Last remaining known possum caught in Westland's Perth River Valley

Monday, 29 June 2020

The last remaining possum seen on camera has since been caught in a trap.

The last remaining possum has been caught in a 12,000-hectare block in the Perth River Valley in South Westland.

Zero Invasive Predators (Zip), a research and development entity, has been eliminating pests from the area, which is bordered by rivers, mountains and the sea, since April last year.

Chief executive Al Bramley said the intensive possum detection and response effort in the site indicates it had now achieved 'possum freedom'.

'This is a major milestone, which has not to our knowledge ever been achieved at this scale on the New Zealand.

Zero Invasive Predators chief executive officer Al Bramley, with various experimental rat, possum and stoat traps.

'Possum freedom means that we are confident there are so few possums present that they are unable to re-establish a viable population, not necessarily that every individual possum has been removed.'

Rangers had been carrying out ground-based detection with a network of 143 lured trail cameras for over 14,000 detection nights and monitoring the 700 traps in the site.

They had now caught all the possums detected on the cameras an aerial 1080 drop in April and July last year. The last remaining possum was caught in a trap on Sunday night.

'When we started there would have been in the region of 15,000. We've been slowly ticking them off,' he said.

The 2kg male possum was caught on camera several times next to, and even on top of, the automated cage traps set to capture it. That only increased the determination of the response team to finally catch it, Bramley said.

A Zip ranger beside the Perth River, where possums are down to zero. Pest control experts hope these churning waters will keep others from re-invading.

A vital member of the team was a possum dog called Pepper.

On The Detail, Sharon Brettkelly meets two people who are doing their best to help achieve New Zealand's Predator-Free 2050 goal. (Video first published November 2019)

The team uses a model called 'remove and protect', under which rats, possums and stoats are eliminated with toxins such as 1080 and traps, and the land defended with detection devices, traps and barriers.

About 10 possums had survived the aerial 1080 drop, while three female rats survived an intense 1080 treatment. No stoats survived. The team left the rats to study how fast they could repopulate.

Zip’s rat and possum eradication in the Perth River Valley is the first time anyone has attempted to clear a mainland tract of pests, then hold the line. As such, it might be a roadmap to a predator-free 2050.

Zip then carried out a targeted aerial 1080 spot treatment in March to remove the emerging population of rats. However, he said it was only up to 90 per cent successful and the rats were able to breed during lockdown when the operation was put on hold. It now had about 20 rats, which the team was hunting.

About 15 stoats started repopulating the area in January, due to their ability to swim across rivers. Some were caught in traps, but others were 'trap-shy'.

Two kea died as a result of the operation, but Bramley said population in area was flourishing with between 100 and 168 birds. No tahr, which were tagged before the operation, were killed and the chamois population was unaffected.

The team had planned to conduct a similar operation in a neighbouring block, but was now looking at hiring unemployed Westland tourism workers to conduct ground operations on farmland using traps.

'If we can clear the predators then we don't need to use widescale 1080 again, and that's honestly what we are shooting for,' he said.

Zip is funded by the Department of Conservation, Predator Free 2050 Ltd, Next Foundation and Morgan family funds and foundations.