Optimizing road underpass design to maximize use by a freshwater turtle (Chelodina oblonga)

Roads affect the connectivity of habitat and inhibit movements of animals as a result of road avoidance and road-related mortalities. Freshwater turtles are particularly vulnerable to mortality on roads, as females must often cross them when they leave the aquatic environment to nest. Ecopassages designed to enable safe movement across roads by wild animals may be an effective measure to reduce adverse impacts. Limited information exists, however, on effective design criteria for freshwater turtles.A willingness-to-utilize study was used to assess factors that may influence the use of a tunnel underpass by the southwestern snake-necked turtle (Chelodina oblonga), a species whose populations are declining, in part, through road-related mortalities of nesting females. Female C. oblonga were sourced from an urban wetland and placed in an enclosure with exits of varying tunnel lengths (12 and 25 m) and lighting treatments ('light' and 'dark') to assess the conditions that would promote successful passage.Generalized linear modelling showed that light treatments had a significantly increased likelihood of successful and faster passage for both 12 and 25 m tunnels than the dark treatments. Tunnel length had no effect either on success or rate of passage.This study provides the first account of the factors that may optimize successful tunnel passage by C. oblonga to reduce road-related mortality, contributing to the conservation and management of the species and freshwater turtles more generally.