Tracking turtles in an urban environment
The Challenge
A local population of native turtles may be negatively impacted by habitat changes (see Figure 1) associated with plans to develop the CSIRO Ginninderra Experiment Station (GES) into an Urban Living Lab. Farm dams and existing water points could be lost or altered during development while urban infrastructure, such as roads and houses, will fragment the landscape disrupting turtle movements causing deaths from traffic. Our project aims to enhance the survival of the turtle population as part of this ecologically sustainable urban development.
Figure 1: The farm dam (at very low summer 2020 level) scheduled for alteration or removal at CSIRO GES
Our Response
In collaboration with the University of Canberra Institute for Applied Ecology and the Ginninderra Catchment Group, we are using our extensive expertise in animal ecology to capture turtles and record their movements across the landscape via the use of satellite-based GPS trackers (Figure 2). The fine-scale location data gathered by the GPS-satellite trackers is an innovative approach to understanding turtle movement ecology. It is an improvement on the previous methodologies of ground-based radio-telemetry and capture-mark-recapture studies, which recorded location information but did not reveal the path taken by turtles between these locations.
This information will allow us to identify turtle movement pathways which will be incorporated into development designs, thereby ensuring population health and sustainability is maintained by retaining connectivity between existing and future water bodies. This approach can also be scaled-up to study larger urban populations or those at a landscape scale such as in rivers or wetlands of the wider Murray-Darling Basin.
Figure 2: GPS tracker on turtle
Results
During the Spring and Summer of 2019/2020, fifty-five turtles were captured, the majority of which were too light to carry the tracker. Five of these turtles were tracked, three provided detailed movement data. All tracked turtles were captured in the main farm dam which is scheduled for removal as part of development plans.
Turtle #1 (Tracker ID MD-02) was tracked for more than 560 metres over 60 days (Figure 3). This turtle moved from the farm dam to a small patch of remnant vegetation and was then recovered in a paddock below the dam where it had died of an unknown cause.
Figure 3: MD-02 movement path (yellow line). CSIRO GES farm boundary in white, farm dam blue circle, local creek blue line.
Turtle #2 (Tracker ID MD-03) was tracked for 35 days and involved an overland path of approximately 1025 metres across paddocks and along vegetated corridors (Figure 4). This turtle was later found dead at the property boundary fence, despite being in the shade of pine trees and buried under leaf litter. It was possibly attempting to reach a local creek beyond the fence but could not get through and died of exposure during several hot summer days.
Figure 4: MD-03 movement path (yellow line)
Turtle #3 (Tracker ID MD-05) was tracked for 31 days over approximately 1080 metres (Figure 5). This turtle followed a similar path to MD-03. After MD-03 had been found dead in this same location it was decided to move MD-05 back to the dam, after which no further points were recorded.
Figure 5: MD-05 movement path (yellow line)
These early results have revealed several movement pathways and locations used by turtles across the property. They also reveal that the boundary fence could be forming a barrier to the natural movements of turtles between the farm dam and the creek beyond the property. Plans are underway with CSIRO managers to determine how this potential barrier can be removed or overcome (e.g. by the provision of turtle-friendly passageways in the fence) to restore connectivity between habitats.
More trapping and tracking is planned for Spring/Summer 2020/2021.
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