Sea Turtle Species Research Articles

Historical Records of Loggerhead Sea Turtle (Caretta caretta) Nesting at Tortuguero, Costa Rica

Costa Rica is considered a hot spot for biodiversity and wildlife conservation in Central America, and sea turtles are a good example of this. Largely distributed along both the Caribbean and Pacific coast, adult females of five of the seven extant sea turtle species select beaches on both coasts as their breeding sites. Although Green Sea Turtles (Chelonia mydas), Leatherback Sea Turtles (Dermochelys coriacea), Hawksbill Sea Turtles (Eretmochelys imbricata), and Olive Ridley Sea Turtles (Lepidochelys olivacea) have been extensively studied in Costa Rica, little information regarding Loggerhead Sea Turtles (Caretta caretta) is available. Thus, we present an exhaustive data record of every Loggerhead encountered at Tortuguero beach (northeastern Caribbean coast of Costa Rica) over the past 60 yr. We collected Loggerhead nesting data between 1957 and 2021 through daytime and nocturnal monitoring activities. We documented 14 Loggerhead Sea Turtle nesting attempts between 1957 and 2021 at Tortuguero. Among them, seven nested successfully, four did not lay eggs, and one's fate is unknown. Additionally, two turtles were killed by jaguars. Mean minimum curve carapace length (CCLmin) measurements for Loggerheads was 98.2 ± 3.7 cm (range, 90.0–101.4 cm). Finally, we found that every encounter occurred between April and July, which coincides with the Loggerhead nesting season in the Northwest Atlantic. Our study is the first assessment of Loggerhead Sea Turtles nesting in Costa Rica, bringing to light new records for this species in the Caribbean Sea.

Effect of water temperature on the duration of the internesting interval across sea turtle species

Sea turtles generally lay several clutches of eggs in a single nesting season. While a negative correlation between water temperatures and the time required between constitutive nesting events (termed the internesting interval) has been previously reported in loggerhead Caretta caretta and green turtles Chelonia mydas, it is not understood whether this relationship remains constant across other sea turtle species. Here, we expanded upon these previous studies on loggerhead and green turtles by using larger sample sizes and including data from species with a wider range of body-sizes; specifically: hawksbill Eretmochelys imbricata, leatherback Dermochelys coriacea, and olive ridley turtles Lepidochelys olivacea. In total, we compiled temperature data from biologgers deployed over internesting intervals on 23 loggerhead, 22 green, 7 hawksbill, 26 leatherback and 11 olive ridley turtles from nesting sites in 8 different countries. The relationship between the duration of the internesting interval and water temperatures in green and loggerhead turtles were statistically similar yet it differed between all other turtle species. Specifically, hawksbill turtles had much longer internesting intervals than green or loggerhead turtles even after controlling for temperature. In addition, both olive ridley and leatherback turtles exhibited thermal independence of internesting intervals presumably due to the large body-size of leatherback turtles and the unique capacity of ridley turtles to delay oviposition. The observed interspecific differences in the relationship between the length of the internesting interval and water temperatures indicate the complex and variable responses that each sea turtle species may exhibit due to environmental fluctuations and climate change.

Responses of three nesting sea turtle species to hard-armoring structures

In the face of modern challenges, analyzing sea turtle nesting trends is critical to better understand impacts to these vulnerable species. The introduction of hard-armoring structures (e.g., seawalls, rock revetments) on sea turtle nesting beaches poses a threat to nesting leatherback (Dermochelys coriacea), loggerhead (Caretta caretta), and green (Chelonia mydas) sea turtles due to habitat loss and turtle interactions with the physical structure. Despite much of Florida’s coastline being protected by some form of hard-armoring technology, research on the impacts of these structures to sea turtles is limited to loggerheads. Our objectives were to (1) examine nest density, nesting success, washout rates, and hatching and emergence success at hard-armoring sites in comparison to a control area and (2) characterize impacts of obstructions encountered by sea turtles nesting in northern Palm Beach County, Florida. Our results indicate that the hard-armoring site showed significantly lower nest density for green turtles and nesting success for loggerheads and green turtles in comparison to a control area. Additionally, nesting success for loggerheads and green turtles that encountered hard-armoring structures was significantly lower in comparison to those that encountered no obstructions or other obstructions (e.g., beach furniture, walkovers, escarpments, etc.). These results suggest that hard-armoring structures negatively impact sea turtle nesting behavior, which could result in loss of energy or other physiological derangements. Green turtles showed the most significant differences between the two sites, likely a result of their typical nest site selection favoring the upper portions of the beach, crawling further distances from the high-water line than loggerheads or leatherbacks. Before additional hard-armoring structures are permitted and installed, governing agencies should first consider more natural methods of protecting shorelines (e.g., dune restoration).

