The Department of Conservation is keeping a close eye on Buller's rare, giant carnivorous snails and says populations at Stockton are secure for now.
About 800 of the snails were frozen to death in 2011 after a technical glitch in a DOC cool room in Hokitika.
DOC communications advisor Trish Grant said Powelliphanta augusta snails, collected in 2006 and 2007 from the summit of Mount Augustus before it was mined, were being monitored using the mark-recapture method.
Just over 6000 snails were collected from Mount Augustus, she said. After a short time in captivity nearly 4000 were translocated to two new sites - the Stockton ridgeline just to the north of Mount Augustus, outside the mining footprint, and Mount Rochfort in the south.
A small remnant snail population remained on the slopes of Mount Augustus below the mined area. The remaining snails had been kept in captivity as a backup to the translocated and remnant natural population.
Long-term monitoring of Stockton snails involved surveys of fixed plots over several nights, at intervals over the summer season.
It had been done now for several years. DOC estimated the total population from the number of marked or unmarked snails found each night.
Data suggested populations at most of the monitored sites were secure in the short to medium term.
There were indications more snails were being recruited into the population, with more snails over 20mm in size being found. Whether those snails were from breeding at the site or snails translocated there was unclear.
Ms Grant said DOC was also undertaking work to protect snail populations at Charming Creek, including a recent possum ground-control operation covering 400ha.
The operation continued the sustained possum control programme running since the mid 1990s to protect Powelliphanta lignaria johnstonii in the Charming Creek area.
No specific monitoring had taken place since the recent operation but there had been a slight increase in numbers of the snails at the site from 2007 to 2012. Possum and rat predation had declined.
Snail monitoring was programmed for 2014. It would provide further data on the status and population trends, said Ms Grant.
DOC monitored 15 species or subspecies of Powelliphanta snails across Buller - 13 of them in predator control areas.
Powelliphanta snails were an integral part of New Zealand's unique fauna, and were as important in evolutionary terms as kiwi, kakapo or moa, she said.
They were highly vulnerable to predation from introduced possums and rats.
- The Westport News