Spatial and temporal variability of immature green turtle abundance and somatic growth in Puerto Rico

Abstract

Understanding conservation needs relies on robust estimates of key population parameters, such as survival, abundance and somatic growth. We investigated the somatic growth and abundance dynamics of 2 aggregations of immature green turtles, at Tortuga Bay and Puerto Manglar (Culebra, Puerto Rico), throughout 15 yr of capture-mark-recaptures. We used nonlinear models to investigate the effects of carapace length, sampling year, growth interval and the presence of fibropapillomas on growth rates, and used the size-specific growth rate function to estimate how long turtles remain at each bay. Abundances were estimated and compared with timespecific growth rate functions, to infer density-dependency effects on somatic growth rates, and trends in abundance were evaluated by fitting generalized linear models. We found foraging site specific growth rates and report the highest mean somatic growth rate for green turtles in the wild (6.1 ± 1.7 cm yr-1, at Puerto Manglar). The size-specific growth rate function was monotonic at both sites, with growth rates declining continuously with increasing carapace length. We inferred minimum ages at maturity of 14 and 22 yr, for Puerto Manglar and Tortuga Bay turtles, respectively. Throughout the 15 yr of this study there was a positive trend in aggregation size at Puerto Manglar (mean annual increase of 10.9%), which was not observed at Tortuga Bay. Our study highlights the influence of geography and habitat quality on somatic growth rates, and delivers robust demographic estimates valuable for local and regional assessments of the conservation status of the green turtle.