Chelonia Research Articles

Steroid Hormone Profiles and Demographic Data for Green Turtles (Chelonia mydas) Inhabiting the Mexican Caribbean Coast

Steroid Hormone Profiles and Demographic Data for Green Turtles (Chelonia mydas) Inhabiting the Mexican Caribbean Coast

Archaeological evidence for long-term human impacts on sea turtle foraging behaviour.

Early conservation efforts to prevent the loss of green sea turtles (Chelonia mydas) from the Caribbean Sea jumpstarted marine habitat and biodiversity protection. However, even there, limitations on historical observations of turtle ecology have hampered efforts to contextualize foraging behaviours for conservation management. We integrate isotopic and zooarchaeological evidence from green sea turtles harvested at the Miskito Cays (Nicaragua) to assess foraging behaviour before and after a step change in harvesting intensity. Highly structured isotopic evidence shows greater foraging adaptability in earlier populations. This provides a counterpoint to recent synthesis, suggesting the ecological non-exchangeability of sea turtles, which complicates conservation planning focused on genetic-stock-based repopulation. In contrast, our results suggest future populations would have a capacity for higher degrees of ecological exchangeability than current perspectives allow. This highlights a need to consider the kinds of longer term perspectives, such as those offered by archaeological materials, when planning for future sea turtle recovery.

Regional foraging areas of green turtles (Chelonia mydas) nesting at Aldabra Atoll: insights from stable isotopes and satellite telemetry

Sea turtles spend the majority of their lives at foraging grounds. These areas are important for population persistence but generally occur in coastal habitats, which are under increasing human pressure. Identifying key foraging areas is therefore an important step to understanding critical sea turtle habitats, and therefore their threats. Isotope ratios (δ15N, δ13C) from skin tissues of 90 green turtles (Chelonia mydas) nesting at the regionally important rookery of Aldabra Atoll, Seychelles, were analyzed with samples collected during two periods: 51 samples from March to September 2021, and 39 samples from January to April 2022. These analyses were complemented by nine satellite tracks to identify key foraging areas. Hierarchical clustering and discriminant function analysis identified two main foraging areas: the East African coast (Tanzania and Somalia) and northern Madagascar. Isotopic values indicated that the majority of green turtles nesting at Aldabra forage at one of these two areas, with slightly more green turtles visiting the East African coast. Geographical isotopic patterns were not found latitudinally, suggesting a potential limit to this approach for coastal areas in the Western Indian Ocean. However, we found longitudinal variation of δ13C and δ15N that few studies have reported. This is the first study in this region to combine satellite telemetry and stable isotope analysis to assign likely foraging areas of green turtles and advances understanding of the complex migration patterns and foraging ecology of this species. We demonstrate the potential and the limitations of stable isotope analysis for identifying/characterizing green turtle foraging areas in this region.

DNA Virome in Cardiac Tissue from Green Sea Turtles (Chelonia mydas) with Myocarditis.

As part of a sea turtle health monitoring program on the central east coast of Queensland, Australia, stranded and sick green sea turtles (Chelonia mydas) were subjected to necropsy and histopathology. A subset of these turtles had myocarditis of varying severity, which could not be attributed to parasitism by spirorchid flukes or bacterial infections. We, therefore, undertook an investigation to determine whether virus infections might be part of the pathogenesis. Deep sequencing revealed abundant DNA virus contigs in the heart tissue, of which CRESS and circoviruses appeared to be the most consistently present. Further analysis revealed the homology of some of the circoviruses to the beak and feather disease virus. While a causative link to myocarditis could not be established, the presence of these viruses may play a contributing role by affecting the immune system and overall health of animals exposed to pollutants, higher water temperatures, and decreasing nutrition.

Observations at a green sea turtle, Chelonia mydas, cleaning station identify three cleaning fish symbionts

Observations at a green sea turtle, Chelonia mydas, cleaning station identify three cleaning fish symbionts

Evidence of oxidative stress responses of green turtles (Chelonia mydas) to differential habitat conditions in the Mexican Caribbean