Non-targeted proteomics reveals altered immune response in geographically distinct populations of green sea turtles (Chelonia mydas)

All seven species of sea turtle are facing increasing pressures from human activities that are impacting their health. Changes in circulating blood proteins of an individual, or all members of a population, can provide an early indicator of adverse health outcomes. Non-targeted measurement of all detectable proteins in a blood sample can indicate physiological changes. In the context of wildlife toxicology, this technique can provide a powerful tool for discovering biomarkers of chemical exposure and effect. This study presents a non-targeted examination of the protein abundance in sea turtle plasma obtained from three geographically distinct foraging populations of green turtles (Chelonia mydas) on the Queensland coast. Relative changes in protein expression between sites were compared, and potential markers of contaminant exposure were investigated. Blood plasma protein profiles were distinct between populations, with 85 out of the 116 identified proteins differentially expressed (p < 0.001). The most strongly dysregulated proteins were predominantly acute phase proteins, suggestive of differing immune status between the populations. The highest upregulation of known markers of immunotoxicity, such as pentraxin fusion and complement factor h, was observed in the Moreton Bay turtles. Forty-five different organohalogens were also measured in green turtle plasma samples as exposure to some organohalogens (e.g., polychlorinated biphenyls) has previously been identified as a cause for immune dysregulation in marine animals. The few detected organohalogens were at very low (pg/mL) concentrations in turtles from all sites, and are unlikely to be the cause of the proteome differences observed. However, the changes in protein expression may be indicative of exposure to other chemicals or environmental stressors. The results of this study provide important information about differences in protein expression between different populations of turtles, and guide future toxicological and health studies on east-Australian green sea turtles.

Beyond fishing: loggerhead turtle impalement by swordfish

Sea turtles are susceptible to a wide range of impacts. In Brazil, the loggerhead turtle Caretta caretta (Linnaeus, 1758) is the main sea turtle species caught incidentally by longline fishing fleets that target the blue shark Prionace glauca (Linnaeus, 1758) and swordfish Xiphias gladius (Linnaeus, 1758). The latter is well known for its predation strategy, which consists of using the rostrum to injure and catch prey. In this study, we recorded for the first time the impalement of a juvenile loggerhead sea turtle by a swordfish during a fishing operation of a Brazilian longline vessel in 2018. Two videos of this interaction were recorded by the shipmaster around 260 km from the Brazilian coast. The sea turtle was incidentally caught with a hook and subsequently attacked by the swordfish. The rostrum initially pierced the anterior left shoulder of the turtle and passed through the body, exiting from the right posterior carapace. Given the position of the attack, considerable internal damage was most certainly done to the turtle. Although the turtle was hauled aboard to remove the hook and then returned to the sea alive, it probably died due to the extent of the injuries caused by the rostrum having passed through the center of the body. Since both swordfish and turtle are pelagic and these interactions are poorly recorded, such encounters may be relatively common. Therefore, this type of information should be included in the data collection protocols of fishery monitoring programs to better understand and scale the bill-stab phenomenon, not only for sea turtles but also in relation to other groups of fauna.

Warm beach, warmer turtles: Using drone-mounted thermal infrared sensors to monitor sea turtle nesting activity

