Trends in abundance and reproductive success of the hawksbill turtle nesting population at Buck Island Reef National Monument, St. Croix, US Virgin Islands

Abstract

Index nesting sites for the Critically Endangered hawksbill turtle Eretmochelys imbricata are essential for assessing population trends and demographics, and informing conservation strategies. Using 29 yr (1988-2017) of saturation tagging data from a protected Caribbean index site, we assessed annual trends in abundance and reproductive success for the hawksbill nesting population at Buck Island Reef National Monument (BIRNM), St. Croix, US Virgin Islands. Approximately 43 ± 21 (mean ± SD) females and 154 ± 60 nests were encountered each year during nocturnal patrols. Remigration interval and inter-nesting period averaged 3.2 ± 1.6 yr and 17.4 ± 7.1 d, respectively. After a significant recovery since 1988, female abundance stabilized during 2007-2017 (p < 0.01, R2 = 0.82), whereas nest abundance declined (p < 0.01, R2 = 0.71) and neophyte recruitment exhibited a decreasing trend. There was no trend in annual mean hatch success (69.4 ± 26.6%), emergence success (63.0 ± 29.1%), and hatchling production (89.2 ± 45.0 individuals clutch-1) during the study period; but clutch size (p < 0.01, R2 = 0.65; 142.8 ± 28.9 eggs clutch-1) and female curved carapace length (p < 0.01, R2 = 0.56; 88.4 ± 4.7 cm) significantly decreased. The BIRNM population has stabilized, but declines in body size and nest abundance highlight the need for evaluating demographics to diagnose the factor(s) driving changes in abundance and productivity. Our study provides a foundation for evaluating Caribbean hawksbill demographics, while contributing a valuable assessment of clutch size and in situ nest success for the species.