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

Abstract

Trends in abundance of different life stages 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, which provides critical information on rookery dynamics across years. Tortuguero, Costa Rica, is the largest nesting colony of the green turtle Chelonia mydas in the Atlantic. Here we present an updated trend in annual clutch abundance spanning over 50 yr of monitoring 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. We 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 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 varied across years (78 695 ± 6727 [mean ± SE], range: 7004-186 640 clutches per year), but increased steadily over the first 37 yr. However, growth slowed gradually from 2000 to 2008, when the curve began to trend downwards. Tortuguero remains the largest aggregation of nesting green turtles within the Caribbean. Phenomena occurring across the population’s range and at several life history stages influence Tortuguero’s nesting trend. Thus, a decreasing trend at Tortuguero may be a warning sign for the Greater Caribbean green turtle metapopulation.

Green and Hawksbill Sea turtles of Eastern Atlantic: New insights into a globally important rookery in the Gulf of Guinea

“…Despite historically facing intense exploitation (Ferreira‐Airaud et al, 2022 ), both green and hawksbill turtle populations nesting in São Tomé are showing a progressive trend, reflecting recovery patterns observed in other rookeries (Barbosa et al, 2018 ; Blumenthal et al, 2021 ; Hudgins et al, 2023 ; Kauffman, 2022 ; Mazaris et al, 2017 ; Restrepo et al, 2023 ; Santos et al, 2013 ; Seminoff et al, 2015 ). The encouraging positive trends observed in both species are indicative of the substantial impact of conservation efforts implemented in the region in recent years.…”

“…Many of these taxa face significant reductions in their population numbers and are at risk of extinction (Butchart et al, 2010;Dulvy et al, 2021;Mortimer & Donnelly, 2008;Pimiento et al, 2020;Restrepo et al, 2023;Wallace et al, 2011), requiring ocean governance with conservation measures (Dulvy et al, 2021;Pimiento et al, 2020) that range from intergovernmental agreements to national and local conservation programs, including protected areas (Duda, 2016;Huang et al, 2022;Lotze, 2021;Maestro et al, 2019).…”

“…Anthropogenic threats often overlap with ecologically important areas used by marine migratory vertebrate species, such as seabirds, mammals, sharks, and sea turtles (Lascelles et al., 2014 ; McCauley et al., 2015 ; Polidoro et al., 2017 ; Sequeira et al., 2019 ). Many of these taxa face significant reductions in their population numbers and are at risk of extinction (Butchart et al., 2010 ; Dulvy et al., 2021 ; Mortimer & Donnelly, 2008 ; Pimiento et al., 2020 ; Restrepo et al., 2023 ; Wallace et al., 2011 ), requiring ocean governance with conservation measures (Dulvy et al., 2021 ; Pimiento et al., 2020 ) that range from intergovernmental agreements to national and local conservation programs, including protected areas (Duda, 2016 ; Huang et al., 2022 ; Lotze, 2021 ; Maestro et al., 2019 ). Even when some sea turtle populations are showing signs of recovery (Mazaris et al., 2017 ), significant conservation concerns persist, underlining the need for a nuanced understanding of specific regional and species characteristics.…”

Archaeological evidence for long-term human impacts on sea turtle foraging behaviour

“…More broadly, from another perspective, these data provide a baseline for one of the most significant remaining forging areas for green sea turtles and one that is closely connected to one of the world’s largest breeding sites [ 113 ]. Understanding the geographical origins and connections between breeding sites and populations using different foraging areas is critical for conservation management and modelling.…”

Motivations and sensitivities surrounding the illegal trade of sea turtles in Costa Rica

“…Recent analysis of the illegal harvesting rates from these projects found that illegal take at each of these sites is declining because of conservation efforts. Despite this, these beaches continue to lose adult turtles and nests to illegal harvesters every season, and this population of green (Chelonia mydas) turtles is in decline (Pheasey et al 2021, Restrepo et al 2023.…”