For decades sea turtle projects around the world have monitored nesting females using labor-intensive human patrolling techniques. Here we describe the first empirical testing of a drone-mounted thermal infrared sensor for nocturnal sea turtle monitoring; on the Osa peninsula in Costa Rica. Preliminary flights verified that the drone could detect similar sea turtle activities as identified by on-the-ground human patrollers – such as turtles, nests and tracks. Drone observers could even differentiate tracks of different sea turtle species, detect sea turtle hatchlings, other wildlife, and potential poachers. We carried out pilot flights to determine optimal parameters for detection by testing different thermal visualization modes, drone heights, and gimbal angles. Then, over seven nights, we set up a trial to compare the thermal drone and operators’ detections with those observed by traditional patrollers. Our trials showed that thermal drones can record more information than traditional sea turtle monitoring methods. The drone and observer detected 20% more sea turtles or tracks than traditional ground-based patrolling (flights and patrols carried out across the same nights at the same time and beach). In addition, the drone operator detected 39 other animals/predators and three potential poachers that patrollers failed to detect. Although the technology holds great promise in being able to enhance detection rates of nesting turtles and other beach activity, and in helping to keep observers safer, we detail challenges and limiting factors; in drone imagery, current cost barriers, and technological advances that need to be assessed and developed before standardized methodologies can be adopted. We suggest potential ways to overcome these challenges and recommend how further studies can help to optimize thermal drones to enhance sea turtle monitoring efforts worldwide.

Method Comparison of β-Hydroxybutyrate Using a Point-of-Care Device and Dry Chemistry Analyzer in Three Sea Turtle Species.

The ketone β-hydroxybutyrate (BHB) serves as an energy source when bodily energy stores are low. Concentrations of this blood analyte are often determined by spectrophotometric quantitative assays with a dry chemistry analyzer; however, rapid assessment with point-of-care devices have the potential to improve assessment of animals in the field or in clinical settings. We measured BHB concentrations in whole blood samples from 54 leatherback (Dermochelys coriacea), 27 loggerhead (Caretta caretta), and 14 green (Chelonia mydas) sea turtles in Florida, US with a point-of-care device and validated its use with corresponding plasma samples and dry chemistry analyzer as the gold standard. Concentrations of BHB highly correlated between the two methods for all three species, with loggerheads showing the best agreement and lowest bias. Therefore, the point-of-care device used for this study (Lucidplus β-ketone monitoring system) is probably appropriate for sea turtle BHB measurements.

Lethal Lesions Caused by Propeller Cuts on the Endangered Green Turtle Chelonia mydas on Liuchiu Island, Taiwan

Green turtle (Chelonia mydas) is the most common sea turtle species in Taiwan. The coastal waters of Taiwan are known to contain foraging grounds for green turtles. Boat strike has been identified as the most common causes of sea turtle mortality in several sea turtle habitats worldwide. However, no relevant studies have investigated wild green turtles with boat strike injuries in Taiwan. In this field study, we conducted morphometric characteristics of 6 endangered green turtles (C. mydas) with boat strike injuries in Liuchiu Island of Pingtung County, Taiwan. This is the first report of its kind on the prevalence of documented boat strike lesions on stranded wild green turtles at their near shore foraging habitat. In 2019, a total of 14 stranded green turtles were dead when first found in Liuchiu Island of Pingtung County, Taiwan. Of these 14, 6 (42.8%) turtles showing evidence of propeller impacts. Conservation strategies including speed limits in key turtle neritic foraging habitats are required to improve their survival in Taiwan.

Point of No Return: Determining Depth at Which Sea Turtle Carcasses Experience Constant Submergence

At-sea mortality information is important for understanding the magnitude of threats to protected sea turtle species. When a sea turtle dies, it typically sinks, starts decomposing, and will eventually float to the surface if the carcass remains intact and enough internal gases accumulate. However, few data are available regarding the rate and duration of these processes to allow estimation of time since death once carcasses are recovered. Twenty-seven Kemp's ridley (Lepidochelys kempii) and 15 green (Chelonia mydas) sea turtle cold-stunned carcasses were placed in wire mesh, weighted cages at varying water depths (10–40 m) and temperatures (18.5°C–28.7°C) in the northern Gulf of Mexico from June 2018 to October 2019. Cameras and temperature-depth-orientation recorders were used to document decomposition progression and carcass buoyancy. Decomposition rate was measured using corrected accumulated degree hours and values of observed time-to-float were compared with predictions based on laboratory and field experiments in previous research. Overall, carcasses did not float when deployed in waters > 30 m when temperatures were < 22°C and carcasses tended to float sooner in ≤ 20 m depths, especially if bottom temperatures were > 24°C. Green sea turtle carcasses floated in a variety of environmental conditions, but onset of positive buoyancy was not very predictable. Buoyancy of Kemp's ridley sea turtle carcasses was inconsistent, but float times were fairly predictable. We did not identify the exact depth at which sea turtle carcasses cannot generate enough gases to float, but that depth is likely very close to 40 m. Carcasses that became buoyant in ≥ 30 m depths tended to float for < 24 hrs before sinking again and, therefore, it is unlikely that they have enough time to drift to shore. This information enhances our understanding of the likelihood of carcasses washing ashore and can be incorporated into carcass backtracking analyses to facilitate identification of mortality causes.

