Refining TBfree operations at Molesworth

This winter OSPRI completed two 1080 aerial operations over 70,000 hectares and the outcomes were excellent for sustainable possum control and deer survival in the high-country environment. 

Prior to both aerial operations, possums and feral deer were radio-collared for tracking purposes to evaluate bait efficacy as part of a trial carried out by Manaaki Whenua - Landcare Research.

Findings from the trials show:

• 95 percent of radio collared deer survived the standard broadcast trial in the Bush Gully and Tarndale blocks.
• From 358 non-collared deer found within the treatment area, 351 were alive, seven dead.
• 100 percent of radio collared possums were eradicated using three different trial techniques: standard broadcast, low sow broadcast and low strip sow.

The introduction of a new deer repellent was a significant factor in reducing deer by-kill numbers says OSPRI Research Manager Dr Richard Curtis.

'We’ve learned from previous 1080 aerial operations at Molesworth and acted on Landcare Research recommendations. The deer repellent was spread over the entire treatment area, and the new formula appears especially suitable for Molesworth’s unique conditions.'

The possum control work was timed to coincide with the start of winter to enable quicker detoxification of the aerial 1080 baits.

OSPRI engaged beforehand with the deer hunters, landowners, farmers, and Molesworth Station, to minimise disruption to farming and recreational activities at Molesworth from TBfree operations.

Dr Curtis says, 'We’re aware that wild deer and hunting are valued by many people and we’re confident that the results of this deer repellent trial at Molesworth will demonstrate that we can balance possum control and minimise impacts on the immediate environment.

'You can never rule out feral deer mortality following an aerial operation, but with greater numbers of deer surviving, this will ensure a rapid population recovery throughout Molesworth.'

Aerial bait sowing innovation

Aerial bait sowing trials over 9,000 hectares at Molesworth and adjoining private land has potential to reshape how OSPRI undertakes TBfree operations in the future.

In an alternative approach to improve efficiency of 1080 aerial control, the volume and density of aerial sow baits was modified.

A ‘strip sowing’ technique in the Saxton block, and a ‘low sow’ broadcast approach in the Severn block were trialled, and this has provided a 65 percent and 50 percent reduction in toxins respectively.

Both trials achieved 100 percent poisoning of possums with lower sowing rates shown to be effective in dryland habitat where the environment supports good access to bait.

These techniques are expected to be more cost effective than the standard 2kg per/hectares per broadcast and still achieve the necessary possum control target rates.