Understanding the ecology and life history of marine turtle populations is fundamental for their effective conservation, especially for those that are harvested for food. This thesis presents a collection of six chapters that progress from the applied to the pure; conservation and management in the first chapters through to animal ecology in the latter. A variety of contemporary and multidisciplinary techniques are utilised to explore the structure, populations dynamics and ecology of two marine turtle species, the green turtle (Chelonia mydas) and the hawksbill turtle (Eretmochelys imbricata), under harvest in the Turks and Caicos Islands (TCI), Caribbean. The work first focuses on the structure of TCI’s small-scale fishery and the demographics of turtles landed and incorporates nesting seasonality, adult take, satellite tracking and genetic structure to suggest evidence-based legislative amendments. As part of the study of this fishery, this work reports on how the harvest might increase prevalence of disease in green turtles. As an exploration into the ecology of turtle stocks found in TCI, the work then describes and compares in- water immature and adult sex ratios, genetic differentiation and sex biased dispersal. Finally, stomach content and habitat matching, and stable isotope analyses provide insights into the foraging ecology and suggested keystone roles of sympatric green and hawksbill turtles.

Marine turtles are an ancient group of reptiles that have been used by humans as a source of protein for over 7,000 years. In recent decades, acknowledgement of the various threats to marine turtles, including the deleterious impact of historical and contemporary use on many populations, led the International Union for the Conservation of Nature (IUCN) to list all seven extant species of marine turtle on their Red List of Threatened Species. Consequently, marine turtles are often given protected status in the national legislation of countries around the world, despite the existence of ongoing use cultures in communities that live with marine turtles. Conservation strategies are challenged by the migratory nature of marine turtles, which have complex life histories typically involving the use of habitats in the jurisdictions of multiple sovereign states as well as the high seas. As a result, a suite of multi-lateral environmental agreements (MEAs) list marine turtles in the most highly protective categories. Thus, governments of sovereign states that have acceded to the various MEAs are committed to conservation strategies requiring national action and cooperative multi-lateral action, which can conflict with interests of communities with a tradition of marine turtle consumption. In this thesis I provide examples of how contemporary scientific research methods can elucidate the migratory behaviours of marine turtles, and can help define range of populations subject to national conservation action and use. I examine specific examples of how this information can inform national and multi-lateral conservation policies and strategies; how those policies and strategies interact and impact on traditional cultures of marine turtle use in the UK Overseas Territories in the Caribbean; and provide an example of the potential benefits of engaging stakeholders with contemporary research methods. This thesis highlights the utility of a multi-disciplinary approach to research underpinning marine turtle conservation and management, which acknowledges the limitations of MEAs and national government capacity, and which incorporates participation of those communities engaged in marine turtle consumption.

Small-scale fisheries (SSF) are poorly documented, yet 90% of the 120 million employed in capture fisheries work in the SSF sector and >1 billion people globally rely on fish as an important source of protein. There is a lack of data on the status of the majority of fisheries in Madagascar owing to the difficulty in surveying the vast coastline and large number of small-scale fishers. In Madagascar, marine turtles and elasmobranchs are important culturally and as sources of income and food for many small-scale fishers. However, very little data exist on the status of these two animal groups. The five chapters of this thesis intend to increase our understanding of the status of marine turtles and elasmobranchs in Madagascar. This is achieved through the assessment of the fisheries, legislation and in the case of turtles, the nesting population. I also document community-based methods for monitoring fisheries and marine turtle nesting, that are easily replicable for gathering data across remote regions. Results show that the turtle fishery in Madagascar appears to have remained at the same level since the 1970s, despite being illegal since the 1990s, with landings estimated to be approximately 10,000 to 16,000 turtles.year-1. To further contextualise the take of turtles in Madagascar, by carrying out a global review, I estimate that the worldwide legal take in turtle fisheries to be over 42,000 turtles.year-1. Contrary to reports from fishers, actual numbers of elasmobranchs (the majority of which are sharks) taken by the traditional (non-motorised) fishery has not declined. Results support previous reports that fishing effort has increased, as well changes in fishing gears, to account for declining catch per unit effort (CPUE) to maintain shark landing numbers. Furthermore, the size of some shark species has significantly declined, even across this study. Community-based turtle nesting monitoring and protection in western Madagascar revealed a small, yet potentially significant, nesting population. Across the 17 current nesting sites recorded, the majority of nesting populations in Madagascar have <50 nests.year-1. A further >40 historic nesting sites were recorded. Community-led monitoring methods not only helped to fill a data gap, but were also found to reduce loss of nests through human disturbance. Misinterpretations, poor enforcement and gaps in current legislation mean that both marine turtles and elasmobranchs are effectively unprotected from overexploitation. This thesis provides recommendations for improved legislation and management of both groups of species and demonstrates that participatory monitoring methods can not only reduce data deficiency, but enhance locally-led management and protection, and increase Madagascar's capacity for improved management and conservation.