Missing Data in Sea Turtle Population Monitoring: A Bayesian Statistical Framework Accounting for Incomplete Sampling

Monitoring how populations respond to sustained conservation measures is essential to detect changes in their population status and determine the effectiveness of any interventions. In the case of sea turtles, their populations are difficult to assess because of their complicated life histories. Ground-derived clutch counts are most often used as an index of population size for sea turtles; however, data are often incomplete with varying sampling intensity within and among sites and seasons. To address these issues, we: (1) develop a Bayesian statistical modelling framework that can be used to account for sampling uncertainties in a robust probabilistic manner within a given site and season; and (2) apply this to a previously unpublished long-term sea turtle dataset (n = 17 years) collated for the Republic of the Congo, which hosts two sympatrically nesting species of sea turtle (leatherback turtle [Dermochelys coriacea] and olive ridley turtle [Lepidochelys olivacea]). The results of this analysis suggest that leatherback turtle nesting levels dropped initially and then settled into quasi-cyclical levels of interannual variability, with an average of 573 (mean, 95% prediction interval: 554–626) clutches laid annually between 2012 and 2017. In contrast, nesting abundance for olive ridley turtles has increased more recently, with an average of 1,087 (mean, 95% prediction interval: 1,057–1,153) clutches laid annually between 2012 and 2017. These findings highlight the regional and global importance of this rookery with the Republic of the Congo, hosting the second largest documented populations of olive ridley and the third largest for leatherback turtles in Central Africa; and the fourth largest non-arribada olive ridley rookery globally. Furthermore, whilst the results show that Congo’s single marine and coastal national park provides protection for over half of sea turtle clutches laid in the country, there is scope for further protection along the coast. Although large parts of the African coastline remain to be adequately monitored, the modelling approach used here will be invaluable to inform future status assessments for sea turtles given that most datasets are temporally and spatially fragmented.

Hawksbill presence and habitat suitability of a marine reserve in Honduras

Marine protected areas (MPAs) have been established to decrease the negative impacts of human activities on important marine habitats. Several sea turtle species reside within MPAs; however, analyses of habitat suitability for sea turtles within many MPAs is typically lacking. Habitat modeling and species mapping have become essential tools in determining areas suitable for species inhabitance. MaxEnt is a popular machine-learning program that uses presence-only occurrence data and is considered the best modeling method in discriminating between suitable and unsuitable habitats. Using MaxEnt, we created species distribution models (SDMs) from presence-only occurrence points for juvenile hawksbills and three environmental variables: boat traffic intensities, prey item distributions, and benthic characterizations, within the Sandy Bay West End Marine Reserve (SBWEMR) in Roatán, Honduras. Area under the receiving operator curve (AUC) values were greater than 0.75, indicating high model accuracy. Jackknife evaluations indicated algal prey item Dictyota spp., boat traffic intensity, and Geodia neptuni sponge abundance had the greatest influence on species distribution. Areas of suitability shifted based on time of day and ranged from a low probability of hawksbill presence (0.0) to a high probability of hawksbill presence (0.8). Regardless of time of day, the SBWEMR is classified as at least moderately suitable (>0.2–0.4), with least suitable habitat (0–0.2) prevalent in the most northeastern region of the reserve. The greatest suitability (>0.6–1) was evident within the mid-region and southern most regions of the reserve. Probability of hawksbill presence increased in accordance with increasing boat traffic, although there was no clear causative relationship between the two. Although the reserve overall is mostly moderately suitable, the SBWEMR remains an important local recruitment and foraging ground for juvenile hawksbills. Hawksbills have been considered resilient, continually functioning beneath their operational limits. However, with continued global depletion of essential habitats over time and lack of effective MPA management, areas of habitat suitable for hawksbill inhabitance may decrease below levels sufficient for hawksbill presence in protected areas of the Western Caribbean.

