Possum control: inside an aerial operation

Date 19 September 2019

Keen to find out what happens at a TBfree aerial possum control operation, a first-timer joins a team of professional contractors in the Clarence Valley above the South Island’s Kaikoura coast.

Before the sun came up, we set off from Kaikoura, the coastal town under a mountain range, and drove for three hours; two on rough farm track through 24 farm gates and six streams. The contractors were already on site, having got there the day before.

We encountered a mob of merinos being brought in for shearing and had a catch-up with farm staff, reminding them to take care of their dogs after the toxic drop, planned for the following week. 

The Prefeed

The method of controlling possum number over large areas of rugged land – anywhere from 5,000 to 40,000 hectares – involves feeding out untreated cereal baits to encourage possums to feed. 

A week or two later possums are offered the same baits treated with a toxin that will knock down their population so that TB infection can’t be maintained.

Up at the high-altitude loading site, where the helicopters lift large buckets of bait for distribution over about 15,000 hectares of steep uplands. The open site is in a stunning location overlooking the Inland Kaikoura Range and nestled below Mount Tapuae-o-Uenuku.

We completed our health and safety briefing and stood in the bitter cold watching the loading operations before the helicopters took their payloads into the hills. 

The helicopter pilots fly GPS-guided ‘swathes’ across the operational area, as if they were ploughing a field. The buckets hung under their machines distribute 12-gram cereal baits through a spinner which casts them across an area of several hundred metres. They penetrate the forest canopy and fall to the ground among the sparse winter tussock and manuka scrub, ready to be eaten by possums.

It’s fascinating to see the data from the helicopters downloaded via Bluetooth into the mapping software -- progress is tracked almost in real time.

Now the prefeed baits are on the ground, possums can eat their fill and prepare their palates: the main course that will be their last meal follows within 10 days. When the next weather window opens, the aerial operation will be repeated, this time with a 0.15 percent dose of sodium fluoroacetate (1080) in the pellets to knock the possum population down close to zero.

The Toxic Drop
Ten days later, we’re back on deck at dawn. We’ve waited for a clear patch of dry weather so that the cereal baits will stay intact. For a successful operation, the weather has to be still for long enough that possums can eat the toxic bait before it rains – a minimum of two nights. Rain quickly breaks down the baits into harmless mush.

Having flown the prefeed, the air and ground crews are familiar with the loading site and the lay of the land. Before the operation starts, pilots fly stock checks to ensure no farm animals remain in the operational area, and placing signs at access points.
The signs warn people accessing the area about the presence of toxic baits. These pose a lethal danger to dogs entering the area until possums have eaten them, or until 100mm of rain has fallen.

Time is money in any work involving helicopters, so – without hurrying – every efficiency is employed to get the job done perfectly. That means sending one chopper with a super-accurate trickle-feeder to put baits into any tricky gullies or corners while the other does the broad main swathes. Like a painting crew with a large factory to complete, some concentrate on ‘cutting-in’ while others roller over the large internal areas.

Health and safety management is taken very seriously at a toxic drop. Access to the loading zone is prohibited to all but essential crew when helicopters were taking off or landing. All those involved in loading operations wear hazard suits, respirators, hard hats and gloves.
Each flight is tracked and checked to ensure no bait has dropped outside consented areas, and to check there are no gaps in coverage which could harbour a pocket of possums. These operations are demanding, high-stakes work for all involved – pilots, ground crew, coordinators and support staff. It’s the front line of possum control work and each op is another step towards TB eradication.

Within 12 hours of the toxic drop, about 90 percent of the possums will have eaten bait and been killed by the poison, stopping the cycle of TB and ensuring that livestock returning to the area will remain free of TB infection.

This is the TBfree programme in action, and in the past 10 years, ground traps and toxins and aerial operations like this have cleared TB-infected possums from more than 2 million hectares of bush, scrub and farmland. That leaves more than 7.5 million hectares to clear before we can say ‘job done’ – OSPRI’s goal is to remove TB from possums by 2040. And a few years beyond that (2055) we aim prove that New Zealand is TB-free.

POSSUM CONTROL operations are the biggest workstream in OSPRI’s disease management business.

Ground operations cover the most land area – more than 4 million hectares each year – but aerial operations (less than 400,000 ha) are completed in remote and rugged country.

Aerial and ground operations progressively eradicate disease from TB management areas area. Work for aerial operations starts sometimes years in advance – consultation with landowners and affected communities, coordinating with other operations and regional strategies, and working with farmers to schedule the best timing and fit in with seasonal livestock movements.

The highly regulated operations have been continually refined over the past 20 years. Accuracy has become pinpoint through the use of satellite guidance (GPS); toxin levels and sowing rates have fallen dramatically as scientific knowledge grows with every operation.

In planning and execution, each operation follows the strictest guidelines and consent conditions from public offices such as the Environmental Protection Authority (EPA) and the Medical Officer of Health, and is completed according to OSPRI’s industry-agreed code, the Aerial Operations Standard Operation Procedure (SOP).

:: See the latest on OSPRI’s disease management operations at ospri.co.nz/pest-ops-status

Clarence 2

Highly skilled pilots fly GPS-guided swathes across the operational area. Cereal baits penetrate the forest canopy and fall to the ground to be eaten by possums.