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Published: 2007-07-31 00:00:00

A recent possum control operation on Mt Pirongia has been a resounding success, says Environment Waikato biosecurity manager John Simmons.

Baits containing 1080 were dropped over about 16,000 hectares of land centering on Mt Pirongia in late June, in a bid to reduce increasing possum numbers.

Quality Monitoring Services, which was contracted to provide an independent assessment of the operation’s success, set traps in the bush to assess possum numbers last week.

The monitoring programme was designed using strict national standards and returned a residual trap catch (RTC) of 0.42 per cent.

“The RTC before the operation was 21 per cent according to Department of Conservation data, so that’s a great result,” Mr Simmons said.

“The performance target for the contractor, EcoFX Limited, was three per cent or less which they’ve bettered, and by a substantial amount.”

Post operational monitoring was carried out at 40 randomly selected points in the operation area. Ten traps spaced 20 metres apart were set at each of these points and left out for three nights. The lines were checked daily and any possums caught were killed and recorded.

“In other words, the equivalent of 1200 possum traps over one night were set and there were only five possums caught in total,” Mr Simmons said.

This monitoring method is used all over New Zealand for assessing possum population densities.

“As it is only a random sample, it cannot be used to give an absolute number of how many possums survived within the Pirongia Forest Park,” Mr Simmons said.

“However, it is a very good result, and given possums breeding rates, we expect the numbers will take in excess of seven years to build up to what the pre-poison levels were.”

Mr Simmons said the use of a helicopter to lower contractors and their gear into the bush had allowed the post operational monitoring to be carried out in only five days.

“If we’d used ground methods, where contractors had to walk into the bush and camp, this operation would have taken the better part of 4-5 weeks of fine weather to complete.”

The aerial possum operation was carried out by Environment Waikato and the Department of Conservation, with approvals from Waipa District Council and Waikato District Health Board.