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Green and hawksbill turtle abundance and population dynamics at foraging grounds in Bonaire and Klein Bonaire, Caribbean Netherlands

Frank F. Rivera-Milán*, Mabel Nava, Kaj Schut, Fernando Simal

*Corresponding author:

ABSTRACT: Green and hawksbill turtles are negatively impacted by natural and anthropogenic disturbances, including an unknown number killed annually in the coastal waters of Bonaire and Klein Bonaire, Caribbean Netherlands. We used N-mixture models, conventional distance sampling and the multiple Lincoln-Petersen method to estimate abundance from transect-count and net-capture surveys. Maximum likelihood and Bayesian generalised linear models were used to assess trends in annual abundance in 2003−2018; and a Bayesian state-space logistic model was developed to generate the posterior distributions of population parameters and make abundance predictions in 2019−2030. Mean annual abundance was 555 green turtles (SE = 149, 2.5 and 97.5 percentiles = 337, 943) and 70 hawksbill turtles (SE = 13, 2.5 and 97.5 percentiles = 49, 101) and there were no trends (z = 1.25 and −1.34, p = 0.21 and 0.18, respectively) in western Bonaire and Klein Bonaire in 2003−2018. Mean annual abundance was 348 green turtles (SE = 135, 2.5 and 97.5 percentiles = 171, 731) and there was a positive trend (z = 5.29, p < 0.001) inside Lac Bay, southeast Bonaire, 2003−2018. Green turtles have higher population growth rate and carrying capacity, and therefore can sustain higher human-induced mortality than hawksbill turtles. However, under low mortality rates (m < 0.100), both can fluctuate stably between the lower and upper limits of carrying capacity. The methodology implemented can be adapted to estimate sea turtle abundance, monitor and model their population dynamics, and assess the negative impact of human-induced mortality in other Caribbean islands.