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ESR prepress abstract   -  DOI:

Recent decline of the green turtle (Chelonia mydas) nesting trend at Tortuguero, Costa Rica

Jaime Restrepo, Emily G. Webster, Iván Ramos, Roldán A. Valverde*

*Corresponding author:

ABSTRACT: Trends in abundance of different life stages for wildlife populations present important opportunities to manage the conservation of threatened species. For marine turtles, most trend assessments are based on long-term monitoring of nesting aggregations, providing critical information on rookery dynamics across the years. Tortuguero, Costa Rica, is the largest nesting colony of the green turtle Chelonia mydas in the Atlantic Ocean. Here we present an updated trend in annual clutch abundance spanning over 50 years of monitoring and conservation efforts at Tortuguero. We conducted weekly censuses recording clutch counts and used a generalized additive model (GAM) fitted for each monitored nesting season separately to predict daily tallies and estimated annual clutch count as the sum of these. We modelled the long-term trend in annual clutch numbers with a Bayesian GAM with a cubic regression spline basis, fit to the estimated annual clutch counts for 1971–2021. Finally, we examined spatio-temporal patterns in clutch counts along the beach by fitting a GAM with a 2-dimensional spline. Clutch estimates presented large interannual variations (mean= 78695 ± 6727 SE, range: 7004–186640 clutches yr–1). Tortuguero’s clutch abundance trend increased steadily over the first 37 years. However, since 2000 this growth slowed gradually until 2008, when the curve began to trend downwards. Despite this, Tortuguero remains the largest aggregation of nesting green turtles within the Caribbean. Phenomena occurring across the population’s distribution range and at several life history stages influence Tortuguero’s nesting trend. Thus, a decreasing trend at Tortuguero may be considered a warning sign for the Greater Caribbean green turtle metapopulation.