Using growth rates to estimate the minimum age and size at sexual maturity in a captive population of the critically endangered Central American river turtle Dermatemys mawii

Abstract

The Central American river turtle Dermatemys mawii is a critically endangered species that has incurred substantial losses over the last several decades due to overhunting. This species is now being considered for head-starting programmes (i.e., captive breeding of turtles for wild release). However, relatively little is known about their life history characteristics, especially with respect to growth and sexual maturation. A robust knowledge of D. mawii life history traits is important in developing conservation management plans. This research is the first known study to maintain hatchlings, juveniles and adults in captivity with regular morphometric data collection. Growth rates were quantified (cm yr-1) and growth parameters were calculated (e.g., growth coefficients) to estimate body size and age at onset of sexual maturity in a group of wild-caught but captive-held and captive-bred D. mawii in Belize. Sizes at the onset of sexual maturity were inferred by segmented linear regressions that identified changes in growth rate by body size. Asymptotic sizes and growth coefficients were calculated using the Fabens method and the Wang method. Parameters from these models were then applied to a modified von Bertalanffy growth equation to estimate age at the onset of sexual maturity. Male and female D. mawii begin sexual maturation at approximately 38.0 cm and 40.0 cm straight-line carapace length, respectively. Ages associated with these sizes were estimated at 13.5–16.9 years (males) and 13.6–17.3 years (females). No previous literature on growth rates or age at maturation for wild or captive D. mawii has been reported, so these results serve as a starting point in conservation management. Given the life history trait of delayed sexual maturity (>10 years), D. mawii may be more sensitive to losses of the adult population; therefore, captive breeding and head-starting programmes may be beneficial with concomitant protection of wild, adult populations.