ISTS Symposium43 Program/Agenda

Climate change is having wide-ranging impacts on sea turtle populations worldwide; however, the effects of increased temperatures vary between species. One example of interspecific variation in response to temperature change in sea turtles is seen in the duration of the inter-nesting interval — the time between two consecutive nesting events in a single nesting season. Specifically, when water temperatures increase, green (Chelonia mydas), hawksbill (Eretmochelys imbricata), and loggerhead (Caretta caretta) turtles typically have shorter inter-nesting intervals. In contrast, previous studies in olive ridley turtles (Lepidochelys olivacea) have not observed any correlation between water temperature and inter-nesting intervals. Nevertheless, these observations require further validation as they were based on a relatively small number of individuals (n = 11). To address this, we used a combination of capture-mark-recapture data (for 96 different individuals) alongside remotely-sensed oceanographic data to assess the relationship between water temperatures and the duration of the inter-nesting interval for olive ridley turtles on the Pacific coast of Costa Rica. Specifically, we patrolled the beaches of Parque Nacional Marino Las Baulas and Playa Cabuyal nightly from October to March from 2010/2011 to 2023/2024 to encounter nesting turtles. When an olive ridley was encountered, it was checked for metal and/or PIT tags. If none were found, they were applied accordingly. From all turtles re-encountered within a single season, we calculated the duration of the inter-nesting interval. Next, we identified a 225 km2 region immediately adjacent to the nesting beaches, as other satellite telemetry studies suggest this is the typical range for inter-nesting olive ridley turtles. For this area, we used data from NASA’s multi-scale ultra-high-resolution (MUR) sensor to calculate mean daily sea surface temperature (SST). The mean observed inter-nesting interval was 22 d (range: 13 to 41 d) and mean SST was 27.96 °C (range: 26.16 to 29.54 °C). While a significant relationship between SST and inter-nesting interval duration was observed, this correlation was weaker than in other sea turtle species. This is likely driven by the capacity of olive ridley turtles to retain fertilized eggs for longer periods than other non-arribada nesting sea turtle species. The correlation between sea surface temperatures and olive ridley inter-nesting intervals suggests that increased temperatures under climate change could negatively affect the capacity of olive ridley turtles to synchronize nesting as required for arribada formation.

The hatching success of sea turtle eggs can be reduced by a variety of biotic and abiotic factors. The beaches of Batoke and Bakinguili on the northern coast of Cameroon serve as nesting sites for sea turtles. Through its annual sea turtle nesting monitoring program initiated in 2016, AMMCO records an average of 03 to 04 nests on these beaches each year, primarily olive ridley nests, and to a lesser extent, leatherback turtle nests (02 nests recorded so far). Poaching of females/nests, insufficient nest monitoring, flooding of the upper beach during exceptional tides, poorly identified nest locations, handling of eggs, and invasion of nests by roots from surrounding vegetation are the main causes attributed to the absence of egg hatching or hatchling emergence, consistently observed either during or after the incubation period. To address this issue, AMMCO began a study in March 2023 to analyze the impact of environmental factors and beach characteristics on the hatching success of sea turtle eggs. The study monitors the physical and chemical properties of the surface of Batoke and Bakinguili beaches, as well as tidal data to track water levels and calculate the average tidal range. The surface temperature of the beaches varies with seasonality (dry and rainy seasons) and the presence or absence of shade. Meanwhile, temperature data recorded by a data logger deployed inside a nest shows an increase reaching lethal levels for the survival of sea turtle eggs (t > 33°C), with a steady rise during the dry season. The volcanic nature of the sand on these beaches may contribute to the accumulation of significant heat fluxes. Studies on granulometric and mineralogical analysis could provide further insights. The annual average tidal range is 1.55 m during spring tides and 1.80 m during high tides. This average tidal range, depending on tidal regimes, is favorable for nest stability at Bakinguili, which has a steeper beach slope than Batoke. Since oceanic forcing is non-linear, it causes structural modifications to the beaches, making Batoke beach prone to erosion. The survival probabilities of the eggs on these beaches could be further exacerbated by the effects of climate change, particularly rising surface temperatures and sea levels. The identified vulnerabilities will be used to determine conservation actions to be implemented, such as establishing an egg incubation system.

