ISTS Symposium43 Program/Agenda

The green sea turtle (Chelonia mydas) inhabits tropical and warm-temperate seas worldwide. The population dynamics of this species are complex and molecular tools are often required to delineate the spatial boundaries of distinct populations. The Red Sea hosts approximately 5000 nesting female green turtles, but research in this region is limited. As a semi-enclosed basin with high endemism due to both geographic barriers and extreme environmental conditions, the Red Sea may foster isolated and genetically distinct populations within this widely distributed species. Previous genetic analysis of only 16 individuals from a single rookery, revealed a unique haplotype, suggesting genetic isolation among Red Sea green turtles.

Here, we expanded the sample size to ~200 tissue samples collected from five rookeries along the Saudi Arabian Red Sea coast. We extracted mitochondrial DNA and sequenced a 670 bp fragment of the mitochondrial DNA d-loop from each sample, revealing five haplotypes within the Red Sea that clustered into two highly divergent haplogroups. Group one contained four haplotypes (CmP71.1 - CmP71.4), three of which were previously unreported. Group two, comprising a single novel haplotype (CmP62.1), was more closely related to haplotypes in the Arabian Gulf. These two divergent groups likely reflect separate colonisation events: an initial event ~2.5 million years ago during the formation of the Red Sea and a subsequent recolonisation ~0.5 million years ago due to eustatic sea level changes, resulting in divergence from other Indo-Pacific clades. Haplotype distribution varied across rookeries, with a slight north-to-south gradient indicated by an increasing prevalence of the CmP62.2 haplotype in southern rookeries, although further sampling is needed to confirm this pattern. Pairwise Fst analysis showed high genetic differentiation between rookeries Ras al Baridi and Jazirat Mashabah and Jazirat Waqqadi, suggesting limited gene flow between these sites. This finding has direct implications for conservation management, as these populations may require separate management strategies. Overall, the data suggests that the isolation of the Red Sea, combined with various geologic and climatic events, has led to the divergence of four endemic haplotypes, underscoring the Red Sea as a unique ocean basin. Moreover, these unique haplotypes may represent evolutionary adaptations to the basin’s historically elevated temperatures. Such adaptations could be broadly relevant across sea turtle populations and species in the face of global climate change.

Unveiling the phylogeography of populations throughout evolutionary history is a challenging task, especially for widely distributed, highly migratory species such as sea turtles. Previous studies on the loggerhead (Caretta caretta) based on control region sequences of mitochondrial DNA (mtDNA) identified three major haplogroups. Haplogroup IA is exclusively found in the Pacific Ocean, haplogroup IB occurs primarily in the Atlantic Ocean and in only one rookery of the Northwest Indian Ocean and haplogroup II is widely spread in the Atlantic Ocean, in all rookeries of the Mediterranean Sea and in one rookery of the Southwest Indian Ocean. Recently, a new mtDNA sub-haplogroup specific to the Southwestern Atlantic was identified. The dynamics that led to the present distribution of the main haplogroups are still under debate. Additionally, the western Atlantic rookeries, which host haplogroups IB and II, display a peculiar latitudinal gradient in the relative frequency of these two haplogroups, suggesting that selection may play a role in maintaining this distribution pattern. The aims of our study were i) to define the most consistent global phylogeographic reconstruction for C. caretta, and ii) to investigate the genetic diversity of sympatric haplogroups II and IB under the hypothesis of thermal adaptation in the western Atlantic. We used samples collected in the Mediterranean basin (Greece, Turkey, Libya, Calabria), Atlantic (Florida, Mexico, Cape Verde) and Pacific Ocean (Hawaii, Perù) for a total of 27 complete mitochondrial genomes, of which 21 assembled in this study and six downloaded from public databases. Using Maximum Likelihood and Bayesian phylogenies, we assessed whether the topology based on complete mitogenomes and the consensus tree built using individual gene trees were different from the topology obtained by mtDNA control region only. Our well-supported phylogenetic trees indicated that haplogroup IB separated from the other haplogroups and colonized the Atlantic Ocean during the closure of the Panama Isthmus (13-2.5 million years ago). The colonization of the Mediterranean Sea occurred later in the Pleistocene via a South African route by haplogroup II coming from the Indo-Pacific and recolonizing some Atlantic rookeries where IB had settled before. A further refinement of this phylogeographic reconstruction would be possible with more mitogenomic sequences from under-sampled areas (e.g Indian, South Pacific and South Atlantic oceans). We found strong relations between the increase in frequency of haplogroup IB and the decrease of temperatures in western Atlantic. We found a relaxation of purifying selection on haplogroup IB, but no statistical significance for positive selection between haplogroups IB and II. This could be due to the intrinsic, very conserved nature of the mitochondrion. Nevertheless, protein models showed that the fixed non-synonymous mutations between haplogroups IB and II may affect the functionality of the mitochondrion membrane for haplogroup IB. Mitochondrial thermal adaptation has been found in anchovies, sardines, salmons, penguins and our results may suggest a similar pattern in sea turtles. Overall, whole mitogenomes have a potential for better understanding the evolutionary history of sea turtles, which is crucial to foresee future trends and implement conservation strategies.

