Relocating Native Land Snails

Snail – the movie is a short documentary about the programme to relocate native land snails from the Mt Augustus ridgeline of Stockton Opencast Mine in the Buller region of the West Coast of New Zealand. Order a free copy of the DVD.

Powelliphanta “Augustus” is a land snail which is native to New Zealand.

During mining operations on the Stockton Plateau this endangered species was living along the Mt Augustus ridgeline. For mining to take place and for Solid Energy to meet its environmental policy to “Reasonably minimise the adverse local environmental affects that may be an unavoidable part of operating coal mines”, a solution had to be sought.

A Wildlife Permit was issued in early 2006 for the capture and relocation of snails, shells and eggs and by the end of 2007 the Department of Conservation (DOC) formally acknowledged that Solid Energy had fulfilled all of the conditions.

A specialist team collected the snails, shells and eggs and then transferred them to DOC in Hokitika for ongoing management and research. DOC staff recorded the details of each snail, providing baseline data for monitoring the snails as they are released back into the wild.

In all, 6,140 snails, 8,057 shells and 1,116 eggs were collected – 10 times higher than original estimates.

Habitat Preservation

Following collection of the snails, much of the original habitat was moved 800 metres north. The technique is called “vegetation direct transfer” and involves precise excavation by mechanical digger so that soil and vegetation is kept largely intact and can be moved to a new location by track.

By late 2007, approximately 4,000 snails had been released onto this and other sites.

New Habitats

Because of the number of snails was larger than expected, further relocation sites were needed. A rigorous process was undertaken to select other sites assessing aspects such as soil and leaf litter depth, seasonal and soil temperature variations and rainfall. Decisions on the release sites have been closely informed by the project’s Technical Advisory Group, formed from DOC and Solid Energy snail/invertebrate specialists and ecologists.

The first snails were released back into the wild into an area next to a site where original habitat has been “direct transferred”. By late 2007 3,900 snails and 1,060 eggs had been returned to the wild, including at two sites on Mt Rochfort, south of Stockton Mine.

Monitoring

About 5% of all released adult snails have been tagged with miniature transponders for short-term monitoring. This has provided valuable information on individual snail response to environmental stresses such as weather and predation.

Captive Management and the Future

At the end of June 2008, a total of 1,797 snails and 254 eggs remain at DOC’s captive management facility in Hokitika, and a number of snails have successfully hatched from eggs. Survival in captivity is very high, at about 94 per cent. Of the eggs,221 had been laid by snails after being moved to the management facility at Hokitika. By the end of June 2008, 408 eggs had hatched, 373 of which had been collected in the wild. The snail eggs take a year or more to hatch.

DOC is currently developing a five-year management plan to address a number of critical issues for native land snails, including:
• ongoing captive management requirements
• strategies for further snail releases
• ongoing monitoring
• ongoing predator control

The effort to collect and relocate native land snails, Powelliphanta “Augustus”, from the Mt Augustus ridgeline at our Stockton Opencast Mine, concluded in May 2007.