NESTING ECOLOGY OF THE LEATHERBACK TURTLE, DERMOCHELYS CORIACEA, AT ESTACIÓN LAS TORTUGAS, COSTA RICA: 2013-2021 AND 2024

The Northwest Atlantic Regional Management Unit of Leatherbacks is projected to represent 99% of the global Leatherback population, underscoring its global significance. Despite this, the sub-population is listed as endangered by the IUCN, with variable nesting trends, highlighting the need for long-term monitoring to better understand it’s population dynamics. This study presents the first nesting data from Estación las Tortugas, a conservation project located on Playa Mondonguillo, along the Caribbean coast of Costa Rica, aimed at supporting regional Leatherback conservation efforts. Field research was conducted over 10 seasons (2013–2021 and 2024) through nightly patrols conducted from March to July. A total of 2,937 nests were recorded, with annual nests numbers remaining stable until 2024. Key nesting parameters included a modal observed inter-nesting period (OIP) of 9 days, consistent with findings from other Caribbean sites. The observed clutch frequency (OCF) and estimated clutch frequency (ECF) were 1.3 and 4.4, respectively, indicating potential underestimation of nests. This is further supported by a low remigration rate (1.3 times), with only 20% of females observed nesting more than once during the study period. Possible explanations for this underestimation include: (1) nesting at alternative sites, (2) nesting on unmonitored beach sections, and (3) unidentified individuals. Morphometric analysis revealed a mean curved carapace length (CCL) of 150.6 cm and width (CCW) of 101.9 cm, smaller than reported for other Caribbean populations. These smaller body sizes were associated with lower reproductive output, as females laid fewer yolked eggs and more shelled albumen gobs (SAGs). A negative binomial regression analysis confirmed that smaller females tend to lay fewer yolked eggs and produce more SAGs. Despite a stable Leatherback population at Estación las Tortugas, the decline in 2024 highlights the need for continued long-term monitoring. Future research should investigate nest underestimation through satellite telemetry, expanded beach coverage, and morning patrols. Additionally, including hatching success data will give a comprehensive assessment of the reproductive output of the beach and inform more effective conservation strategies.