking has made it possible to outline their migration routes, we still have little knowledge of how they select their foraging grounds and adapt their migration to dynamic environmental conditions. Here, we analyzed the trajectories and diving behavior of 19 adult green turtles (Chelonia mydas) during their post-nesting migration from French Guiana and Suriname to their foraging grounds off the coast of Brazil. First Passage Time analysis was used to identify foraging areas located off Ceará state of Brazil, where the associated habitat corresponds to favorable conditions for seagrass growth, i.e. clear and shallow waters. The dispersal and diving patterns of the turtles revealed several behavioral adaptations to the strong hydrodynamic processes induced by both the North Brazil current and the Amazon River plume. All green turtles migrated south-eastward after the nesting season, confirming that they coped with the strong counter North Brazil current by using a tight corridor close to the shore. The time spent within the Amazon plume also altered the location of their feeding habitats 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 the plume. These adjustments reveal the remarkable plasticity of this green turtle population when reducing energy costs induced by migration.
Highlights
Seasonality drives the availability and aggregation of resources, and is one of the main ecological factors affecting the evolution and the ecology of long-distance migrants [1]
With the exception of one turtle that stopped off the coast of Cayenne in 2012 (#115446, foraging event in Phase 1) rather than at the very end of turtle tracks, the searching activity recorded spans from June to mid-September, and foraging areas were found to be located at the very end of the turtle tracks, along the shores of Ceará and Paraíba states, Brazil (Fig 1 and S1 Table)
Twenty-one percent of the turtles used fine-scale foraging (
Summary
Seasonality drives the availability and aggregation of resources, and is one of the main ecological factors affecting the evolution and the ecology of long-distance migrants [1]. In most cases, the requirements of migratory animals temporally and spatially match the peak of resource abundance, avoiding resource depletion Migrant organisms time their movements according to their life stages and their different activities (growth, breeding, etc.) in order to exploit seasonal resources that vary at temporal and spatial scales, generally travelling long distances to reach appropriate sites for their needs [2]. It is crucial to assess the dispersal movements and the habitat used by migrating animals in order to understand their ecology and facilitate the implementation of adequate conservation policies [3] This migratory behavior has been studied in a wide range of marine groups such as mammals [4,5], birds [6], fish [7,8] and reptiles [9,10,11]. The turtles migrate after the nesting season to replenish their body reserves, foraging in areas of high productivity in order to maximize their foraging efficiency
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