Land use surrounding wetlands influences urban populations of a freshwater turtle

Urbanization is one of the most influential land use changes globally and continues to affect wetland ecosystems and their biota. Freshwater turtles, which rely on both terrestrial and aquatic habitats to complete their life cycles, are one of the most endangered vertebrate groups, with approximately 60% of species threatened. Although habitat alteration caused by urbanization is recognized as one of the main threats to freshwater turtles, there is a paucity of studies quantifying the effects of terrestrial habitat change on turtle populations. The aim of this study was to determine how terrestrial land use change, associated with urbanization, influences the viability of freshwater turtle populations. Thirty-three wetlands were sampled for the southwestern snake-necked turtle (Chelodina colliei Gray, 1856) (Chelidae) between October 2016 and February 2017 within a region of continuing urban intensification. Land use and habitat types were classified at the aquatic-terrestrial interface and within a 300-m band around each wetland. Generalized linear mixed models were used to identify the land use variables that best explained the relative abundance of C. colliei. Turtle abundance and population structure varied widely among wetlands. The percentage of residential land use, and the presence and accessibility of fringing native vegetation, was positively associated with the relative abundance of C. colliei. The association with residential land use may be an artefact of historical land use, whereas the association with native vegetation is probably because adjacent vegetation provides connectivity with suitable nesting sites, and thus facilitates increased recruitment. This study shows how the modification of terrestrial habitat around wetlands may directly influence the population viability of freshwater turtles. Protection and restoration of native vegetation fringing urban wetlands is crucial to support the viability of remnant freshwater turtle populations.