Kélonia

Marine turtles are globally threatened. Crucial for the conservation of these large ectotherms is a detailed knowledge of their energy relationships, especially their at-sea metabolic rates, which will ultimately define population structure and size. Measuring metabolic rates in free-ranging aquatic animals, however, remains a challenge. Hence, it is not surprising that for most marine turtle species we know little about the energetic requirements of adults at sea. Recently, accelerometry has emerged as a promising tool for estimating activity-specific metabolic rates of animals in the field. Accelerometry allows quantification of the movement of animals (ODBA/PDBA, overall/partial dynamic body acceleration), which, after calibration, might serve as a proxy for metabolic rate. We measured oxygen consumption rates (V(O(2))) of adult green turtles (Chelonia mydas; 142.1±26.9 kg) at rest and when swimming within a 13 m-long swim channel, using flow-through respirometry. We investigated the effect of water temperature (T(w)) on turtle and tested the hypothesis that turtle body acceleration can be used as a proxy for V(O(2)). Mean mass-specific V(O(2)) (sV(O(2))) of six turtles when resting at a T(w) of 25.8±1.0°C was 0.50±0.09 ml min(-1) kg(-0.83). sV(O(2))increased significantly with T(w) and activity level. Changes in sV(O(2)) were paralleled by changes in respiratory frequency (f(R)). Deploying bi-axial accelerometers in conjunction with respirometry, we found a significant positive relationship between sV(O(2)) and PDBA that was modified by T(w). The resulting predictive equation was highly significant (r(2)=0.83, P<0.0001) and associated error estimates were small (mean algebraic error 3.3%), indicating that body acceleration is a good predictor of V(O(2)) in green turtles. Our results suggest that accelerometry is a suitable method to investigate marine turtle energetics at sea.

BACKGROUND: A strong behavioural plasticity is commonly evidenced in the movements of marine megafauna species, and it might be related to an adaptation to local conditions of the habitat. One way to investigate such behavioural plasticity is to satellite track a large number of individuals from contrasting foraging grounds, but despite recent advances in satellite telemetry techniques, such studies are still very limited in sea turtles. METHODS: From 2010 to 2018, 49 juvenile green turtles were satellite tracked from five contrasting feeding grounds located in the South-West Indian Ocean in order to (1) assess the diel patterns in their movements, (2) investigate the inter-individual and inter-site variability, and (3) explore the drivers of their daily movements using both static (habitat type and bathymetry) and dynamic variables (daily and tidal cycles). RESULTS: Despite similarities observed in four feeding grounds (a diel pattern with a decreased distance to shore and smaller home ranges at night), contrasted habitats (e.g. mangrove, reef flat, fore-reef, terrace) associated with different resources (coral, seagrass, algae) were used in each island. CONCLUSIONS: Juvenile green turtles in the South-West Indian Ocean show different responses to contrasting environmental conditions - both natural (habitat type and tidal cycle) and anthropogenic (urbanised vs. uninhabited island) demonstrating the ability to adapt to modification of habitat.

The green turtle Chelonia mydas is classified as endangered because of global declines over the past few centuries due to human exploitation and habitat destruction, particularly the loss of nesting areas. We used the number of tracks as an indicator of breeding female abundance at their nesting sites to study the seasonality and trends of turtles breeding at 3 islands in the SW Indian Ocean: Europa, Tromelin and Grande Glorieuse, over 20 yr. On Tromelin, tracks were counted along the entire nesting beach, but on Europa and Grande Glorieuse counts were limited to a proportion of the island. Europa and Tromelin exhibited similar seasonal patterns, with a well-defined peak during the wet season (November–February), compared to a dry season peak for Grande Glorieuse (March–June). The main season was significantly longer on Grande Glorieuse (288 ± 43 d) than on Europa (218 ± 60 d), with Tromelin intermediate (252 ± 43 d). There was greater variation in the start of a season compared to the median and end at all sites throughout the study. Approximately 7178 ± 3053 (n = 19) tracks were recorded annually on the entire nesting beach on Tromelin, compared with 1480 ± 666 (n = 19) on 16% of nesting beaches on Grande Glorieuse and 1361 ± 903 (n = 23) on 26% of beaches on Europa. The number of tracks has increased significantly on Europa (3% yr–1) and Grande Glorieuse (6% yr–1). The increasing number of nesting turtles illustrates the effectiveness of conservation measures on sites formerly exploited by humans.

