Hatchling sea turtles are highly phototactic, a trait that is instrumental in the process of seafinding after emergence from a nest. However, anthropogenic lights can cause hatchlings to misorient towards human developments rather than towards the ocean. To combat this misorientation while still providing adequate lighting for human properties, turtle-safe lights are employed. These lights cause minimal misorientation in hatchlings by employing wavelengths least attractive to hatchlings; however, what “turtle-safe” is, may be species specific. Greens, loggerheads, and leatherbacks have been investigated for threshold of detection, or the lowest intensity light to still illicit a phototactic response, showing higher thresholds for longer wavelengths of light (such as orange or yellow) and lower thresholds for shorter wavelengths (blue or indigo). Hawksbill turtles are underrepresented in the literature of phototactic studies, having never been investigated for thresholds of detection. They may prove more sensitive to light due to their preference for nesting in dense vegetation where light levels are low. Hatchlings for our experiment were collected from fourteen nests over two field seasons (with multiple clutches generally being necessary to determine a threshold intensity) and were kept in ambient climatic conditions for no longer than one hour before testing. To determine the hawksbill hatchling detection threshold for visual light, we used a Y-maze choice experiment where hatchlings were presented with a single-wavelength LED source at one end of the maze and no light source at the other end of the maze. Wavelengths tested were 415 (violet), 470 (blue), 535 (green), 555 (green), 590 (yellow), 601 (orange), and 660 nm (red). The intensity of light was controlled using a series of neutral density filters. Light intensity was measured pre-experimentation using a S400 Optical Meter and S247 Flat-Response Sensor Head situated at the decision point of the maze. Each hatchling was chosen randomly for experimentation and tested only once. To determine threshold intensities, hatchlings were tested using the up-down staircase statistical method, using 1.0 log steps down and 0.3 and 0.7 log steps up. A one-tailed binomial test was used to determine if a significant number of hatchlings were attracted to a specific intensity of light. Hawksbill hatchlings displayed detection thresholds intermediary to those studied in other species at most wavelengths (i.e., they had less or equal sensitivity as greens or loggerheads, and equal or more sensitivity as leatherbacks). The exceptions to this were at 555 nm and 470 nm. Hawksbills were more sensitive to green light of 555 nm than any previously tested species. They were also less sensitive to blue light (470 nm) than any previously tested species. Hawksbill sensitivity to blue light was on the same order of magnitude as that of red light. Red light required the highest intensity to illicit a phototactic response, while green light of 555 nm could illicit a response at the lowest intensity. Our results may be critical for informing standards for beachfront lighting, as we illustrate that even at very low intensities, light across the visual spectrum may still attract hawksbill hatchlings.

Peninsular Malaysia is bordered by the South China Sea and climatically influenced by the El Niño Southern Oscillation (ENSO) which is often drier than usual during El Niño and wetter than usual during La Niña. Malaysia has been very much affected by climate change leading to a worsen ENSO events. Notably, ENSO's impact extends beyond climate, potentially influencing the recovery of the green turtle (Chelonia mydas) populations through variations in hatching success rates which is very sensitive with the changes of temperature. This research examines the correlation between ENSO phases and hatching success at Chagar Hutang Turtle Sanctuary (CHTS), a critical nesting ground for green turtles, which could indicate broader implications for population recovery trends. Leveraging two decades of data (2003-2022) from the Sea Turtle Research Unit (SEATRU) at UniversitiMalaysia Terengganu, we employed statistical analyses to explore this relationship. Nest monitoring and beach patrol records from the CHTS provide a robust dataset for analysis via SPSS software. We specifically focus on the average nesting site air temperatures and corresponding hatching success rates, utilizing multiple regression analysis to understand (i) temporal temperature trends in Terengganu state, (ii) annual mean green turtle hatch rates per clutch, and (iii) the interplay between these temperature trends and hatch rates. Preliminary results suggest a negative correlation between warmer temperatures and hatching success, with an anticipated decrease in hatchlings emergence under these conditions. The findings could signal a significant ENSO-mediated environmental influence on the reproductive viability of Chelonia mydas, shedding light on adaptive strategies crucial for the conservation of this species.

