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Native land snail update

24 August 2011

Native land snail update

The latest monitoring information from the Powelliphanta augusta land snail relocation programme at Stockton Opencast Mine in Buller suggests at least one of the resettled groups of the native snail is capable of being self sustaining.

In 2006 and 2007 a project was begun to move P augusta snails from a ridgeline area at Stockton which was to be mined. Since then, mine owner Solid Energy has been working with the Department of Conservation (DoC) to determine which of several sites, including the remaining areas of their original habitat, have the most beneficial habitat for the displaced snails. Research in support of this has been undertaken by DoC and Lincoln University’s Bio-Protection Research Centre and the Faculty of Agricultural and Life Sciences. The organisations’ cooperative research aims to learn more about the creatures’ life cycle, including the best conditions to improve snail reproduction and growth. The overall goal is to establish one new viable population in the wild. The current programme runs until 2016.

Of the 6,140 snails collected in 2007, about 4,000 were released into areas within or near Stockton and a variety of monitoring methods have been used since then to determine their progress. At the same time the Department of Conservation has been running a captive management and research programme in Hokitika for the remaining snails.

Mark Pizey, Solid Energy’s General Manager Environment, says the data from monitoring carried out over summer and progress made in the captive management programme and habitat research suggest there is reason to be more confident about having a sustainable population in the wild.

“There are two reasons for our increased confidence,” he says. “The first is that we are seeing faster growth rates among the snails in the wild than was expected. This is one of the areas where conservative assumptions were made because nobody really knew how fast they grow, how long they take to reach adulthood and so on. Faster growth than was assumed is likely to have a positive impact on the numbers you need for a self-sustaining population.

“The second cause for confidence is from that survival data. The survey and analysis method we are using has been running for three years, which is the minimum time the population modelling experts have said we need to be able to make any useful inferences about the snails’ long-term sustainability,” Mr Pizey says. “In the one area where we have three years of survey data, the survey model suggests a survival rate of between 82 and 95 per cent. We had earlier been told that we needed to see adult snail survival rates of between 80 and 85 per cent for a population to be considered sustainable.

“So on the face of it, that’s very encouraging and we are extremely pleased,” Mr Pizey says. “However, this particular group of snails – where we have three years’ data -- was released into what we consider to be the most promising of all the alternative habitat areas. Because of this, and because every extra set of monitoring data improves the model’s certainty, I think we must continue to be cautious. In another year, we will have three years of survey data for some of the other release areas and that will give us a better general idea of how the released populations are faring.”

Progress in captive management programme and in habitat research

The Department of Conservation team in Hokitika has made substantial progress in the last year in ensuring it has the techniques needed to safeguard the snail species’ survival while the field trials are taking place.

Improvements to the husbandry of newly hatched snails have greatly increased the survival of hatchlings and improved juvenile recruitment. Overall survival has improved as a result, with the captive population now recording annual survival of around 90 per cent. Changes to the conditions and the way the snails are housed inside the environmental chambers have resulted in a far higher proportion of adult snails producing eggs. This summer alone, during the peak November to March breeding season, more than 700 eggs were produced.

“With this increasing confidence about both the relocated and captive populations, we are considering whether we should make another release into additional resettlement areas,” Mark Pizey says. “We will make a decision about this in the next few months.”

Dr Stephane Boyer, Lincoln University’s Lecturer in Restoration Ecology, is leading a research effort aimed at assessing habitats to gauge if an area contains the right food sources to support the snails. “Dr Boyer and Professor Steve Wratten’s work means we now know a great deal more about the snails’ diet in the wild, which allows us to look at a potential release site and have much more confidence that it provides the right prey,” Mr Pizey says.

Why has the snail’s name changed over the years?

Initially the animal was dubbed Powelliphanta “Augustus”, a title which indicated certainty that the snail was a member of the Powelliphanta genus, but uncertainty about whether it was a distinct species. A paper by Kath Walker and others has since been published which concluded that the snails from Mt Augustus are genetically different from P patrickensis snails (and other species found on the West Coast) and the snail was therefore given the new name Powelliphanta augusta. The established scientific protocol around nomenclature puts all genus and species names into italics. “Augustus” became augusta as this is the correct Latin name.


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