The population of a rare species of snail only found in the Buller region is on the rise.
Thousands of the snails were captured and bunged in the chiller when the expansion of the Stockton Mine threatened their habitat.
The Department of Conservation collected and relocated 4000 of the slimy snails from the Stockton Mine in 2006, in a bid to save the native species.
At the time the mine was extending its operations and as part of its environmental policy it had to protect endangered species.
"We only ever anticipated that we would be keeping them alive, and not having the breeding success that we've had," biodiversity ranger Rodney Phillips says.
The snails, which can grow as large as 8cm feed off just four worms a month, inhaling each one within a second.
They're kept in captivity in Hokitika where a specialist team monitors their breeding programme.
In the past decade 7400 have been released back into their habitat near the Stockton Mine.
"We're monitoring the ones we put out to see how they're doing and they seem to be doing okay," DoC operations manager Ian McClure says.
"Not much was known about them until we brought them back to captivity. We now know a lot about how to look after them how they breed and what conditions they like."
All of the snails are expected to be returned to suitable habitats in the wild within the next few years.