A living ark
A pest-free Sanctuary
The key to restoring Karori Sanctuary back to its pre-human state is to ensure introduced mammalian pests are kept out - via our 8.6km exclusion fence. The presence of introduced pests, such as possums and stoats, has had a dramatic effect on the range of native wildlife and plants all over New Zealand.
A possum participating in early fence trials
It is estimated that possum browsing, before the fence was built, removed 400 tonnes of vegetation from the Sanctuary valley in a year, severely affecting regionally rare plant species such as northern rata, tree fuchsia and kohekohe. Habitat loss and predation from rats, stoats, ferrets and cats saw the number of native bird species that would have been present in the Sanctuary decline from about 20 to less than 10, all in low numbers.
By 2000 Karori Sanctuary was free of introduced pests. This feat created a number of world-firsts:
- The first time 13 species had been targeted for eradication at once
- The first eradication operation targeting hedgehogs and hares
- The first pest-free zone in an urban environment
- The first eradication operation on the mainland targeting rodents, cats, possums, mustelids and rabbits.
A five-phase eradication programme was implemented:
| Date | Action |
|---|---|
|
December 1998 |
Eradication planning completed. |
|
August 1999 |
8.6 km perimeter fence completed. |
|
June - September 1999 |
Possum trapping conducted by Wellington Regional Council.
|
|
Distribution of poison bait over two days.
| |
|
October 1999 - January 2000 |
Ground-based techniques including trapping used to detect and eradicate remaining animals.
|
The Sanctuary operations team now focus on the time-consuming and difficult task of monitoring for any signs of reinvasion. Unfortunately mice were detected in 2000 and have continued to reinvade since then, probably due to minor flaws in the fence caused by settling or objects bumping into the fence. While modifications were made to the fence, we have been unable to prevent reinvasion and have been trialling further design modifications to be undertaken in the future.
In 2004 and 2008 weasels were detected and an eradication programme using traps began immediately. To increase the chances of a successful weasel eradication, especially because females can be very difficult to trap when breeding, mice were poisoned. Mice are the preferred prey of weasels.
The monitoring programme and the rapid response to any pest reinvasions will continue to be an ongoing task for the Sanctuary as part of its 500 year restoration strategy.
More information
- Karori Sanctuary's fence
- Summary of Rodent Control Measures at Karori Sanctuary (43kb, pdf).
- Eradication of Pests from Karori Wildlife Sanctuary: A Brief Summary (Paper presented at Mainland Island Hui, St Arnaud 10-13 July 2000) (PDF file, 112kb).
