Determining abundance and survival of sea turtles at foraging areas: a logistically feasible field approach using multiple analytical methods
Citation
Foley, A. M., B. E. Witherington, T. L. McDonald, S. Hirama, R. F. Hardy, and B. A. Schroeder (2026). “Determining abundance and survival of sea turtles at foraging areas: a logistically feasible field approach using multiple analytical methods”. In: Endangered Species Research 59. DOI: 10.3354/esr01502.
Keywords
Loggerhead Caretta, Green turtle, Abundance, Survival, Distance sampling, Spatially explicit mark-recapture, Schnabel method, Foraging area
Abstract
The importance of monitoring long-term trends in abundance and survival of sea turtles at foraging areas has been asserted for decades, but few studies have accomplished this. We report on 19 yr (2000–2018) of monitoring these trends in Florida Bay (Florida, USA) and present the corroborative results of 3 analytical methods as an example of a successful, cost-effective, and logistically feasible approach for monitoring sea turtle abundance and survival in coastal foraging habitats. We conducted transect surveys for loggerheads Caretta caretta and green turtles Chelonia mydas annually over 4–10-d periods, with a mean total transect length of 200 km yr–1. Concurrently, we captured loggerheads 1320 times, representing 886 individuals. Loggerheads were primarily large immatures and adults, whereas all green turtles were immatures. A distance sampling model estimated an annual mean of 537 loggerheads and 378 green turtles. Annual numbers of green turtles rose from <100 to >600 over the 19 yr period, while no trend was observed for loggerheads. A closed mark–recapture model (MR) and spatially explicit open mark–recapture models (SMR) estimated annual means of 568 and 597 loggerheads, respectively. We observed no change in annual abundance estimates based on trend lines, even when adults and immatures were considered separately by sex. As determined by the SMR, the mean annual survival of adult and immature female loggerheads was ≥0.90, whereas annual survival of immature male loggerheads was 0.75. These survival estimates for Northwest Atlantic loggerheads are the first based on a foraging area study.