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Winter possum control for Wainuiomata and Orongorongo water catchments

Winter possum control for Wainuiomata and Orongorongo water catchments

Greater Wellington will carry out possum control using 1080 in the Wainuiomata and Orongorongo water supply catchments (including the Wainuiomata Recreation Area) between July and October 2005. The operation is one of three possum control operations planned for the Wainuiomata district.

The operation is needed to help maintain the region’s high quality water supply and protect public health. The catchment areas provide nearly twenty percent of the water supply for the Wellington metropolitan region.

The Wainuiomata water treatment plant, which treats water from both catchments, will be shut-down before the operation starts. Greater Wellington will then carry out a rigorous testing programme to monitor the breakdown of the 1080, in accordance with Ministry of Health guidelines, and will only re-open the treatment plant after receiving approval from the region’s Medical Officer of Health. Greater Wellington has four water treatment plants in its system, so the closure of the Wainuiomata plant will not affect supply to the public.

Greater Wellington’s Forestry Manager Barry Leonard says, "recent monitoring in the area has shown that possum numbers need to be tackled now. Possums carry diseases such as Giardia and Cryptosporidium and destroy the forest vegetation, which helps to keep our source water clean. Our treatment processes are designed to remove these contaminants from the water, but it’s good practice to tackle the source of the risk too. The operation will maintain an extra level of security for the community."

Aerial application has been chosen because of the area’s rugged terrain. Cereal bait containing 1080 poison will be applied by helicopter over the entire 7,350-hectare catchment area. From July the operation will start as soon as a suitable window of weather occurs. A GPS satellite-based navigation system will ensure accurate delivery. The bait will be applied at a rate of 2kg per hectare, equivalent to one bait pellet per 33 metres square. 1080 is the only poison licensed for aerial application.

Mr Leonard says that a range of measures were being put in place on the ground to minimise the possibility of people or domestic animals coming into contact with the 1080.

"The catchments are generally closed to the public, but we’ll be putting up warning notices on all main access points as a precaution when the poison is laid and a flood warning system will be in place. There is a risk to dogs if we get flooding and dead possums are washed out of the catchments. If there is a heavy rain event, council staff will patrol the Wainuiomata River and will notify the public if needed."

Full details of the public warning measures to be used will be publicised closer to the beginning of the operation.

The operation follows confirmation from independent experts that 1080 is the most efficient and effective means of possum control for the area. It is water soluble, so that any poison in uneaten baits breaks down after rainfall. In water and soil, 1080 is broken down by micro-organisms into harmless, non-toxic substances.

Bird monitoring, after an earlier 1080 operation in the area in 1999, showed an increase in the number of native birds, mainly due to a decrease in the number of rats, possums and stoats for at least one breeding season. New Zealand Forest and Bird support the use of 1080.

1080 drop location map
1080 drop location map
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