The TBfree programme’s goal of eradicating TB in wildlife by 2040 is delivered through targeted possum control and wildlife surveillance. Eradicating the disease relies on strong community engagement and liaison with landowners and land users affected by operational activities.

Over 20,000 possums have been removed from the area since work began. Possums need to be kept to low numbers over multiple years to eradicate the disease.

Dunedin Special Focus Area map

Flagstaff ground control

Possum control is currently underway and will be completed by 30 June 2021. Dogs should be kept on lead while all warning signs are in place.

Heyward ground control

Work in this area has been completed for the year and the caution period has been lifted.

Mount Cargill ground control

Possum control began 14 September. Contractors are using traps and Feratox bait bags, subject to landowner approval. Dogs should be kept on a lead until warnings signs are removed.

OSPRI-LCT HALO Project Collaboration

OSPRI is excited to be working with the Halo Project to support the establishment of a long-term volunteer possum trapping network in urban communities in Dunedin. Over 300 traps have already been deployed.

Information for pet owners

There are strict safety, quality assurance and monitoring requirements around the use of pest control techniques. The toxins being used pose an extremely low poisoning risk to pets. To minimise primary poisoning, bait will be in bait stations or bags and there will be no toxins or traps within 30m or in sight of tracks. The toxins being used are slow-acting and dogs would need to eat a number of carcasses (possums or rats) to be affected.

Due to the use of toxin, dog owners should keep their dogs on lead in the area while warning signs are in place. If you think your pet has been poisoned, contact your local vet for help or advice.

For more information on where to walk your dog, visit the DCC website. You can call OSPRI’s Dunedin Office on 03 477 9829 if you're interested in a free dog muzzle.

Cats are not targeted in OSPRI operations. Toxins are not attractive to cats, however, trapping will be used in places. It is recommended that cats should be restricted from venturing into possum control operational areas.

Why is OSPRI undertaking possum control?

All cattle and deer herds around Dunedin are currently clear of TB. This is great progress considering there have been seven herd infections since 2015.

Possums are the main transmitter of TB from wildlife to farmed cattle and deer and when herds first become infected, wildlife surveys found infected possums around Mount Cargill.

To stop TB spreading, we need to keep possum numbers low for a number of years. Ground-based possum control has been undertaken in parts of the Mount Cargill TB Management Area and this work will continue into 2021.

Biodiversity benefits

Possums eat native plants and are a major predator of our native birds, preying on eggs and chicks. By keeping possum numbers low with targeted pest control, native wildlife and bush get a chance to thrive.

Large-scale pest control benefits native wildlife. However, kākā are present around Dunedin and may access bait stations. Careful consideration is given to the methods used in any possible kākā habitat.

OSPRI contractors have removed over 20,000 possums from around Dunedin. That’s from 12,500 hectares since 2016 (between Waitati, Aramoana south to Flagstaff).

As well as the collaboration with the Halo Project in urban areas, OSPRI is working with other Predator Free Dunedin partners to develop a succession plan that ensures the gains made by TB control work are continued beyond TB eradication.

OSPRI Possum Control in Flagstaff

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Methodology

All methods comply with animal welfare regulations and all methods require landowner permission.

Where live capture traps are used, contractors must check these daily. No traps will be placed within 30m or within sight of public tracks.

Toxins include Feratox in bait bags and brodifacoum in Philproof bait stations in some areas. No bait will be placed within 30m or within sight of public tracks.

Information on brodifacoum

Why is brodifacoum used for possum and rat control? Brodifacoum has been used in possum and rat baits in New Zealand since 1992. Many people know brodifacoum by its marketed brand name Pestoff. It can be purchased from your local hardware store.

Rats and possums rarely associate poisoning symptoms with eating this bait. This is due to the time lag between eating a lethal dose and the onset of symptoms (usually several days).

Brodifacoum poses a low risk to dogs. They could suffer brodifacoum poisoning if they scavenge several possum carcasses containing brodifacoum.

If your dog eats poison or a poisoned carcass induce vomiting with washing soda crystals.

If an animal or pet displays the following symptoms take it to the nearest veterinary clinic, where they can administer Vitamin K1, an effective antidote:

  • bleeding gums
  • blood in urine and faeces
  • depression
  • vomiting.

Under the Meat (Residues) and the Game Regulations, MPI advises that feral animals intended for sale to a game pack house cannot be hunted in areas where poisons have been laid.

Appropriate declarations have to be supplied to establish that the animals have been obtained from areas free of contaminants.

Therefore, landowners and hunters are advised not to sell feral animals taken:

  • from an operational area within nine months after the termination of poisoning
  • within 2km (5km for feral pigs) of a poisoning operation boundary.

The policy applies for feral animals intended for personal consumption.

Very low levels of brodifacoum are used in possum bait. Brodifacoum is not soluble in water and binds strongly to soils – making it almost immobile. It will degrade slowly in soils with pH5.5 to pH8 under aerobic or flooded conditions and plants do not absorb it.

Baits are only used in bait stations, so it is unlikely the poison will be found in water.

Brodifacoum can remain in animal livers and may present a danger to other species through both secondary and tertiary poisoning. The half-life of brodifacoum in possum livers is about 36 weeks.

Large-scale pest control benefits native wildlife. However, kākā are present around Dunedin and may access bait stations. Careful consideration is given to the methods used in any possible kākā habitat.

Challenges

The operations around Dunedin involve a wide variety of terrain from urban areas to rural farmland, forest and scrub, both flat and mountainous. The damp coastal vegetation hosts high numbers of possums.

Possums aren’t the only ones using the area. The TB Management Area is on the city’s doorstep and hosts large numbers of dog walkers, trampers and mountain bikers. The balance between the efficacy and cost of control methods and the needs of recreational users is an important part of discussions with landowners.

Research papers

Cost-effective control of Tb in the Northern South Island High Country (NSIHC): Identifying the habitats and vector species requiring control — (R-80629) Byrom A, Nugent G, Yockney I, Poutu N, Whitford J, McKenzie J, Shepherd J, Porphyre T 2007. LC0708/033. 85p.

Spatial prediction of brushtail possum (Trichosurus vulpecula) distribution using a combination of remotely sensed and field-observed environmental data — Porphyre, T., McKenzie, J., Byrom, A. E., Nugent, G., Shepherd, J., & Yockney, I. (2014). Wildlife Research, 40(7), 578-587.

Reduced spillover transmission of Mycobacterium bovis to feral pigs (Sus scrofa) in New Zealand following population control of brushtail possums (Trichosurus vulpecula) — Nugent, G.; Whitford, J. Yockney, I.J.; Cross, M.L. 2012. Epidemiology and Infection 140: 1036–1047.

Relative Utility of Tb Hosts as Sentinels for Detecting TB< — Nugent, G.; Whitford, J. 2008. Animal Health Board Project No. R-10652. Landcare Research Contract Report: LC0708/032. 38