ISTS42 Program/Agenda

Understanding the effect of increasing temperatures on organisms at the population level, and their resilience to these changes, is of paramount importance to promote their conservation in a warming planet. Climate change poses a particular threat to oviparous vertebrates that exhibit temperature-dependant sex determination (TSD) through suboptimal sex allocation, making the relationship between sex ratio and incubation temperature an important life history parameter for conservation. For sea turtles, warmer temperatures reduce the proportion of males being produced, which may reduce population viability if extreme feminisation occurs. At Tortuguero beach, Costa Rica the largest green turtle rookery in the Atlantic Ocean, the sex ratio has remained unstudied since the 1980s. Here we characterised the thermal incubation environment at this site using an embryo growth model and in-situ empirical data (2017-2021) to define the pivotal temperature (PT) (ratio 1:1) and transitional temperature range (TRT) without the need for lethal sampling of hatchlings and thus estimate primary sex rations of hatchlings produced. A PT of 29.09^oC and TRT of 26.85 – 31.34^oC (4.49^oC range) resulted in estimated primary hatchling sex ratio of 76% female (range = 71% -88% female between 2017-2021). Microhabitat had a significant influence on sex ratio (χ ²_{(4, 248)} = 35.50, P < 0.001). The highest proportion of males were seen to be produced during the months of June, and within the shaded vegetation zone. These results will be useful for the future monitoring of climate change impact on sex ratios in green turtles within the Atlantic basin.

Sea turtles are responding to climate change by colonizing new nesting areas. The recent increase in loggerhead sea turtle (Caretta caretta) nesting activity in the western Mediterranean seem to reflect a process of colonization that may be mediated by global warming. Since 2001, sporadic nesting has been recorded on Spanish Mediterranean beaches. However, since 2014, nesting activities have been recorded every year. Out of the 150 nesting activities recorded until summer 2023, 70 were egg-laying activities, with an average of 5.38±7.65 nests per year (2001-2023).

In 2023, a total of 29 confirmed nests and 17 other activities were recorded, which suggests the establishment of a nesting population on the Spanish Mediterranean beaches. The numbers in 2023 nearly tripled the previous maximum number of nesting activities per year recorded in Spain (11 in 2020). Additionally, nesting occurred in all Spain's Mediterranean regions, with more intensive activity observed in the northern half of the Spanish Mediterranean coast (Balearic Islands, Catalonia, and the Valencia Community). Although a few areas have multiple nests recorded, nesting is still scattered throughout the coastline, and no beaches with regular nesting have been identified yet.

Records from 2023 confirmed that the nesting season lasts from early June to the end of August, but this year, the earliest and latest nesting date records were broken. The finding of a clutch hatched in October 2023 confirms previous observations that hatchling emergences can occur until this month.

At least 8 of the 70 nests recorded since 2001 were discovered either after observing hatchlings emerging from the nest or crawling by the beaches attracted by promenade/urban lights (five), discovered when uncovered by waves after storm surges (two), or depredated (one); without knowing neither the time of nesting nor the nesting female. This suggests that several clutches laid on our beaches go undetected every year, which means that nesting numbers could be even higher than reported.

Despite increased monitoring efforts and awareness campaigns made by Spanish and regional administrations and institutions in all regions, regular monitoring is not in place along most of the Spanish coast due to scattered nesting activity..

Tourist activity in Spain is massive in summer months. The Spanish Mediterranean receives millions of tourists from other parts of Spain and other European countries every summer, and the night-time activity on beaches results in a considerable source of acoustic and light pollution that hampers sea turtle nesting activity. Beach cleaning with machinery or urban development near beaches also pose further threats to nesting and hatching success. Therefore, beach monitoring efforts should be increased to protect nest, and if necessary, clutches should be relocated for successful incubation. Moreover, working with local authorities is crucial to ensure the coexistence of tourism, an economically significant activity in the area, with the increasing sea turtle nesting activity on Spanish Mediterranean coasts. Considering the increasing trend observed in Spain and in other countries of the western Mediterranean, this nesting activity should no longer be considered sporadic but indicative of new nesting populations.