Important foraging and nesting habitats for Caribbean green sea turtles (Chelonia mydas) exist within the Mesoamerican Reef System in the Mexican Caribbean. During the last 25 years, urban development and touristic activities have drastically increased in Quintana Roo, Mexico. Moreover, in the last decade, massive pelagic sargasso blooms have also afflicted this region; however, information about the biochemical responses of Caribbean green turtles to these inputs is absent. This study aimed to assess if the oxidative stress indicators in the red blood cells of green turtles are valuable biomarkers of the extent of the anthropic impact in this region. Persistent organic pollutants (POPs) were also measured in the plasma of free-living green turtles during 2015–2018 to characterize these habitats further. As biochemical biomarkers, the production rate of superoxide radical (O2•-), carbonylated protein content, and lipid peroxidation (TBARS) levels, and the activities of superoxide dismutase, glutathione S-transferase (GST), catalase, glutathione peroxidase were measured in erythrocytes. A 15 % occurrence of fibropapillomatosis (FP) was revealed, with tumor size being positively correlated with CAT activity in the affected individuals. A multivariate analysis embracing all oxidative stress markers discriminated green turtles between years of capture (p < 0.001), with those sampled during 2015 presenting the highest production of O2•- (p = 0.001), activities of GST (p < 0.001), levels of TBARS (p < 0.001) and carbonylated proteins (p = 0.02). These local and temporal biochemical responses coincided with the first massive Sargassum spp. bloom reported in the region. The results of this study corroborate the utility of the oxidative stress indicators as biomarkers of environmental conditions (sargasso blooms and POPs) in the green turtle as sentinel species.

Should I stay or should I go? The influence of environmental conditions on green turtle residence time and outward transit in foraging areas

Foraging animals move through the environment to satisfy their requirements for food, rest, reproduction and risk-avoidance. Understanding how animals respond to changing environmental conditions can help to characterise favourable habitat and determine whether they might be motivated to depart when those habitats become unsuitable. Foraging green turtles are typically residents that scarcely move in response to environmental changes or disturbances. Some individuals though, exhibit high mobility at fine scales. We developed an analysis of Fastloc GPS tracks of 61 green turtles using cox regression models and generalised linear mixed models to investigate the influence of a suite of environmental characteristics on the length of residence time and probability of turtles transitioning between two behavioural modes, “stay” or “go”. Decisions to move (“go”) were influenced by short-term changes in the local environmental conditions. Individuals were more likely to “stay” when temperature increased during their stay and were more likely to “go” when turbidity decreased, and they entered deeper habitats. This result implies that foraging and resting (“staying”) primarily occurs in benthic, shallow, warm habitats, while transit (“going”) is facilitated in deeper, clear water. We also determined that individuals within the green turtle foraging aggregation respond differently to environmental cues to move and hypothesise that a diversity of strategies within a foraging aggregation could confer its resilience to disturbance events. Our study provides new evidence of the factors influencing movements in green turtles and can aid in predicting how they may respond to future changes and enhance risk mitigation efforts through dynamic and adaptive planning.

Inter-island nesting dynamics and clutch survival of green turtles Chelonia mydas within a marine protected area in the Bijagós Archipelago, West Africa

Understanding spatial heterogeneity in reproductive success among at-risk populations facing localised threats is key for conservation. Sea turtle populations often concentrate at one nesting site, diverting conservation efforts from adjacent smaller rookeries. Poilão Island, Bijagós Archipelago, Guinea-Bissau, is a notable rookery for green turtles Chelonia mydas within the João Vieira-Poilão Marine National Park, surrounded by three islands (Cavalos, Meio and João Vieira), with lower nesting activity. Poilão’s nesting suitability may decrease due to turtle population growth and sea level rise, exacerbating already high nest density. As the potential usage of secondary sites may arise, we assessed green turtle clutch survival and related threats in Poilão and its neighbouring islands. High nest density on Poilão leads to high clutch destruction by later turtles, resulting in surplus eggs on the beach surface and consequently low clutch predation (4.0%, n = 69, 2000). Here, the overall mean hatching success estimated was 67.9 ± 36.7% (n = 631, 2015–2022), contrasting with a significantly lower value on Meio in 2019 (11.9 ± 23.6%, n = 21), where clutch predation was high (83.7%, n = 98). Moderate to high clutch predation was also observed on Cavalos (36.0%, n = 64) and João Vieira (76.0%, n = 175). Cavalos and Meio likely face higher clutch flooding compared to Poilão. These findings, alongside observations of turtle exchanges between islands, may suggest a source-sink dynamic, where low reproductive output sink habitats (neighbouring islands) are utilized by migrants from Poilão (source), which currently offers the best conditions for clutch survival.

