Beach erosion aggravates the drastic decline in marine turtle populations in French Guiana

International audienceAbstract Yalimapo beach, near the Maroni River estuary in French Guiana, is an important turtle nesting site. The interaction of massive mud banks migrating alongshore from the distant Amazon River with discharge from the Maroni River generates strong beach morpho-sedimentary changes. The eventual degradation of the marine turtle nesting habitats resulting from these changes represents a threat to the offspring, and consequently, to the turtle population. Field operator counts of green and leatherback turtle nests were combined with high-resolution topographic measurements of the beach over four field surveys in 2012 and 2014 to map the topographic modifications susceptible to affect nesting on Yalimapo beach. We assumed that the survival of nests was at stake when the depth of sand between the egg chamber and the topographic surface (i.e. the top) of the beach was  10 cm represented unfavourable conditions for nest safety with unequal nest survival across the beach. Erosion of the beach surface exceeding a depth of 50 cm therefore results in nest destruction. Digital elevation models were produced to quantify the topographic modification of nesting on Yalimapo beach and highlight the endangered nesting areas. As the modification of the beach is not linear, some sectors are more eroded than others, resulting in unequal nest survival across the beach. Overall, up to 40% of the nests were presumed destroyed over the 2 years of survey, but true losses would depend on the species and the preferential locations of their nesting habitats. The relatively unfavourable conditions that prevailed during the 2 years of the survey are consistent with persistent erosion of Yalimpao beach since 2011. This ongoing erosion could explain in part the drastic decline of the leatherback turtle population in western French Guiana over the period 2001–2018. The substrate quality and dynamics of the nesting beach in relation to the preferred nesting habitat of each species are therefore critical issues that should be considered in the conservation strategies of marine turtles. The beach nesting conditions of marine turtles in French Guiana, as elsewhere, could be further aggravated in the future by climate change effects, including sea-level rise

Habitat use and diving behaviour of gravid olive ridley sea turtles under riverine conditions in French Guiana

The identification of the inter-nesting habitat used by gravid sea turtles has become a crucial factor in their protection. Their aggregation in large groups of individuals during the inter-nesting period exposes them to increased threats to their survival - particularly along the French Guiana shield, where intense legal and illegal fisheries occur. Among the three sea turtle species nesting in French Guiana, the olive ridley appears to have the most generalist diet, showing strong behavioural plasticity according to the environment encountered. The large amounts of sediments that are continuously discharged by the Amazon River create a very unusual habitat for olive ridleys, i.e. turbid waters with low salinity. This study assesses the behavioural adjustments of 20 adult female olive ridleys under such riverine conditions. Individuals were tracked by satellite from Remire-Montjoly rookery in French Guiana using tags that recorded the location and diving parameters of individuals, as well as the immediate environment of the turtles including the in situ temperature and salinity. Data concerning potential preys was provided via collection of epifauna by a trawler. Multiple behavioural shifts were observed in both horizontal and vertical dimensions. During the first half of the inter-nesting season, the turtles moved away from the nesting beach (27.6 ± 26.4 km), performing deeper (14.2 ± 8.7 m) and longer (33.2 ± 22.2 min) dives than during the second half of the period (8.6 ± 10.3 km, 10.6 ± 5.1 m and 26.4 ± 19.4 min). Olive ridleys remained in waters that were warm (range: 26–33 °C) and which fluctuated in terms of salinity (range: 19.5–36.4 psu), in a relatively small estuarine habitat covering 409 km2. If olive ridleys were foraging during this period, the potential preys that might be available include were mostly crustaceans (47%) and fish (26%), as expected for the diet of this generalist species during this period. This study highlights the numerous behavioural adaptations of this species in response to the unusual riverine conditions of the French Guiana continental shelf

The Gulf Stream frontal system: A key oceanographic feature in the habitat selection of the leatherback turtle?

