Field ranger Chad Cottle, Zero Invasive Predators' Susannah Aitken and field ranger Ethan Perry at Scone Hut, which was a home base for some workers as they cleared predators from the backcountry. Photo: Tess Brunton / RNZ
An ambitious project is clearing predators from more than 100,000 hectares of South Westland wilderness, farmland and townships.
Predator Free South Westland project aims to eliminate every possum, rat and stoat - and their goal is in sight.
They have already been removed from more than 90 percent of the project area from the Southern Alps to the sea.
Zero Invasive Predators, known as ZIP, was leading the collaborative mahi after a successful trial in the Perth Valley.
They had been tackling the project area in blocks, using AI and trail cameras, targeted aerial operations, high-tech traps, detection dogs and bait stations.
The project uses natural barriers, not fences, to slow the invasion - the Whataroa River to the north-east, the Waiau River to the south-west, the Southern Alps and the Tasman Sea.
The project's operations coordinator Nate St Hill joined in 2019, and said technology had been crucial in their mission to eliminate, not suppress predators.
"We were using chew cards for detection and at that point, we were working in 10,000 hectares in the backcountry and we had 2000 chew cards across that landscape. We just started dabbling in trail cameras, now we're doing a wild detection with AI cameras," he said.
A different type of bait was also being phased in as block baits wore away every four or so weeks while a gel-based dispenser needed to be replaced about every three months and they were looking at how to extend that to every six months, St Hill said.
Technology had an important role in helping to drive down the cost of maintenance with a rough goal of getting to $30 annually for each hectare, he said.
A predator free gate on a swing bridge over Scone Creek. Photo: Tess Brunton / RNZ
"This project's at the phase where we're just finishing the initial removal for the last piece of the footprint, mainly in some of the farmland areas and we are in maintenance for 90 percent of the project area and we're now working how do we do maintenance really efficiently."
Flying out from Franz Josef, a bird's eye view of the project area shows rugged bush, snowy peaks, wild rivers, farmland and towns.
With a weather window, the helicopter took us to Scone Hut, a backcountry DOC hut that was a home base for some of the workers clearing predators in the earlier years.
Field ranger Ethan Perry said DOC tracks felt like highways compared to some of the terrain they went through.
"In the front country on the coast, you're crawling through kiekie and supplejack, which kiekie just cuts you and supplejack, you just get tangled through and you're crawling, your pack gets caught," Perry said.
"Back here, those are some big hills that we flew over. It's pretty easy bush to get through back here, but every now and again then you come across a bluff and you need to find a new way around."
The West Coast could be a harsh testing ground for gear.
The project's operations manager Nate St Hill says they're trying to drive the maintenance costs down so it's more efficient to keep the predators out. Photo: Chad Cottle / Supplied
In recent years, there has been auroras that cut satellite coverage, lightning strikes that hit the gateways that allow information to be shared from a network of cameras, and, of course, keas.
"If it can live on the coast, it can probably live anywhere. The main thing is putting up with rain," Perry said.
At the start, workers would stay in DOC huts or tents before a network of bivvies were added.
It takes about nine hours to walk from the road into Scone Hut or a 12 minute helicopter ride.
It was nicknamed 'the Palace' as it was kitted out with bunks, lights, a fire and internet access so they could file updates and keep in touch with family and friends during days-long stints in the backcountry.
Field ranger Chad Cottle said Scone Hut was home for part of his time in the backcountry.
"Our whole job revolves around the weather, everything with river levels," he said.
That was easier to manage now they spent most of their time in the 'front country', which was a drive, not a flight away.
It also meant they could schedule backcountry work for decent weather windows.
"If we know there's a good bit of weather coming, we'll just get everyone we can get and do multiple chopper flights," he said.
Field ranger Chad Cottle services an AI camera near Scone Hut that can identify predators and send a snapshot of their thermal signature back to base for staff to double check. Photo: Tess Brunton / RNZ
A short, but slippery, walk from Scone Hut was a specially designed AI camera.
It turns on when it detects body heat, records thermal signatures, identifies a predator (possum, rat or stoat) and sends snapshots back to base.
They were phasing out trail cameras, Cottle said.
"It sends us a little snapshot of what that heat signature looks like and we can go and say 'yes, that does look like possum' and then we'll go 'right, we've got a possum there, we've now got to respond to it'," he said.
"That's all within 24 hours it can do that so that's the advantage of these. You don't have to service them every six weeks and then classify the images and go 'ok, yep, there's one there and it's already six weeks after it's been here so it might have moved on'."
An AI camera needed a visit roughly every nine months which meant fewer helicopter trips and workers could focus on other areas.
The lure they used to attract predators to the camera was unexpected, but it was a winner.
"Nothing beats mayonnaise. Mayonnaise lasts through minus temperatures, hot temperatures and it lasts for a year and it's still good," he said.
Mayonnaise is used in auto dispensers to lure predators to detection cameras. Photo: Tess Brunton / RNZ
The mahi could be hard in rugged and remote terrain and relying on weather windows, but Cottle said it was worth it to see a much healthier forest.
"The first couple of years, we had almost no kākāriki. I don't remember seeing any or hearing any the first two years of this project," he said.
"In the years afterwards, in like 2020 and 2021, we just noticed they were just starting to come back and they were everywhere. There were flocks of 16 or so we were seeing trees above us."
The majority of the project was on public conservation land, but it also covered land under Iwi, council, LINZ and private owners as well as Franz Josef, Whataroa, Ōkārito and The Forks.
The focus had been on farmland in recent years.
As the rural elimination team lead, Pouri Rakete-Stones said having community buy-in and building relationships with landowners was vital.
"It could take two to three to four weeks just from the start, having that conversation, having them comfortable with what we're going to do on the ground and then getting permissions or access permissions signed, and then being able to do the work after we've done that so they need to be comfortable with the work that we're doing," he said.
The mahi did not stop as they neared their elimination target, he said.
Rural elimination team lead Pouri Rakete-Stones says there's been good community buy-in to the project. Photo: Tess Brunton / RNZ
"If we start slacking off, then there's the potential to go back to how it was. It might take a little bit longer to get back to where it was, where we don't want to be again.
"Staying in the fight and making sure that we get to the predator free vision and we make sure that that actually happens."
Zero Invasive Predators communication coordinator Susannah Aitken hoped the project would inspire people that national predator free goal was doable
"It's hugely ambitious but I think what this project demonstrates is that it's achievable which is a really exciting thing," she said.
DOC started funding the project's maintenance this year through the Tomorrow Accord.
With elimination on the horizon, the mission was not to lose the precious wins and keep the predators from reinvading.
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