The increase in nesting activity in the Western Mediterranean of the loggerhead turtle (Caretta caretta) is considered to be a response to changing environmental conditions resulting from global warming. In this context, it is important to trace the origin of individuals nesting in the Western Mediterranean and to evaluate the associated possible fitness consequences. To do so, we analysed 87 samples of hatchlings belonging to 21 nests laid along the Spanish eastern coast in 2023. Samples were processed using the 2bRAD genotyping method, obtaining a total of 5,925 curated SNPs. First, we inferred the population of origin of the samples using Individual Assignments and a previously built baseline including nesting individuals from several populations in three regional management units (Northwest Atlantic, Northeast Atlantic and Mediterranean). The hatchlings of almost all nests (19) were assigned to the eastern Mediterranean region (predominantly Greece or the Levantine region), one nest associated to the Northwest Atlantic (indicating that both parents had the same Atlantic origin), and one was classified as an admixture of Northwest Atlantic and the Mediterranean regions. Second, we tested whether hatchlings had morphometric differences according to the origin of their parents and whether admixed individuals had higher bilateral asymmetry, an indicative of potential outbreeding depression. Nests were morphometrically studied according to the inferred origin of the breeders: Mediterranean, Atlantic and admixed. We also confirmed that there is no sexual dimorphism regarding the carapace of hatchlings for the three types of nests, to ensure that there is no sex bias. The three groups showed statistically different carapace morphologies: the Atlantic group had a more hydrodynamic shape, the Mediterranean group had a rounder shape, and the hybrid group showed an intermediate morphology. These findings suggest that the size differences that are detected in adults from natural populations may have a genetic basis, as we detected shape differences already in hatchlings from different origins laid in the same region. Additionally, the effect of the centroid size on shape varied among the groups studied, raising the question whether different subpopulations have distinct strategies for survival in the premature stages. Furthermore, the hybrid nest presented higher values of fluctuating asymmetry (FA), which could be associated to outbreeding and potentially negatively affecting fitness. This study provides a foundation for future research concerning the effect of hybridization on reproductive fitness and highlights the need to evaluate the vulnerability of the rising establishment of a resident population in the Western Mediterranean.

Juvenile green sea turtles are commonly seen in the Intracoastal Waterway in St. Augustine, FL, USA. Typically, these turtles would be feeding on submerged aquatic vegetation (SAV) but the turbidity of the local waters prevents the growth of adequate SAV. To compensate, juvenile turtles are seen feeding on the biofouling community growing on local docks. Starting 3 June 2020, two marinas: Camachee Cove Yacht Harbor and Conch House Marina, were walked weekly and all sea turtles were photographed, specifically aiming for the head scales. Photographs were captured using a Canon EOS Rebel T7 digital camera and all photos were uploaded to Internet of Turtles (IoT). The IoT program uses machine learning and multiple computer assisted algorithms to determine matches between new observations and turtles already identified in the database. As of 30 June 2024, 459 turtles seen in the wild were identified as unique turtles. Of these 459 turtles, 287 were seen once, while one turtle was seen 60 times from June 2020 – April 2023. When calculating days between first and most recent sighting, 30 turtles were documented between 1 – 2 years, 17 were seen between 2 – 3 years, and seven were seen between 3 – 4 years. It appears there are two recruitment periods of new turtles to the Intracoastal Waterway based on the prevalence of new turtles to the database: May – June and October – November. These data indicate green sea turtles use this area as a foraging ground and have residence times lasting years while members of the population change throughout the year.