Predictive modelling reveals Australian continental risk hotspots for marine debris interactions with key threatened species.

Anthropogenic debris is a global threat that impacts threatened species through various lethal and sub-lethal consequences, as well as overall ecosystem health. This study used a database of over 24,000 beach surveys of marine debris collated by the Australian Marine Debris Initiative from 2012 to 2021, with two key objectives: (1) identify variables that most influence the occurrence of debris hotspots on a continental scale and (2) use these findings to identify likely hotspots of interaction between threatened species and marine debris. The number of particles found in each beach survey was modelled alongside fifteen biological, social, and physical spatial variables including land use, physical oceanography, population, rainfall, distance to waste facilities, ports, and mangroves to identify the significant drivers of debris deposition. The model of best fit for predicting debris particle abundance was calculated using a generalized additive model. Overall, debris was more abundant at sites near catchments with high annual rainfall (mm), intensive land use (km2), and that were nearer to ports (km) and mangroves (km). These results support previous studies which state that mangroves are a significant sink for marine debris, and that large ports and urbanized catchments are significant sources for marine debris. We illustrate the applicability of these models by quantifying significant overlap between debris hotspots and the distributions for four internationally listed threatened species that exhibit debris interactions; green turtle (26,868 km2), dugong (16,164 km2), Australian sea lion (2903 km2) and Flesh-footed Shearwater (2413 km2). This equates to less than 1% (Flesh-footed Shearwater, Australian sea lion), over 2% (green sea turtle) and over 5% (dugong) of their habitat being identified as areas of high risk for marine debris interactions. The results of this study hold practical value, informing decision-making processes, managing debris pollution at continental scales, as well as identifying gaps in species monitoring.

Chelonia mydas detection and image extraction from noisy field recordings

&lt;span lang="EN-US"&gt;Wildlife videography is an essential data collection method for conducting research on animals. The video recording process of an animal like the &lt;em&gt;Chelonia Mydas&lt;/em&gt; turtle in its natural habitat requires the setting up of special camera traps or by performing complex camera movement to capture the animal in frame whilst the cameraman maneuvers over uneven terrain while filming. The result is hours of footage that only have the presence of the intended subject in it for seconds whilst the rest is background footage; or noisy and blurry footage that has only several usable frames among thousands of noisy and unusable ones. This presents a problem that deep learning models can help to assist, especially in detecting a wildlife subject and extracting usable data from hours of noise and background footage. This paper proposes the use of machine learning models to detect and extract wildlife images of &lt;em&gt;Chelonia Mydas&lt;/em&gt; turtles to help prune through hundreds and thousands of frames from several video footages. Our paper shows that utilizing a custom model with various confidence scores can label and crop out images in noisy field video recordings of &lt;/span&gt;&lt;em&gt;&lt;span lang="EN-US"&gt;Chelonia Mydas &lt;/span&gt;&lt;/em&gt;&lt;span lang="EN-US"&gt;turtles with up to 99.89% of output images correctly cropped and labeled.&lt;/span&gt;

Status and impacts to sea turtles in Vietnam

Sea turtles face a great danger of extinction because of human impacts, and the number of turtle occurrence is decreasing. By interviewing fishermen, coastal residents and authorities combined with field surveys in some places where turtles regularly lay eggs, such as Con Dao and Ninh Thuan, the results show that 05 species of sea turtles were found in Vietnam: The Green (Chelonia mydas), Hawksbill (Eretmochelys imbricata), Olive Ridley (Lepidochelys olivacea), Loggerhead (Caretta caretta) and Leatherback (Dermochelys coriacea). Among them, Green turtles are the most abundant and distributed in all surveyed localities; Hawksbill and Olive Ridley were smaller in number; and Loggerhead and Leatherback were the two species with the least number. Only 03 species remaining to breed on the beaches: Green, Olive Ridley, and Leatherback. The Hawksbill turtles used to lay eggs in the past but have been no longer recorded. Con Dao is a home for the largest number of breeding Green turtles. The reasons for the decline of turtles in Vietnam were the collection of eggs and nesting turtles, fisheries bycatch, development of coastal infrastructure and waste pollution, habitat degradation, and illegal trade in sea turtle products.