Changes in phenology, the timing of seasonal activities, are among the most frequently observed responses to environmental disturbances and in marine species are known to occur in response to climate changes that directly affects ocean temperature, biogeochemical composition and sea level. We examined nesting seasonality data from long-term studies at 8 green turtle (Chelonia mydas) rookeries that include 21 specific nesting sites in the South-West Indian Ocean (SWIO). We demonstrated that temperature drives patterns of nesting seasonality at the regional scale. We found a significant correlation between mean annual Sea Surface Temperature (SST) and dates of peak nesting with rookeries exposed to higher SST having a delayed nesting peak. This supports the hypothesis that temperature is the main factor determining peak nesting dates. We also demonstrated a spatial synchrony in nesting activity amongst multiple rookeries in the northern part of the SWIO (Aldabra, Glorieuses, Mohéli, Mayotte) but not with the eastern and southern rookeries (Europa, Tromelin), differences which could be attributed to females with sharply different adult foraging conditions. However, we did not detect a temporal trend in the nesting peak date over the study period or an inter-annual relation between nesting peak date and SST. The findings of our study provide a better understanding of the processes that drive marine species phenology. The findings will also help to predict their ability to cope with climate change and other environmental perturbations. Despite demonstrating this spatial shift in nesting phenology, no trend in the alteration of nesting dates over more than 20 years was found.

Age is a fundamental life history attribute that is used to understand the dynamics of wild animal populations. Unfortunately, most animals do not have a practical or nonlethal method to determine age. This makes it difficult for wildlife managers to carry out population assessments, particularly for elusive and long-lived fauna such as marine turtles. In this study, we present an epigenetic clock that predicts the age of marine turtles from skin biopsies. The model was developed and validated using DNA from known-age green turtles (Chelonia mydas) from two captive populations, and mark-recapture wild turtles with known time intervals between captures. Our method, based on DNA methylation levels at 18 CpG sites, was highly accurate with a median absolute error of 2.1 years (4.7% of maximum age in data set). This is the first epigenetic clock developed for a reptile and illustrates their broad applicability across a broad variety of vertebrate species. It has the potential to transform marine turtle management through a nonlethal and inexpensive method to provide key life history information.

Understanding how ocean currents impact the distribution and connectivity of marine species, provides vital information for the effective conservation management of migratory marine animals. Here, we used a combination of molecular genetics and ocean drift simulations to investigate the spatial ecology of juvenile green turtle (Chelonia mydas) developmental habitats, and assess the role of ocean currents in driving the dispersal of green turtle hatchlings. We analyzed mitochondrial (mt)DNA sequenced from 358 juvenile green turtles, and from eight developmental areas located throughout the Southwest Indian Ocean (SWIO). A mixed stock analysis (MSA) was applied to estimate the level of connectivity between developmental sites and published genetic data from 38 known genetic stocks. The MSA showed that the juvenile turtles at all sites originated almost exclusively from the three known SWIO stocks, with a clear shift in stock contributions between sites in the South and Central Areas. The results from the genetic analysis could largely be explained by regional current patterns, as shown by the results of passive numerical drift simulations linking breeding sites to developmental areas utilized by juvenile green turtles. Integrating genetic and oceanographic data helps researchers to better understand how marine species interact with ocean currents at different stages of their lifecycle, and provides the scientific basis for effective conservation management.

The international research program “ReNovRisk-CYCLONE” (RNR-CYC, 2017–2021) directly involves 20 partners from 5 countries of the south-west Indian-Ocean. It aims at improving the observation and modelling of tropical cyclones in the south-west Indian Ocean, as well as to foster regional cooperation and improve public policies adapted to present and future tropical cyclones risk in this cyclonic basin. This paper describes the structure and main objectives of this ambitious research project, with emphasis on its observing components, which allowed integrating numbers of innovative atmospheric and oceanic observations (sea-turtle borne and seismic data, unmanned airborne system, ocean gliders), as well as combining standard and original methods (radiosoundings and global navigation satellite system (GNSS) atmospheric soundings, seismic and in-situ swell sampling, drone and satellite imaging) to support research on tropical cyclones from the local to the basin-scale.

