Caretta Research Articles

Citizen science enhances understanding of sea turtle distribution in the Gulf of California.

Citizen science is a valuable tool for addressing spatial distribution gaps in endangered species, especially in data-limited regions. Given the logistical and financial challenges of studying migratory species, this cost-effective approach contributes to strategic conservation planning. The Bay of La Paz, located in Baja California Sur, México, is considered an ecologically important region within the larger Gulf of California. Due to its rich biodiversity and abundant natural resources, the region serves as a hub for ecotourism and fishing, affording diverse opportunities for community-based scientific initiatives. This paper examines the value of citizen science contributions from three diverse community groups (i.e., coastal residents, SCUBA divers, and artisanal fishers) to help scientists obtain information on sea turtle distribution in the Bay of La Paz. Our findings represent the first records of loggerhead turtles (Caretta caretta) in the bay based on ten citizen science reports that include live and dead turtles (either observed swimming, as bycatch, or stranded), providing new information on an endangered pelagic species identified in a coastal bay. Although the sample size is small, our diversity of sources and sighting types highlight the value of collaborative citizen science initiatives in complementing traditional research methods.

The journey of loggerhead turtles from the Northwest Atlantic to the Mediterranean Sea as recorded by the stable isotope ratios of O, C and N of their bones

The journey of loggerhead turtles from the Northwest Atlantic to the Mediterranean Sea as recorded by the stable isotope ratios of O, C and N of their bones

Growing older, growing more diverse: Sea turtles and epibiotic cyanobacteria.

Cyanobacteria are known for forming associations with various animals, including sea turtles, yet our understanding of cyanobacteria associated with sea turtles remains limited. This study aims to address this knowledge gap by investigating the diversity of cyanobacteria in biofilm samples from loggerhead sea turtle carapaces, utilizing a 16S rRNA gene amplicon sequencing approach. The predominant cyanobacterial order identified was Nodosilineales, with the genus Rhodoploca having the highest relative abundance. Our results suggest that cyanobacterial communities become more diverse as sea turtles age, as we observed a positive correlation between community diversity and the length of a sea turtle's carapace. Since larger and older turtles predominantly utilize neritic habitats, the shift to a more diverse cyanobacterial community aligned with a change in loggerhead habitat. Our research provides detailed insights into the cyanobacterial communities associated with loggerhead sea turtles, establishing a foundation for future studies delving into this fascinating ecological relationship and its potential implications for sea turtle conservation.

The contribution of fish to the diet of loggerhead sea turtles in the western Mediterranean revisited

Early juvenile loggerhead turtles (Caretta caretta) rely on gelatinous zooplankton, whereas individuals larger than 40 cm curved carapace length are adapted to crush hard-shelled invertebrates. Nevertheless, fish were reported to be the staple food of loggerhead turtles in the western Mediterranean 30 years ago. Here, the temporal consistency of such a fish-based diet of loggerhead turtles is assessed through gut content analysis and stable isotope analysis of samples from the Mediterranean coast of Spain spanning three decades. The gut contents of 134 juvenile loggerhead turtles (curved carapace length range: 27–71 cm) from three different periods (1991, 1999–2008 and 2010–2017) were analyzed, as well as a subsample of the same turtles (n = 10 in each period) for both bulk and compound-specific stable isotope ratios (CSIA-AA). Gut content analysis revealed a decline in the frequency of occurrence and numerical abundance of fish and an increasing contribution of gastropods and bivalves throughout time, although pelagic tunicates were always the most frequently observed prey. The δ15Nbulk of turtle bone also dropped throughout the study period, but the values of the stable isotope ratio of N in phenylalanine (δ15NPhe) indicated that 52.5% of that variability was due to a baseline shift over time. Accordingly, the trophic position estimated from CSIA-AA did not follow the decreasing pattern of δ15Nbulk, but fluctuated throughout time. The overall evidence indicates that fish consumption by loggerhead turtles in the study region declined through time, but the trophic position of loggerhead turtles did not change simultaneously. This is probably because low trophic prey such pelagic tunicates and filter-feeding bivalves and suspension-feeding gastropods were the bulk of the diet during the whole study period and fish played a minor role, even when their frequency of occurrence peaked. Past levels of high fish consumption might be due to high levels of fishery discards, currently declining because of the recent reduction of the fishing fleet.

