The first key to restoring the sanctuary valley back to its pre-human state was to remove introduced mammalian pests so our native species can thrive. The eradication process happened in various stages, before, during, and after the erection of the fence.
In 1998 the eradication planning was completed. The plan was ambitious: the world’s first eradication targeting 13 species at once (opposed to the standard 1 or 2 species), the world’s first eradication operation on the mainland targeting rodents, cats, possums, mustelids and rabbits and the world’s first eradication operation targeting hedgehogs and hares. During this time, all necessary consents are obtained.
In 1999 50 km of tracks are cut for bait stations, and transmitters are put on 3 stoats and 2 feral cats to monitor survival during eradication operation. The death of the three radio-tagged stoats showed that poison was effective for this species.
Possum trapping then starts, conducted by Wellington Regional Council. Three tonnes of possums were trapped and over 1000 possums killed in 8 weeks. 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 rātā, tree fuchsia and kohekohe.
Resource Consent is then obtained for aerial application in the Sanctuary of cereal baits containing brodifacoum– the first ever approval to distribute brodifacoum baits by air in a mainland operation (previously only permitted on off-shore islands). Distribution of poison bait over two days - 4.5 tonnes of bait spread by helicopter and by hand.
Later that year bait stations and tracking tunnels are also installed for ground control and monitoring of rodents, mustelids, and hedgehogs; surveys also undertaken for possums, cats, lagomorphs (rabbits and hares), deer, pigs, goats & cattle; no evidence of surviving rodents (including mice), mustelids, cats, hares, deer, pigs, goats & cattle following the bait drop.
The last 4 possums removed in November and last hedgehog (Custer) trapped in December 1999.
In 2000 the last rabbit is shot. Pest mammal eradication complete - no rats or mice detected in follow-up monitoring. ZEALANDIA is officially the world’s first pest-free zone in an urban environment!
Unfortunately later that year mice were detected and have continued to reinvade since then, most likely due to minor flaws in the fence caused by settling or objects bumping into the fence.
In 2004 weasels are detected - the first known incursion since removal and assumed to have been due to a spillway issue. Both this incursion and a subsequent one in 2008 were successfully managed and no further mustelids detected.
In 2006 the Southern Bell frog was detected and successfully removed from the sanctuary, the first successful “eradication” of this pest species in New Zealand.