New research has proved predator-proof fencing and trapping can significantly increase the survival of endangered grand and Otago skinks but has also raised questions about their future management.
The Department of Conservation research was undertaken over three years at its skink reserves at Macraes Flat and was published today in the New Zealand Journal of Ecology.
Lead researcher Dr James Reardon, former grand and Otago skink programme manager, said controlling predators such as stoats, cats, ferrets and hedgehogs to near eradication inside a predator-proof fence or within an intensively trapped area enabled localised recovery of skinks.
It was probably the first proven example of successful mainland management for endangered New Zealand lizards, he said.
Skinks were classified as nationally endangered, the highest threat status, and lived in only 8% of their former range. Estimates of remaining numbers range from 1400 to 5000 individuals for each species.
The study showed Otago skinks within the fence and trapping core showed growth rates of 1.67 and 1.92 at the two sites.
Substantial increases in grand skink numbers were found within the two areas, with growth of 1.32 and 1.48.
While there was no change in Otago skinks at an unmanaged site, grand skinks at an unmanaged control site had a "catastrophic decline". Over the three years, the population declined 85%, from 76 skinks to 11.
A rapid decline over five days coincided with a sighting of a stoat hunting skinks on rocks.
The findings suggested Otago skinks had higher growth rates and generally higher survival rates than grand skinks.
"We suspect grand skinks, because of such habitat selection, lower population growth rates and more limited distribution, are at present the more vulnerable of the two species."
As a result, the researchers said it was "questionable" whether the two species should be treated as a single management unit, as they were now.
"Nevertheless, given the punctuated declines and lack of population recovery observed at our unmanaged sites, both skink species appear to be susceptible to extinction."
While both trapping and fencing allowed populations to recover, trapping was the more cost-effective and had been extended at Macraes Flat.
