Atlantic Leatherback Migratory Paths and Temporary Residence Areas

BACKGROUND: Sea turtles are long-distance migrants with considerable behavioural plasticity in terms of migratory patterns, habitat use and foraging sites within and among populations. However, for the most widely migrating turtle, the leatherback turtle Dermochelys coriacea, studies combining data from individuals of different populations are uncommon. Such studies are however critical to better understand intra- and inter-population variability and take it into account in the implementation of conservation strategies of this critically endangered species. Here, we investigated the movements and diving behaviour of 16 Atlantic leatherback turtles from three different nesting sites and one foraging site during their post-breeding migration to assess the potential determinants of intra- and inter-population variability in migratory patterns. METHODOLOGY/PRINCIPAL FINDINGS: Using satellite-derived behavioural and oceanographic data, we show that turtles used Temporary Residence Areas (TRAs) distributed all around the Atlantic Ocean: 9 in the neritic domain and 13 in the oceanic domain. These TRAs did not share a common oceanographic determinant but on the contrary were associated with mesoscale surface oceanographic features of different types (i.e., altimetric features and/or surface chlorophyll a concentration). Conversely, turtles exhibited relatively similar horizontal and vertical behaviours when in TRAs (i.e., slow swimming velocity/sinuous path/shallow dives) suggesting foraging activity in these productive regions. Migratory paths and TRAs distribution showed interesting similarities with the trajectories of passive satellite-tracked drifters, suggesting that the general dispersion pattern of adults from the nesting sites may reflect the extent of passive dispersion initially experienced by hatchlings. CONCLUSIONS/SIGNIFICANCE: Intra- and inter-population behavioural variability may therefore be linked with initial hatchling drift scenarios and be highly influenced by environmental conditions. This high degree of behavioural plasticity in Atlantic leatherback turtles makes species-targeted conservation strategies challenging and stresses the need for a larger dataset (>100 individuals) for providing general recommendations in terms of conservation

Olive ridley turtle Lepidochelys olivacea in French Guiana: back from the brink of regional extirpation?

Short CommunicationsInternational audienceThe estimated number of olive ridley marine turtles Lepidochelys olivacea nesting annually in 2002–2007 in French Guiana was 1,716–3,257, the highest ever recorded in the country and similar to nesting numbers recorded in neighbouring Suriname c. 40 years ago, where the species has now severely declined. A shift of nesting females from Suriname to French Guiana beaches and improvement of nationwide marine turtle monitoring appear to be the most plausible explanations for the current high level of nesting recorded in French Guiana. The species' nesting status in French Guiana therefore appears less critical than previously documented but ongoing threats suggest the need to reinforce regional conservation efforts in the West Atlantic

Study and conservation of the Guiana Dolphin (Sotalia guianensis) (Van Bénéden, 1864) in French Guiana

The Guiana dolphin (Sotalia guianensis) occurs in warm and shallow waters of the Atlantic Ocean and the Caribbean Sea, from southern Brazil to Honduras, including estuarine and freshwater habitats such as Maracaibo Lake (Venezuela), and the Orinoco River. In 2018, the Guiana dolphin was reclassified from Data Deficient to Near Threatened on the global IUCN Red List. Nevertheless, the conservation status identified by national and regional Red Lists is even more alarming. In French Guiana, for example, the species is classified as Endangered based on strong pressures such as bycatch. In this region, the Guiana dolphin inhabits river mouths and coastal waters where most anthropogenic activities occur. Better knowledge of the biology and ecology is needed in French Guiana to help inform effective conservation actions. Here, we present ongoing studies to map the distribution of Guiana dolphins along the French Guiana coast and estimate abundance in a hotspot area. Aerial survey campaigns were conducted during the dry season in 2013, 2014, 2015, and 2019. Eight flights were conducted and 146 dolphins belonging to 39 groups were observed. Boat-based line-transect surveys were also conducted in the coastal waters of Cayenne in 2017 and 2018. Twenty-one survey trips were conducted covering 999.06 km. Three hundred and eighty-two dolphins belonging to 63 groups were observed. The total abundance in the Cayenne area was estimated at 128 dolphins (% CV = 30.92; CI (95%) = 70-235) with a density of 0.80 ind./km² (% CV = 30.92; CI (95%) = 0.44-1.47). Additionally, a descriptive analysis was performed on stranding data collected in French Guiana between 2014 and 2020 to identify the major cause of death and seasonality in the stranding events. In total, 43 dolphins were found, especially on the beaches of Rémire-Montjoly, Cayenne, and Kourou: bycatch was the major identifiable cause of death. We recommend a local conservation strategy and actions to be undertaken in the short- and medium-term to address different issues: knowledge, threats, conservation, and cooperation

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

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

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

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

The influence of oceanographic features on the foraging behavior of the olive ridley sea turtle Lepidochelys olivacea along the Guiana coast

International audienceThe circulation in the Western Equatorial Atlantic is characterized by a highly dynamic mesoscale activity that shapes the Guiana continental shelf. Olive ridley sea turtles (Lepidochelys olivacea) nesting in French Guiana cross this turbulent environment during their post-nesting migration. We studied how oceanographic and biological conditions drove the foraging behavior of 18 adult females, using satellite telemetry, remote sensing data (sea surface temperature, sea surface height, current velocity and euphotic depth), simulations of micronekton biomass (pelagic organisms) and in situ records (water temperature and salinity). The occurrence of foraging events throughout migration was located using Residence Time analysis, while an innovative proxy of the hunting time within a dive was used to identify and quantify foraging events during dives. Olive ridleys migrated northwestwards using the Guiana current and remained on the continental shelf at the edge of eddies formed by the North Brazil retroflection, an area characterized by low turbulence and high micronekton biomass. They performed mainly pelagic dives, hunting for an average 77% of their time. Hunting time within a dive increased with shallower euphotic depth and with lower water temperatures, and mean hunting depth increased with deeper thermocline.This is the first study to quantify foraging activity within dives in olive ridleys, and reveals the crucial role played by the thermocline on the foraging behavior of this carnivorous species. This study also provides novel and detailed data describing how turtles actively use oceanographic structures during post-nesting migration

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