ABSTRACT The tropical and subtropical nearshore marine environments of Queensland, Australia sustain diverse and unique marine wildlife. Continuous population growth and land-use changes along the Queensland coastline are known to exert numerous anthropogenic pressures on these marine ecosystems, including the delivery of high sediment loads. Sediments also provide a transport pathway for persistent organic pollutants (POPs) from rural and urban catchments into the marine environment. While such pollutants are known to be elevated in marine sediment and biota from nearshore areas in Queensland, their input and distribution pathways, as well as exposure and associated risks to wildlife populations are only partially understood. Mounting evidence suggests that POPs may contribute to population declines in marine wildlife species; however, limited information is available regarding the accumulation and effects of these contaminants in endangered or threatened marine turtles. This study aimed to redress some of these information gaps using a case study approach in marine turtle habitats of Moreton Bay, and other embayments in Queensland. Among persistent organic pollutants (POPs), dioxins (polychlorinated dibenzo-p-dioxins; PCDDs) and to some extent also dioxin-like PCBs (polychlorinated biphenyls; PCBs) were found to be widespread and often present at elevated (ppb) levels in surface sediments from Moreton Bay. However, while PCDD/F toxic equivalencies (TEQs) are above international (Canadian) sediment quality guidelines at numerous sites in Moreton Bay, in general TEQs across the Bay are relatively low compared to those from contaminated locations near dense industrial activities. POP contamination in surface sediments across Moreton Bay was investigated by a combination of GIS spatial mapping, geostatistical and traditional statistical modalities. High spatial variability and complex spatial distribution patterns were revealed. High resolution GIS kriging model outputs from the mid to southern Bay facilitated identification of distinct sediment contamination zones, with highest PCB and PCDD/F levels present in nearshore locations, associated with nearby river systems. While primarily governed by organic carbon, a multitude of physical, chemical and hydrological factors were identified to influence the spatial variance of PCDD/F concentrations. The main parameters governing PCDD/F spatial distribution were identified as sediment geochemistry, water depth and anthropogenic alterations of the physical environment and, together, all quantifiable explanatory variables (including hydrodynamic flushing) explained ≈75% of spatial PCDD/F variance. Together, the interaction of these parameters results in complex distribution patterns and highly variable concentrations even among neighbouring sites of 1-3 km resolution. These results suggest that prediction models of POP distributions in the nearshore marine environment may require high-resolution validation, and highlights that the design of low resolution monitoring strategies can have profound impacts on the reliability of contaminant information or any subsequent extrapolations. This knowledge and methodology can be utilised to optimise on-going and future near-shore sediment monitoring programs both locally and in other regions around the world. Using the spatial distributions of dioxin-like contaminants within sediments, this study provided an opportunity to assess field-based relationships between habitat contamination and local marine biota contamination. Detectable levels of PCDD/Fs and dioxin-like PCBs were measured in all green, hawksbill, loggerhead and flatback marine turtle tissues. POP concentrations in sediments were found to significantly correlate with those in the herbivorous green turtle from different sediment contamination zones. These findings demonstrate that sediments represent an important secondary contaminant source and lead to redistribution of POPs to the marine food chain. POP concentrations and TEQs clearly increased from sediment to turtles as well as with increasing trophic levels in marine turtle species. The results from this study demonstrate that the extent of sediment contamination within foraging habitats governs marine turtle exposure, while, trophic status and to some extent age influence contaminant exposure within a particular contamination zone. Despite the relatively low TEQ in sediments from Moreton Bay, TEQ levels in green turtle sub-populations foraging from near-shore locations and higher trophic loggerhead and flatback turtles are similar or elevated compared to those reported for other marine wildlife from Moreton Bay and elsewhere, even compared to higher trophic species from locations impacted by dense industrial activities. High bioaccumulation potential of 2,3,7,8-PCDD/F and dioxin-like PCBs compounds were