International audienceAlthough some associations between the leatherback turtle Dermochelys coriacea and the Gulf Stream currenthave been previously suggested, no study has to date demonstrated strong affinities between leatherbackmovements and this particular frontal system using thorough oceanographic data in both the horizontal andvertical dimensions. The importance of the Gulf Stream frontal system in the selection of high residence time(HRT) areas by the North Atlantic leatherback turtle is assessed here for the first time using state-of-the-artocean reanalysis products. Ten adult females from the Eastern French Guianese rookery were satellite trackedduring post-nesting migration to relate (1) their horizontal movements to physical gradients (Sea SurfaceTemperature (SST), Sea Surface Height (SSH) and filaments) and biological variables (micronekton andchlorophyll a), and (2) their diving behaviour to vertical structures within the water column (mixed layer,thermocline, halocline and nutricline). All the turtles migrated northward towards the Gulf Stream north wall.Although their HRT areas were geographically remote (spread between 80–30 °W and 28–45 °N), all the turtlestargeted similar habitats in terms of physical structures, i.e. strong gradients of SST, SSH and a deep mixedlayer. This close association with the Gulf Stream frontal system highlights the first substantial synchronizationever observed in this species, as the HRTs were observed in close match with the autumn phytoplankton bloom.Turtles remained within the enriched mixed layer at depths of 38.5 ± 7.9 m when diving in HRT areas, likely tohave an easier access to their prey and maximize therefore the energy gain. These depths were shallow incomparison to those attained within the thermocline (82.4 ± 5.6 m) while crossing the nutrient-poor subtropicalgyre, probably to reach cooler temperatures and save energy during the transit. In a context of climate change,anticipating the evolution of such frontal structure under the influence of global warming is crucial to ensure theconservation of this vulnerable species

Identification of marine key areas across the Caribbean to ensure the conservation of the critically endangered hawksbill turtle

International audienceAcquisition of data on animal movement when developing management strategies is a common challenge in species conservation, especially when dealing with a critically endangered species as the hawksbill turtle Eretmochelys imbricata. To reach the objective of the 2008 national action plan for Martinique Island (French West Indies), the present paper examines horizontal and vertical movements in juveniles (n = 3) and adults life stages (11 females and 2 males) of 16 hawksbill turtles. Our results reveal the strong site fidelity of individuals to their foraging grounds (mean male foraging home range: 89.3 ± 20.2 km 2 , mean female foraging home range: 336 ± 284.7 km 2 , mean juvenile foraging home range: 157.3 ± 71.2 km 2) and to the females' inter-nesting areas (mean home range: 284.2 ± 523.7 km 2). A spatial foraging overlap occurred between juveniles and males as they shared 41% of their 95% kernel foraging habitat. The turtles performed mainly long and shallow dives within the first 20 m deep around Martinique Island, occupying shallow waters close to shore. The migratory routes of the adult females revealed regional connectivity between the Caribbean islands, crossing 31 exclusive economic zones and international waters, and featuring distinct foraging grounds. This finding reinforces the significance of a cooperative network at the Caribbean scale to ensure the efficient conservation of this critically endangered species

Food selection and habitat use patterns of immature green turtles (Chelonia mydas) on Caribbean seagrass beds dominated by the alien species Halophila stipulacea

Marine herbivores face rapid changes in the coastal ecosystems where they forage. In the Caribbean, the recent and fast expansion of the invasive phanerogam species Halophila stipulacea is threatening native seagrass ecosystems. So far, H. stipulacea is escaping most Caribbean herbivores, certainly because of its recent introduction or lower nutritional value. We investigated the impact of H. stipulacea invasion on fine-scale foraging habitat selection and food resource selection of immature green turtles at critical foraging sites in Les Anses d’Arlet, Martinique. The analysis of seagrass distribution and nutritional content, together with turtle behaviour and resource selection, showed that H. stipulacea may be of contrasting interest to green turtles. Compositional analysis confirmed the lower nutritional value of H. stipulacea compared to the native species, but the invasive species showed higher digestibility than native ones, which calls into question the energetic advantage of consuming the native plants over the exotic plant. Thus, although green turtles mostly selected the native seagrass Thalassia testudinum in multispecies seagrass beds, some individuals fed on H. stipulacea. Accordingly, in bays entirely invaded by H. stipulacea, one possibility for resident green turtles is to increase foraging on this species, but, if so, the consequences on their growth and survival still remain to be determined. As the expansion of H. stipulacea may have been facilitated by factors such as shipping, anchor scarring and fishing activities, protection of native seagrass beds and immature green turtles from human disturbances is urgently required to ensure the long-term adaptation of green turtles to this new foraging environment

High fidelity of sea turtles to their foraging grounds revealed by satellite tracking and capture-mark-recapture: New insights for the establishment of key marine conservation areas

