It is well documented that humans may have a major impact on native ecosystems including the animals that reside within them. In Australia, over the past 200 years there have been major changes to the landscape, including land clearing, habitat fragmentation, urbanisation, the creation of roadways, and the introduction of exotic species. Freshwater turtles are one taxon that has been affected by both terrestrial and aquatic changes. The long-necked turtle Chelodina longicollis (Shaw 1794) is the most widespread, and abundant freshwater turtle in Australia. Because of their broad geographic range, their ability to survive within a diversity of aquatic habitats, urban and rural, and because they have a penchant for terrestrial movement, they are an appropriate species to use as a case study on the effect of urbanisation on the long-term viability of freshwater turtles. In addition, because C. longicollis represent the largest vertebrate biomass in many impoundments, their demise is likely to have a major impact on the functioning of these systems. This study was undertaken in Sydney, the largest city in Australia, in areas that have had significant habitat change due to urbanisation, and continue to have rapid change due to increasing density and extent of urbanisation. It was observed that C. longicollis remain the ubiquitous freshwater turtle, although recruitment to the population varied both at different human population density, and among wetlands, and there was little to no recruitment in the urban and suburban sites. Another native freshwater turtle, Emydura macquarii was found at all three sites (urban, suburban and peri urban). In the peri urban site there were very few of this species netted, whilst at both the urban and suburban sites they were in greater numbers, with E. macquarii in greater density than C. longicollis in the urban area. Successful recruitment of E. macquarii was only observed to have occurred in the suburban site and not in the other two sites (suburban, peri urban). A potential impact on C. longicollis was competition from other species such as Trachemys scripta elegans the feral red-eared slider that has demonstrated to outcompete native species in many areas of the world, including Australia. In the peri-urban area it was found that wetland characteristics were influencing the population structure in wetlands, and juveniles were more prevalent in wetlands with low dissolved oxygen and higher percentages of emergent vegetation. It was also observed that over the decade of the study, there was a shift in the population structure to a female bias in the population. Females were also shown to have greater site fidelity than males. Approximately 15% of females were recaptured in the wetland of first capture 13 years after they were first netted in the wetland, although no males were recaptured after this length of time. These females were also in better condition than those that had been netted only in the more recent study period. Vehicle collision impacted both sexes of C. longicollis in all stages of their lifecycle. Females were killed in higher numbers in the nesting season (spring) than at other times, potentially exacerbating the impact on local populations. Casual observation may indicate that C. longicollis, and where they are present, Emydura macquarii, have viable populations, even within wetlands within the most densely populated area of Sydney. However, in these long-lived animals, lack of, or limited, recruitment to the population, losses due to vehicle collision during terrestrial movement, supplementary feeding, water quality, and loss of wetlands in the urbanising areas, question whether the populations over the longer term are viable in the urbanised/rapidly urbanising areas of the Sydney Basin. Without knowledge of longevity and age of senescence, it is effectively impossible to predict when the population will become non-sustainable. However, without intervention such as raising the awareness of the plight of freshwater turtles, the provision of safe nesting sites, mitigation measures to reduce vehicle collision, and removal of exotic animals, the population will decline over time.
| Date of Award | 2014 |
|---|
| Original language | English |
|---|