estimated for green turtles using biota to sediment accumulation factors. Selective accumulation of toxicologically more potent (i.e. lower chlorinated) PCDD/Fs was observed for higher trophic marine turtles, resulting in increasing TEQs for the carnivorous species. Biomagnification was also observed for some non-2,3,7,8-substituted dioxin congeners which typically do not accumulate in most biota. These results are proposed to be due to relatively high accumulation efficiency and/or low metabolic capacity for these POP compounds in marine turtles. These findings are also hypothesised to reflect temperature dependant, greater bioavailability of hydrophobic chemicals in sub-tropical and shallow marine systems. An additional pilot study revealed that in contrast to PCDD/Fs and PCBs, levels of persistent flame retardants (polybrominated diphenyl ethers; PBDEs) were relatively low in marine turtles and other marine species (dugong, fish and shellfish) from Moreton Bay. This suggests relatively low level input of these more recent industrial products into the marine environment. However, as elevated levels of PBDEs have been reported in blood from the general population of Australia, ongoing transport from the terrestrial to the marine system and redistribution of these contaminants, similar to PCDD/F and PCBs, would be expected to occur into the future. Limited information is available regarding the sensitivity of reptiles to and effects of POPs, however, studies have shown that reptiles are sensitive to POPs albeit with uncharacterised relative potency. In the absence of robust toxicological information for reptiles or marine turtles, the potential risks associated with PCDD/F and PCB exposure of Queensland turtle populations was evaluated using toxicity for sensitive biological endpoints observed in mammals and birds. Using probabilistic methodology for marine turtles from Queensland, the body burden of up to 31% and 55% of green and loggerhead turtles, respectively, are above the threshold levels where the most sensitive physiological effects are observed in mammals and birds. While this evaluation illustrates that the contaminants investigated have the potential to impact on the health of marine turtle populations, it must be highlighted that it is compromised by the lack of species-specific (and in this case, class-specific) information, the uncertainty of which is often considered to represent a factor of at least 10. The findings of the present study indicate that exposure to POPs has the potential to adversely affect the health of Queensland’s marine turtle populations, and highlight the need for robust information on reptile specific sensitivity to these compounds.

Gaining a good understanding of marine turtle mating systems is fundamental for their effective conservation, yet there are distinct gaps in our knowledge of their breeding ecology and life history, owing largely to the difficulty in observing these highly mobile animals at sea. Whilst multiple mating by females, or polyandry, has been documented in all marine turtle species, the fitness consequences of this behaviour have not been fully investigated. Furthermore, male mating patterns, operational sex ratios and the number of males contributing to breeding populations are poorly understood, impeding accurate assessments of population viability. In this thesis, I use molecular-based parentage analysis to study, in detail, the genetic mating system of two green turtle (Chelonia mydas) populations. In the focal population in northern Cyprus, I show that, despite exhibiting a strongly female-biased hatchling sex ratio and contrary to our expectations, there are at least 1.3 breeding males to every nesting female. I go on to assess the breeding frequency of male turtles in the population and determine that males do not breed annually at this site, demonstrating that the observed relatively equal sex ratio of breeders is not the result of a few males mating every year, but that the number of breeding males in the population is greater than expected. I show that 24% of nesting females in the population produce clutches with multiple paternity, but do not detect any fitness benefits to polyandrous females, and discuss the potential role of sexual conflict in influencing female mating decisions. Finally, I reveal a high frequency of multiple paternity in green turtle clutches on Ascension Island, one of the largest green turtle rookeries in the world, and discuss possible causes of variation in the level of polyandry among marine turtle populations. The results presented here shed new light on aspects of marine turtle mating systems that are challenging to study, and illustrate the value of molecular data, not only in describing mating patterns, but in elucidating aspects of life history and behaviour that would otherwise be very difficult to ascertain.