Decoding sex-specific metabolomic biomarkers in the loggerhead sea turtle (Caretta caretta)

There is need for advancing minimally invasive diagnostic techniques for sex differentiation at early life-stage classes in sea turtles. The objectives of this study were to determine whether there are sex-specific effects on the metabolome of the loggerhead sea turtle (Caretta caretta) and to identify potential biomarkers for sex classification at early life-stage classes (50 post-hatchling and 50 juvenile). Comprehensive analyses including plasma chemistry (n = 100) and untargeted (n = 48) metabolomic analyses were performed. Unlike with plasma chemistry analytes, there were significant differences in the metabolomic profiles between sexes. Nine metabolites differed significantly between sexes, with several metabolites deserving greater attention as potential biomarkers: C22H32O6 and pantothenic acid was higher in females than in males, and carboxylic acid ester (C10H16O5), 1-methylhistidine and C7H14N2O7 was higher in males than females. These differences remained constant both across and within the same life-stage class. This work identified a discernible effect on the metabolic profile based on sex of loggerhead sea turtles and it suggests that these metabolites and/or their ratios could serve as potential biomarker candidates for sex classification in this species.

Metal Bioaccumulation and Biochemical Responses in Loggerhead Turtles (Caretta caretta) from the Gulf of Gabès (Tunisia)

Caretta caretta (Cheloniidae, Cryptodira) is a species of turtle considered a ‘flagship species’ in the Mediterranean Sea. Unfortunately, the circular marine currents and semi-enclosed configuration of the Mediterranean Sea encourage the accumulation of pollutants (metals, pesticides, etc.) emitted by human activities. Tunisia suffers particularly from coastal urbanisation and industrial development. Metal concentrations (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) were measured in distinct tissues (heart, kidney, liver, lung, muscle) of loggerhead turtles stranded in the Gulf of Gabès (Tunisia) to estimate the pollution levels in this emblematic species. High concentrations of arsenic and cadmium were found in marine turtles. Therefore, the differential accumulation of metals was measured in the tissues. For example, the liver appears to be a preferential organ for the accumulation of copper, iron, silver and zinc. In contrast, cobalt and cadmium were more concentrated in the kidneys, while arsenic, chromium and nickel were mainly found in the muscles. Antioxidant enzyme responses (catalase, GPx and SOD) and lipid peroxidation were more expressed in the liver and kidneys than in the muscles.

Assessing the phenology and reproductive output of loggerhead turtles in relation to climatic variables at Patara Beach, Türkiye

AbstractLoggerhead turtles (Caretta caretta), being ectothermic organisms, could be especially susceptible to climate change effects, and may exhibit climate‐related variation in their reproductive behaviours such as phenology, annual nest numbers, clutch size, hatching success, incubation period and sex ratio. This study investigated the reproductive phenology and outputs of loggerhead turtles and their relationships with climatic variables over a 5‐year period (2019–2023) at Patara Beach, Türkiye. We found significant fluctuations in atmospheric temperature, sea surface temperature and relative humidity, and that female turtle emergences on Patara Beach could temporarily adjust their phenology in response to these minor environmental changes. We highlight the importance of understanding the impacts of phenological shifts on the ability to satisfy the conditions over the nesting season that determine reproductive output. Our statistical analyses also showed that increasing sea water temperatures and atmospheric temperatures, as well as decreasing precipitation and relative humidity, had direct and/or indirect effects on the nesting phenology and reproductive output of loggerhead turtles. The findings from this study indicate that atmospheric temperature significantly affected incubation period, hatching success rate, the number of dead embryos and the number of empty eggshells. Additionally, relative humidity had a significant impact on the incubation period and the number of empty eggshells. In this context, rising temperatures led to drier nest conditions, decreased incubation periods and increased nest temperatures, resulting in higher proportions of female offspring. In conclusion, there are still gaps in our understanding of the effects of climate change on the reproductive biology of loggerhead turtles, and more studies are needed at both the Mediterranean and global scales to better understand these effects.