Summary Measuring the energy requirements of animals under natural conditions and determining how acquired energy is allocated to specific activities is a central theme in ecophysiology. Turtle reproductive output is fundamentally linked with their energy balance so a detailed understanding of marine turtle energy requirements during the different phases of their life cycle at sea is essential for their conservation. We used the non‐invasive accelerometry technique to investigate the activity patterns and energy expenditure ( EE ) of adult green turtles ( Chelonia mydas) foraging year‐round at a seagrass meadow in Mayotte ( n = 13) and during simulated oceanic migration (displacement from the nesting beach) off Mohéli ( n = 1), in the south‐western Indian Ocean. At the foraging site, turtles divided their days between foraging benthically on the shallow seagrass meadow during daylight hours and resting at greater depth on the inner side of the reef slope at night. Estimated oxygen consumption rates (s ) and daily energy expenditures ( DEE ) at the foraging site were low (s during the day was 1·6 and 1·9 times the respective resting rate at night during the austral summer and winter, respectively), which is consistent with the requirement to build up substantial energy reserves at the foraging site, to sustain the energy‐demanding breeding migration and reproduction. Dive duration (but not dive depth) at the foraging site shifted significantly with season (dive duration increased with declining water temperatures, T w ), while overall activity levels remained unchanged. In parallel with a significant seasonal decline in T w (from 28·9 ± 0·1 °C to 25·3 ± 0·4 °C), there was a moderate (˜19%) but significant decline in DEE of turtles during the austral winter (901 ± 111 kJ day −1 ), when compared with the austral summer (1117 ± 66 kJ day −1 ). By contrast, the turtle moved continuously during simulated oceanic migration, conducting short/shallow dives in the day, which (predominately at night) were interspersed with longer and deeper ‘pelagic’ dives. Estimated oxygen consumption rates during a simulated migration (1·25 ± 0·16 mL O 2 min −1 kg −0·83 ) were found to be significantly increased over the foraging condition, equal to ˜3 times the resting rate at night (0·42 ± 0·02 mL O 2 min −1 kg −0·83 ), and daily energy expenditure amounted to 2327 ± 292 kJ day −1 , underlining the tremendous energetic effort associated with breeding migration. Our study indicates that the accelerometry technique provides a new and promising opportunity to study marine turtle energy relations in great detail and under natural conditions. A lay summary is available for this article.

, N = 1), we report the discovery of circling events where animals consecutively circled more than twice at relatively constant angular speeds. Similar circling behaviors were observed across a wide variety of marine megafauna, suggesting these behaviors might serve several similar purposes across taxa including foraging, social interactions, and navigation.

Situated about 500 km off the Malagasy east coast, the island of Tromelin is a key nesting site for the endangered green turtle, Chelonia mydas, in the south Western Indian Ocean. Nesting turtles found in this isolated island have been closely monitored since the 1970s, but the most recent estimates of nesting parameters date from 1986. Using mark–recapture data, track counts, and nests monitoring data collected over the 2009/2010 nesting peak, reproductive characteristics, population size, and offspring production were updated and discussed in the light of the track survey undertaken from 1986 to 2010. Females showed a consistent reproductive behaviour compared with previous studies in terms of clutch frequency (2.75 ± 1.46) and nesting success (0.65). Nest indices such as hatching success (0.76 ± 0.25) and emergence success (0.61 ± 0.33) were also included in the range of values calculated in the 1980s. Importantly, the estimated number of nesters and production in eggs and hatchlings were similar to older estimates, suggesting a relative demographic stability. For the 2009/2010 year-long nesting season, the size of the nesting population was estimated at about 1500 individuals, which produced around 480,900 eggs (± 103,900), resulting in 289,200 emerging hatchlings (± 152,000). These results are promising and support the effectiveness of conservation measures undertaken in the Iles Eparses, but further comparable monitoring is needed in the coming years to confirm the stability in Tromelin's green turtle nesting population.

Despite the large number of species distribution modelling (SDM) applications driven by tracking data, individual information is most of the time neglected and traditional SDM approaches commonly focus on predicting the potential distribution at the species or population‐level. By running classical SDMs (population approach) with mixed models including a random factor to account for the variability attributable to individual (individual approach), we propose an innovative five‐steps framework to predict the potential and individual‐level distributions of mobile species using GPS data collected from green turtles. Pseudo‐absences were randomly generated following an environmentally‐stratified procedure. A negative exponential dispersal kernel was incorporated into the individual model to account for spatial fidelity, while five environmental variables derived from high‐resolution Lidar and hyperspectral data were used as predictors of the species distribution in generalized linear models. Both approaches showed a strong predictive power (mean: AUC &gt; 0.93, CBI &gt; 0.88) and goodness‐of‐fit (0.6 &lt; adjusted R 2 &lt; 0.9), but differed geographically with favorable habitats restricted around the tagging locations for the individual approach whereas favorable habitats from the population approach were more widespread. Our innovative way to combine predictions from both approaches into a single map provides a unique scientific baseline to support conservation planning and management of many taxa. Our framework is easy to implement and brings new opportunities to exploit existing tracking dataset, while addressing key ecological questions such as inter‐individual plasticity and social interactions.

