Slow and unsteady: growth of the Australian eastern long-necked turtle near the southern end of its natural range

Abstract

Knowledge of growth rates and maturation times of freshwater turtles is important in assessing population viability. I analysed growth of Australian eastern long-necked turtles (Chelodina longicollis) from individual capture–recapture records spanning periods of up to 17 years for a population in Gippsland, Victoria, close to the high-latitude end of the species’ natural range. Juvenile growth was rapid and similar among individuals but adult growth was usually slow, highly variable among individuals and erratic within individuals over time. In addition, asymptotic body lengths were disparate among individuals for both males and females. Von Bertalanffy growth models fitted separately to males plus unsexed juveniles and females plus unsexed juveniles performed better than logistic models but tended to underestimate growth rates for very small and very large turtles and overestimate growth for medium-sized individuals. Sexual maturity was estimated to be achieved at 10 years in males and 16 years in females, which is late compared with most estimates for other populations of C. longicollis and for other turtle species in south-eastern Australia. The high variability of individual growth in this population makes age estimation from body size unreliable beyond the first few years of life.