Mixed stock analysis identifies natal origins of green turtles at foraging grounds in southeastern Australia

IntroductionIdentifying critical habitats for marine turtles and connectivity between genetic stocks and the foraging grounds they use is a conservation priority worldwide. Green turtles (Chelonia mydas) are impacted by a wide range of anthropogenic threats that can vary by geographic region and the ontogenetic stage of the individual. In Australia, the strengthening of the East Australian Current due to climate change is increasing ocean temperatures, particularly in southern New South Wales (NSW), which is having large-scale impacts on the distribution and abundance of marine resources. Green turtles are frequently observed in temperate southern NSW waters, but our knowledge of their habitat use, migration patterns and the impact of threatening processes is limited.MethodsTo assess the origins of green turtles from foraging grounds in southeastern Australia, samples were obtained from green turtles of all size classes (post-hatchlings to adults) that had stranded along an ~870 km expanse of the NSW coast and Lord Howe Island between 1997 and 2021. Mitochondrial DNA control region sequences for 283 individuals were compared to 25 potential source genetic stocks in the Indo-Pacific using mixed-stock analysis.ResultsA total of 26 haplotypes were identified in NSW, of which 14 had been previously observed at a rookery, eight had been identified previously, but not at a rookery (i.e. orphan haplotypes), and four were previously undescribed. Mixed-stock analysis revealed that NSW waters support multiple genetic stocks but are dominated by those of the southern Great Barrier Reef and New Caledonia genetic stocks. A small proportion of green turtles originated from more distant stocks in the Indo-Pacific region.DiscussionUnderstanding the connectivity between green turtle rookeries and foraging grounds provides an opportunity to assess the impact of anthropogenic threats to turtle stocks, and in turn, prioritize management actions for the conservation of green turtles across regional, national and international jurisdictions.

Marine Turtle Identification, Sightings, and Nesting Area Mapping in Batanes Province, the Philippines

The Batanes archipelago – a province designated by the Philippine government as a protected area – possesses abundant marine resources and diverse ecosystems that serve as optimal habitats for marine turtles to forage, reproduce, and nest. Ivatans, the native inhabitants of Batanes who are also indigenous peoples, possess knowledge of the existence of marine turtles in their coastal waters; however, published reports are still unavailable. This study provides significant data on species identification, observations, and the distribution of nesting areas across the province. This study presents novel findings, revealing that green sea turtles Chelonia mydas and hawksbill turtle Eretmochelys imbricata thrive in the coastal waters of Batanes. A household survey using a semi-structured questionnaire (n = 90), 48 key informant interviews, and site monitoring were utilized as data collection methods and examined using descriptive data analysis. We randomly selected respondents from the household surveys from each municipality and pre-identified key informants based on their roles in each municipality (e.g. government officials, fisherfolk leaders). Likewise, 45% of the respondents claimed that they usually encounter marine turtles a few times a week, specifically during their fishing operations. The mapped nesting sites showed a wide range across the province; three were already established by the Provincial Environment and Natural Resources Office. The data gathered, and findings of this study serve as a basis for local resource managers – particularly in implementing initiatives for sustainable management, conservation, and protection of marine turtle biodiversity in Batanes. Before developing conservation and management strategies, involving the community in decision-making is crucial to address potential concerns – significantly when a specific ethnic group such as the Ivatans on Batanes Island – is affected.

Sea turtles of the Benin coast: Pressure and ethnozoology

Sea turtles are threatened by factors associated with overfishing. To identify these factors, we investigated the fishing pressure and the ethnozoological knowledge of turtles along the Benin coast. A questionnaire-based field survey was undertaken in 48 villages on the Atlantic coast through structured interviews. In total, 479 fishermen and 15 traditional healers were interviewed between July and August, 2020. The Use Value in terms of the types of utilisation of the body parts of the turtles, and the frequency of citation, were calculated. More than eighty percent of the interviewees confirmed the use of turtles for food, medicine, and artisanal purposes. Communities demonstrated nonspecific preference for the four-known species – leatherback turtle, Olive Ridley turtle, green turtle, or hawksbill turtle --within the research area. The flesh is the most used body part (Use Value = 1.5 for food). Body parts of turtles such as the fat, bones etc. are used to treat several diseases, particularly asthma, fever, hypertension, cough, colds, epilepsy, brittle bones in children, and paralysis. The test used shows that the Use Values of sea turtles vary significantly at the 5 % threshold from one sociolinguistic group to another. Our research indicates that integrating traditional ecological knowledge on animal-based food and medicines could be extremely useful when developing strategies for sustainable management and conservation of marine species, and in particular sea turtles.

