Turtle Size Research Articles

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.

Speaking Deads: Sea Turtle Mortality Areas and Fisheries Overlaps Identified Through Backtracking of Stranded Carcasses in the Adriatic Sea

ABSTRACT Interaction with fishing gears represents the main anthropogenic threat at sea for sea turtles worldwide, and identifying the hotspots of turtle bycatch is a priority knowledge gap. Turtle stranding data represent a source of information about mortality areas at sea that are not fully exploited. This study aims to infer turtle mortality areas of turtles stranded along the Italian Adriatic Coast in the period 2019–2021 (1432 records), through backtrack modelling of carcasses. Specifically, the decomposition process of eight loggerhead carcasses was monitored, and the relationship between floating period (FP), turtle size and sea temperature was modelled through a generalized additive model. Oceanographic information was then used to track the routes of floating carcasses back, knowing their size and decomposition stage, and finally estimate the likely area of mortality. A complementary numerical experiment of connectivity between coastal and offshore areas gave indication that areas of potential mortality are relatively close to the coast, particularly in the northern Adriatic. Stranded turtles probably represent just a small fraction (17%–25%) of total at‐sea mortalities in the study area (Italian Adriatic waters), with decomposition rates, season and distance from shore influencing their stranding likelihood. Hence, strandings can inform only about spatio‐temporal variability of coastal mortality hotspots. Inferred areas of turtle mortality were most likely located in the North and Central Adriatic all over the year and overlap with heatmaps of fishing effort, obtained from vessel monitoring system (VMS) and automatic identification system (AIS) data, in the Gulf of Manfredonia and in the North‐West Adriatic in the cold (September–December) and warm (May–August) periods, respectively.

A note on carapace size of the Malaysian giant turtle, Orlitia borneensis (Testudines: Geoemydidae) in Peninsular Malaysia, and the species’ conservation status

A note on carapace size of the Malaysian giant turtle, Orlitia borneensis (Testudines: Geoemydidae) in Peninsular Malaysia, and the species’ conservation status

Intraspecific Variation in Mercury Contamination of Alligator Snapping Turtles (Macrochelys temminckii).

Macrochelys temminckii (alligator snapping turtle) is an aquatic turtle endemic to the southeastern United States that was proposed for listing under the Endangered Species Act in 2021. In the present study we analyzed total mercury (THg) concentrations in skeletal muscle, tail clips, and nail tissue of 93 M. temminckii sampled from 14 waterbodies in eastern Texas (USA). Our objectives were to assess (1) the degree of correlation between internal tissue (skeletal muscle and tail clip samples) and keratin (nail samples), (2) the influence of ecological factors (turtle size and waterbody/sampling site) on THg concentrations, and (3) whether THg concentrations were high enough to pose a risk to human consumers. The mean (±SE) THg concentrations of muscle and nail were 1.16 ± 0.08 μg/g dry weight and 4.21 ± 0.24 μg/g dry weight, respectively, and THg concentrations were highly dependent on the sampling site. The THg concentrations of nails were correlated with muscle concentrations (R2 = 0.56, p < 0.001). The effect of body size on THg concentrations varied by sampling site, indicating that size is not a good predictor of Hg concentration across sites. Finally, THg concentrations in M. temminckii of eastern Texas were high enough to pose a potential risk to human health based on US Environmental Protection Agency dietary guidelines. Environ Toxicol Chem 2024;43:1903-1913. © 2024 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Mercury biomagnification in the food chain of a piscivorous turtle species (Testudines: Chelidae: Chelus fimbriata) in the Central Amazon, Brazil.

Due to their natural history and ecological attributes, turtles are excellent organisms for studies of heavy metal contamination. Turtles have a large geographical distribution, occupy different aquatic habitats, and occupy various trophic levels. The present study investigated mercury bioaccumulation in the carnivorous chelonian Chelus fimbriata (Matamata turtle) and Hg biomagnification in relation to its aquatic food chain in the middle Rio Negro, AM-Brazil. Tissue samples of muscle, carapace and claws were collected from 26 C. fimbriata individuals, as well as collections of autotrophic energy sources found in the turtle's aquatic habitat area. The samples were collected in February-March/2014 and analyzed for THg concentrations and carbon (δ13C) and nitrogen (δ15N) stable isotopes. The highest THg levels were found in claws (3780 ng.g-1), carapace (3622 ng.g-1) and muscle (403 ng.g-1), which were found to be significantly different [F(2.73) = 49.02 p < 0.01]. However, THg concentrations in muscle tissue were below the consumption threshold indicated by the WHO and Brazilian Health Ministry. The average δ13C and δ15N values in Matamata samples were -31.7‰ and 11.9‰, respectively. The principal energy source sustaining the food chain of C. fimbriata was found to be terrestrial shrubs, with smaller contributions from emergent aquatic herbaceous plants and algae, while δ15N values showed its trophic position to be two levels above the autotrophic energy sources. There was a positive correlation between THg and turtle size, while a significant relationship was found between THg and δ15N, showing strong biomagnification in the food chain of C. fimbriata: y = 0.21x + 0.46; r2 = 0.45; p < 0.001, for which the slope presented a value of 0.21.

