Department of Conservation ranger John Keene said it was difficult to estimate the total number of Otago and grand skinks in the area.
However, five pest-proof fences around the 4000ha Macraes Flat area had significantly bolstered skink numbers.
"In 2005, numbers were estimated at 400 Otago skinks and 800 grand skinks."
Skink numbers had quadrupled within areas where five pest-proof fences were erected, doubled within the 2500ha Doc monitoring site, and "slightly improved" on the perimeter of the site, he said.
Mr Keene said efforts to bolster the skink population through predator control started in the late 1990s.
Intensive predator control started in the area in 2005.
Despite the growth in the skink populations, the trapping operation required long-term effort to ensure the survival of the species, he said.
"Running traps 365 days a year makes it an expensive operation. Recent costings for the pest control component of this project have been in the order of $120,000 per annum."
Trap types included both kill and live capture traps, as well as shooting operations, he said.
Cats posed a particular risk to the skinks.
"Cat control is seen as a key aspect of the project and we catch several hundred per year in this operation.
"There is a large population of cats in the surrounding landscape meaning reinvasion is a constant problem."
A measured trapping approach which targeted a variety of predators was necessary to prevent a drastic change in the ecosystem.
"We don’t view things in isolation, as removing cats from the ecosystem potentially creates more opportunities for other predators like stoats, ferrets, weasels and rats."
Protecting the "cryptic and dispersed" species required long-term pest management.
"We continue to review the operation to make it more efficient and effective, but ultimately we need to be in it for the long haul."
