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The impacts of roads on the population dynamics and ecology of the oblong turtle (Chelodina oblonga) at Blue Gum, Booragoon and Piney lakes

Giles, Jacqueline (2001) The impacts of roads on the population dynamics and ecology of the oblong turtle (Chelodina oblonga) at Blue Gum, Booragoon and Piney lakes. Honours thesis, Murdoch University.

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Roads and urbanisation are an integral part of modem human existence. As urbanisation sprawls further out in Perth, it encompasses more and more natural habitat and the effects on the fresh-water, long-necked turtle Chelodina Oblonga are largely unknown. The main aim of this thesis was to assess the impacts of roads on the population dynamics and ecology of C. oblonga.

This research took place at three suburban wetlands on the Swan Coastal Plain: Blue Gum Lake Reserve, Booragoon Lake and Piney Lake Reserve. These wetlands form a part of the Beeliar wetland chain and differ in varying degrees by the nature of the roads surrounding them, the size of terrestrial buffer and the size, depth and degree of eutrophication of the water body. Booragoon and Piney Lakes are divided by the Leach Highway, which is a major six-laned arterial highway, while Blue Gum Lake is surrounded by quieter suburban roads.

The turtle populations were investigated using a 'mark-recapture' program over a 9 month period with a total of 14 sampling periods. Turtles were trapped mostly using baited modified funnel traps. They were measured, weighed and a number of ecological indicators were recorded. They were then numbered and released. Nest predation was also recorded. This was evidenced by excavation of a small hole with broken egg shells scattered nearby. These were pegged and mapped. The number of corpses was also recorded, indicating road mortality and/ or predation.

Results indicated the presence of a substantial adult population at Blue Gum Lake, with very little evidence of juvenile recruitment into this population. Turtles here were in slightly poorer condition overall. Carapace injuries were evident here suggesting that suburban roads do result in direct impacts, but were not complete barriers to nesting movements. A relatively small terrestrial buffer surrounds this lake and nest predation appeared to be heavy, however the level of impact on recruitment could not be determined.

Only a small population was present at Booragoon Lake and consisted of only older individuals. There was no evidence of juvenile or adult recruitment for both females and males. While the Leach Highway has probably selected against many of the nesting females in the past, it appears many other pressures have been exerted on this population. There is an exceptionally small terrestrial buffer surrounding this lake and nest predation was heavy and probably significant given the small estimated population size. This wetland is also heavily utilised by nesting waterfowl, a number of which include hatchlings and adult turtles in their diet. So it is likely that this wildlife are taking an excessive toll on the turtle population present. The process of local extinction appears to be well underway for C. oblonga.

The population at Piney Lake appeared to be overall the most healthy. There was evidence of successful recruitment into the young age classes indicating that this may be a self-sustaining population. The terrestrial buffer is comparatively large and while nest predation was evident here, it did not appear to be as significant as the extent of nest predation occurring at Blue Gum and Booragoon Lakes. This study found that roads impacted in a multiplicity of ways and to varying degrees on the turtle populations present at Blue Gum, Piney and Booragoon Lakes. Effects are both direct and indirect and occur over a number of spatial and temporal scales and long-term monitoring of the population dynamics of C. oblonga is recommended. Further research is needed to ascertain whether nest predation is significant. Predator control may be essential for the long term survival of C. oblonga. The apparent preference of nesting females for the southern aspect at each wetland needs to be confirmed, as this suggests that the reservation of an adequate terrestrial buffer on the south side of a wetland may be very important.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Engineering Science
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Davis, Jenny and Kuchling, Gerald
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