Age and growth rate estimated by skeletochronology in loggerhead sea turtles from French Mediterranean waters

Abstract Skeletochronology was used to determine the ages of 30 loggerhead sea turtles (Caretta caretta) found in French Mediterranean waters. Histological sections were performed with 30 humeri collected on stranded C. caretta on the coast of Provence and the Gulf of Lion. Lines of arrested growth (LAGs) were used to evaluate age, considering only one period of arrested growth per year. Two successive LAGs delimit an interval that is proportional to the individual’s body growth. In a first step, we created a skeletogram for each individual that identified its LAGs. Secondly, we measured the areas delineating successive intervals to determine individual growth patterns over the years. Two methods were used to deduce sea turtle age from histological sections: the correction factor (CF) method and the growth rate (GR) method, the latter using Von Bertalanffy growth function. Age estimations varied from 4.3 to 24.7 years (mean ± SD = 10.1 ± 4.8) with the CF method and from 6.2 to 25.6 years (mean ± SD = 12.2 ± 5.2) with the GR method, with no significant difference between the methods. The study sample was thus mostly composed of juveniles, which is also the most frequent life stage observed in the study area. The annual curved carapace length growth rate calculated with every LAG interval varied from 1.0 to 6.9 cm/year (mean ± SD = 3.5 ± 1.4, ). High variability in interindividual growth rates were observed, which is of interest in understanding the complex lifecycle of these long-lived marine reptiles.

Inferring the origin of new D-loop haplotypes of loggerhead sea turtles (Testudinata: Cheloniidae) from the Southwest Atlantic lineage

The populations of the loggerhead turtles, Caretta caretta, present four main D-loop mitochondrial haplogroups that are distributed across the Indo-Pacific, Mediterranean, and Atlantic oceans. The Southwestern Atlantic (SWA) is one of the Regional Management Units (RMUs) of loggerheads, characterized by unique haplotypes, high nest density, and distinct life history traits. Detecting new D-loop haplogroups is important, particularly endemic ones, as they can enhance our understanding of their life history within the RMUs and contribute to the resolution of mixed stock analysis. In this study, we conducted a series of phylogenetic delimitation and network analyses to identify, validate, and infer the origin of four new D-loop haplotypes detected in the loggerhead populations from the SWA. Our findings demonstrate that these new D-loop haplotypes are valid and unique to the SWA lineage, potentially aiding in the delimitation of individuals’ origins and the inference of their lineage.

Post-release survival of loggerhead sea turtles (Caretta caretta) incidentally hooked in a North Atlantic pelagic longline fishery

Estimating mortality of sea turtles incidentally captured in fishing gear is essential to understanding fishery impacts on sea turtle populations. Loggerhead turtles (Caretta caretta) are a component of bycatch in pelagic longline fisheries, including those operating in Atlantic Canada. In this study, we used pop-up satellite archival tags (PSATs) attached to 62 loggerhead turtles incidentally hooked in Atlantic Canadian shallow-set pelagic longline gear (2012–2018) to estimate associated post-release survival. Consistent with conventional fishing practices, hooks were not removed from turtles prior to release. Analysis of diving behaviour, ocean temperature, and ambient light level was used to assign fates to turtles. Post-release survival was calculated using the Kaplan-Meier estimator with right censoring. Based on this method, the annual survival probability of an individual loggerhead post-release is 0.877 ± SE 0.052. While it is commonly assumed that hook location is an important variable in predicting fates of turtles after release, there was no difference in survival of deep-hooked (swallowed hook) versus shallow-hooked turtles. These results indicate higher survivorship among hooked loggerheads captured in shallow-set pelagic longline gear than prevailing wisdom and suggest that at least some of the population impacts on loggerhead turtles conventionally attributed to pelagic longline interactions may be linked to other threats.

Trismus in cold-stunned Kemp's ridley (Lepidochelys kempii) and loggerhead (Caretta caretta) sea turtles.

