Tracking green turtle nesting trends at a remote oceanic rookery

Trindade Island, Brazil, is a small, remote volcanic island located 1140 km off the coast of southeastern Brazil. The green turtle ( Chelonia mydas ) nesting aggregation on Trindade is genetically distinct, the largest in the southwest Atlantic, and represents the southern limit of green turtle nesting in the Atlantic. Projeto TAMAR (a Brazilian conservation program) has monitored the nesting aggregation discontinuously since 1982. In 2009, a standardized protocol was established for the two beaches (Andradas and Tartarugas) with the highest nest abundance. Data from December 2009 through April 2017 (except 2013) were used in this study. Annual numbers of tracks left by females that emerged onto the beach vary between 558 and 3317 tracks for Andradas and between 760 and 3559 tracks for Tartarugas. Mean nesting probabilities (probability that an emerging female deposits eggs) for all years were 0.22 (95% HDI (highest posterior density interval) = 0.14–0.30) for Andradas and 0.45 (95% HDI = 0.37–0.53) for Tartarugas. Nesting probabilities varied among and within years and had a negative relationship with daily track counts. During our study, annual estimates of nests were stable on both Andradas (range 38–2001) and Tartarugas (range 248–2769). Nest abundance estimates between 1991 and 2008 from an earlier study indicated a stable population, extending the duration of apparent stability to 26 years with the caveat that the studies used different estimation methods. This stability is in contrast with the increasing trends for most green turtle nesting aggregations in the Atlantic.