Growth in a cold environment: body size and sexual maturity in a northern population of spotted turtles, Clemmys guttata

Abstract

Using mark-recapture data collected from 1978 to 1997, we examined growth rates, adult body size, and age and size at sexual maturity of spotted turtles (Clemmys guttata) in a northern temperate climate. Relative instantaneous growth rate analyses indicated that growth rates were inversely related to body size, individual variation in growth rate was high, and females and males did not differ with respect to growth rates. Growth of our spotted turtles was described well by both the von Bertalanffy and logistic growth models, although the von Bertalanffy model provided a slightly better fit to our data. Asymptotic sizes and intrinsic growth factors did not differ between the sexes. Northern spotted turtles reach a larger mean adult body size relative to southern populations. Turtles were not sexually size dimorphic with respect to carapace length; however, plastron length was greater in females than in males. Sexual maturity was reached at a larger size (a carapace length of approximately 103 mm for females and 105 mm for males) and estimated age (12-15 years for females and 11-13 years for males) in northern spotted turtles relative to more southerly conspecifics.