Identification of key marine areas for conservation based on satellite tracking of post-nesting migrating green turtles (Chelonia mydas)

International audienceThe green turtle (Chelonia mydas) is classified as an endangered species on the IUCN Red List since 1986.This species is especially threatened in South America due to bycatch by fisheries along the northeasterncoasts. It is particularly crucial to identify specific marine areas for conservation measures to safeguardgreen turtle rookeries in Suriname and French Guiana. Our study provides valuable information to attainthis goal, describing the satellite tracking of post-nesting migration routes used by 16 green turtles fittedwith Argos/GPS Fastloc satellite tags at the end of the nesting season. The data we obtained show a singlemigratory corridor: all the turtles followed a similar eastward route along the Guianan and the Braziliancoast. The GPS signal was lost for two individuals a few weeks after tracking commenced, suggesting thatthey were caught by fishermen. Thirteen turtles reached the coast of the state of Ceará (Brazil), wherethey spent at least one month. One turtle continued 700 km further to the coastal regions of Natal andRecife (Brazil), which are known feeding areas of the green turtle populations nesting on AscensionIsland. The migratory corridor is essentially narrow, with a width of 22 km for most of the distancecovered. It constitutes a major dynamic link between the nesting and feeding areas and crosses threeRegional Management Units of the Atlantic basin. Since green turtles face a high risk of being caughtin fishing nets, measures of protection should be implemented along this corridor

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

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

Summary of the linear model performed to relate the <i>TimePhase2</i>* to intrinsic variables.

<p>TimePhase2* refers to the time (in days) spent within the plume and FG to Foraging Grounds.</p><p>Summary of the linear model performed to relate the <i>TimePhase2</i>* to intrinsic variables.</p

Histograms of (A) the maximum dive depth (m) and (B) the maximum dive duration (min) recorded by the 14 Argos-Fastloc GPS tags for the two behavioral modes, i.e. transiting (gray) and foraging (black).

<p>Histograms of (A) the maximum dive depth (m) and (B) the maximum dive duration (min) recorded by the 14 Argos-Fastloc GPS tags for the two behavioral modes, i.e. transiting (gray) and foraging (black).</p

Locations of the 19 green turtles equipped in 2012 and 2014 for the two behavioral modes, i.e. transiting (gray) and foraging (black).

<p>The red square indicates the migration departure point. The shoreline was extracted from NOAA National Geophysical Data Center, Coastline.</p

Box plots of (A) the SST (°C), (B) the K_d (m^-1), (C) the Bathymetry (m) and (D) the Slope (°) extracted at turtles’ locations for the two behavioral modes, i.e. transiting (grey) and foraging (black).

<p>Box plots of (A) the SST (°C), (B) the K_d (m^-1), (C) the Bathymetry (m) and (D) the Slope (°) extracted at turtles’ locations for the two behavioral modes, i.e. transiting (grey) and foraging (black).</p

Distributions of (A) SST (°C) and (B) K_d (m^-1) along the 19 turtles’ tracks.

<p>The foraging grounds are represented by the red ellipses and the black solid line refers to the 100 m isobaths. K_d refers to the Diffuse Attenuation Coefficient and was logged transformed for a better contrast. The shoreline was extracted from NOAA National Geophysical Data Center, Coastline.</p

Mean direction and velocity of the currents over the whole study area for the 2012 and 2014 tracking periods extracted daily from Mercator-Ocean GLORYS-2v1 (Global Ocean ReanalYsis and Simulations). The trajectory of turtle #115452 (red) is superimposed on the current.

<p>For a better visual representation, the spatial resolution of the current direction is set to 0.75 degrees. The shoreline was extracted from NOAA National Geophysical Data Center, Coastline.</p