Measuring Turtle Nest Predation of the Lake Joondalup Turtles (Chelodina oblonga) 2011/2012
Monitoring of Turtle (Chelodina oblonga) nest predation at Lake Joondalup as an indicator of the effectiveness of an ongoing fox control program.
The work was carried out on behalf of the Friends of Yellagonga by Kevin McLeod (Chairman) ably assisted by fellow member Sue Walker.
Predation of turtle nests has been known for some time. Historically Lake Joondalup carried a high population of turtles with large numbers being observed moving around during nesting events. These numbers no longer occur (pers. com.). No scientific work has been done to determine population size. A population study in 2010 (J.Giles) showed no turtles captured below 9cms and a skew towards older ages.
Foxes predate on a wide range of small native species and are extremely efficient in finding and eating turtle eggs. An effective fox control program should result in higher survival of turtle eggs, hatchlings and small native animals being available as a population buffer and a food source for native predators.
Since urbanization of the lake surrounds no fox hunting or control had been carried out. Foxes were regularly seen moving around the lake. A subsequent trapping effort saw 13 foxes removed. (Animal Pest Management Report 2010)
It has been decided to carry out continual fox control at least annually. Nest predation is still observed however.
Monitoring is an important part of any Pest Animal Control Program (Australian Pest Animal Strategy NRM Ministerial Council).
It was decided to monitor the results of fox predation on turtle nests as this was comparatively easy to observe over time. The nests dug up have no relationship to fox numbers other than that there was at least one involved and possibly more.
A path runs between Picnic Cove and Neil Hawkins Park along the Western edge of Lake Joondalup. It was proposed to walk along the path and note any nest dug up within two meters each side.
The path measures 2000 meters so the area inspected is 8000 square meters.
The exercise was done every two weeks from before the laying season until the end.
Its planned to repeat the exercise annually for comparisons.
Note: Two main nesting events occurred, one in October and the second in December. In both cases the nests were dug up within 24 hours. Further minor nesting occurred with predation as shown in the graph.
In light of the data perhaps additional techniques could be tried such as an effort made to find the nest before the fox and supply a protective grid. The Friends of Yellagonga will continue efforts to increase hatchling recruitment into the Lake.
Image shows approximate positions of predated turtle nests with a yellow pin and the track followed.
Last Updated on Sunday, 13 May 2012 15:08