Declines of freshwater turtles associated with climatic drying in Australia's Murray-Darling Basin

Context. While much attention has been paid to the effects of global temperature increases on the geographical ranges and phenologies of plants and animals, less is known about the impacts of climatically driven alteration of water regimes. Aims. To assess how three species of freshwater turtle in Australia's Murray-Darling Basin have responded to long-term decline in river flow and floodplain inundation due to climatic drying and water diversions. Methods. Turtle populations were sampled in a section of the Murray River and its floodplain in 1976-82 following a wet period and in 2009-11 at the end of the most severe drought on record. Catch per unit effort, proportional abundance in different habitat types and population structure were assessed in both periods. Key results. Catch per unit effort in baited hoop nets declined by 91% for the eastern snake-necked turtle (Chelodina longicollis) and 69% for the Murray turtle (Emydura macquarii), but did not change significantly for the broad-shelled turtle (Chelodina expansa). In addition, total catches from a range of sampling methods revealed a significantly reduced proportion of juvenile C. longicollis and E. macquarii in 2009-11, suggesting a fall in recruitment. Key conclusions. The decline of C. longicollis was likely due mainly to drought-induced loss of critical floodplain habitat in the form of temporary water bodies, and that of E. macquarii to combined effects of drought and predation on recruitment. C. expansa seems to have fared better than the other two species because it is less vulnerable to nest predation than E. macquarii and better able than C. longicollis to find adequate nutrition in the permanent waters that remain during extended drought. Implications. Declining water availability may be a widespread threat to freshwater turtles given predicted global impacts of climate change and water withdrawals on river flows. Understanding how each species uses particular habitats and how climatic and non-climatic threats interact would facilitate identification of vulnerable populations and planning of conservation actions.