Movement ecology studies are essential to protect highly mobile threatened species such as the green turtle (Chelonia mydas), classified as an endangered species by the IUCN. In 2019, the South Atlantic subpopulation has been downlisted to ‘Least Concern’, but the maintenance of this status strongly relies on the pursuit of research and conservation, especially on immatures, which contribute to the demographic renewal of this subpopulation. Identifying marine areas used by immatures is therefore crucial to implement efficient measures for the conservation of sea turtles in the Caribbean. We analysed data of capture-mark-recapture of 107 (out of 299) immatures recaptured at least once in Martinique, and satellite tracked 24 immatures to investigate their site fidelity and habitat use. Our results revealed a strong fidelity to foraging grounds, with mean residence times higher than 2 years, and with a high degree of affinity for specific areas within the coastal marine vegetation strip. Home ranges (95% kernel contour) and core areas (50% kernel contour) varied from 0.17 to 235.13 km2 (mean ± SD = 30.73 ± 54.34 km2) and from 0.03 to 22.66 km2 (mean ± SD = 2.95 ± 5.06 km2), respectively. Our findings shed light on a critical developmental area for immature green turtles in the French West Indies, and should help to refine Regional Management Units and reinforce the cooperative network aiming at ensuring conservation of the species at international scale

Food selection and habitat use patterns of immature green turtles (Chelonia mydas) on Caribbean seagrass beds dominated by the alien species Halophila stipulacea

International audienceMarine herbivores face rapid changes in the coastal ecosystems where they forage. In the Caribbean, the recent and fast expansion of the invasive phanerogam species Halophila stipulacea is threatening native seagrass ecosystems. So far, H. stipulacea is escaping most Caribbean herbivores, certainly because of its recent introduction or lower nutritional value. We investigated the impact of H. stipulacea invasion on fine-scale foraging habitat selection and food resource selection of immature green turtles at critical foraging sites in Les Anses d′Arlet, Martinique. The analysis of seagrass distribution and nutritional content, together with turtle behaviour and resource selection, showed that H. stipulacea may be of contrasting interest to green turtles. Compositional analysis confirmed the lower nutritional value of H. stipulacea compared to the native species, but the invasive species showed higher digestibility than native ones, which calls into question the energetic advantage of consuming the native plants over the exotic plant. Thus, although green turtles mostly selected the native seagrass Thalassia testudinum in multispecies seagrass beds, some individuals fed on H. stipulacea. Accordingly, in bays entirely invaded by H. stipulacea, one possibility for resident green turtles is to increase foraging on this species, but, if so, the consequences on their growth and survival still remain to be determined. As the expansion of H. stipulacea may have been facilitated by factors such as shipping, anchor scarring and fishing activities, protection of native seagrass beds and immature green turtles from human disturbances is urgently required to ensure the long-term adaptation of green turtles to this new foraging environment

Fine scale geographic residence and annual primary production drive body condition of wild immature green turtles ( Chelonia mydas ) in Martinique Island (Lesser Antilles)

The change of animal biometrics (body mass and body size) can reveal important information about their living environment as well as determine the survival potential and reproductive success of individuals and thus the persistence of populations. However, weighing individuals like marine turtles in the field presents important logistical difficulties. In this context, estimating body mass based on body size is a crucial issue. Furthermore, the determinants of the variability of the parameters for this relationship can provide information about the quality of the environment and the manner in which individuals exploit the available resources. This is of particular importance in young individuals which growth quality might be a determinant of adult fitness. Our study aimed to validate the use of different body measurements to estimate body mass, which can be difficult to obtain in the field, and explore the determinants of the relationship between body mass and size in juvenile green turtles. Juvenile green turtles were caught, measured, and weighed for six years (2011-2012; 2015-2018) at six bays in the west of Martinique Island (Lesser Antilles). Using different datasets from this global database, we were able to show that the body mass of individuals can be predicted from body measurements with an error of less than 2%. We built several dataset including different morphological and time-location information to test the accuracy of the mass prediction. We show a year and north-south pattern for the relationship between body mass and body measurements. The year effect for the relationship of body mass and size is strongly correlated with net primary production but not with sea surface temperature or cyclonic events. We also found that if the bay locations and year effects were removed from the analysis, the mass prediction degraded slightly but was still less than 3% on average. Further investigations of the feeding habitats in Martinique are still needed to better understand these effects and to link them with geographic and oceanographic conditions

Fibropapillomatosis Prevalence and Distribution in Immature Green Turtles (Chelonia mydas) in Martinique Island (Lesser Antilles)

International audienc