Canberra-based ecologist Dr Don Fletcher was commissioned by the Invasive Species Council to develop a report on wild horse numbers within the park as the NSW government continues to take a cautious and careful approach to the contentious issue.

Under the latest management numbers to mid-April published by the NSW government, 507 horses have been removed from the park since July last year.

Of these, 489 have been rehomed, 14 sent to the knackery, and four died during the trapping process.

A large number of mares in foal or with foals at foot with foals were also released.

A new "wild horse heritage management plan" is still under development with a first draft expected in late June. The Invasive Species Council says Dr Fletcher's report provides solid scientific information on the population numbers and the efficacy of the current management program.

Dr Fletcher steps cautiously away from endorsing an aerial culling program but says any attempt to scale up the current trapping and removal program, which was introduced to political appease the Snowy Mountain wild horse support groups, would require a huge logistics operation and carry a very significant cost.

"I think what this study shows is that the [horse] issue is now too big to overhaul it by any conceivable trapping program," Dr Fletcher said.

"There was a chance back in 2003 after the major bushfires which hit Canberra also took out a significant part of the northern park, that the [horse] population could then have been brought down to manageable numbers.

"But that opportunity is now long gone and every year we're seeing another 2000 [horses] added to the population."

Invasive Species Council Chief executive Andrew Cox says the NSW government needs to "listen to the science".

He said they needed to "unshackle the parks service so that it can get on with the business of protecting our national parks, not feral horses".

The ACT government has an unashamed "zero-tolerance" approach to wild horse encroachment into the Namadgi National Park, adjacent to the northern edge of the Kosciuszko.

Contrary to the methods employed over the border, the ACT's 2020 feral horse management says that "due to animal welfare, operator safety and cost concerns, loading and transporting trapped horses for rehoming is not considered a viable option for broad scale feral horse management in the Namadgi National Park".

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