Possum is scourge of farm and forest

Recovering rock wren populations show the benefits of possum and pest control. Photo / File

Managing disease in farmed cattle and deer is one stream of the TBfree programme's work. It underpins the value and reputation of the meat and milk New Zealand exports.

The other essential work the programme manages is possum control — taking and keeping numbers down at a level where disease can't keep cycling in wildlife.

That possum control work has two big benefits for New Zealand: eradicating bovine TB to protect the primary sector while supporting the goals of the predator-free movement.
The TBfree programme managed by OSPRI aligns with programmes designed to protect and defend New Zealand's biodiversity and environmental health, such as the Department of Conservation's Battle for Our Birds and Predator Free 2050.

All these programmes have a common problem — the brushtail possum. The introduced marsupial is the main transmitter of bovine TB between wildlife and farmed livestock. It is also a major threat to New Zealand's native bush and birdlife. Possum control brings benefits for both disease prevention and environmental protection.

Since it was imported from Australia in the 19th century, with the idea of establishing a fur industry, it has enjoyed its own form of predator-free environment; it's hunted by no other animal than man. And with access to a limitless larder of its favourite food, the possum has become the scourge of our natural environment.

Their appetites have destroyed forests — Manaaki Whenua Landcare Research estimates possums gobble about 21,000 tonnes of vegetation per day (300 grams wet weight per possum x 70 million possums) — and they're partial to a side order of native birds' eggs, or even newly hatched chicks. They're also the main transmitter, or 'vector', of bovine TB.

In the past eight years, OSPRI has eradicated TB from possums across more than two million hectares of disease risk area. That leaves less than eight million hectares to treat before TB eradication in possums can be declared. Low numbers have already been achieved across most of it, and we're on target to achieve eradication ahead of the 2040 target date.

The opportunity for New Zealand is to take the gains made in reducing possum numbers and continue the campaign to achieve a Predator Free country by 2050. This aspirational goal relies on a strategic vision — the collective impact of a co-ordinated regional and community-based approach.

The community-based approach — where good citizens trap possum and kill pests — might work in some localities and regions, but the challenges of eradicating predators in the vast unpopulated areas of landscape where pests graze and predate unfettered present a larger challenge.

Predator Free 2050 has been described as New Zealand's 'moon shot'. As such, a huge co-ordinated strategic approach to planning, management and systems development — along the lines of that which enabled the real moon shot — will be required.

OSPRI's TB Plan has laid a substantial foundation and refined a systematic approach that forms a solid foundation for PF2050's shot at the moon. A carefully managed transition from TB eradication towards a longer-term multi-species predator-eradication goal will retain the systems, the knowledge and the infrastructure to give New Zealanders their best opportunity of creating a unique TB-free, predator-free paradise.

• Nick Hancox is a senior policy adviser at OSPRI