Increasing mean global temperatures due to climate change may potentially threaten organisms with temperature-dependent sex determination (TSD), such as sea turtles, resulting in skewed sex ratios and subsequent population declines. This study expands upon pri thor work, such as Tolen et al. (2021), which found that the relocation of Green Turtle (Chelonia mydas) egg clutches from their natural nest site into artificially constructed nests significantly alter incubation temperatures and sex ratios, raising the incubation temperature by 1.8°C and increasing the proportion of female hatchlings by 45% at Chagar Hutang and Perhentian Islands, Malaysia. Continuing this line of research, our current study focuses on the sex ratio estimation of Green Turtle hatchlings in 2023 at Chagar Hutang, one of Peninsula Malaysia's most important nesting sites, located on Redang Island. We employed a dual approach: (i) a direct method involving gonad histology on 74 deceased hatchlings to examine their sex, and (ii) an indirect method using 22 unit temperature data loggers in 11 incubating nests to monitor nest incubation temperatures during the thermosensitive period (TSP). Satellite-derived weather and sea surface temperature (SST) data for the entire year were also obtained from the Malaysian Meteorology Department to estimate the 2023 sex ratio. Preliminary results indicate a continuation of the trend toward a highly female-biased sex ratio for the Chagar Hutang green turtle hatchlings, which aligns with earlier findings. These results underscore the need for immediate conservation measures to mitigate the potential long-term implications of climate change and management practices on the sex ratio and viability of sea turtle populations.

Leatherback sea turtle (Dermochelys coriacea) nests have highly variable hatching success that trends lower than that of other sea turtle species. Many eggs fail and show no signs of embryonic development when necropsied. To understand this egg failure, it is fundamental to identify whether eggs with no signs of development are infertile or have very early-stage embryos that die before signs of development become apparent during necropsy. To investigate the rates of infertility versus early-stage death, 300 freshly oviposited leatherback eggs were collected from 10 nests and incubated ex situ in the lab. These eggs were closely monitored throughout incubation, and if egg chalking (a sign of development resuming after diapause) did not occur, eggs were necropsied. Perivitelline membranes of necropsied eggs (n=8) were collected and analyzed for the presence of sperm or embryonic cells using fluorescent microscopy protocols that have been used successfully in avian and other reptile fertility studies. These techniques previously were not confirmed to work in sea turtles. This study positively identified the presence of embryonic cells in the perivitelline membranes of 3 out of the 8 unchalked eggs, with the other 292 eggs either resulting in successful hatching or in dead embryos. This resulted in a fertility rate of 98%. Additionally, this study successfully utilized fluorescent microscopy in degraded eggs from in situ nests. Our results are the first to demonstrate high fertility in leatherback sea turtle nests of southeastern Florida and validate the use of fluorescent microscopy protocols to detect fertility in sea turtles.

Before the emergence of sea turtle hatchlings is completed, there is a period of inactivity on the surface, defined in this work as activation time. In order to characterize and understand the factors involved in this activation time, 85 Caretta caretta nests were monitored by photo-trapping and 25 thermometers were placed in the sand of a hatchery on Ervatão beach (Boa Vista Island, Cape Verde). The camera traps were useful in the study of the activation time, defined as the time from when a first movement or hatchling was detected from the surface until at least one hatchling fully emerged from the nest. The activation time proved to be highly variable and had a mean of 39 minutes and 24 seconds. Of the variables analyzed, hatching and emergence successes, the number of hatchlings, and incubation time were the only variables with a statistically significant effect on the activation time. Nests with larger groups of hatchlings and higher hatching and emergence successes had longer activation times. This may be due to a higher volume of hatchlings in the nest chamber, which enables their detection from the surface to be earlier. These longer activation times may also be due to higher rates of O² consumption and CO² production and/or early excavation due to group effect, whereby turtles would arrive more tired at the surface requiring longer resting times. In addition, temperature fluctuations within the nests could also be also responsible for the longer activation times. However, hatchlings from nests with longer incubation times had shorter activation times, probably due to increased body and locomotor development. The activation time is an understudied stage of the emergence process, but of great conservation interest because of its high vulnerability to predation.