Keywords: Water levels, average tidal range, beaches, sea turtles

Sandy beaches are vital ecosystems that provide essential services such as storm buffering and water purification. Acting as transitional habitats between terrestrial and marine environments, they support functional connectivity and serve as important foraging and breeding grounds for species like sea turtles. Despite these ecological roles, beaches are often valued primarily for their economic and recreational benefits. However, with increasing coastal development and climate change, these natural habitats are becoming degraded or lost as processes essential to coastal health are disrupted. Coastal developments are frequently considered in isolation, with impacts seen as limited to the development footprint. Yet over time, these individual actions accumulate into a “tyranny of small decisions,” resulting in widespread ecological effects such as coastal squeeze—a particularly urgent issue in the Red Sea—reducing beaches’ resilience to sea-level rise. The Red Sea supports nesting populations of green (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata), with several key rookeries located along the Kingdom of Saudi Arabia (KSA) coastline. However, data collection along this coast has been limited, often constrained to short-term, project-specific monitoring, leaving the full distribution of nesting sites unknown. With Saudi Arabia's rapid infrastructural transformation toward Saudi Vision 2030—including large-scale coastal developments along the Red Sea—comprehensive mapping of nesting sites is needed to guide holistic shorescape management. To address these data gaps, the newly established General Organisation for Conservation of Coral Reefs and Turtles in the Red Sea (SHAMS) has consolidated historical nesting data, engaged local stakeholders, and analysed remote sensing imagery to map known and potential nesting sites for green and hawksbill turtles. This initiative has identified over 1,800 beach sites along 1,760 km of coastline. For sites without current stakeholder monitoring, ground-truthing via track and nest counts, supplemented by drone surveys, was conducted over one year. From the resulting map of nesting sites a 200 m landward coastal buffer zone, consisting of a 150 m crawling distance and a 50 m disturbance buffer was established. This spatial layer is now publicly accessible across the Kingdom and will be a critical resource for SHAMS as it initiates long-term monitoring at index sites. Coupled with other layers such as habitat and threat mapping, this data will inform a detailed, multi-objective systematic conservation plan and coastal zonation for the KSA Red Sea coastline, balancing the protection of sea turtles and their habitats with developmental needs through adaptive management. This shorescape approach is a critical step toward sustainable coastal management for the Kingdom of Saudi Arabia’s Red Sea coastline.

Climate change, rising sea levels and the increasing intensity of storms are all contributing factors that could disrupt sea turtle life cycles, with some of these impacts already being observed globally. In the Cayman Islands, both loggerhead (Caretta caretta) and green (Chelonia mydas) turtle nesting populations are recovering from near-extinction due to over-harvesting and now face these emerging threats.

Using data from 2020-2024, we report on the impacts of nest wash-over from tropical storms on hatching success for both species, with an aim to determine best management practices in the face of climate change.

Variation was found year to year, but overall, a total of 584 of 2324 nests (19.6% of total loggerhead nests and 28.2% of total green turtle nests) were recorded as washed over from storm surge, from a total of 9 named storms. Overall, wash-over to nests that were left in-situ were found to have significantly lower hatching success than those unaffected; a reduction of 23.42% and 25.6% was recorded for loggerhead and green turtles, respectively.

The incubation stage at the time of wash-over was found to have a significant impact on embryo survival for both species, with a greater effect on loggerhead turtles. Eggs washed over within the first 10 days of development had a lower hatch success and survival rate than those at a later stage. For loggerhead and green turtles, the mean hatch success of washed-over nests was 61% (N=69) and 48% (N=183) for nests that were at least 11 days post their lay date, but only 23% (N=12) and 22% (N=15) for nests washed over before this stage. Further analysis regarding timing of wash-over events and the impact on incubation duration and hatchling phenotype will also be presented.

