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 native wildlife.
Rat numbers are now extremely low in the operational area, down to being undetected in rat monitoring. Possum and stoat numbers will also have been considerably knocked down.
Helicopter distribution of cereal baits containing 1080 toxin took place over around 11,000 hectares of the Anatoki area on October 30. Ship rat numbers were at the time on the verge of reaching plague proportions due to a beech mast creating an abundant beech seed winter food supply enabling more rats to survive. With more rodents to feed on, it was also expected stoat numbers would have been high over summer.
The pest control operation was primarily aimed at protecting three species of threatened giant Powelliphanta snails from possums and rats - one species is ranked ‘nationally critical’, the same threatened status as kakapo. It will also benefit threatened native plant species in the area, including three species of beech mistletoes – red, scarlet and yellow – due to there being fewer possums to browse them.
Predation on nesting native birds and their young, including kakariki, whio and great spotted kiwi, during the breeding season will have been reduced, resulting in more chicks fledging to boost populations.
Department of Conservation Golden Bay Area Manager John Mason said the reduction in pests resulting from the aerial 1080 pest control operation was good news for the area’s native species.
“Rat and possum number need to be kept to very low levels to protect the threatened Powelliphanta snails – to less than 1% detected in our monitoring of these predators. That has been achieved in the Anatoki pest control operation and it is a very pleasing result in terms of protecting the area’s native species from these pests.”
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. The percentage of tunnels showing evidence of rats walking through them over one night was used to gauge their population density at Antatoki.
Prior to the pest control operation, 29% of tunnels showed evidence of rats. In monitoring three weeks after the operation, no sign of rats was found in tracking tunnels in the operational area.
For comparison purposes, rat monitoring was also carried out in the adjoining Waingaro catchment where no pest control had taken place. There, 39% of tracking tunnels showed evidence of rats.
Possum monitoring is carried out using trap lines with possum population density assessed from the numbers caught in traps over three nights.
“Prior to the pest control operation, the trap catch of possums was 7%. The operational methods used at Anatoki are known to achieve a possum trap catch of less than 1%.
“Possum numbers can be gauged from possum interference with rat tracking tunnels. In the Waingaro control site, where no pest control took place, 20% 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, strongly indicating possum numbers have been considerably reduced there.
“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 is also to take place later in summer. The operation continued the benefits to the Anatoki area’s native species of a previous aerial 1080 pest control operation there in 2004.
The threatened Powelliphanta snails species the operation was carried out to protect are the ‘nationally critical’ Powelliphanta “Anatoki Range” and, Powelliphanta hochstetteri anatokiensis and Powelliphanta superba superba.