To describe the presentation, clinical findings, diagnosis, treatment, and outcome of cases of trismus (lockjaw) in cold-stunned sea turtles. 4 Kemp's ridley (Lepidochelys kempii) and 1 loggerhead (Caretta caretta) sea turtle. Cold-stunned sea turtles that presented with difficulty or inability to open their jaw between 2009 and 2023 were included. Information retrieved from medical records included signalment, physical exam findings, diagnostic information, definitive diagnosis via either advanced imaging or histopathology, treatment, and clinical outcome. Turtles presented between 4 and 48 days into rehabilitation. Three were diagnosed by advanced imaging (CT or MRI), and 2 were diagnosed based on clinical signs and postmortem histopathology. Treatment was multimodal and consisted of antibiotics (5/5), nonsteroidal anti-inflammatories (5/5), vitamin E (3/5), intralesional steroid therapy (3/5), acupuncture (3/5), antifungals (2/5), anti-inflammatory parenteral steroids (2/5), physical therapy (2/5), therapeutic laser (2/5), and supportive feeding via either total parenteral nutrition (1/5), or tube feedings (2/5). Two animals were released, 2 died naturally, and 1 was euthanized. Trismus (lockjaw) is an uncommon finding in stranded cold-stunned sea turtles that can have a significant impact on animal welfare if not diagnosed and treated. This report describes the condition to aid clinical case management and resource allocation in rehabilitation facilities.

Elucidating the Origins of Stranded Loggerhead Sea Turtles (Caretta caretta) in the Eastern Mediterranean through Mitochondrial DNA Mixed-Stock Analysis

It is widely recognized that the examination of haplotypes among sea turtles inhabiting nesting beaches holds significant importance. Yet, an effective conservation effort of a population also requires an investigation of the origin of sea turtles that strand on the shore, especially as many of these result from interactions with fisheries. In consideration of this, we analyzed the haplotypes of 542 stranded individuals from the Eastern Mediterranean and identified a total of 9 different haplotypes. Two of these were new haplotypes, one individual was found in Marmaris, Türkiye, and the other in a stranded species in northern Cyprus. Mixed-stock analysis demonstrated that the majority of the individuals stranded in western Türkiye originated from nesting beaches in the same area (33%), followed by Dalyan, Türkiye (25%), and Cyprus (21%). The partial mixed-stock analysis of individuals stranded in the Dalyan–Dalaman region of Türkiye revealed that most originated from Dalaman (45%) and Dalyan (21%), followed by western Greece (11%). The partial mixed-stock analysis for the Eastern Mediterranean showed that the majority of individuals originated from western Türkiye (69%), followed by Cyprus (11%) and Dalyan (7%). These findings, by quantifying the relative contributions of each region, provide valuable insights for guiding conservation efforts regarding Caretta caretta in the Mediterranean marine environment.

DNA Methylation Carries Signatures of Sublethal Effects Under Thermal Stress in Loggerhead Sea Turtles.

To date, studies of the impacts of climate warming on individuals and populations have mostly focused on mortality and thermal tolerance. In contrast, much less is known about the consequences of sublethal effects, which are more challenging to detect, particularly in wild species with cryptic life histories. This necessitates the development of molecular tools to identify their signatures. In a split-clutch field experiment, we relocated clutches of wild, nesting loggerhead sea turtles (Caretta caretta) to an insitu hatchery. Eggs were then split into two sub-clutches and incubated under shallow or deep conditions, with those in the shallow treatment experiencing significantly higher temperatures in otherwise natural conditions. Although no difference in hatching success was observed between treatments, hatchlings from the shallow, warmer treatment had different length-mass relationships and were weaker at locomotion tests than their siblings incubated in the deep, cooler treatment. To characterise the molecular signatures of these thermal effects, we performed whole genome bisulfite sequencing on blood samples collected upon emergence. We identified 287 differentially methylated sites between hatchlings from different treatments, including on genes with neurodevelopmental, cytoskeletal, and lipid metabolism functions. Taken together, our results show that higher incubation temperatures induce sublethal effects in hatchlings, which are reflected in their DNA methylation status at identified sites. These sites could be used as biomarkers of thermal stress, especially if they are retained across life stages. Overall, this study suggests that global warming reduces hatchling fitness, which has implications for dispersal capacity and ultimately a population's adaptive potential. Conservation efforts for these endangered species and similar climate-threatened taxa will therefore benefit from strategies for monitoring and mitigating exposure to temperatures that induce sublethal effects.