Marine turtle numbers are in a state of flux around the world. Six of the seven remaining species of these long-lived animals are threatened; with the seventh being listed data deficient. Reasons for these fluctuations are speculated to be due to human related impacts (direct) and increase in disease occurrence caused by changes in the natural environment (indirect). Most direct impacts have been identified and strategies implemented to mitigate their effects with varying degrees of success; however the indirect effects on marine animals remain an understudied area. This thesis outlined the development of ante- and post-mortem diagnostic techniques to identify prevalent diseases affecting two marine turtle species in southern Queensland over a four year (2006-2009) period. This data was used to determine the impact of disease on turtle survivorship. Two-hundred and ninety green turtles (Chelonia mydas) from Moreton and Shoalwater Bays were captured, clinically assessed and blood sampled. Clinically healthy animals (n = 211) were used to derive biochemical and haematological reference intervals using two methods. Comparisons with clinically unhealthy animals (n = 25) indicated all unhealthy animals had at least some plasma biochemical and haematological values outside the derived intervals (albumin, 48% of unhealthy animals; alkaline phosphatase (ALP), 35%; aspartate transaminase (AST), 13%; creatinine, 30%; globulin, 3%; glucose, 34%; lactic dehydrogenase (LDH), 26%; phosphorus, 22%; sodium, 13%; thrombocytes, 57%; and monocytes, 5%). Amongst small immature animals, those with Chelonibia testudinaria plastron barnacle counts of at least 20 were approximately three times more likely to be unhealthy than turtles with no barnacles. In addition, small immature and mature turtles were more likely to be unhealthy than large immature turtles (Chapter 2). By the same method, 101 loggerhead turtles (Caretta caretta) in Moreton Bay were assessed and bled. Clinically healthy animals (n = 63) were used to derive intervals. Comparisons with clinically unhealthy animals (n = 23) indicated 82% and 45% had at least one biochemical and hematological result, respectively, outside of at least one of the calculated intervals. Neither sex nor maturity (mature versus large immature) influenced the risk of being clinically unhealthy (Chapter 3). A standardised approach to post-mortem examination of marine turtles for veterinary clinicians with a concurrent descriptive review of gross and microscopic pathological lesions commonly seen during examination in Australia (Chapter 4) was used to accurately determine diseases and causes of death in 100 green turtles submitted from various regions of southern Queensland for examination. Spirorchiid parasitism was found to be the most frequently occurring cause of mortality (41.8%), followed by gastrointestinal impaction (11.8%), microbiological infectious diseases (5.2%) and trauma (5.2%). Spirorchiid parasitism with associated inflammation (75%) was the most frequently occurring disease followed by gastrointestinal impaction (5.1%). Season and turtle age had limited influences on disease. Severity of spirorchiidiasis in the brain was independent of severity in other organs (Chapter 5). From these examinations, the most prevalent disease syndrome (spirorchiidiasis) and a previously unreported finding in Australian waters (corneal fibropapillomatosis) were selected to be examined in greater detail. Spirorchiid parasites from four organs in five green turtles were identified by established morphological and molecular techniques. Morphological study of adults identified Carettacola sp. in the serosal wall of the gastrointestinal tract, Hapalotrema mehrai in the heart and Learedius learedi in the spleen. Worms from the brain probably belonged to the genus Neospirorchis. DNA sequences from a portion of the 28S ribosomal RNA gene were obtained; but only matches for Hapalotrema mehrai and Learedius learedi were made. The prevalence and severity of this disease warrants further investigation into development of molecular techniques for use as a prognostic tool for turtles entering rehabilitation (Chapter 6). Chelonid corneal fibropapillomatosis, a previously unreported disease manifestation in Australia, was identified in 0.5% of 787 examined green turtles in 2008 (Chapter 7). This novel syndrome was shown to reduce visibility, potentially negatively affecting turtle survivorship and should be monitored for further spread. Findings from this thesis and the published literature were used to derive a mathematical model to determine the effects of identified diseases on Moreton Bay green turtle survivorship. This model demonstrated diseases at current prevalence will not negatively affect survivorship but an adverse environmental disruption or an increase in current disease frequency may threaten these animals (Chapter 8). Information presented in this thesis was used to test the general hypothesis ‘Differences in disease and health between stranded and functional populations of marine turtles will indicate major and currently unmeasured causes of population decline.’ This hypothesis was partially upheld. Differences in disease and health status between stranded and functional populations were demonstrated, but more work is required to comprehensively examine these statuses. Diagnostics and continued environmental assessment should become the focus of future investigations. These findings should be incorporated in future management strategies.