Molecular Identification and Novel Mitochondrial COI Gene Haplotypes of Nesting Kemp’s Ridley Turtles (Lepidochelys kempii) in Rancho Nuevo Sanctuary, Mexico

One hundred new COI sequences of nesting female Kemp’s ridley turtles (Lepidochelys kempii) were obtained in the Rancho Nuevo Sanctuary (RNS). The COI sequences were analyzed and contrasted with others retrieved from BOLD and GenBank with the aim of investigating genetic variability, genetic divergence, and haplotypes of the nesting female population at RNS. Four new COI haplotypes for Kemp’s ridley were described; two are redundant with (LK-RN01) 97 and (LK-COI-01) 17 specimens belonging to the RNS and other localities, respectively. Nucleotide (0.00052) and haplotype (0.303) diversity showed low and conserved COI values The fixation index (FST) between these main redundant haplotypes showed a high degree of differentiation with ~1. Genetic divergence clearly demonstrated two different Kemp’s ridley nesting populations, one from RNS and a second outside Mexico. Phylogenetic COI analysis was useful to differentiate these redundant (LK-COI-01 and RNS LK-RN01) haplotypes and, therefore, these different Kemp’s ridley populations. In addition, phylogenetic COI analysis clearly separates Kemp’s ridley turtles from other sea turtle species, supporting its use as a barcode marker.

Detection and population genomics of sea turtle species via noninvasive environmental DNA analysis of nesting beach sand tracks and oceanic water.

Elusive aquatic wildlife, such as endangered sea turtles, are difficult to monitor and conserve. As novel molecular and genetic technologies develop, it is possible to adapt and optimize them for wildlife conservation. One such technology is environmental (e)DNA - the detection of DNA shed from organisms into their surrounding environments. We developed species-specific green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtle probe-based qPCR assays, which can detect and quantify sea turtle eDNA in controlled (captive tank water and sand samples) and free ranging (oceanic water samples and nesting beach sand) settings. eDNA detection complemented traditional in-water sea turtle monitoring by enabling detection even when turtles were not visually observed. Furthermore, we report that high throughput shotgun sequencing of eDNA sand samples enabled sea turtle population genetic studies and pathogen monitoring, demonstrating that noninvasive eDNA techniques are viable and efficient alternatives to biological sampling (e.g., biopsies and blood draws). Genetic information was obtained from sand many hours after nesting events, without having to observe or interact with the target individual. This greatly reduces the sampling stress experienced by nesting mothers and emerging hatchlings, and avoids sacrificing viable eggs for genetic analysis. The detection of pathogens from sand indicates significant potential for increased wildlife disease monitoring capacity and viral variant surveillance. Together, these results demonstrate the potential of eDNA approaches to ultimately help understand and conserve threatened species such as sea turtles.

Size scaling of sea turtle reproduction may reconcile fundamental ecology and conservation strategies at the global scale

AbstractAimThe body size of marine megafauna can influence population dynamics because larger females have disproportionally greater reproductive output. We explored how this size scaling relationship can affect predictions of population size structure in nesting sea turtles by combining a phylogenetically controlled meta‐analysis with a long‐term field nesting survey.LocationGlobal (meta‐analysis) and Malaysia (field survey).Time periodPresent.Major taxa studiedSea turtles.MethodsWe extracted body size and reproductive parameters of all sea turtle species from the literature and estimated the reproductive‐energy output using allometric models. We then examined the relationship between body size and the proportion of protected nesting beaches by country as an indicator of conservation efforts on body size. Long‐term monitoring (1993–2019) of body size and nesting data on green turtles (Chelonia mydas) from Redang Island (Malaysia) was used to examine temporal changes in body size and fecundity and to test whether the size scaling of fecundity was isometric (linear) or allometric (curvilinear).ResultsWe show that the total reproductive‐energy output of larger nesting females was, on average, disproportionately greater in all sea turtle species. We found no strong correlations for countries with a higher proportion of protected nesting sites with female size. Finally, we showed that scaling‐derived calculations of population‐level yearly reproductive output in the green turtle population from Redang Island were more accurate when using a hyperallometric (rather than an isometric) relationship at the individual level.Main conclusionsUnderstanding ecosystem function and conservation effort requires accurate predictions of population trends. Our findings highlight the necessity to account for scaling effects of body size in predicting anthropogenically mediated population shifts, and the need to protect large females in order to facilitate effective population replenishment.

