Distribution, abundance and population structure of the threatened western saw-shelled turtle, Myuchelys bellii, in New South Wales, Australia

Abstract

The western saw-shelled turtle is listed as threatened globally, nationally, and within the Australian state of New South Wales. Although nearly all of the geographic range of the species lies within New South Wales, little information has been available on the distribution, abundance and structure of New South Wales populations. Through a survey of 60 sites in 2012–15, I established that M. bellii is much more widely distributed in New South Wales than has previously been recognised, comprising four disjunct populations, including two in the New South Wales portion of the Border Rivers basin. It occurs mainly in larger, cooler rivers upstream of barriers to dispersal of the Macquarie turtle, Emydura macquarii macquarii. Although M. bellii is locally abundant, its populations are greatly dominated by large adults and recruitment appears to be low. Eye abnormalities are common in some populations but do not necessarily impair body condition or preclude long-term survival. The species is threatened by competition with E. macquarii, which appears to be expanding its range through translocation by humans, and possibly by predation, disease and drought. Long-term monitoring of M. bellii is needed to assess population trends and responses to threats, and active management to restrict the further spread of E. macquarii is probably required to ensure the persistence of M. bellii throughout its current range.