Estimating body mass in the leatherback turtle Dermochelys coriacea

Abstract

Body mass is a major life history trait and provides a scale for all living processes of organisms. Unfortunately body mass cannot be easily measured for many species, because of the logistical difficulties involved in actually catching and weighing them. This is particularly true for sea turtles which are large vertebrates that spend most of their life at sea. Here we developed a general linear model to predict body mass from 17 morphometric measurements obtained from 49 leatherback turtles nesting in Awala Yalimapo beach, French Guiana, South America. A stepwise backward analysis removing independent parameters with P > 0.001 indicated that body mass can be estimated with 93% accuracy by Body Mass (kg) = - 709.146 + 3.391MedianBodyCirc (cm) + 2.664SCCL (cm), where SCCL is the standard curvilinear carapace length and MedianBodyCirc is body circumference at half of SCCL. A sensibility test showed that this parsimonious model is robust, as estimated body mass may change by 0.7-1.3% for 1-2 cm changes in SCCL, by 0.9-1.7% for 1-2 cm changes in circumference. Leatherback turtles from French Guiana were larger and heavier than in all other nesting sites studied so far, suggesting either that gravid leatherbacks feed during the nesting season in French Guiana, and/or that this species may exhibits site-specific growth strategies. Further studies are required to test these hypotheses, including implementation of similar simple models for other nesting populations, in order to better understand the life history of this endangered species.