Present status of conservation and management of sea turtle in Cox’s Bazar district, Bangladesh

The study was conducted to know the present status of conservation and management of sea turtle in Cox’s Bazar district, Bangladesh. Two species of sea turtles have been making nest in Bangladesh. A total of 251 turtle individuals were found. The highest nesting frequency of Olive ridley (108) and Green turtles (10) were observed in February. About 21,942 hatchlings were produced and released by the hatcheries for conservational step. A total of one hundred people were selected randomly for taking interview to assess their knowledge and attitude towards sea turtle conservation and management. Most of the respondents were fishermen (55%), student and housewife were 20% and 8%, 5% were found involving in business and rest 12% were involved in others activities. About 45% of the respondents thought that turtles were beneficial while other 40% of the respondents thought turtles were harmful. The rest of the respondents (15%) answered that they were not sure whether sea turtle was beneficial or harmful. Most of the fishermen did not know about Turtle Excluder Devices (TEDs) or its uses. It was found that the nesting of sea turtles was reducing and there was lack of knowledge among the people of the study area about the importance of sea turtle conservation and management.

Inter-annual variability in breeding census data across species and regions

There is an intense interest in long-term trends of species abundance that may reflect, for example, climate change or conservation actions. Less well studied are patterns in the magnitude of inter-annual variability in abundance across large spatial scales. We collated abundance time-series for 133 nesting sites across the globe of the seven sea turtle species. Inter-annual variability in nest numbers was lowest in loggerhead turtles (Caretta caretta), Kemp’s ridley (Lepidochelys kempii) and flatback turtle (Natator depressus) and highest in green turtles (Chelonia mydas), likely reflecting their lower trophic position compared to other species and hence tighter coupling of food availability to environmental conditions each year. The annual number of nests in green turtles could vary by 60-fold between successive years. We identified regional patterns in the magnitude of inter-annual variability in green turtle nest numbers, variability being highest for nesting beaches around Australia and lowest in the western Indian Ocean and equatorial Atlantic. These regional patterns are likely linked to corresponding patterns of environmental variability with, for example, areas subjected environmental extremes as part of the El Nino Southern Oscillation (ENSO) showing high inter-annual variability in nest numbers.

Surveys of the Angolan coast uncover the largest olive ridley sea turtle nesting population in the Atlantic and the largest non-arribada population globally

AbstractKnowledge of the abundance and distribution of species is important for designing and prioritizing conservation and management activities. Despite numerous existing studies on the distribution and status of sea turtles, we still lack knowledge about certain populations, especially in Angola, which is considered to be the southernmost range of nesting sea turtles in the eastern Atlantic. This study provides an overview of the status, size and distribution of the olive ridley sea turtle Lepidochelys olivacea population nesting along the coast of Angola, and its relevance in the context of other olive ridley turtle nesting populations in the Atlantic. Aerial and ground surveys were conducted along 1,410 km of Angolan coastline and daily beach monitoring over 53.9 km of seven permanent study sites at a range of latitudes during 2011–2020. Angola hosts the largest olive ridley turtle nesting population in the Atlantic, and the largest non-arribada population globally. Although the population appeared relatively stable, the pressures from various threats on land (e.g. consumption of turtles and eggs) and at sea (captures in fishing gear) necessitate the development of a comprehensive management plan, improved and strengthened legislation and law enforcement, and a cohesive approach to conserving all sea turtle species in Angola.

Foraging ecology of the olive ridley sea turtle (Lepidochelys olivacea) from the Mexican Central Pacific based on stable isotopes