Coralline Algal Population Explosion in an Overgrazed Seagrass Meadow: Conditional Outcomes of Intraspecific and Interspecific Interactions

Interactions such as mutualism and facilitation are common in ecosystems established by foundation species; however, their outcomes vary and show conditionality. In a Mexican Caribbean Bay, a seagrass-coralline algae (rhodoliths) mutualism protects the seagrass Thalassia testudinum from green turtle overgrazing. We postulate that the state of the seagrass meadow in this bay depends on the strengths of the interactions among seagrasses, green turtles, and coralline algae. Spatio-temporal changes through satellite imagery showed rhodolith bed developed rapidly from 2009 (undetected) to 2016 (bed of 6934 m2). Typically, such rapid expansion of the rhodoliths does not occur in seagrass meadows. An in situ growth experiment of coralline algae showed that a combination of reduction in light and wave movement (usual in dense seagrass meadows) significantly reduced their growth rates. In the rhodolith beds, the growth rates of the coralline algae Neogoniolithon sp. and Amphiroa sp. were high at 9.5 mm and 15.5 mm per growth tip y−1, respectively. In a second experiment, we found lower mortality in coralline algae within a rhodolith bed compared to algae placed outside the bed, likely explained by the reduced resuspension that we found in a third experiment, and this positive feedback may explain the high population increase in the rhodoliths, once established when the turtles grazed down the seagrass canopy. Therefore, the grazing-protection mutualism between seagrasses and coralline algae is thus conditional and came into existence under a co-occurrence of intensive grazing pressure and rapid population growth of coralline algae facilitated by positive feedback from increased growth and reduced sediment resuspension by the dense rhodolith bed.

A Study on Combating Illegal Trade in Green Sea Turtles based on a Multi-Model Strategy

This study addresses the long-standing and increasingly complex issue of global illegal wildlife trade, proposing a system solution aimed at monitoring and combating this trade, with a special emphasis on the protection of green sea turtles. The ARIMA Predict Model was utilized to demonstrate that increased enforcement efforts and higher operational expenses are significantly associated with reduced volumes of illegal wildlife trade. An illegal trade risk model was developed, employing SLSQP to enhance accuracy, constrained by budget allocation, maximum RFID reader capacity, and device failure rates. Furthermore, the Sea Turtle Movement Model was crafted by examining seasonal behaviors, agent-based movement patterns, temperature preferences, stochastic elements, and simulation time steps, enabling the delineation of migratory paths of sea turtles across different seasons. Ant Colony Optimization (ACO) was applied to optimize patrol routes. The findings underscored the necessity for additional governmental support, encompassing legal authorization, environmental access, international collaboration, and financial backing. The project’s effectiveness was assessed using the Risk Reduction Coefficient Model and Monte Carlo simulations, which significantly reduced illegal trade by 34.43%, with projections indicating continued declines over the subsequent five years.

Comparative study of the reptilian cornea's microstructure

BackgroundThe cornea of various vertebrate is considered a major part in the glop, which acts as a powerful lens, providing a sharp retinal image, and meantime acts as an excellent defensor for other corneal layers.ResultsThe four reptilian families [Scincidae (Chalcides ocellatus); Chamaeleontidae (Chameleon chameleon); Cheloniidae (Chelonia mydas) and Testudiniae (Testudo kleinmanni)] investigated in the current study were gathered across Egypt. After being taken out of the orbit, the cornea under inquiry was ready for light, specific stain and scanning electron microscopy. The epithelium, stroma, and endothelium are the three corneal layers that are common to all four species of reptiles. All other species lack Bowmen's and Descemet's membranes, with the exception of C. ocellatus and T. kleinmanni. The latter layers of Chalcides ocellatus display a strong affinity for Periodic Acid Schiff stain. Epithelial cells with a variety of forms, from hexagonal to atypical polygonal cells, cover the outer corneal surface. These epithelial cells are coated in short microplicae, microvilli, and microholes of varied diameters. There are a few blebs scattered around their surface.ConclusionThe current study concluded that various habitats have various significant effects on the cornea's microstructure characteristics and its physiological trends to accommodate different environmental surroundings.

