Silver Peaks aerial operation: your questions answered

Date 12 June 2017


Q: Why is the Silver Peaks aerial operation necessary?

To eradicate bovine TB – the mission of the TBfree programme – possum numbers need to be kept low – around one to two animals every 10 hectares. Scientific surveys can then confirm that disease is no longer present. Monitoring has shown that further control work is needed in the 8,600 Silver Peaks area to reduce the possum population and minimise the risk of the disease spreading through wild animal populations and onto farmed cattle and deer.

The need for the operation has been thoroughly assessed. The forest terrain is prime habitat for possums, which transmit bovine tuberculosis to domestic cattle and deer. Recent outbreaks of TB among possums and livestock in the nearby Mount Cargill area show that disease is present in the region. The Silver Peaks block was last aerially treated in 2011; the Silver Stream portion has not received aerial control before.

Q: What does an aerial operation involve?

An aerial operation uses helicopter distribution of cereal baits containing biodegradable sodium fluoroacetate (1080) poison to target possums. There are a number of control techniques available to possum control contractors, but the key to effective control is using the appropriate method for the job, depending on a number of factors such as the terrain, local wildlife, previous control work and the objective for the area.

Hand-laid traps and toxins account for about 70% of bovine TB possum control work. The remaining area is controlled using aerially applied 1080.

Aerial operations can be used for quick and effective control in hard-to-access areas, or large tracts of land, where ground control is impractical. All operations must have consent from the Ministry of Health, and there are strict protocols governing health and safety considerations where and whenever toxins are used.

Pest control for TB management also provides a range of conservation and biodiversity benefits, including helping to reduce the number of rats and stoat that threaten native birds and plants.The Parliamentary Commissioner for the Environment supports the use of aerial 1080 for animal pest control. The commissioner completed an extensive review into the use of 1080, in which she strongly endorsed its continued use in New Zealand. Please visit to read this report.

Q: When will the Silver Peaks operation take place?

The operation requires periods of settled weather. The toxic baits are biodegradable and water soluble, so wet weather can hamper the effectiveness of an operation. The operation is proposed for the first fine weather window in mid-June.

Q: What did the consultation process entail?

OSPRI undertook an open national consultation process for four months from November 2016, and invited feedback from interested stakeholders and the wider community. The 2017 national plan for TBfree pest control operations is here. This was distributed directly to landowners and administrators, councils and regional representatives of affected parties. This process resulted in a number of submissions about the planned Silver Peaks aerial from members of the public.

All land owners and land occupiers within and adjacent to the area to be treated have been notified of the operation in writing and personally visited to ensure all necessary safety measures and precautions are observed. A public information event in March at the Orokonui Eco-sanctuary was publically notified and invitations sent to stakeholders, affected land occupiers and interested parties, including those who made submissions on the Silver Peaks operation.

The meeting provided a further opportunity for dog owners to discuss the operation directly with OSPRI staff. As a result of the consultation feedback, OSPRI has worked with the Dunedin City Council to ensure that all registered dog owners were made aware that the Silver Stream Catchment area will be out of bounds to dogs for up to 12 months after the operation. More information can be accessed here -

Q: Why has an aerial drop of toxic bait been preferred over possum trapping for their fur?

The aerial distribution of 1080 baits is used to control populations of possums in large areas of forested terrain that is difficult or impractical to access. Most possum control in the region is done by local contractors using ground-based traps and hand-laid toxins. The remaining, far smaller area is controlled using aerially applied pellets containing biodegradable 1080. Aerial control is efficient, cost effective and has been extremely successful at knocking possum numbers down to very low levels in the past. It is preferred in areas like Silver Peaks due to the rugged nature of the terrain.

Our long experience is that commercial fur trapping alone will not reduce possums to low enough densities to prevent maintenance and transmission of bovine TB. Fur trappers will stop working when possums can no longer be caught at a profit – but at this population level, TB can still persist in remaining possums. Fur hunters will also avoid hard to reach area such as thick gorse or very steep gullies, which may well still harbour infected possums.

Q: Some dog owners say the size of the operation area limits off-lead exercise areas for city dogs. Were dog walkers’ concerns considered when selecting the area?

The impact on all recreational users to the area, including dog owners, was carefully considered in planning the Silver Peaks aerial operation. Dunedin City Council has identified several alternative off-lead exercise areas for use until the operational area is once more open and safe for dogs, and these are promoted to dog owners via newsletter and information available on the DCC website -

Dog owners have been consulted on this operation since November 2016, concerns have been listened to, and activity adjusted accordingly.
OSPRI has distributed guidance on keeping dogs safe and ensured information is available to dog owners enabling good decisions and actions to protect their dogs and keep them away from the designated operation areas.

Q: What advice is given to people who normally use the area that is being targeted by this operation?

Members of the public are requested to follow the instructions on warning signs erected prior to the toxic application. When the operation is flown, the Silver Stream catchment and affected tracks will be closed to all users for about 15 days. After that, the reserve will re-open to the general public, but will remain closed to dogs for up to 12 months, and hunting permits for the catchment will be suspended to ensure dog safety.

Read the Silver Peaks aerial operation factsheet for more information.

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