Small-scale movements and site fidelity of two sympatric sea turtle species at a remote atoll

Understanding natural movement patterns and ecological roles of marine megafauna is a research priority best studied in areas with minimal human impact. The spatial distribution patterns specifically for immature turtles at foraging grounds have been highlighted as a research gap for effective management and conservation strategies for sea turtle populations. Capture–mark–recapture (CMR) records (n = 2287) of 1672 immature green (Chelonia mydas) (n = 1158) and hawksbill turtles (Eretmochelys imbricata) (n = 514) from a long-term (1981–2021) in-water CMR program at Aldabra Atoll, Seychelles, were analyzed for 10 sites (0.35–25 km apart). Site fidelity was not correlated with either season or turtle size. Green turtles had lower site fidelity than hawksbill turtles. Green turtles showed avoidance (i.e., opposite of fidelity) of three sites, while hawksbill turtles displayed high fidelity to two sites. Sites displaying non-random behavior (avoidance and/or fidelity) did not share the same benthic habitat types. Results indicate that fidelity can be detected at a fine scale with CMR, but that further exploration into the habitat characteristics of the sites and the ecological roles of both species at the atoll is needed.

Bigger is better: age class‐specific survival rates in long‐lived turtles increase with size

AbstractVital rates for small, non‐breeding individuals are important components of population dynamics for many species, but often individuals of these sizes are difficult to locate, capture, and track. As such, biologists frequently lack reliable estimates of juvenile survival because sample sizes and recapture rates for this life stage are low. Long‐lived animals often take many years to reach sexual maturity and spend much of this time in the smaller size classes, making them sensitive to changes in survival rates. We estimated the survival rates of all size classes for the northern map turtle (Graptemys geographica) using a mark‐recapture dataset with &gt;3,500 captures from 2019–2021 and 210 nests from 2018–2021. As turtle size increased, annual survival probability increased regardless of sex. Estimated annual survival probability for turtles &gt;18 cm long (i.e., adult females &gt;15 years) was about 0.95, over 4 times higher than turtles that were 3 cm long (i.e., hatchlings &lt;1 year; 0.22 annual survival probability). Although we did not observe a difference in survival probability between sexes of any size class, adult females are nearly twice the size of adult males, leading to an increased annual survival probability for females of 0.95, compared to 0.80 for males. Changes in adult survival had the greatest influence on population estimates over time, with temporary decreases, such as those due to poaching or an environmental disaster, potentially leading to unrecoverable decreases in the overall population size. Our study provides detailed survival rates for all size classes in a long‐lived turtle, which are necessary to assess population stability and can be used to determine the most effective conservation or management practices.

Size records and demographics of an Eastern Painted Turtle (&lt;i&gt;Chrysemys picta picta&lt;/i&gt;) urban population near the northern limit of the species’ range in eastern Canada

Understanding variation in demographics and life history across species ranges and differing landcover types is valuable for conservation planning. We examined the population demographics of a small urban population of Eastern Painted Turtle (Chrysemys picta picta) in New Brunswick, Canada, near the northern limit of the species’ range. We captured turtles using hoop traps and by hand during four sampling periods. We estimated that our population included 17 females, nine males, and 29 juveniles in late summer 2015 using Jolly-Seber population size estimates. We captured several very large females at our study site; 5/17 females (29%) were larger than previous size records for the subspecies. Growth rates for juveniles were greater than most populations of Eastern Painted Turtles reported elsewhere. Growth rates at our site were significantly greater for smaller (younger) turtles and for females compared to males. Overwinter survivorship estimates were 100% from late summer 2014 to spring 2015. Active season (2015) survivorship was 100% for females, 89% for males, and 93% for juveniles. We speculate that the large body sizes found at our study site were achieved through high survivorship and larger growth rates compared to other areas reported previously. Our data supports previous findings that body size of Painted Turtles increases with latitude, and additionally, growth may have been enhanced by increased nutrient levels common in human-modified landscapes.