Nesting sites within the Caribbean region are home to approximately half of the global hawksbill
turtle (Eretmochelys imbricata) nesting population. Given the Critically Endangered status of
hawksbill turtles by the IUCN and the changing climate, it is crucial to assess hatchling
production and investigate the effects of sand temperature and water content on index nesting
beaches. Recent research has identified Sandy Point National Wildlife Refuge (SPNWR) in St.
Croix, US Virgin Islands, as a nesting beach with a high density of hawksbill nesting activity,
with nest numbers increasing 4.5% yearly since 2003. Our study analyzed hawksbill hatch
success from 2021 to 2023, nest incubation temperatures from 2021 to 2023, and nest water
content for the 2023 peak season. We used nest incubation temperatures to predict hatchling sex ratios and investigate the relationship between sand temperature and hatch success. Elevated sand temperatures during development have multiple consequences for hatchling production and survival. Nest incubation temperatures of 35°C or higher have lower hatch success rates. In this study, nest incubation temperatures from the peak season in 2021 to 2023 indicate that SPNWR is a mainly female hatchling-producing beach. However, hawksbill nests incubating outside the peak season are exposed to sand temperatures 2°C lower than the pivotal temperature for hawksbills. Also, the average hatch success of clutches laid outside peak season months was 10% higher than within peak season, suggesting seasonal differences in the survival of eggs and the sex ratios of hatchlings. Several clutches laid in the 2021 and 2023 peak seasons experienced incubation temperatures above 35°C. Measurement of nest water content of nests showed that nests were exposed to a wide range of sand water contents, ranging from 0.037 to 0.67 m³/m³. Clutches laid on the southern shore of Sandy Point had higher sand water content and lower incubation temperatures compared to the western and northern shores. Additionally, linear modeling identified a negative relationship between hatch success, the average daily moisture range, and the average daily maximum temperature in nests. These findings suggest that as climate change progresses, provided nesting seasons do not shift, hawksbill hatchling production in the Caribbean may decrease and should continue to be monitored.

The Arabian Peninsula is characterised by high levels of solar radiation and low levels of rainfall, with many species inhabiting the region at the edge of their thermal tolerance. None more so than species that display temperature-dependent sex determination such as sea turtles where population demographics are sensitive to environmental temperature. Previous studies in the region show sand temperature profiles at many nesting sites above the supposed pivotal temperature and in some cases above the thermal maximum. This suggests that populations persisting in the region are either highly feminized, suffer high mortality or, alternatively, adapted to elevated incubation temperatures. During the 2023 green turtle nesting season 20 nests were equipped with HOBO temperature and movement G-loggers to monitor profiles during incubation. After 63 days, loggers were retrieved and the nests were excavated to determine hatching success. Movement loggers allow us to define incubation duration and establish the thermal reaction norm of embryo growth. Based on this model, the embryonic stages for any nest with a time series of temperature can be predicted and the thermosensitive period of development for sex determination can be inferred. The predicted sex ratio is then determined using a constant temperature equivalent (CTE) model taking into the growth rate of the embryo, the time at each temperature, the force of the effect of temperature during the thermosensitive period and the thermal reaction norm of sexualization for each temperature. Unsurprisingly, high incubation temperatures between 30-35°C were recorded for nests monitored. For embryo growth our models predicted a decline in growth rate at temperatures greater than 30°C, suggesting a negative effect on green turtle embryos at high temperatures, likely producing hatchlings which are smaller and less fit. Furthermore, the pivotal temperature was estimated at 30.06°C suggesting a highly feminized sex ratio, yet, the primary sex ratio was projected at 86% female, starkly less than other estimates for other green turtle populations. We attribute this to a wide range in transitional temperature (4.67°C), where both males and females are produced within a single clutch. Here, we observe a differential response in embryo growth and sexualisation to temperature as temperatures higher than 30°C have a lower influence on CTE because of the lowered growth rate. It seems that turtles in this region are well-adapted to elevated temperatures in some aspects of their biology (sex ratio) but not others (embryo development rate declines for temperatures above 30°C). Monitoring sea turtle populations persisting at higher incubation temperatures in extreme environments like the Arabian Peninsula can be used as a proxy to estimate how other populations worldwide may respond to global warming and shed light on the plasticity of these organisms under thermal stress.