Characterisation, prevalence and antibiogram of Aeromonas hydrophila in turtles: insights into virulence factors, antimicrobial resistance genes and innate immunity

ABSTRACT Bacterial infection poses a significant threat to the health and survival of turtles, both in their natural habitats and in captivity. Notably, the presence and interactions of bacteria, such as those belonging to the Aeromonas genus, have been identified for their adverse impact on turtle health and ecosystem dynamics. This study investigated the prevalence, antibiotic susceptibility, virulence factors, and antimicrobial resistance genes of Aeromonas hydrophila in Trachemys scripta elegans (Red-eared Slider) and Chelonia mydas (Green Turtle). The study also examined the innate immunity of T. scripta elegans and C. mydas. Buccal and cloacal swabs from 39 turtles were collected and examined alongside 45 water samples to try to isolate and amplify A. hydrophila. Polymerase chain reaction (PCR) amplifications were then sequenced to identify the presence of specific genes associated with virulence, and antimicrobial resistance. The findings revealed that A. hydrophila had a prevalence rate of 35.9% in all examined turtle species, with 14 water samples accounting for 31% of the total samples. Buccal samples from Green and Red-eared turtles showed a higher rate of A. hydrophila isolates than cloacal samples. Sensitivity to norfloxacin (85.71%), gentamycin (71.42%), and ceftriaxone (64.28%) was observed, whereas resistance to amoxicillin (64.28%), ampicillin (57.14%), and rifamycin (57.14%) was apparent. Antibiotic resistance genes, including blaTEM and blaSHV, in A. hydrophila isolates, were present in 42.86% and 28.5% of the samples, respectively. PCR analysis confirmed the genetic identity of A. hydrophila, and five virulence genes were detected: AHCYTOEN (100%), followed by aerolysin (92.8%), alt and act (85.7%), and lipase (78.5%). Genetic sequences of the isolates had a 99% identity with the reference strains in GenBank. Furthermore, the study found the innate immunity of turtles to be robust due to serum lysozyme activity, bactericidal killing assay (BKA), total leukocyte count, heterophil/lymphocyte ratio, and packed cell volume (PCV%), all of which help to protect them from infections. Overall, this research highlights the need for continued monitoring and management of antibiotic resistance in aquatic ecosystems.

Sea turtle strandings in the temperate Southwest Atlantic: Analysis of drivers and potential causes

Abstract Marine megafauna are subject to several threats due to the increasing exploitation of marine ecosystems. Mortality is frequently evidenced by the occurrence of stranded individuals in coastal zones; however, conclusive identification of its drivers and causes is challenging. In this study, we explore the hypothesis that bycatch in trawling is one of the anthropic drivers of sea turtle strandings in the temperate Southwest (SW) Atlantic, where green (Chelonia mydas), loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) turtles forage seasonally. Beach survey data during March, April and May from 2014 to 2018 were used to characterize strandings and relate their spatio‐temporal distribution to physical and anthropic variables. Loggerhead (47.4%) and leatherback turtles (49.3%) were the most common stranded species, whereas green turtles were recorded only occasionally (3.3%). Based on the size distribution, strandings reflected both juvenile and adult mortality, with variations between species. Generalized linear models showed that sea turtle strandings were influenced by winds and sea surface temperature, while there was no evidence of a relationship with fishing effort. Further studies should assess drowning due to bycatch as a cause of turtle death, since interaction with fisheries is commonly reported in the area and drowned animals may or may not wash ashore. This study raises awareness and assesses, for the first time, the mortality of threatened sea turtle species in a poorly known region of its distribution.

Fine-scale foraging ecology and habitat use of sympatric green and hawksbill turtles in the Western Indian ocean

Using stable isotope analysis of carbon and nitrogen of turtle tissues and putative prey items, we investigated the diet of immature green turtles and hawksbill turtles foraging in the lagoon of Aldabra Atoll, a relatively undisturbed atoll in the southern Seychelles. Aldabra offers a unique environment for understanding sea turtle ecology. Green turtles mostly consumed seagrass and brown algae while hawksbill turtles mainly consumed mangroves and invertebrates. Green turtles showed a dietary shift with size (a proxy for age). There was minimal niche overlap between species and evidence of small-scale foraging site fidelity with turtle tissue reflecting site-specific prey. This highlights the ecological importance of seagrass and mangrove habitats and suggests that turtles play a role in controlling algal biomass at Aldabra. This study is the first to closely examine the foraging ecology of these sympatric turtle species in the Western Indian Ocean, a globally important region for both species.