Health status and genetic compositions of green turtles (Chelonia mydas) foraging in Brunei Bay.

Long-term monitoring of sea turtle aggregations is critical for understanding the impacts of environmental changes on their population health and habitat suitability. Brunei Bay is a significant foraging ground for green turtles in the South China Sea. We analyzed the body size, hematology and body condition of green turtles for their health status in their foraging ground in Brunei Bay over a period of nine years (2011-2019). Additionally, we used mitochondrial DNA (mtDNA) to evaluate changes in the size and genetic composition of green turtle aggregations. Our findings revealed that the size composition of the green turtle population varied seasonally, but there were no significant temporal changes in genetic and size compositions. Hematology parameters and Fulton's body condition index were consistent with those reported for apparently healthy green turtles. Furthermore, we found that blood reference intervals indicated the turtles were healthy. These results provide valuable baseline data for future comparisons with other foraging aggregations and for long-term monitoring of green turtles in Brunei Bay.

Movement behavior and passive dispersal of a reintroduced population of alligator snapping turtles

AbstractMaladaptive movement behavior is a leading cause of failure for reptile reintroductions, thus characterizing movement for translocated populations is important to project success. From 2014–2016 we radio‐tracked 183 immature reintroduced alligator snapping turtles (Macrochelys temminckii) using very high frequency telemetry in a stream in southern Illinois, USA. We assessed environmental, temporal, morphometric, and microhabitat factors influencing movement, including post‐release dispersal from reintroduction sites, movement probability, and step length. We used directional statistics to investigate the effects of precipitation and age on directional movement in the stream. Numerous factors influenced active movement, including ambient temperatures, time since release, use of log jams, turtle size, and age. Precipitation had an age‐biased effect on movement. Directional analyses suggested that movement was largely passive as turtles were swept downstream with increased discharge. Overall, the behavior of reintroduced alligator snapping turtles was similar to that reported in wild populations. Passive downstream transport has implications for reintroduced and natural populations as a force for unintentional emigration in channelized streams under current conditions and future high flow regimes.

Diet of hawksbill turtles (Eretmochelys imbricata) in the Gulf of California, Mexico

Abstract Hawksbill turtles (n = 56) in a foraging ground around Isla San Jose, Gulf of California, Mexico, were caught, measured, and their skin and scutes sampled. Tissue samples from putative prey species were collected from observed hawksbill feeding areas in the foraging ground. Measurements of each turtle's straight carapace length were used to estimate the average life stage of the population. Tissue samples were processed for stable carbon and nitrogen isotope analysis to estimate foraging habits of turtles in this location. The majority (96.4%) of measured individuals' straight carapace length fell in the size range considered to be juveniles. A Bayesian mixing model analysis of the δ13C and δ15N values of hawksbill skin and potential prey indicated that hawksbills consume primarily invertebrates and algae, with lesser contributions from seagrass and mangrove material. There was a positive linear relationship between turtle size and the δ13C values from scute samples, and an increase in the δ13C values of five individuals recaptured in subsequent years suggested a potential location shift from a pelagic habitat in the turtles' post‐hatching, earliest juvenile years to the nearshore foraging area around Isla San Jose in their later juvenile years.

Maximum Body Size of the Suwannee Alligator Snapping Turtle (Macrochelys suwanniensis)

The published literature does not provide a consensus regarding maximum body sizes of North America's largest wild freshwater turtles (genus Macrochelys). The largest known wild M. suwanniensis (Suwannee Alligator Snapping Turtle) currently exists as a curated specimen measuring 713 mm straight-midline carapace length, 801 mm maximum carapace length, 619 mm maximum carapace width, and 236 mm maximum head width. The turtle was never weighed, but we used morphometric data from our studies in the Santa Fe and Suwannee rivers to estimate that it weighed ∼76.4 kg (168 lbs) when captured. Our 95% prediction interval (67.6–86.3 kg [149–190 lbs]) suggests that speculative estimates and anecdotal reports of M. suwanniensis that weigh ≥90 kg (≥200 lbs) are dubious.

Using baited remote underwater videos to survey freshwater turtles

AbstractNew and innovative techniques utilizing underwater cameras have the potential to track changes in turtle populations whilst being less invasive and time intensive than traditional trapping surveys. In this study, we trialled the use of Baited Remote Underwater Videos (BRUVs) in five upland streams to test if BRUVs could be used for abundance, size and sex estimates of freshwater turtles. We also compared BRUVs to cathedral traps and identified key considerations for future use of this method, such as whether the time of day influenced results. Our study successfully detected 83 turtles from 52 h of footage and identified all species known to occur in the study area. The deployment time did not significantly influence relative abundance. BRUVs also produced statistically similar catch per unit effort estimates to cathedral trapping techniques. No small turtles (i.e. juveniles) were detected, and difficulties with visibility, sex accuracy and carapace measurements are discussed for future BRUV use. Our study shows that BRUVs are a useful, time effective, non‐invasive technique to collect relative abundance and species richness estimates for freshwater turtles.

