A major conservation plan is being developed to protect the South Island's unique alpine environment from Himalayan tahr.
The large goat-like animals were introduced to New Zealand during the early days of European settlement.
The Department of Conservation (DOC) said tahr were wrecking native alpine tussocks in their search for food and destroying the eco-systems in the South Island's alpine regions.
But it was hoped that a renewed focus on tahr could help reduce the population.
Sixteen hundred metres above sea-level, overlooking the picturesque Lake Pukaki on the Ben Ohau Range, it is easy to miss the signs of tahr.
For the untrained eye, the steep mountains look like any other, with tussocks and rocks scattered around.
But DOC's biodiversity monitoring ranger, Ingrid Gruner, said for those who know the area it was quite different.
"I guess with my experience and what I've seen in other places, I can tell you that this used to look quite different. There used to be tall tussocks here possibly quite dense in places especially in the more moist areas," she said.
"There would have been denser tussocks they will have been up to your waist," Gruner said.
The Himalayan tahr has long been a problem following its introduction to New Zealand.
DOC's tahr control programme manager James Holborow said there were about 35,000 of the animals on public conservation land, with more believed to be on private land and Crown leased land.
The only way to kill them is by shooting, either on a helicopter or on the ground.
"So high numbers of tahr have quite strong localised impacts, we won't necessarily see those impacts everywhere in the environment. But what we see is tahr tend to heard together and where they heard together, they'll tend to have quite strong effects," Holborow said.
He said DOC was in the early stages of developing a new plan to cull tahr.
He said the plan was likely to indicate the areas DOC would focus on to reduce tahr numbers.
"Probably likely to be two phases of planning. We will need to do some more tahr control next winter. So we'll be working with our treaty partner Ngāi Tahu to develop that plan with their tahr stakeholders. And then we're also trying to make sure we can have a longer term plan that will run for say the next five or so years," Holborow said.
It's also now easier for hunters to record how many tahr they have killed.
"We're publishing information on where we've observed bull tahr over last winters control to give ideas where the populations are. We have also got a recreational tahr app that we've developed with the Game Animal Council and the New Zealand Tahr Foundation. Hunters can use that app to report the tahr that they're shooting when they're out hunting," Holborow said.
It was hoped the plan would reduce tahr numbers to about 10,000, which will hugely benefit native tussocks.
DOC ecologist Brian Rance, said tussocks played a vital role in preserving the alpine eco-system.
"These snow tussocks, they are really like the trees in the forest. You know, they're the canopy species. So they're dominant in the vegetation here and also like a forest, they're old, they're very long lived. These species will grow and live for several hundred years," Rance said.
Gruner said despite the tahr control plan, it would take many years for the tussocks to recover.
"It's a slow process because we're in a very cold environment that is covered in snow for much of the year. So it's not an annual thing so you won't see any difference next year. We've got some sites over on the West Coast where things probably are a little bit more fast growing," she said.
Despite the slow pace of regeneration, Gruner said today's actions would help preserve the long-term future of New Zealand's pristine alpine environment.