NESTING ECOLOGY OF LEATHERBACK (DERMOCHELYS CORIACEA), GREEN (CHELONIA MYDAS), AND OLIVE RIDLEY (LEPIDOCHELYS OLIVACEA) TURTLES IN PLAYAS GRANDE AND VENTANAS, COSTA RICA

Parque Nacional Marino Las Baulas (PNMB) in Costa Rica was established in 1991 to protect Playas Grande, Ventanas, and Langosta, which are known nesting beaches for leatherback turtles (Dermochelys coriacea) in the eastern Pacific Ocean, where green turtles (Chelonia mydas), and olive ridley (Lepidochelys olivacea) also nest. This study analyzes PNMB nesting data from the 2012-2013 to the 2022-2023 seasons to update information for conservation efforts on leatherback and olive ridley turtles, and to provide baseline data on green turtles. Data were collected on Playas Grande and Ventanas during the leatherback nesting season (October-March) by conducting night and morning patrols where individuals were identified and/or tagged.

Overall, leatherback estimates decreased, green turtle estimates fluctuated, and olive ridley estimates remained stable. Throughout the duration of the study, leatherback turtles had higher activity rates in Playa Grande, green turtles had higher activity rates in Playa Ventanas, and olive ridleys had similar activity rates in both beaches. Peak nesting activity varied among species, with leatherbacks nesting early in the dry season, green turtles nesting throughout the dry season, and olive ridleys peaking at the end of the rainy season. Since data collection was focused during the leatherback nesting season, activity for green and olive ridleys is likely underrepresented. Leatherbacks had a high proportion of confirmed nest with minimal body pits that might be expected due to consistent monitoring. Green turtles had more false crawls and body pits, attributed to their skittish behavior as well as their lower monitoring priority within the project. Olive ridleys also had a high proportion of confirmed nest counts, with estimates likely benefiting from this species’ shorter nesting duration, which allowed for more efficient patrolling. Each species displayed distinct nesting zone use. Leatherbacks predominantly nested closer to the high tide line, with deep nest depths allowing for stable temperatures. Green turtles favored shaded conditions higher up the beach near or in the vegetation which may reduce exposure to heat. Olive ridleys primarily nested below the high tide line despite their shallower nest depths. This may be due to their nests developing more often during the rainy season which is associated with lower sand temperatures.

Despite park conservation efforts, Playa Grande and Ventanas shifted from being one of the largest nesting sites in the Pacific in the 1990s to just having four leatherbacks in 2022 season. Current PNMB conservation policies mainly protect leatherbacks, leaving green and olive ridley turtles under-protected and under-monitored, especially outside the leatherback nesting season. Due to declining leatherback populations and increasing green turtle activity, conservation efforts in the park should be adapted to provide year-round monitoring and protection for all East Pacific sea turtle species.