The ReNovRisk-Cyclone program aimed at developing an observation network in the south-west Indian ocean (SWIO) in close synergy with the implementation of numerical tools to model and analyze the impacts of tropical cyclones (TC) in the present and in a context of climate change. This paper addresses the modeling part of the program. First, a unique coupled system to simulate TCs in the SWIO is developed. The ocean–wave–atmosphere coupling is considered along with a coherent coupling between sea surface state, wind field, aerosol, microphysics, and radiation. This coupled system is illustrated through several simulations of TCs: the impact of air–sea flux parameterizations on the evolution of TC Fantala is examined, the full coupling developed during the program is illustrated on TC Idai, and the potential of novel observations like space-borne synthetic aperture radar and sea turtles to validate the atmosphere and ocean models is presented with TC Herold. Secondly, the evolution of cyclonic activity in the SWIO during the second half of the 21st century is assessed. It was addressed both using climate simulation and through the implementation of a pseudo global warming method in the high-resolution coupled modeling platform. Our results suggest that the Mascarene Archipelago should experience an increase of TC related hazards in the medium term.

While scientists have been monitoring the movements and diving behaviour of sea turtles using Argos platform terminal transmitters for decades, the precise navigational mechanisms used by these animals remain an open question. Until now, active swimming motion has been derived from total motion by subtracting surface or subsurface modelled ocean currents, following the approximation of a quasi-two-dimensional surface layer migration. This study, based on tracking and diving data collected from 25 late-juvenile loggerhead turtles released from Reunion Island during their pre-reproductive migration, demonstrates the importance of considering the subsurface presence of the animals. Using a piecewise constant heading model, we investigate navigation strategy using daily time-at-depth distributions and three-dimensional currents to calculate swimming velocity. Our results are consistent with a map and compass strategy in which swimming movements follow straight courses at a stable swimming speed (approx. 0.5 m s −1 ), intermittently segmented by course corrections. This strategy, previously hypothesized for post-nesting green and hawksbill turtles, had never been observed in juvenile loggerheads. These results confirm a common open-ocean navigation mechanism across ages and species and highlight the importance of considering diving behaviour in most studies of sea turtle spatial ecology.

In marine turtles, the sex of hatchlings is determined by their egg incubation temperature. Global warming may increase the extinction risk by skewing hatchling sex ratios. Assessment of this risk at the population level requires the identification of sex in hatchlings and juveniles. However, available methods are typically lethal, highly invasive, or difficult to conduct at a large scale. Changes in DNA methylation, an epigenetic modification, have been characterized as part of sex differentiation pathways in some species with environmentally determined sex, but so far not in marine turtles. Neither have epigenetic biomarkers for sex been developed into rapid assays suited to research on wildlife. In this study, we aimed to develop a rapid, minimally invasive, and inexpensive method to identify the sex of marine turtles. We used reduced representation bisulfite sequencing DNA methylation data from adult green sea turtle ( Chelonia mydas ) skin biopsies to identify 16 genomic regions exhibiting differential methylation between males and females (adjusted p-value &amp;lt; 0.01). We designed methylation sensitive qPCR assays for these regions and tested their capacity to identify the sex of turtles ranging in age between 3-34 years. The qPCR assay identified the correct sex in turtles &amp;gt; 17 years. However, the sex of younger turtles could not be accurately identified. This suggests the sex differences distinguishable by the assay were adult specific, reflecting the training data on which the sex-specific regions were identified, and likely linked to late-stage ontogenetic changes associated with sexual maturity. Epigenetic biomarkers are a promising tool for wildlife research because they can be minimally invasive and high throughput. Future research into sex-specific differentially methylated regions in hatchlings and juveniles should be based on genome-wide DNA methylation data from a wider age range, which includes hatchlings.

