Plot, Virginie, De Thoisy, Benoît, Blanc, Stéphane, Kelle, Laurent, Lavergne, Anne, Roger-Bérubet, Hélène, Tremblay, Yann, Fossette, Sabrina, Georges, Jean Yves, Département Ecologie, Physiologie et Ethologie (DEPE-IPHC), Institut Pluridisciplinaire Hubert Curien (IPHC), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS), Institut Pasteur de la Guyane, Réseau International des Instituts Pasteur (RIIP), Association Kwata - Etude et protection de la nature [Guyane], WWF Guianas, WWF, MARine Biodiversity Exploitation and Conservation (UMR MARBEC), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), This study was financially supported by Hardman Company‐Tullow Oil, Créocéan, Interreg, Région Guyane, Région Guadeloupe, Région Martinique and WWF Guianas. This study was carried out under CNRS‐IPHC institutional license (B67 482 18) with individual licenses attributed to JYG (67–220 and 04–199 delivered by Direction des Services Vétérinaires du Bas Rhin, 05/04/PN, 05/07/PN, 06/13/PN, 06/14/PN, 07/02/PN and 07/06/PN delivered by Direction Régionale de l’Environnement and Préfecture de Guyane). VP was supported by a studentship from the French Ministry of Research and by the projet MIRETTE funded by the ANR (http://projetmirette.fr). The study adhered strictly to both the legal requirements of the countries in which the work was carried out and all institutional guidelines., We are very grateful to Kwata field workers (particularly Sébastien Barrioz, Guillaume Feuillet, Eddy Poirier), CNRS‐IPHC students who contributed to field work and CARET partners (STINASU, Suriname) for their contribution to data collection in the field. We thank Graeme Hays and three anonymous referees for their constructive comments of the original version of the manuscript. The spelling and English was revised and edited by Munro Language Services., ANR-07-JCJC-0122,MIRETTE,Migration et Reproduction chez les Tortues marines: Trajectoires Ecophysiologiques(2007), Université de Strasbourg (UNISTRA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), and Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut de Recherche pour le Développement (IRD)
International audience; 1. The assessment of species extinction risk has been well established for some time now. Assessing the potential for recovery in endangered species is however much more challenging, because complementary approaches are required to detect reliable signals of positive trends. 2. This study combines genetics, demography and behavioural data at three different time-scales to assess historical and recent population changes and evidence of reproductive synchrony in a small population of olive ridley sea turtle Lepidochelys olivacea. Lepidochelys is considered as the most extraordinary example of reproductive synchrony in reptiles, yet to date, it has only been reported in large populations. 3. Using Bayesian coalescent-based models on microsatellite nuclear DNA variability, we demonstrate that effective population size in olive ridleys nesting in French Guiana has dramatically declined by 99% over the last 20 centuries. This low current population size is further illustrated by the absence of genetic mitochondrial DNA diversity in the present nesting population. Yet, monitoring of nesting sites in French Guiana suggests a possible recovery of the population over the last decade. 4. Satellite telemetry shows that over the first 14 days of their 28-days inter-nesting interval, i.e. when eggs maturation is likely to occur, gravid females disperse over the continental shelf. They then gather together with a striking spatiotemporal consistency close to the nesting site, where they later emerge for their second nesting event. 5. Our results therefore suggest that reproductive synchrony also occurs in small populations. Olive ridleys may ensure this synchrony by adjusting the duration of the second half of their internesting interval prior to landing, possibly through social mediation. 6. Such reproductive synchrony may be related to the maintenance of some species-specific strategy despite former collapse and may contribute to the present population recovery. The gregarious behaviour of reproductive individuals close to shore where human-induced perturbations occur is however a cause for conservation concern for this still poorly known species.