AUTOLOGOUS OR ALLOGENIC BLOOD PLEURODESIS AS TREATMENT FOR PNEUMOCOELOM IN FOUR SEA TURTLES (LEPIDOCHELYS KEMPII, CARETTA CARETTA).

Pneumocoelom secondary to primary pulmonary disease was diagnosed via CT (three cases) or radiographs and coelioscopy (one case) in one Kemp's ridley (Lepidochelys kempii) and three loggerhead (Caretta caretta) sea turtles. All cases were suspected to be caused by trauma to the lung, and all exhibited positive buoyancy disorders. Coelomocentesis alone was ineffective at resolving each pneumocoelom, suggesting a large and persistent tear in the pulmonary parenchyma. An autologous (in three cases) or allogenic (in one case) blood patch pleurodesis was performed. The pneumocoelom was resolved in all four cases with no noted postoperative complications. Follow-up diagnostic imaging confirmed resolution of the pneumocoelom in three cases, and all four patients were successfully rehabilitated and had normal buoyancy at the time of release. One rehabilitated loggerhead was satellite tagged, and the tracking data demonstrated that the animal was still alive and moving normally 126 d postrelease, when the tag stopped transmitting. In sea turtles, an autologous or allogenic blood patch pleurodesis can be safely performed in cases of persistent pneumocoelom secondary to traumatic primary pulmonary disease.

Potential drivers and implications of a balanced breeding sex ratio in a small population of an imperiled species with environmental sex determination.

Small populations of imperiled species are susceptible to the negative consequences of skewed sex-ratios. In imperiled species with environmental sex determination such as sea turtles, examining sex ratios across a range of environments and population abundance levels can provide insight into factors that influence population resilience, which can then be the foci of management plans for these species. Breeding sex ratios (the ratio of actively breeding males to females during a reproductive season; BSRs) extrapolated from genetic parentage analyses are a common approach for enumerating sex ratios in sea turtles. Such analyses also allow for the characterization of multiple paternity within sea turtle clutches, which should reflect BSRs and breeding behaviors. We characterized the first BSR for a breeding assemblage of loggerhead sea turtles (Caretta caretta) belonging to the temperate, low-abundance Northern Gulf of Mexico Recovery Unit using genotypes of 16 microsatellite loci from nesting females and hatchlings. Unlike prior studies at both more-tropical and more-temperate, and higher-abundance, Recovery Units in this region, we found a balanced BSR of 1.3:1 males:female and a low incidence (~17%) of multiple paternity. This suggests that there are relatively few males breeding at this assemblage and within this Recovery Unit. Beaches in this region are expected to produce substantial numbers of male hatchlings based on sand temperature data. The relative dearth of mature males may then be due to hydrologic disturbances that disproportionately affect the fitness and survival of male hatchlings, or due to demographic stochasticity. More work is needed to study the factors that might influence male hatchling production and fitness in this region, particularly as climate change is predicted to lead to feminization in global sea turtle populations. Our work demonstrates the broad utility of characterizing BSRs and other sex ratios across a range of populations in imperiled, environmentally sensitive species.

Productive foraging grounds enhance maternal condition and offspring quality in a capital breeding species.

Feeding ecology is an essential component of an organism's life, but foraging comes with risks and energetic costs. Species in which populations exhibit more than one feeding strategy, such as sea turtles, are good systems for investigating how feeding ecology impacts life-history traits, reproduction and carried over effects across generations. Here, we investigated how the feeding ecology of loggerhead sea turtles (Caretta caretta) nesting at the Cabo Verde archipelago correlates with reproductive outputs and offspring quality. We determined the feeding ecology of female turtles before and during the breeding season from stable isotope analysis of carbon and nitrogen and correlated isotopic ratio with female and offspring traits. We found that female turtles feeding at higher trophic positions produced larger clutches. We also found that females with higher δ13C values, typical of productive foraging areas, had greater fat reserves, were less likely to be infected by leech parasites and produced heavier offspring. The offspring of infected mothers with higher δ13C values performed best in crawling and self-righting trials than those of non-infected mothers with higher δ13C values. This study shows adult female loggerheads that exploit productive areas build capital reserves that impact their reproductive success and multiple proxies for offspring quality. Overall, our findings provide valuable insights into the complex interplay between feeding ecology and reproductive success, and reveal the transgenerational carry-over effects of both feeding ecology and health on offspring quality in sea turtles.