Crabs of the genus Planes (family Grapsidae) live on floating debris and pelagic animals and spend their lives rafting at the surface of the open ocean. Among living substrata, Planes minutus is frequently found associated with sea turtles. However, prior to this study, crabs had never been documented on sea turtles in continental Africa or in the western Indian Ocean. We found P. minutus associated with olive ridley sea turtle Lepidochelys olivacea nesting and foraging/pre-nesting in Gabon, and with loggerhead Caretta caretta and green sea turtle Chelonia mydas foraging off the east coast of South Africa, as well as loggerheads nesting in Cape Verde and loggerheads foraging off Réunion. No crabs were found on nesting loggerheads surveyed in Oman. We integrate these new findings with a review of all known records of Planes–sea turtle interactions in the Atlantic and Indian oceans and the Mediterranean Sea, to better understand the geographic distribution and ecological characteristics of such associations.

Implementing effective conservation measures to manage migratory populations is challenging, especially in a relatively inaccessible dynamic environment such as the ocean. With limited financial and human resources, efforts must be intelligently prioritized to achieve conservation success and reduce uncertainties of conservation efforts. The southwest Indian Ocean (SWIO) hosts some of the world’s most important breeding grounds for the Critically Endangered hawksbill turtle Eretmochelys imbricata . However, knowledge gaps remain about the movement patterns of this species. Between 2007 and 2022, we deployed 17 satellite tags onto hawksbill turtles from scattered locations in the SWIO: 16 nesting females—Granitic Islands, Seychelles (n = 9); north Madagascar (n = 5); Moheli, Comoros (n = 1); Juan de Nova, Terres australes et antarctiques françaises (n = 1)—and 1 female bycaught in fisheries (east Madagascar). We found strong variability in migratory movements amongst individuals, particularly in terms of distance and movement persistence. Detailed analysis of movement persistence reveals that these individuals behave differently in neritic and oceanic habitats, with a lower movement persistence in neritic habitats. We identified a total of 12 foraging areas scattered throughout the SWIO, both in coastal and open-sea neritic habitats. These results reinforce the need to consider the importance of neritic habitats, for both migration and foraging, in conservation policies. The quantification of the degree of migratory variability is particularly important to developing conservation plans and strategies at both the national and international level, including the delineation of regional management units (RMUs) in the Indian Ocean.

Abstract A free‐ranging juvenile hawksbill sea turtle ( Eretmochelys imbricata ) presented to the rehabilitation centre with a chronic full thickness laceration of the right carpal joint, leaving the distal part of the flipper attached by only 2 cm of soft tissue. Open luxation of the carpal joint was noted on radiographs. Surgical reconstruction was elected despite extensive transection and osteo‐articular damage. Soft tissues were debrided and sutured. A cerclage wire was used to improve bone apposition. A type II external skeletal fixator was placed to promote soft tissue healing and pseudojoint formation. The turtle adapted well to the external fixator. Osteolysis was documented on radiographs four weeks postoperatively, and lesions improved with florfenicol treatment. The fixator was removed 3.5 months after the procedure. A year postoperatively, the function of the operated limb was normal, and the turtle was released into the ocean.

Temperature is of central importance to life and structures biological processes across levels of organization. For ectothermic marine turtles, temperature profoundly affects their metabolism, overall physiology, behaviour and distribution. Marine turtles are globally threatened and a detailed understanding of their energy requirements is essential to comprehend their role in marine ecosystems and to guide conservation efforts. We used flow-through respirometry to study the effects of seasonal changes in water temperature (Tw) on the resting oxygen consumption rates (V̇O2) of three sea turtle species (green, loggerhead and hawksbill turtles). Tw changes between winter and summer (maximum range: 20.3-31.9°C) had a clear effect on mass-specific V̇O2 (sV̇O2) that increased on average by ∼50% across species in summer. Hence, the thermal sensitivity of metabolism was similar in all species with Q10 values ranging between 2.1 and 2.7, typical for reptiles. Changes in sV̇O2 were paralleled by changes in respiratory frequency (fR) in all species. In separate trials with loggerhead turtles resting and swimming in a tank, we recorded body acceleration (PDBA) together with V̇O2 to investigate the effects of activity on metabolism and to establish a predictive equation that can be used to estimate turtle energy expenditure at sea from the recording of body acceleration. Moderate swimming activity increased sV̇O2 up to 3.2 times over resting. We found a significant positive relationship between sV̇O2 and PDBA (r2=0.63, P<0.0001) with small associated error estimates, indicating that body acceleration is a good predictor of V̇O2 in loggerhead turtles, similar to what has previously been reported for green turtles.