Washed over nests also had a greater chance of survival if they were laid more than 10m from the high-water mark.

Nest relocation is undertaken as a last resort as it is known to lower hatching success and may have negative impacts on hatchling fitness. Relocating nests further from the water to drier sand also has potential to impact sex ratios unfavourably. More than 100 nests were relocated due to incoming storms at various stages of incubation and analysis of the success of these nests will also be reported.

Although sea turtle eggs show some resilience to wash-over, our findings indicate that they are most vulnerable during the early stages of development for both species, and this should be considered when prioritising nests to relocate in the event of a tropical storm. We recommend continued data collection to assess of hatch success, particularly for nests impacted by wash-over. Monitoring of clutch temperatures should be implemented for in-situ and relocated nests so that climate change impacts to nests are considered in management plans, which must also ensure that interventions are indeed beneficial to the species.

Sea level rise and coastal erosion continue to impact shorelines globally, endangering lives and livelihoods, especially in Small Island Developing States (SIDS). Trinidad stands out as a crucial habitat for one of the world's largest populations of leatherback turtles. With over 10,000 turtles nesting on the island, it accounts for 80% of the Caribbean's leatherback population. This study focuses on the Matura coastline in northeast Trinidad, a significant nesting site recording 5,000 to 7,000 crawls annually.

The effects of erosion at Matura Beach are persistent throughout the year, with many nests being washed away or inundated, leading to low hatching and emergence success rates. This study aims to conduct drone surveys followed by post-flight image analysis to quantify nest loss due to erosion, assess shoreline changes over recent seasons, and identify suitable locations for establishing on-beach hatcheries for nest relocations. By determining which nests should be moved and where to relocate them, we aim to adopt a more targeted approach, thereby increasing emergence success at Matura Beach.

Drone flights were conducted monthly over two years during low tide. Orthomosaics and Digital Surface Models (DSMs) were generated from the flight data, allowing us to identify the open sandy shores preferred by leatherbacks. Nest points were added for each period, and we tracked how the beach changed over time, and where the nests would be in comparison to where it was laid. Our analysis revealed that between 15% to 30% of buried nests could be threatened annually due to erosion patterns, and we were also able to isolate the best potential locations, based on shoreline changes, on the beach for nest relocations. These outputs will be employed in the coming season to further validate the study results.

Incubation conditions play a critical role in sea turtle embryonic development. While much attention has been paid to incubation temperature, with respect to survival, moisture and gas exchange are equally important. Developing embryos must maintain osmotic balance and exchange respiratory gases with the surrounding environment. Inundation of the clutch by waves or groundwater may disrupt these exchanges and can increase mortality if detrimental conditions persist for a sufficient duration. Previous research on loggerhead turtles (Caretta caretta) in the northern Gulf of Mexico suggests that this threshold is around ≥2 wash-over events or ≥10 hours of submersion. However, beaches utilized by different nesting populations have different levels of inundation exposure based on their typical slope and elevation profiles, sand grain size and compaction, and hurricane frequency. Over evolutionary time, these exposure differences may select for differences in nest site selection and/or embryonic inundation tolerance. Preliminary analyses of nest productivity following wave exposure from two different southeastern US populations suggest this may be the case. From 2012 to 2022, loggerhead turtle nests that were washed over in Alabama (northern Gulf of Mexico Recovery Unit) but not otherwise disturbed had lower hatching success rates than those in North Carolina (Northern Recovery Unit). Nests that were washed over at least once in Alabama had an average hatching success of 36.9% ± 29.6% SD (n = 113), whereas those in North Carolina averaged 62.3% ± 43.8% (n = 124). This is despite washed over nests experiencing a greater frequency of inundation in North Carolina (2.6 wash-overs ± 2.1 SD) versus Alabama (1.7 wash-overs ± 1.1 SD). Additional analyses are underway to investigate other factors that may influence these rates. Considering the threats posed by sea level rise, hurricane intensification, and urban beach management, understanding differences in inundation tolerance is useful for population-level species management.

The findings and conclusions in this abstract are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the United States Government.