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Globally, nest counts for many sea turtles now routinely exceed pre-conservation levels but also exhibit increased inter-annual variability. Mixed trend interpretations support population growth constraints but differ regarding why. Here we used a closed-loop population simulator to report generalized patterns of demographic change under assumptions of random variability that tended both above and below the null model scenario of no change over decades. Random changes in nine life history parameters spanning sea turtle hatching to eventual sexual maturity from 1950 through 2018 provided context for comparison with three decades of published nesting data for a globally important loggerhead sea turtle ( Caretta caretta ) population through 2018. Six demographic metrics (nests, mature abundance, immature abundance, mature sex ratio, immature sex ratio, and neritic survival equivalent [NSE]) computed from simulations better predicted each other than their respective prediction by any of the annual simulator inputs. Irrespective of maturity status, abundance fluctuated widely and inversely to age group sex ratio. The ratio of older (ages 20–29) to younger (ages 10–19) individuals provided the best lagged (21 years) prediction of annual nest counts. Our novel findings substantiate demographic metrics for monitoring, plus forecast a future annual nest count oscillation even with high survival (0.93).

Restricted range, and subsequently small population size, render Kemp’s ridley sea turtles ( Lepidochelys kempii ) the most globally endangered sea turtle species. For at least two decades preceding conservation, high egg harvest rates reduced annual cohort recruitment. Despite > 50 years of dedicated conservation, annual nest counts remain well below a landmark 1947 level. Prior studies attribute less robust than anticipated nest count rebound to multiple contemporary concerns; however, analyses herein convey optimistic interpretation. In objective 1, improved analysis of the ratio of hatchlings to nests since 1966 suggested age structure stabilization as a more likely basis for nest count trends after 2005 than density-dependent effects. In objective 2, multiple regression revealed a lagged (≤ 13 years prior) climate influence on nests (adj. r 2  = 0.82) and hatchlings per nest (adj. r 2  = 0.94) during 2006–2022. In objectives 3 and 4, a simulator modeled population response to changes in a suite of demographic rates including survival. Across 32 models, high survival and dynamic cohort sex ratio, sexual maturity age, and the ratio of clutch frequency to remigration interval best explained nesting trends during 1966–2022. These novel findings provide alternative perspective for evaluating species recovery criteria and in turn refine future nest trend expectations.

Determining sex ratios of endangered populations is important for wildlife management, particularly species subject to sex-specific threats or that exhibit temperature-dependent sex determination. Sea turtle sex is determined by incubation temperature and individuals lack external sex-based traits until sexual maturity. Previous research utilized serum/plasma testosterone radioimmunoassays (RIA) to determine sex in immature/juvenile sea turtles. However, there has been a growing application of enzyme-linked immunosorbent assay (ELISA) for wildlife endocrinology studies, but no study on sea turtles has compared the results of ELISA and RIA. This study provides the first sex ratio for a threatened East Pacific green sea turtle (Chelonia mydas) foraging aggregation, a critical step for future management of this species. Here, we validate a testosterone ELISA and compare results between RIA and ELISA of duplicate samples. The ELISA demonstrated excellent correspondence with the RIA for providing testosterone concentrations for sex determination. Neither assay proved reliable for predicting the sex of reproductively active females with increased testosterone production. We then applied ELISA to examine the sex ratio of 69 green turtles foraging in San Diego Bay, California. Of 45 immature turtles sampled, sex could not be determined for three turtles because testosterone concentrations fell between the ranges for either sex (females: 4.1-113.1 pg/mL, males: 198.4-2,613.0 pg/mL) and these turtles were not subsequently recaptured to enable sex determination; using a Bayesian model to predict probabilities of turtle sex we predicted all three 'unknowns' were female (> 0.86). Additionally, the model assigned all turtles with their correct sex (if determined at recapture) with 100% accuracy. Results indicated a female bias (2.83F:1M) among all turtles in the aggregation; when focusing only on putative immature turtles the sex ratio was 3.5F:1M. With appropriate validation, ELISA sexing could be applied to other sea turtle species, and serve as a crucial conservation tool.

A recent analysis suggested that historical climate forcing on the oceanic habitat of neonate sea turtles explained two-thirds of interannual variability in contemporary loggerhead (Caretta caretta) sea turtle nest counts in Florida, where nearly 90% of all nesting by this species in the Northwest Atlantic Ocean occurs. Here, we show that associations between annual nest counts and climate conditions decades prior to nest counts and those conditions one year prior to nest counts were not significantly different. Examination of annual nest count and climate data revealed that statistical artifacts influenced the reported 31-year lag association with nest counts. The projected importance of age 31 neophytes to annual nest counts between 2020 and 2043 was modeled using observed nest counts between 1989 and 2012. Assuming consistent survival rates among cohorts for a 5% population growth trajectory and that one third of the mature female population nests annually, the 41% decline in annual nest counts observed during 1998-2007 was not projected for 2029-2038. This finding suggests that annual nest count trends are more influenced by remigrants than neophytes. Projections under the 5% population growth scenario also suggest that the Peninsular Recovery Unit could attain the demographic recovery criteria of 106,100 annual nests by 2027 if nest counts in 2019 are at least comparable to 2012. Because the first year of life represents only 4% of the time elapsed through age 31, cumulative survival at sea across decades explains most cohort variability, and thus, remigrant population size. Pursuant to the U.S. Endangered Species Act, staggered implementation of protection measures for all loggerhead life stages has taken place since the 1970s. We suggest that the 1998-2007 nesting decline represented a lagged perturbation response to historical anthropogenic impacts, and that subsequent nest count increases since 2008 reflect a potential recovery response.

