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We examine inherent variation in carbon and nitrogen stable isotope values of multiple soft tissues from a population of captive green turtles Chelonia mydas to determine the extent of isotopic variation due to individual differences in physiology. We compare the measured inherent variation in the captive population with the isotopic variation observed in a wild population of juvenile green turtles. Additionally, we measure diet-tissue discrimination factors to determine the offset that occurs between isotope values of the food source and four green turtle tissues. Tissue samples (epidermis, dermis, serum, and red blood cells) were collected from captive green turtles in two life stages (40 large juveniles and 30 adults) at the Cayman Turtle Farm, Grand Cayman, and analyzed for carbon and nitrogen stable isotopes. Multivariate normal models were fit to the isotope data, and the Bayesian Information Criterion was used for model selection. Inherent variation and discrimination factors differed among tissues and life stages. Inherent variation was found to make up a small portion of the isotopic variation measured in a wild population. Discrimination factors not only are tissue and life stage dependent but also appear to vary with diet and sea turtle species, thus highlighting the need for appropriate discrimination factors in dietary reconstructions and trophic-level estimations. Our measures of inherent variation will also be informative in field studies employing stable isotope analysis so that differences in diet or habitat are more accurately identified.

Age at sexual maturity (AgeSM) is one of the most serious demographic data gaps for sea turtle populations. Better estimates of AgeSM and associated variance would improve evaluation of population dynamics and responses of populations to disturbances and conservation measures. A population of Kemp's ridleys Lepidochelys kempii was raised in captivity under the same conditions from hatchlings to several years after maturity. Data collected from 14 female Kemp's ridleys at Cayman Turtle Farm over a 16 yr period allowed us to determine mean and variance in age, length, mass, and body condition at maturity, average pre-maturity growth rates, and post-maturity growth rates, as well as interactions among these parameters. Age, length, and mass at maturity exhibited considerable variance, with ranges of 5 to 12 yr, 47.0 to 61.0 cm, and 20.0 to 36.8 kg, respectively. Pre-maturity length growth rate is the best single predictor of AgeSM, accounting for 87% of the variation in AgeSM. Pre-maturity mass growth rate is the best single predictor of size at maturity, accounting for 51 and 65% of variation in length at maturity and mass at maturity, respectively. Although estimates of age and size at maturity from captive Kemp's ridleys cannot be applied to wild populations because of the effect of nutrition, the amount of variation around age and size at maturity in Kemp's ridleys from Cayman Turtle Farm is a good first approximation of inherent (or genetic) variation in these parameters for wild Kemp's ridleys. Population models for Kemp's ridleys that now employ a knife-edge estimate of AgeSM would be improved by incorporating a maturity schedule that reflects the variation in AgeSM.KEY WORDS: Age at sexual maturity · Size at sexual maturity · Indeterminate growth · Lepidochelys kempii · Sea turtle Resale or republication not permitted without written consent of the publisherEndang Species Res 25: 57-67, 2014 This variation is primarily a result of variation in LengthSM and not of growth after sexual maturity, because growth rates are largely negligible after maturity (Carr & Goodman 1970, Bjorndal et al. 1983, 2013a, Broderick et al. 2003, Price et al. 2004. Whether the variation in LengthSM is a result of inherent (or genetic) variation or environmental factors is not known. Whatever the cause, selection of an appropriate population-wide LengthSM for estimating AgeSM is problematic. Several measures have been used; minimum size and mean size of nesting females are the most common.A few records of AgeSM in sea turtles have resulted from marking hatchlings so they can be recognized at maturity or by tagging head-started turtles -turtles that have been reared in captivity usually for a year before release (Bell et al. 2005, Shaver & Wibbels 2007, Limpus 2009). Individual records of age at sexual maturity are very valuable and are not known for most populations. However, as these rare estimates trickle in, the extent to which they can be used to represent population estimates depends upon the amount of variation i...

Ex situ management is an important conservation tool that allows the preservation of biological diversity outside natural habitats while supporting survival in the wild. Captive breeding followed by re‐introduction is a possible approach for endangered species conservation and preservation of genetic variability. The Cayman Turtle Centre Ltd was established in 1968 to market green turtle (Chelonia mydas) meat and other products and replenish wild populations, thought to be locally extirpated, through captive breeding. We evaluated the effects of this re‐introduction programmme using molecular markers (13 microsatellites, 800‐bp D‐loop and simple tandem repeat mitochondrial DNA sequences) from captive breeders (N = 257) and wild nesting females (N = 57) (sampling period: 2013–2015). We divided the captive breeders into three groups: founders (from the original stock), and then two subdivisions of F1 individuals corresponding to two different management strategies, cohort 1995 (“C1995”) and multicohort F1 (“MCF1”). Loss of genetic variability and increased relatedness was observed in the captive stock over time. We found no significant differences in diversity among captive and wild groups, and similar or higher levels of haplotype variability when compared to other natural populations. Using parentage and sibship assignment, we determined that 90% of the wild individuals were related to the captive stock. Our results suggest a strong impact of the re‐introduction programmme on the present recovery of the wild green turtle population nesting in the Cayman Islands. Moreover, genetic relatedness analyses of captive populations are necessary to improve future management actions to maintain genetic diversity in the long term and avoid inbreeding depression.

Age is a fundamental life history attribute that is used to understand the dynamics of wild animal populations. Unfortunately, most animals do not have a practical or nonlethal method to determine age. This makes it difficult for wildlife managers to carry out population assessments, particularly for elusive and long-lived fauna such as marine turtles. In this study, we present an epigenetic clock that predicts the age of marine turtles from skin biopsies. The model was developed and validated using DNA from known-age green turtles (Chelonia mydas) from two captive populations, and mark-recapture wild turtles with known time intervals between captures. Our method, based on DNA methylation levels at 18 CpG sites, was highly accurate with a median absolute error of 2.1 years (4.7% of maximum age in data set). This is the first epigenetic clock developed for a reptile and illustrates their broad applicability across a broad variety of vertebrate species. It has the potential to transform marine turtle management through a nonlethal and inexpensive method to provide key life history information.