Increasing atmospheric and nearshore sea surface temperatures pose a significant threat to many sea turtle populations through feminization of hatchling sex ratios, diminished hatchling fitness, and reduced hatchling production. The intrinsic ability (or lack thereof) of nesting females to counteract such climate change effects through changes in nesting phenology, latitudinal distribution, or microclimate selection has significant implications for conservation management. Temperate nesting beaches are of particular interest as these may provide significant male contributions to the operational sex ratios at in-water breeding sites and could serve as refugia for more tropical nesting populations to move into. Bald Head Island, North Carolina, USA is a regionally important temperate beach which lies toward the northern limit of the loggerhead sea turtle (Caretta caretta) nesting range in the western North Atlantic. Previous work demonstrated declining incubation durations coincident with increasing seasonal air temperatures and decreasing precipitation from 1991 to 2015. Mean incubation durations of in situ undisturbed nests fell from 59.2 days to 52.5 days during this period, corresponding to an increase in estimated female sex ratios from 55% to 88%. However, despite a sustained increasing trend in air temperature, mean incubation durations from 2019 to 2023 have increased to 57.4 days – durations not seen since the mid-2000s – with an estimated female sex ratio of 69%. Preliminary analyses suggest recent increases in precipitation were partly responsible for this observed lengthening, meaning biological or behavioral factors are likely responsible for the remainder. Nests laid earlier in the season or on the eastern aspect of the island have longer incubation durations, but there was no observed trend in phenology or alongshore distribution through time to suggest shifts toward these conditions. Additional trends such as maternal identity, clutch size, and cross-shore nest placement are still under investigation to determine their respective contributions to the recent increase in male hatchling production. Understanding the extent and limits of this intrinsic capacity of sea turtles to adjust their reproductive efforts to changing climatic conditions will help us to determine if, when, and which management interventions may become necessary to preserve this threatened species throughout their range.

Marine turtles are highly migratory species that utilize various habitats for development, reproduction, and foraging. Protecting these vital habitats is crucial for conserving marine turtle populations. Layang Layang (Swallow Reef), an oceanic atoll within the Spratly Islands under the Malaysian administration, about 300 km northwest of Kota Kinabalu, Sabah, Malaysia, has been previously identified as a foraging area for the green turtles (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata). In 2022, comprehensive surveys, on the beach and in water, were carried out to update our knowledge of the marine turtles in Layang Layang. During these surveys, a total of 25 turtles were sighted over four days of diving across all dive sites, with an occurrence of 0 to 4 individuals observed per dive. The central lagoon seemed to be a favored foraging spot for immature green turtles with an observed surfacing rate of 7 to 10 turtles per hour. These smaller turtles (<60 cm) likely recently completed their oceanic phase, but further investigations are needed to confirm this. Interestingly, we discovered evidence of marine turtles nesting on the reclaimed beach, marking the first documented instance of nesting within the Spratly Islands. The presence of marine turtle body pits provides strong evidence of nesting activity in the area. In-water surveys also revealed an outbreak of crown-of-thorns starfish and a significant decrease in coral cover. Recognizing the importance of Layang Layang as a foraging and nesting site for marine turtles, we emphasize the need to protect these habitats and consider designating Spratly Islands as an international marine park, despite political disputes over its affiliation. The results of this survey are important as they establish a significant baseline dataset for developing effective conservation strategies and management plans, vital for safeguarding these migratory species and their habitats.

Generally known that ecological patterns and other environmental elements influence the behavior of neonates as well as their success in hatching and rate of emergence. Also, there are other threats such as predators, is an important source of mortality for the eggs and hatchlings of sea turtles. Turtle nesting areas typically contain a mixture of vegetated and non-vegetated habitats, and habitat selection by both nesting turtles and nest predators can lead to uneven patterns of predation risk across the landscape.

These makes extremely important to study how these processes work and relate to the nesting of sea turtle populations, as this knowledge can be used in nest translocation and protection programs.

It is worth mentioning the lack of published work comparing species emergence patterns. Our goal in this study is to identify and compare emerging patterns between the three species hatchlings. Additionally, determine whether the emergence process and predation are related.

In northwest Costa Rica, on the Gulf of Papagayo (10° 400N, 85° 390W), is Cabuyal Beach, an energetic beach that regularly changes throughout each season. Different habitats can be found along the shore; at the southern end is an open estuary linked to a mangrove, and the forest stretches behind it. In contrast, the northern end is more suited for turtle nesting since it is rocky with areas of sand. During the sea turtle reproductive season of 2018–2019, the sampling was done between January and March.

The cameras were positioned close to the nests (behind or laterally) close to their emergence or that had emergency indicators (sand depression or hatchlings). This allowed for the recording of the process without the need for direct human presence.

A total of 18 nests of different species (11 green turtle, 6 olive ridley and 1 leatherback) were analyzed in the different emergence phases (time spent on videos = 78.41 minutes).

The emergency process occurs mostly at night, this pattern is confirmed in our data, with the exception of some neonates that emerged during the day, and this could be justified by being nests of green turtles that predominate in shaded areas. With the recordings of the photo trap cameras, was possible to obtain the real time of emergencies and also identified 4 types of predators (raccoons, ants, birds and dogs), in the initial phase of process of emergence.

