Concern at relocated snails' death rates in wild

Death rates of rare snails released back into the wild north of Westport vary from about 17 per cent to 40%, the Department of Conservation (DOC) says.

DOC collected more than 6000 snails from the Stockton opencast coalmine ridgeline between June 2006 and July 2007 before Solid Energy started mining up to $400 million worth of coal.

Conservancy advisory scientist Ingrid Gruner said 1800 snails remained in captivity, along with 225 which had hatched from eggs.

A total of 3913 had been released to the wild at two locations on the Stockton plateau, north of the original site, and on Mount Rochfort.

Mortality rates varied considerably between sites and different parts of the sites, Gruner said.

"In the least successful area we have lost 40% of the released snails over 14 months," she said.

However, in the best area only 17.5% of monitored snails were found dead in 17 months, she added.

Gruner said 40% mortality was more than would be expected in a natural population, while 17.5% was within the natural mortality range.

It was still early days to decide whether the relocation programme was successful.

DOC's goal was to establish at least one self-sustaining population.

Whether that could be achieved would not be known for several years. NZPA

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