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

Alexandra G. Gulick*, Kristen A. Ewen, Clayton G. Pollock, Zandy M. Hillis-Starr

*Corresponding author:

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 years (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, U.S. Virgin Islands. Approximately 43  EMBED Equation.DSMT4  21 (mean  EMBED Equation.DSMT4  SD) females and 154  EMBED Equation.DSMT4  60 nests were encountered each year during nocturnal patrols. Remigration interval and inter-nesting period averaged 3.2  EMBED Equation.DSMT4  1.6 yr and 17.4  EMBED Equation.DSMT4  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  EMBED Equation.DSMT4  26.6%), emergence success (63.0  EMBED Equation.DSMT4  29.1%), and hatchling production (89.2  EMBED Equation.DSMT4  45.0 individuals clutch-1) during the study period; but clutch size (p < 0.01, R2 = 0.65; 142.8  EMBED Equation.DSMT4  28.9 eggs clutch-1) and female curved carapace length (p < 0.01, R2 = 0.56; 88.4  EMBED Equation.DSMT4  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.