The impact of urbanisation on the south-western snake-necked turtle (Chelodina colliei

Anthony Santoro

Urbanisation is one of the most influential forms of land use change globally and continues to apply increasing pressure on biodiversity. Freshwater turtles are one of the most endangered vertebrate groups with current assessments suggesting 45-50% of all species are under threat. The habitat alteration caused by urbanisation has been identified as one of the main threats to freshwater turtle populations, but there have been relatively few studies that have quantified its impact. The status of Chelodina colliei, a turtle endemic to south-western Australia, in the urban wetlands of the Swan Coastal Plain (SCP) remains largely unknown. However, recent studies that have occurred in a limited number of wetlands on the SCP have suggested the populations may be experiencing declines. The overall aim of this study was to assess the impact of land use modification caused by urbanisation on C. colliei populations. It was predicted that increasing levels of urbanisation around wetlands would result in reduced abundances and modified population structures. Specific aims were to quantify the land use surrounding a sub-set of wetlands on the SCP, determine the abundance and population structure of C. colliei in those wetlands, and determine the association between land use and turtle populations. Thirty-five wetlands were sampled for C. colliei using modified funnel traps between October 2016 and February 2017. Surrounding land use of these wetlands was assessed and classified into different types, within three perimeters (50, 300, and 500 m from the water’s edge) using Google Earth Pro. Principal Component Analysis was used to assess if surrounding land use differed between wetlands and to classify wetlands as either natural or modified. ANOSIMs were used to assess if the categories were significantly different in all perimeters. The population structures of C. colliei were compared between wetland types using Mann Whitney U tests. Model averaging was used to identify the most influential land use variables on the relative abundance of C. colliei. The study found that wetlands grouped dichotomously based upon surrounding land use, with natural having over 50% of the surrounding land use as bushland, whereas modified wetlands had less than 50%. Chelodina colliei population abundances and structures differed between those groups, with greater abundances and population viability in natural wetlands. The availability and accessibility of fringing bushland was the most important land use variable associated with the relative abundance of C. colliei. The positive association with bushland was likely due to it providing suitable nesting sites for C. colliei. This study increases our understanding of the status of C. colliei in urban wetlands and demonstrates, for the first time, that surrounding land use has a direct effect. It has important implications for wetland management and suggests protection and restoration of fringing bushland around urban wetlands is crucial for enhancing the viability of remnant C. colliei populations.

The impact of urbanisation on the south-western snake-necked turtle (Chelodina colliei

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