Marine turtles have historically contributed to economic activity through consumptive harvest for food, tools, and decorative objects. Only recently have they begun to benefit humans economically through non-consumptive roles, primarily as a focal point of educational eco-tourism. In recent years, the annual number of turtle walks conducted around the Archie Carr National Wildlife Refuge (ACNWR) has risen. This expansion contributed to a statistically significant increase in attendance from 2,162 in 2001 to 3,047 participants in 2014. I examined the regional economic impacts of marine turtle eco-tourism around the ACNWR using social surveys and an economic impact analysis tool. IMPLAN, an input-output modeling package, has been used in tourism industries around the U.S. since 1992, but this study is the first to use this tool to evaluate the holistic economic effects of marine turtle-based eco-tourism within a selected region. During the 2014 turtle walk season (June through July), surveys were distributed at six different turtle walk locations within Brevard and Indian River Counties, Florida, along the central Florida Atlantic coast. Adults attending the turtle walks (n=2,274) were given time before the educational presentation began to complete a one-page survey. Approximately 93% of turtle walk participants completed surveys. Due to market interactions within this two-county region, turtle walks contributed a minimum of three new jobs and a conservative estimate of almost $250,000 (USD) to the local economy during the two-month turtle walk season. Using financial comparisons and economic impact tools, like IMPLAN, can improve our understanding of the many roles, especially non-consumptive uses, sea turtles have in our communities. This information can be useful in resource management and conservation-based decision making.

Le plan de restauration des tortues marines aux Antilles françaises a été validé par le Conseil National pour la Conservation de la Nature en 2006. Les captures accidentelles dans les filets de fond, i.e. les trémail, folle et filet droit, sur le plateau continental constituent la principale menace. Des filets faisant varier la hauteur, le maillage et l’inclinaison ont été comparés à des filets professionnels au cours de 226 pêches expérimentales. Le trémail est peu sélectif. Des filets à profil bas permettent d’obtenir des rendements comparables et réduiraient les captures de tortues. Les captures accidentelles sont plus abondantes dans les trémails et les folles. Les pêches à longs temps de calée provoquent plus de 90% de taux de mortalité de tortues et augmentent les quantités de rejets. Près de deux milliers de tortues seraient capturées chaque année aux Antilles françaises, avec une mortalité avoisinant les 60%. Les tortues adultes pêchées l’ont été en période de nidification et les tortues dites résidentes sont dans la grande majorité des juvéniles ou sub-adultes, cause de la surexploitation locale passée et signe de populations non stables. La menace « pêche » est d’autant plus importante qu’elle touche les femelles nidifiantes, meilleurs espoirs de rétablissement des stocks. En étroite collaboration participative avec les professionnels de la mer, la protection des tortues et des ressources marines passerait par une réduction de la hauteur des filets et de leurs temps de calée et l’interdiction totale ou partielle de ceux à mailles larges. / The national marine turtles recovery plan in FWI was adopted in 2006 by the National council for the nature conservancy. The bottom nets bycatch, i.e. the trammel, folle and gill nets, on the continental shelf are the main threat. Experimental nets with different heights, meshing and incline was compared to professional ones during 226 experimental trials. Trammel net is non selective. Low profile nets maintain a similar productivity and reduce the turtle bycatch. Trammel and folle nets cause more bycatch. The long soak times lead to more than 90 % of turtles mortality and more discards. Each year, about two thousands of turtles would be captured in FWI, with a mortality rate closed to 60 %. The mature turtles were captured during the nesting season and the resident ones are mostly juveniles or sub-adults, because of the local past overexploitation and indicator of non stable populations. The “fishery” threat is particularly important it affect nesting females, best stocks recovery hope. Closely to the marine professionals, the marine turtle and resources protection would be effective thanks to the reduction of the height and soak times nets and the total or partial ban of large meshing size nets.