Offspring survival is a vital demographic factor that drives population success. To put it simply, there is a trade-off between parental investment in individual offspring and their survival. In the case of sea turtles, where there is no parental care, egg predation by invasive and native species can have severe impacts, and negatively affect species recovery. On the island of Diego Garcia, Chagos Archipelago (Indian Ocean), we assessed the levels of egg predation within green turtle (Chelonia mydas) clutches between 2021-2022. We found that native coconut crabs (Birgus latro) and ghost crabs (Ocypode spp.) as well as introduced black rats (Rattus rattus) predated on eggs, entering nests by digging tunnels in the sand. Whole eggs were often removed from clutches, made apparent through observations and differences between initial clutch and final excavation counts. Clutch size at oviposition (mean = 127.8 eggs, range = 74-176, n = 23) was significantly larger than at excavation (mean = 110.9 hatched and unhatched eggs, range = 9-147, n = 16), i.e., a 13.2% decrease. Where both measurements at oviposition and excavation were available for the same clutch there was a similar decrease of 13.9%. On other occasions, egg predation was recorded where egg contents were eaten within the nest. Ultimately, hatching success was 64.9%, while 3.1% of eggs were predated in the nest, 18.1% did not survive incubation and 13.9% of eggs were removed from the nest.

To place our results in the context of sea turtle egg predation around the world, we reviewed evidence from 34 sites and identified 36 predators that were either native (e.g., crabs and goannas, n = 30) or invasive (e.g., rats and pigs, n = 8). A predator could also be identified and reported as both native and invasive (e.g., dogs) depending on site. Globally, the most important predators were medium sized mammals (e.g., pigs, red foxes), crabs (e.g., Ocypode spp.) and goannas (Varanus spp.). To the best of our knowledge, we report the first cases of coconut crab and rat predation on sea turtle eggs. In conclusion, we highlight the need to consider whether predation intervention is necessary and whether nest protection and/or invasive predator eradication may be used to increase egg survival and in turn population recovery.

Bioko Island, Equatorial Guinea, is a major nesting beach within the southeast Atlantic regional management unit, a region whose population is considered data deficient. Despite Bioko’s importance, research pertaining to the island’s leatherback nest ecology and reproductive success remains limited. Here, we report on nest parameters and describe the long-term hatching and emergence success rates of marked in situ leatherback nests that made it to full incubation, on Bioko Island. Data was collected over nine nesting seasons on two beaches, identified as Beach E (2008–2014) and Beach D (2016–2019). We calculated seasonal and total average hatching success (H), emergence success of all nests (E_A; H ≥ 0), and emergence success of hatched nests (E_H; H > 0) for both beaches. The average H on Beach E was 0.21 ± 0.03 (n = 126), E_A was 0.15 ± 0.02 (n = 126), and E_H was 0.31 ± 0.04 (n = 63). On Beach D, the average H was 0.64 ± 0.07 (n = 21), E_A was 0.56 ± 0.08 (n = 21), and E_H was 0.69 ± 0.06 (n = 17). H and E_A varied by season on Beach E but E_H did not, none of these varied by season on Beach D. The major outliers on Beach E were the 2011-2012 and 2012-2013 seasons, which were significantly lower than the other seasons but not each other, indicating a likely shift in weather/ocean patterns. On average, nest temperature was lower on Beach E (27°C) than on Beach D (33°C), which could relate to the dynamics of the beach, or the multi-annual variation in weather patterns. We found that hatching success was higher in nests with more total shelled albumin gob (SAGs) mass (Beach E). The mass of SAGs in a nest increased as the total egg mass increased; on average, SAG mass made up between 6.2% (Beach E) and 9.9% (Beach D) of total clutch mass. Further, emergence success (E_A) was also higher in nests with heavier eggs (both average and total mass). Finally, for all nests, larger females (curved carapace length) laid heavier eggs, and therefore had generally higher hatchling and emergence success. Larger turtles did not, however, lay more eggs. These findings provide insight into the reproductive success of leatherback nests on one of the most productive nesting beaches. The spatial and temporal variations, and relatively low hatching success on Beach E reported here, may provide information to stakeholders who aim to implement management strategies to boost the reproductive success of leatherbacks nesting on Bioko Island.