Sixteen satellite-tagged adult male loggerhead sea turtles ( Caretta caretta) dispersed widely from an aggregation near Port Canaveral, Florida, USA (28°23′N, −80°32′W) after breeding. Northbound males migrated further (990 ± 303 km) than southbound males (577 ± 168 km) and transited more rapidly (median initial dive duration = 6 (IQR = 4–16) versus 19 (IQR = 10–31) min, respectively).. Migration occurred along a depth corridor (20–40 m) except where constricted by a narrow continental shelf width. Males foraged in areas 27 ± 41 km 2  day −1 at locations <1–80 km from shore for 100.1 ± 60.6 days, with variability in foraging patterns not explained by turtle size or geography. Post-breeding dispersal patterns were similar to patterns reported for adult female loggerhead sea turtles in this region and adult male loggerhead sea turtles elsewhere in the northern hemisphere; however, foraging ground distributions were most similar to adult female loggerhead sea turtles in this region.

Marine turtles exhibit temperature-dependent sex determination (TSD), and there is widespread concern that global warming is raising nest incubation temperatures, resulting in increasingly female-skewed sex ratios in “feminized” populations. We assessed the sex ratio of a mixed-stock aggregation of immature green turtles ( Chelonia mydas ) at a midocean developmental foraging ground in the Northwest Atlantic from 1975 to 2018. We used plasma testosterone concentrations, measured by radioimmunoassay (RIA) and calibrated by laparoscopy, to determine the sex of 2,724 green turtles captured 3,940 times in Bermuda (32°18′ N, 64°46′ W) waters. A logistic regression model correctly predicted the sex of 99.5% of turtles (189/190) with associated testosterone concentrations whose sex had been verified via laparoscopy. Empirical evaluation of the trend in sex ratio using four related data sets showed a significant increase (2.8–4.0% yr −1 ) in the sex ratio (F/M) over the course of the study. Using growth rates to predict the year of arrival of turtles in Bermuda, we estimated the sex ratio of recruiting cohorts over 4 decades. Mixed-stock analysis of mtDNA sequences of 602 turtles that recruited to Bermuda between 1970 and 2018 suggested that multiple, geographically dispersed rookeries contributed to the Bermuda aggregation making it regionally representative. Changes in rookery contributions and strong population increases at certain rookeries may partly explain the increasing trend in the sex ratio. But the steady rate of increase over decades and the increasing female percentage of arriving cohorts are consistent with impacts of global warming at source rookeries.

Health assessments of endangered wildlife are essential for conservation and management, as populations cannot recover if the individuals within them are unhealthy. We analyzed blood analytes in immature Kemp’s ridley sea turtles, established reference intervals and identified changes in blood analytes associated with growth. Abstract Health assessments of wildlife species are becoming increasingly important in an ever-changing environment. Kemp’s ridley sea turtles (Lepidochelys kempii; hereafter, Kemp’s ridleys) are critically endangered and incur several on-going threats to their population recovery; therefore, it is imperative to advance the understanding of baseline blood analyte data as a diagnostic and monitoring tool. For in-water, trawl-captured, immature Kemp’s ridleys (minimum N = 31) from Georgia, USA, the objectives of this study were to (1) establish reference intervals (RIs) for packed cell volume (PCV) and 27 plasma biochemistry analytes and (2) determine length-specific relationships in blood analytes. We observed significant positive correlations between minimum straight carapace length and PCV, amylase, calcium:phosphorus ratio, cholesterol, magnesium, triglycerides, total solids, total protein and all protein fractions (e.g. alpha-, beta- and gamma-globulins); aspartate aminotransferase and chloride showed significant negative relationships. These results suggest that certain blood analytes in Kemp’s ridleys change as these animals grow, presumptively due to somatic growth and dietary shifts. The information presented herein, in due consideration of capture technique that may have impacted glucose and potassium concentrations, represents the first report of blood analyte RIs for Kemp’s ridley sea turtles established by guidelines of the American Society for Veterinary Clinical Pathology and will have direct applications for stranded individuals in rehabilitative care and for future investigations into the health status of wild individuals from this population.

Total mercury concentrations were measured in diamondback terrapin blood and scutes collected from four sites in South Carolina, USA, and at a superfund site in Brunswick, Georgia, USA. There was a strong correlation between mercury concentrations in the two terrapin body compartments (Kendall's tau = 0.79, p < 0.001). Mercury concentrations in terrapin scute and blood and in salt marsh periwinkles, Littoraria irrorata, were significantly higher in Brunswick (scute x̄ = 3810.2 ng/g, blood x̄ = 746.2 ng/g) than from all other sites (scute x̄ = 309.5 ng/g, blood x̄ = 43.2 ng/g, p < 0.001). Seasonal fluctuations of total mercury in the blood and scutes of terrapins collected in the Ashley River, South Carolina, were significantly lower in August than in April, June, or October in blood (p < 0.001); however, scute concentrations did not vary seasonally. Overall, we found higher concentrations of mercury in the scutes of females than males (n = 32, p < 0.05). Larger females may preferentially prey on larger food items, like large periwinkles, which had significantly higher mercury levels in their body tissues than smaller periwinkles (p < 0.001). Methylmercury levels in terrapin scutes were measured, revealing that 90% of the total mercury stored in this compartment was in the organic form. A methylmercury biomagnification factor of 173.5 was calculated from snails to terrapin scutes, and we found that mercury levels in scutes were representative of the mercury levels in other compartments of the ecosystem. These findings show that terrapin scutes are good predictors of mercury pollution and that this species could be used as a bioindicator for assessing mercury contamination of estuarine systems.