Climate change threatens to disrupt biological systems around the globe, sparking debate over natural capacity for adaptation in a fragmented landscape. Marine turtles are evolutionarily ancient and have survived millions of years of prehistoric climate change, but are threatened by the rapidity of modern warming and a history of severe overexploitation that has left most populations depleted. This thesis explores a nesting aggregation of the green turtle (Chelonia mydas) in northern Cyprus, where a longitudinal programme of both intensive and extensive monitoring enables insight into individual and population level parameters and processes. Nesting on the two coastlines covered by this project is in the early stages of recovery, possibly in response to exhaustive nest protection efforts over the last twenty years. Saturation tagging at one key site allows us to confirm that recruitment of new breeders is an important driver of this trend, and that average clutch frequency has remained stable around three nests per female per year, validating nest-count derived abundance estimates at a regional scale. Concern has been raised, however, regarding recent changes in fishing practices which are impacting the local juvenile neritic phase, which may have a lagged effect on the recovery of this nesting population. A collaborative tracking effort including all other countries with major nesting in the Mediterranean allows us to identify major foraging grounds for this species, with two hotspots accounting for >50% of tracked individuals, as well as coastal and pelagic seasonal corridors of high use. Bycatch levels and mortality rates for turtles in these key areas are largely unknown and should be prioritised for investigation. Hatchling sex ratios from the main study beach are extremely female-biased (estimated 97% female for the twenty year period 1993-2012). A 1oC rise in average incubation temperatures threatens near complete hatchling feminisation on this beach, whilst a 2oC rise could reduce hatch success to less than 50%. Thermal effects on hatchling morphometrics are evident, with a 1oC rise in temperature reducing average length, width and weight by 1%, 2% and 3% respectively. More favourable incubation conditions were found early in the season, in deeper nests laid by larger females, and on beaches of lighter sand. In contrast, adult sex ratios at the main site are male-biased, posing questions regarding sex-specific survival rates and optimal hatchling sex ratios. A phenological shift towards earlier nesting is demonstrated for the first time in this species, and could potentially ameliorate warming effects. Carry-over climate forcing effects from the foraging ground influence the breeding frequency of individuals, driving population level responses in annual magnitude of nesting. This work emphasises the utility and necessity of long-term individual-based monitoring programmes in elucidating population trends and climate responses in iteroparous species with non-annual breeding.

Le déplacement animal joue un rôle déterminant dans la structuration spatiale et la dynamique des populations biologiques, en particulier des espèces fortement mobiles. L’espace et l’environnement font ainsi partie intégrante du cycle de vie des tortues marines. Ce travail de thèse propose de caractériser l’écologie spatiale des tortues marines, du stade juvénile au stade adulte, dans le Sud-ouest de l’océan Indien, principalement par l’usage de deux méthodes : la télémétrie satellitaire et la modélisation individu-centrée. Il montre en premier lieu que la phénologie de la reproduction de la tortue verte à travers la région est principalement liée à la température de surface de la mer au voisinage des sites de reproduction. Sont ensuite étudiés les patrons de dérive des nouveau-nés générés par les courants océaniques qui impacteraient inégalement leurs traits d’histoire de vie selon l’emplacement du site de naissance. Concernant le stade immature, les résultats suggèrent un cycle de développement trans-équatorial pour la tortue caouanne dans l’océan Indien. Pour le stade adulte, cette étude caractérise les couloirs et la connectivité migratoires de la tortue verte dans la région. Enfin, l’intégration de ces résultats permet de comprendre la structuration des patrons migratoires régionaux et leur influence sur la dynamique des populations. L’ensemble des connaissances acquises fournit un support concret d’aide à la décision pour la mise en place de plans de gestion et de conservation des tortues marines dans le Sud-ouest de l’océan Indien. Cela souligne l’importance d’une approche à grande échelle pour la protection d’un patrimoine biologique partagé par plusieurs nations. / Animal movement is crucial to the ecology of spatially structured population, particularly for highly mobile species. Marine turtles’ life cycle is indeed closely related to spatial and environmental factors. This work analyses the spatial ecology of marine turtles, from early juvenile to adult stages, in the Southwest Indian Ocean, primarily through the use of two methods: satellite tracking and individual-based modeling. Firstly, this analysis argues that green turtle’s reproductive phenology across the region is mainly related to the sea surface temperature in the vicinity of the nesting site. Then, it shows how drifting trajectories of hatchlings in oceanic currents unevenly influence their life history traits depending on the position of the natal site. By tracking late juvenile stage, this work also suggests a trans-equatorial developmental cycle for loggerhead turtle in the Indian Ocean. At adult stage, it describes migratory corridors and connectivity for green turtle across the region. Finally, an integrative approach considering all these results allows for an understanding of the regional migratory patterns and their influence on population dynamics. The results of this work provide a practical policy decision tool for management and conservation of marine turtles in the Southwest Indian Ocean and highlight the need for a large-scale approach in the protection of biological resources and heritage shared by multiple nations.