Description and quantification of micronucleus and nuclear abnormalities in erythrocytes of the sentinel green turtle (Chelonia mydas) with fluorescence microscopy.

Contamination in marine ecosystems is of the most critical threats to marine turtles. The identification of useful biomarkers to detect and monitor the physiological and clinical effects of pollutants on these populations will allow early detection of alterations (e.g., mutagenic damages) that could risk their viability or favor the development of diseases, thus threatening the biodiversity of these ecosystems and human population. This study is aimed at describing and quantifying nuclear anomalies in peripheral blood erythrocytes of green turtles (Chelonia mydas) from three distinct foraging areas in Mexico (Akumal, Xcalak, and Punta Herrero). We developed a novel morphological index that could be used as a biomarker to identify abnormal nuclei in peripheral blood erythrocytes. Here we describe for the first time in C. mydas, with a species-specific staining protocol, distinct nuclear abnormalities such as blebbed, lobed, notched, eight shape nuclei, and binucleated cells. These nuclear abnormalities were present in >90 % of the subjects (n=30). Moreover, 50 % of the organisms presented erythrocytes with micronuclei. The number of nuclear abnormalities did not correlate with size of the green turtles or differ between sites, or health status. We found a higher frequency of green turtles with nuclear abnormalities in the southern region (Punta Herrero and Xcalak) with the highest frequency of micronucleus and buds. The former could be associated to the constant exposure to chemical pollutants of oceanographic origin in the southern coast of Quintana Roo. Furthermore, the increasing anthropogenic pollution in Akumal could also explain the highest variability in the number of nuclear abnormalities presented in resident individuals. We propose that a long-term monitoring programs of green turtle populations in the Mexican Caribbean that include a micronucleus test could be a useful to determine possible mutagenic damage in these animals.

Long-term changes in body size of green turtles nesting on Trindade Island, Brazil: Signs of recovery?

Trindade Island is an important wildlife refuge in the South Atlantic Ocean and hosts the largest nesting population of green turtles (Chelonia mydas) in Brazil, about which temporal ecological dynamics are still not well understood. The present study examines 23 years of nesting for green turtles at this remote island to evaluate annual mean nesting size (MNS) changes and post-maturity somatic growth rates. Our results show a significant decrease in annual MNS over the study; Whereas MNS during the first three consecutively monitored years (1993–1995) was 115.1 ± 5.4 cm, during the last three years (2014–2016) it was 111.2 ± 6.3 cm. There was no significant change in post-maturity somatic growth rate over the course of the study; the mean annual growth rate was 0.25 ± 0.62 cm/year. These findings suggest an increase in the relative proportion of smaller, presumptive neophyte nesters appearing in Trindade during the study period.

Phthalate metabolites in loggerhead marine turtles (Caretta caretta) from the Mediterranean Sea (East Spain region)

The exposure of marine reptiles to phthalates has received considerable attention due to the ubiquitous occurrence of these contaminants in the marine environment. The occurrence of phthalate metabolites is established in human populations and marine mammals, but data is scarce for marine reptiles. In this study, concentrations of 18 phthalate metabolites were determined in liver samples from 79 loggerhead marine turtle (Caretta caretta) samples collected between 2016 and 2021 in the limits of the Valencian Community (East Spain). For this purpose, the phthalate metabolites were purified from the livers by solid phase extraction and were quantified by UPLC-MS/MS. Fifteen phthalate metabolites were detected in the samples. Monoethyl phthalate (mEP), monomethyl phthalate (mMP), mono-n-butyl phthalate (mBP), phthalic acid (PA) and mono-n-hexyl phthalate (mHxP) were the most abundant metabolites, accounting for detection rates >85%. The highest median concentrations were found for PA (24.2 ng/g dry weight, d.w.) and mHxP (20.3 ng/g d.w.) followed by mMP (12.0 ng/g d.w.), mEP (5.76 ng/g d.w.) and mBP (4.26 ng/g d.w.). The sum of the medians of these five phthalate metabolites (Σ5PhMet) indicated that concentrations were higher for turtles during year 2020, while a negative association was found between [Σ5PhMet] and the turtle size. To our knowledge, this is the first study on the biomonitoring of 18 phthalate metabolites in loggerhead marine turtles, and results show that western Mediterranean loggerhead turtles are usually exposed to these contaminants.

