Powelliphanta operation knocks back predator numbers
An aerial 1080 pest control operation in Kahurangi National Park’s Anatoki River area in October has significantly reduced predator numbers, curbing an expected explosion in rat and stoat numbers, and making the area safer for giant land snails and native wildlife, says the Department of Conservation.
Helicopter distribution of cereal baits containing 1080 toxin took place over nearly 11,000 hectares of the Anatoki area on October 30. At that time, ship rat numbers were threatening to reach plague proportions due to a beech mast that created an abundant winter food supply. Stoats had been expected to be plentiful over summer because of the good supply of rats for them to prey on.
The pest control operation was primarily aimed at protecting three species of threatened Powelliphanta snails from possums and rats. One species is ranked “nationally critical” and has the same threatened status as kakapo. The operation will also benefit three species of beech mistletoes because there are fewer possums to browse on them, and reduce predation on nesting native birds and their young, including kakariki (native parakeet), whio (blue duck) and great spotted kiwi, during the breeding season.
Department of Conservation Golden Bay area manager John Mason said the monitoring showed good news for the area’s native species.
“Rat and possum numbers need to be kept very low to protect the threatened Powelliphanta snails – to less than 1 per cent detected in our monitoring of these predators. That’s been achieved in the Anatoki operation. It’s a very pleasing result.”
Rat population data is gathered using lines of tracking tunnels. Bait inside the tunnels lures the pests inside and their footprints are tracked using ink pads. Prior to the pest control operation, 29 per cent of tunnels showed evidence of rats. In monitoring three weeks after the operation, no sign of rats was found.
For comparison purposes, rat monitoring was also carried out in the adjoining Waingaro catchment where no pest control had taken place. There, 39 per cent of tracking tunnels showed evidence of rats.
“Possum numbers can be gauged from possum interference with rat tracking tunnels. In the Waingaro control site, where no pest control took place, 20 per cent of the rat tracking tunnels showed signs of possum interference. But in the Anatoki area after the operation there was no evidence of possum interference with tunnels, so possum numbers have been considerably reduced there. The operational methods used at Anatoki are known to achieve a possum trap catch of less than 1 per cent,” said Mr Mason.
“Aerial 1080 pest control operations are also known to achieve a big reduction in stoat numbers through secondary poisoning from eating poisoned rodents. We will be carrying out stoat monitoring to assess their numbers after Christmas.”
Further rat monitoring will occur later in the summer.
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