This behavioral study employing trap cameras is innovative, taken in count the previous research. Contributes to improving our comprehension of the behavior of these species at an important phase in their life. It provides the capacity to gather more information concurrently from several nests, eliminating human interference, and capture real-time images of the emergence process and threats. For future studies the use of cameras can be useful for management the efforts in the conservation of sea turtles.

These highlight the advantages of trap cameras in future studies, understanding the predator behavior in the different phases of the emergence process. Developing management strategies to achieve conservation goals, especially when the species of concern are threatened.

The loggerhead sea turtle (Caretta caretta) exhibits temperature-dependent sex determination, and current nesting populations are compromised by the combination of highly female-skewed sex ratios among nesting beaches and a decrease in the viability of embryo development due to elevated thermal incubation conditions in a warming world. Then, the future of the species depends on whether it can adapt to quick temperature changes or colonize new areas to reproduce with more suitable temperatures for clutch incubation. Loggerhead turtle colonization is occurring in the western Mediterranean, including the Spanish coast. Records of nesting events are increasing every year. Considering forecasts of the loss of viability of current nesting rookeries in the eastern Mediterranean and the Atlantic, the establishment of new populations can help to ensure the long-term survival of the species. Nest incubation temperature studies allow us to study ecology of the nests, vital demographic parameters such as hatchling sex ratio, and thermal conditions affecting hatching and emergence success. Here we evaluate natural incubation temperature regimes of 24 nests laid between 2018 and 2023 on Spanish coast beaches (Andalusia, Balearic Islands, Catalonia, Murcia and Valencia Community). Hatchling sex ratio (estimated as average temperature during the middle third of incubation period) and mean metabolic heating data of these nests are also analyzed. Dataloggers (HOBO® TidbiT® MX Temp 400, MX2203, ±0.2°C accuracy) were deployed in the center of the clutch to record incubation temperature every 30 minutes. In 17 of the nests, control datalogger was deployed in the sand at 70-100 cm apart from the nest at the same depth of the clutch to evaluate embryo metabolic heating. The incubation period ranged 45-61 days. Average nest temperature ranged from 27,67°C to 31,54°C and average temperature in the middle third of the incubation ranged from 27,35°C to 31,62°C. The maximum temperature during this period increased between 1,25°C and 3,53°C, while the mean temperature also increased during the middle third of the incubation period (metabolic heating: 0,47±0,35°C) compared with sand temperature records and continued to increase during the last third (metabolic heating: 1,30±0,34°C). Results suggest a high variability on nest incubation temperatures among Spanish beaches. The results showed a variable estimated sex ratio among nests, indicating that male-female proportions in Spain’s beaches can be more balanced eastern Mediterranean nesting areas. These results imply that Spanish beaches have a great potential to produce both males and females to guarantee a female recruitment and the establishment of regular nesting areas, but also to become both a spatial and temporal thermal refuge for the species according to male hatchling production. Further studies are needed to determinate areas and periods within the season where females and males are produced, to ensure an adequate management for the conservation of the emergent nesting population of the species in the western Mediterranean under a climate change scenario.

The current climate warming is a challenge to biodiversity that could surpass the adaptation capacity of some species. Hence, understanding the means by which populations undergo an increase in their thermal tolerance is critical to assess how they could adapt to climate warming. Specifically, sea turtle populations could respond to increasing temperatures by (1) colonizing new nesting areas, (2) nesting during cooler times of the year and/or (3) by increasing their thermal tolerance. Differences in thermal tolerance of clutches laid by different females would indicate that populations have the potential to adapt by natural selection. Here we used exhaustive information on nest temperatures and hatching success of leatherback turtle (Dermochelys coriacea) clutches over 14 years to assess the occurrence of individual variability in thermal tolerance among females. We found an effect of temperature, year and the interaction between female identity and nest temperature on hatching success, indicating that clutches laid by different females exhibited different levels of vulnerability to high temperatures. If thermal tolerance is a heritable trait, individuals with higher thermal tolerances could have greater chances of passing their genes to following generations, increasing their frequency in the population. However, the high rate of failure of clutches at temperatures above 32 °C suggests that leatherback turtles are already experiencing extreme heat stress. A proper understanding of mechanisms of adaptation in populations to counteract changes in climate could greatly contribute to future conservation of endangered populations in a rapidly changing world. Our results can guide management actions to mitigate short-term effects of climate warming on sea turtles, while allowing adaptation in the long-run.