Sea turtle biologists have made sustained efforts to understand the global status of leatherback sea turtle populations. However, despite progress in assessments, demographics, and ecology, key uncertainties persist in tracking leatherback population trends. Trend analyses have historically focused on nesting beaches, with nest counts providing a widely used index for population abundance. Here, we analysed 20 years of annual nest abundance at four main nesting beaches (Soropta, Bluff, Playa Larga and Chiriquí) in Bocas del Toro province and the Comarca Ngäbe-Buglé, Panama, which constitute the largest nesting leatherback sea turtle population in Central America. We conducted daily nest counts during the leatherback season. We standardized the Soropta nest counts, as the survey extent varied over time. We calculated catch per unit effort (CPUE) to account for sampling effort differences. We used the Information-Theoretic approach for model selection, based on Akaike’s Information Criterion correction for small sample sizes, using linear regression to assess population trends and discrete rate of population growth (λ). Soropta exhibited a positive nesting trend (8.9% year^-1; λ = 1.089; 1.076 – 1.10 95% CI). Bluff (- 8.8% year^-1; λ = 0.911; 0.892 - 0.930 95% CI) and Playa Larga (- 8.3% year^-1; λ = 0.917; 0.9045 - 0.930% CI) indicated declining nesting populations, while Chiriquí had a stable population (λ =0.993; 0.982 - 1.004 95% CI). For CPUE, the data yielded a stable population for all beaches combined (λ = 0.997; 0.995 – 0.999 95% CI). Overall, distinct nesting trends were observed at each leatherback sea turtle nesting beach. Given that females from different nesting sites mix at shared foraging grounds, this suggests that local factors may be influencing beach-specific nesting trends. The delicate balance of leatherback nesting in Bocas del Toro archipelago, along with its critical importance within the Western Caribbean, makes continuous monitoring and conservation efforts essential in this region, as well as increased protection from governmental agencies.

Green turtles (Chelonia mydas) and hawksbills (Eretmochelys imbricata) are consistently present along the Red Sea, where they are considered to spend a significant portion, if not all, of their life cycle. Monitoring efforts on these populations in Saudi Arabia (KSA), extending from the early 1980s to the present, have provided valuable insights into nesting behavior and index of abundance for both species, particularly in the northern Red Sea. However, knowledge of these aspects remains limited for the central and southern regions, highlighting gaps in rookery distributions and nesting seasonality. In alignment with the mission of SHAMS (General Organization for the Conservation of Coral Reefs and Turtles in the Red Sea) to enhance the understanding of sea turtle ecology and populations dynamics in the region, this baseline study aims to systematically identify the nesting sites and establish the nesting seasons for both species along the different regions of the KSA Red Sea.

To achieve this objective, we first conducted a detailed analysis of high-resolution satellite imagery to identify potential nesting areas, supported by an extensive literature review of previously documented sites. A total of 1,829 nesting sites (potential or confirmed) were identified along the 1,760 km coastline of the KSA Red Sea, with 1,176 on the mainland and 653 on islands. A rapid assessment methodology was employed to ground truth nesting activity; nests per species were recorded and geo-referenced through drone and/or on-foot surveys, while beach characterization, habitat assessment, and threat evaluation completed the site assessment.

SHAMS has surveyed 679 of these sites to date, confirming nesting activity at 407 sites, with half located in the northern region. Among these, 108 sites support both species, 93 are exclusive to green turtles, and 85 solely to hawksbill turtles (species identification was not possible at the remaining confirmed nesting sites). Based on the nesting density and ecological significance of each site, we aim to identify index sites for focused monitoring, enabling accurate assessments of nesting season durations and other key reproductive and demographic parameters across the Red Sea.

These index sites will also serve as references for establishing protected areas, such as the case of the Four Sister Islands, currently in the early stages of being proposed as an Important Marine Turtle Area (IMTA). This pristine archipelago, located in the Farasan Banks of the southern Red Sea, comprises four small islands with a combined nesting area of approximately 0.15 km². It has recorded 2,431 nesting events for green turtles and 401 for hawksbills, representing the largest combined rookery for both species documented in the Red Sea.

A network of protected areas will contribute toward implementing harmonized conservation programs across the KSA. This is particularly important for the hawksbill turtle, a species listed as critically endangered on the IUCN Red List, as the southern waters of the Red Sea may serve as a vital ecological refuge, crucial for the species' long-term viability within the Northwest Indian RMU (Regional Management Unit).