Correlations between local geoclimatic variables and hatchling body size in the sea turtles Caretta caretta and Chelonia mydas

It has been widely demonstrated that air and sand temperatures influence the anatomy of sea turtle hatchlings. We examined the impact of precipitation during the nesting season on the hatchling body size of loggerhead and green turtles from 37 beaches worldwide. Longitudinal data collected between 2012 and 2018 from Florida (US) and from a sample on Bõa Vista Island (Cabo Verde) carried out in 2019 showed that loggerhead body size at hatching was negatively correlated with precipitation, while precipitation was not correlated with hatchling body size in green turtles. A meta-analysis revealed that precipitation is positively correlated with hatchling mass in loggerhead turtles, while it is positively correlated with straight carapace length and width in green turtle hatchlings. The strongest influence of precipitation was found in the middle of the incubation period of loggerhead turtles in Cabo Verde, and we posit that this is due to an increase in the uptake of water for embryonic growth. These findings highlight the great importance of understanding the correlated effects of regional environmental variables, such as precipitation, on the development of sea turtle hatchlings and will have an impact on the evaluation of ongoing conservation and climate change discussions.

Antibiotic Resistance of Bacteria Isolated from Clinical Samples and Organs of Rescued Loggerhead Sea Turtles (Caretta caretta) in Southern Italy.

Antimicrobial resistance affects all environments, endangering the health of numerous species, including wildlife. Increasing anthropic pressure promotes the acquisition and dissemination of antibiotic resistance by wild animals. Sea turtles, being particularly exposed, are considered sentinels and carriers of potential zoonotic pathogens and resistant strains. Therefore, this study examined the antibiotic resistance profiles of bacteria isolated from loggerhead sea turtles hospitalised in a rescue centre of Southern Italy over a 9-year period. Resistance to ceftazidime, doxycycline, enrofloxacin, flumequine, gentamicin, oxytetracycline and sulfamethoxazole-trimethoprim was evaluated for 138 strains isolated from the clinical samples or organs of 60 animals. Gram-negative families were the most isolated: Vibrionaceae were predominant, followed by Shewanellaceae, Pseudomonadaceae, Enterobacteriaceae and Morganellaceae. These last three families exhibited the highest proportion of resistance and multidrug-resistant strains. Among the three Gram-positive families isolated, Enterococcaceae were the most represented and resistant. The opportunistic behaviour of all the isolated species is particularly concerning for diseased sea turtles, especially considering their resistance to commonly utilised antibiotics. Actually, the multiple antibiotic resistance was higher when the sea turtles were previously treated. Taken together, these findings highlight the need to improve antimicrobial stewardship and monitor antibiotic resistance in wildlife, to preserve the health of endangered species, along with public and environmental health.

Genetic characteristics of loggerhead turtles in the coastal corridor of the North West Pacific, around the Cape Muroto, Japan

Genetic characteristics of loggerhead turtles in the coastal corridor of the North West Pacific, around the Cape Muroto, Japan

An investigation of some persistent organic pollutants in loggerhead sea turtles (Caretta caretta)

The study assessed persistent organic pollutants (POPs) in Caretta caretta turtles along Turkish coasts, analyzing bioaccumulation in accessible organs and discerning sex-related differences. Ten adult turtles (5 males, 5 females) from Mugla province were sampled post-mortem. Various tissues were analyzed for organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and polycyclic aromatic hydrocarbons (PAHs) using gas chromatography–mass spectrometry. DDT distribution showed no sex-based difference, with concentrations highest in fat tissue followed by liver, kidney, muscle, spleen, and heart. Male PCB concentrations ranked highest in fat, followed by kidney, liver, spleen, muscle, and heart, while females showed a similar trend. PAH concentrations were highest in fat for both sexes, followed by various organs. Limited PBDE concentrations hindered comprehensive evaluation. Overall, C. caretta act as effective bioindicators for monitoring environmental pollution, with certain POPs exhibiting sex and organ-based variations.