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To characterize the movements and habitat use of juvenile green turtles ( Chelonia mydas ) in benthic developmental habitat, we deployed Fastloc-GPS-enabled satellite transmitters on 16 individuals captured as part of a multi-decade study of green turtles on the Bermuda Platform. We characterized residence areas, distinct use areas within them, and seasonal movements based on an average of 562 Fastloc-GPS positions and 284 tracking days per turtle. We estimated residence area sizes using traditional home range methods, e . g ., 90% utilization distribution (UD) (mean 2.29 ±2.71 km 2 ) and 50% UD (mean 0.54 ±0.69 km 2 ). Total residence area size increased significantly over the 8-year study, from <1 km 2 before 2013 to ≥3 km 2 in 2018 (R 2 = 0.51, F1,14 = 14.55, p = 0.0019), corresponding to a period of decline in seagrass habitat and suggesting increased foraging effort. We identified three types of distinct use areas within residence areas where tracked turtles typically exhibited behavioral fidelity: foraging, resting, and cool weather refugia. These distinct use areas were smaller than high-use areas from previous studies; e . g ., seagrass meadow foraging areas averaged 0.05 km 2 . Most turtles made daily transits between foraging and resting sites; for some individuals, these involved crossing frequently used vessel navigation channels. Seasonal variation in behavior suggested that the overwintering strategy for green turtles on the Bermuda Platform involves “optional dormancy,” during which turtles spent less time on seagrass meadows and made brief excursions to distinct deeper habitats. Four individuals made directed (mean path straightness = 0.93 ±0.02 SD) developmental migrations away from Bermuda toward known adult foraging range. Results of our study further knowledge of the green turtle life cycle at a high-latitude site; they demonstrate that green turtles show fidelity to distinct use areas within developmental habitats over many years and exhibit seasonal movements.

To characterize the movements and habitat use of juvenile green turtles (Chelonia mydas) in benthic developmental habitat, we deployed Fastloc-GPS-enabled satellite transmitters on 16 individuals captured as part of a multi-decade study of green turtles on the Bermuda Platform. We characterized residence areas, distinct use areas within them, and seasonal movements based on an average of 562 Fastloc-GPS positions and 284 tracking days per turtle. We estimated residence area sizes using traditional home range methods, e.g., 90% utilization distribution (UD) (mean 2.29 ±2.71 km.sup.2) and 50% UD (mean 0.54 ±0.69 km.sup.2). Total residence area size increased significantly over the 8-year study, from <1 km.sup.2 before 2013 to [greater than or equal to]3 km.sup.2 in 2018 (R.sup.2 = 0.51, F1,14 = 14.55, p = 0.0019), corresponding to a period of decline in seagrass habitat and suggesting increased foraging effort. We identified three types of distinct use areas within residence areas where tracked turtles typically exhibited behavioral fidelity: foraging, resting, and cool weather refugia. These distinct use areas were smaller than high-use areas from previous studies; e.g., seagrass meadow foraging areas averaged 0.05 km.sup.2 . Most turtles made daily transits between foraging and resting sites; for some individuals, these involved crossing frequently used vessel navigation channels. Seasonal variation in behavior suggested that the overwintering strategy for green turtles on the Bermuda Platform involves \"optional dormancy,\" during which turtles spent less time on seagrass meadows and made brief excursions to distinct deeper habitats. Four individuals made directed (mean path straightness = 0.93 ±0.02 SD) developmental migrations away from Bermuda toward known adult foraging range. Results of our study further knowledge of the green turtle life cycle at a high-latitude site; they demonstrate that green turtles show fidelity to distinct use areas within developmental habitats over many years and exhibit seasonal movements.

Mortality from being struck by a motorized watercraft is considerable for many aquatic vertebrates around the world, including sea turtles. We studied stranded (i.e., dead, sick, or injured) sea turtles found in Florida, USA, during 1986–2014 and identified those with sharp force or blunt force injuries indicative of a vessel strike. About a third of stranded loggerheads (Caretta caretta), green turtles (Chelonia mydas), and leatherbacks (Dermochelys coriacea) had a vessel-strike injury (VSI). The frequency of this injury was lower but still substantial for stranded Kemp’s ridleys (Lepidochelys kempii; 26.1%) and hawksbills (Eretmochelys imbricata; 14.8%). Over the study period, the annual number of stranded loggerheads, green turtles, and Kemp’s ridleys with a VSI increased as did the annual number of vessels registered in Florida. Eighty-one percent of the stranded turtles with a VSI were found in the southern half of Florida and 66% of those were found along the southeast coast. By coastal county, the proportion of stranded sea turtles with a VSI was positively related to the mean annual number of registered vessels. The percentage occurrence of a VSI was highest for adult loggerheads, green turtles, and leatherbacks, and reproductively active individuals appeared to be particularly vulnerable to these injuries. We conducted necropsies on 194 stranded sea turtles with a VSI and concluded that this injury was the cause of death or the probable cause of death in ≥92.8% of these cases. During 2000–2014, we estimate that the mean annual numbers of stranded sea turtles that died from a VSI were 142–229 loggerheads, 101–162 green turtles, 16–32 Kemp’s ridleys, 4–6 leatherbacks, and 2–4 hawksbills. Considering that only about 10–20% of sea turtles that died likely washed ashore, the overall annual mortality may have been 5–10 times greater than that represented by strandings. Most of the significant clusters of stranded sea turtles with a VSI occurred at inlets or passes and the probability that a stranded sea turtle had a VSI decreased with increasing distance from inlets or passes, navigable waterways, and marinas. We suggest focusing initial management efforts on reducing watercraft-related mortality for all sea turtle species around 8 inlets in southeast Florida, reproductively active loggerheads and green turtles along the coast of southeast Florida, and Kemp’s ridleys and adult male loggerheads at passes along the coast of southwest Florida. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

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.

Dispersal is a fundamental driver of population dynamics and connectivity in marine organisms but is often poorly characterized due to the cryptic nature of pelagic life stages. The initial ‘lost year’ model proposed for surface-pelagic juvenile marine turtles assumed that they passively drifted following a brief swim-frenzy stage. However, mounting evidence indicates that these juveniles engage in directed swimming that affects their trajectories. Dispersal modeling (DM) offers an inferential approach to estimate distributions and connectivity, but model validation remains challenging with sparse empirical data. We sequenced mitochondrial DNA from 121 surface-pelagic juvenile green turtles Chelonia mydas collected in the northern Gulf of Mexico (GoM) from 2009 to 2015 and conducted mixed stock analyses (MSAs) to compare contribution estimates with published DM predictions assuming passive drift. MSA indicated that a large majority of juveniles originated from local nesting populations within the GoM, with contributions markedly divergent from published DM predictions assuming passive drift. DM predictions for western GoM rookeries fell well below their MSA 95% credible intervals (DM: 2%, MSA point estimates: 49–58%), whereas the DM predictions for Caribbean Mexico (Quintana Roo) were larger than the MSA 95% credible intervals (DM: 51–65%, MSA point estimates: ≤5%). Therefore, directed swimming by surface-pelagic green turtles, recently demonstrated via telemetry, likely has profound consequences for their dispersal at the population scale. These results emphasize the value of additional in situ studies of this life stage, as well as the need to integrate swimming behavior into DM to refine fine-scale predictions.