Skeletochronology of the endangered side-neck turtle, Podocnemis expansa

Abstract

Previous preliminary mark-recapture studies, and assessment of carapace length and annuli of the endangered giant Amazonian river turtle, Podocnemis expansa, have provided some insight Into various aspects of their population structure and overall biology. Many questions still remain, however, particularly pertaining to the attainment of sexual maturity, nesting age of females, and longevity of individuals. The current study examines the feasibility of using skeletochronology on the bones of Podocnemis expansa, to obtain data pertaining to these questions, as well as to acquire individual ontogenetic age data. Material for the analysis was opportunistically obtained from 'kitchen remains' and leftovers of natural predators. Our results showed that even after being subjected to such harsh treatment, all the bones in our sample preserved histological detail. By the application of skeletochronology, we estimate the individual ages of all specimens and these compared favourably with age data obtained previously. In spite of our limited sample size, we found a positive relationship between the number of growth rings and carapace length, a slower increase in body size for the larger individuals, and we tentatively suggest that sexual maturity may have occurred at about 5-6 years of age. On the basis of the findings of this pilot study, we suggest that skeletochronology can be effectively used on this endangered taxon. Furthermore, as skeletochronology can also reliably permit deductions about the age profile of individuals that fall prey to predators, it also has the potential of assisting in the development of effective conservation strategies.