Knowledge regarding the trophic ecology, including the feeding habits of olive ridley sea turtles (Lepidochelys olivacea), is scarce. Although few investigations have been carried out, some results are contradictory. We described several foraging aspects of this sea turtle species in the Mexican Central Pacific (MCP) using stable isotopes of carbon (δ13C) and nitrogen (δ15N). Data were analyzed by sex, size classes (adult/subadult), season (rainy/dry), and location (coastal/oceanic). Surveys were conducted during February 2012–June 2014. A total of 120 olive ridley sea turtles were captured, of which 86 were adults and 32 subadults; 40 were females and 46 males, while the sex of two adult individuals was unidentified. Descriptive statistics and Bayesian analyses of δ13C and δ15N values were performed. A similar isotopic niche width (δ15N) between males and females was found; while it was wider in adults compared to subadults. A wide δ13C range by sex (females) and by size (adults) was evidenced. Values of δ15N differed significantly, with lower values observed during rainy seasons. There were no significant differences in δ13C or δ15N between turtles captured in the coastal and oceanic areas. We infer that olive ridley sea turtle feeding areas occur in coastal areas due to the occurrence of upwellings that increases primary productivity; and during the rainy season, most sea turtles fed in coastal and intermediate areas, as oligotrophic characteristics resulted in turtles increasing their feeding range. The isotopic difference between olive ridley sea turtles and the items that were sampled in the region, suggests that crustaceans, cnidarians, and small pelagic fishes are potential prey of these turtles, which support the argument that these are opportunistic foragers. The present study highlights the importance of the MCP region for the ecology and conservation of olive ridley sea turtles, which seem to feed in the region.

Ontogenetic allometry underlies trophic diversity in sea turtles (Chelonioidea)

Despite only comprising seven species, extant sea turtles (Cheloniidae and Dermochelyidae) display great ecological diversity, with most species inhabiting a unique dietary niche as adults. This adult diversity is remarkable given that all species share the same dietary niche as juveniles. These ontogenetic shifts in diet, as well as a dramatic increase in body size, make sea turtles an excellent group to examine how morphological diversity arises by allometric processes and life habit specialisation. Using three-dimensional geometric morphometrics, we characterise ontogenetic allometry in the skulls of all seven species and evaluate variation in the context of phylogenetic history and diet. Among the sample, the olive ridley (Lepidochelys olivacea) has a seemingly average sea turtle skull shape and generalised diet, whereas the green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) show different extremes of snout shape associated with their modes of food gathering (grazing vs. grasping, respectively). Our ontogenetic findings corroborate previous suggestions that the skull of the leatherback (Dermochelys coriacea) is paedomorphic, having similar skull proportions to hatchlings of other sea turtle species and retaining a hatchling-like diet of relatively soft bodied organisms. The flatback sea turtle (Natator depressus) shows a similar but less extreme pattern. By contrast, the loggerhead sea turtle (Caretta caretta) shows a peramorphic signal associated with increased jaw muscle volumes that allow predation on hard shelled prey. The Kemp’s ridley (Lepidochelys kempii) has a peramorphic skull shape compared to its sister species the olive ridley, and a diet that includes harder prey items such as crabs. We suggest that diet may be a significant factor in driving skull shape differences among species. Although the small number of species limits statistical power, differences among skull shape, size, and diet are consistent with the hypothesis that shifts in allometric trajectory facilitated diversification in skull shape as observed in an increasing number of vertebrate groups.

Network analysis of sea turtle movements and connectivity: A tool for conservation prioritization

AbstractAimUnderstanding the spatial ecology of animal movements is a critical element in conserving long‐lived, highly mobile marine species. Analyzing networks developed from movements of six sea turtle species reveals marine connectivity and can help prioritize conservation efforts.LocationGlobal.MethodsWe collated telemetry data from 1235 individuals and reviewed the literature to determine our dataset's representativeness. We used the telemetry data to develop spatial networks at different scales to examine areas, connections, and their geographic arrangement. We used graph theory metrics to compare networks across regions and species and to identify the role of important areas and connections.ResultsRelevant literature and citations for data used in this study had very little overlap. Network analysis showed that sampling effort influenced network structure, and the arrangement of areas and connections for most networks was complex. However, important areas and connections identified by graph theory metrics can be different than areas of high data density. For the global network, marine regions in the Mediterranean had high closeness, while links with high betweenness among marine regions in the South Atlantic were critical for maintaining connectivity. Comparisons among species‐specific networks showed that functional connectivity was related to movement ecology, resulting in networks composed of different areas and links.Main conclusionsNetwork analysis identified the structure and functional connectivity of the sea turtles in our sample at multiple scales. These network characteristics could help guide the coordination of management strategies for wide‐ranging animals throughout their geographic extent. Most networks had complex structures that can contribute to greater robustness but may be more difficult to manage changes when compared to simpler forms. Area‐based conservation measures would benefit sea turtle populations when directed toward areas with high closeness dominating network function. Promoting seascape connectivity of links with high betweenness would decrease network vulnerability.