Underwater vocalizations of Trachemys scripta elegans and their differences among sex–age groups

The aim of this study was to identify underwater vocalizations in red-eared turtles (Trachemys scripta elegans) and assess differences between sexes and ages. We recorded the underwater vocalizations of the red-eared sliders and identified 12 call types through manual visual and aural inspection of the recordings. Similarity analysis verified that manual classification was relatively reliable. The call types of the turtle were described and displayed as spectrograms and waveforms. The turtles produced fewer high-frequency call types than low-frequency types in all recordings. Statistical analysis revealed significant differences in the frequencies and duration of the calls of red-eared turtles between different sexes and ages. Males vocalized pulse calls very frequently, whereas a high proportion of high-frequency call types was emitted by the female adult group. The male subadult group emitted higher frequencies of Type A, B, and C calls, which is in accordance with the phenomenon that vocal frequency is often inversely proportional to the turtle size. Some call types produced by red-eared turtles were above the frequency range of their known hearing range. This may have been a by-product of the sound production mechanism or it may have adaptive value in mitigating interference to communication from low-frequency noise common in natural waters in communication The behavioral implications of these vocalizations and whether turtles can hear such high sounds warrant further study.

Trace elements concentration in blood of nesting Kemp's Ridley turtles (Lepidochelys kempii) at Rancho Nuevo sanctuary, Tamaulipas, Mexico.

The concentrations of trace elements including As, Zn, Cu, Se, Pb, Hg and Cd, were determined in the blood of nesting Kemp's ridley turtles (Lepidochelys kempii) at Rancho Nuevo sanctuary, Tamaulipas, Mexico during 2018-2020. The sequential concentrations analyzed were Zn> Se> Cu> As> Pb; while Cd and Hg concentrations were below the limits of detection (0.01 μg g-1). No significant differences were observed between the concentrations of trace elements (p> 0.05) by year, except Se levels, possibly resulting from recorded seasonal differences in turtle size. No relationships among turtle size vs elements concentration were observed. In conclusion, essential and toxic trace elements concentrations in the blood of nesting Kemp's ridley turtles may be a reflex of the ecosystem in which the turtles develop, that is, with low bioavailability of elements observed in the trophic webs in the Gulf of Mexico.

Long-term changes in adult size of green turtles at Aldabra Atoll and implications for clutch size, sexual dimorphism and growth rates

Around the world, declines in the mean size of nesting sea turtles have been reported with concerns of a concomitant decrease in the reproductive output of populations. Here, we explore this possibility using long-term observations of green turtles (Chelonia mydas) at Aldabra Atoll, Seychelles. Based on > 4500 individual measurements over 21 years (1996–2016), we found the curved carapace length of nesting females declined by about 0.64 cm per decade, from 111.43 to 110.08 cm. For 391 individuals that were measured more than once with measurement interval of 2.8–19 years apart, the mean growth rate was 0.14 cm year−1. Comparisons between the size of adult females and males were based on 23 and 14 weight measurements, 107 and 33 carapace length measurements and 103 and 33 carapace width measurements, respectively, taken during 1981–1983. Adult females were larger than males, with the sexual dimorphism index, i.e. the ratio of size of the larger sex to the smaller, being 1.09 and 1.10 for carapace length and width, respectively, and 1.25 for weight. Smaller females tended to lay fewer eggs per clutch but the decrease in female mean size was accompanied by increases in numbers of turtles nesting annually, such that the estimated total numbers of eggs per year increased from 1.3 million to 2.0 million between 1996 and 2016. Therefore, a decrease in mean size of nesting females has not compromised egg production for this population.

Density Estimation in Terrestrial Chelonian Populations Using Spatial Capture–Recapture and Search–Encounter Surveys

Having an accurate estimate of population size and density is imperative to the conservation of chelonian species and a central objective of many monitoring programs. Capture–recapture and related methods are widely used to obtain information about population size of chelonians. However, classical capture–recapture methods have strict spatial sampling requirements and do not account for lack of geographic closure caused by movement of individuals in and out of the surveyed landscape. Newly developed spatial capture–recapture (SCR) models address these limitations by specification of explicit models for spatial sampling as well as the spatial distribution of individuals in the population. Spatial capture–recapture models have not yet been applied to the study of chelonian populations. Here we demonstrate their application to a population of box turtles in Maryland that has been studied for 75 yr. Results support dramatic declines in population size of box turtles since the 1940s.