ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01253

ABSTRACT: Abundance estimates corrected for changes in detection are needed to assess population trends. We used transect-count surveys and N-mixture models to estimate green turtle Chelonia mydas and hawksbill turtle Eretmochelys imbricata detection and total abundance at foraging grounds in Bonaire during 2003−2018, and we used these total abundance estimates to fit a Bayesian state-space logistic model and make abundance predictions for 2019−2030. During 2019−2022, we also recorded distance categories to estimate detection and total abundance using distance sampling and N-mixture models. Here, we focus on distance sampling to estimate observer detectability and total abundance, and to determine if total abundance increased, declined, or did not change during 2019−2022 and when compared with 2003−2018 estimates and 2019−2030 predictions. Detectability averaged 0.53 (SE = 0.02) for green turtles and 0.51 (SE = 0.06) for hawksbill turtles. Density (ind. km⁻²) and population size (individuals in the 4 km² survey region) averaged 72.1 (SE = 17.3) and 288 (SE = 69) for green turtles and 21.8 (SE = 4.6) and 87 (SE = 18) for hawksbill turtles. Green turtle total abundance did not change during 2019−2022 (p > 0.05) but remained low when compared with 2003−2018 estimates and 2019−2030 predictions. Hawksbill turtle total abundance declined between 2020 and 2021 (z = 2.15, p = 0.03) and increased between 2021 and 2022 (z = −3.04, p = 0.002) but 2019−2022 estimates were similar to 2003−2018 estimates and 2019−2030 predictions. Our methodology can be used to monitor sea turtle populations at coastal foraging grounds in the Caribbean.