A rare and threatened species of West Coast snail has been captured on camera laying an egg for the first time.
The Powelliphanta augusta snail was being weighed by Department of Conservation (DOC) ranger Lisa Flanagan in when the little egg emerged from its neck.
DOC had been managing a captive population of the snails in chilled containers since 2006, when Solid Energy started mining their habitat on the Mt Augustus ridgeline on the western side of the Stockton Plateau near Westport.
Flanagan said it was a special moment after 12 years looking after the snails.
"It's remarkable that in all the time we've spent caring for the snails, this is the first time we've seen one lay an egg.
"We caught the action when we were weighing the snail. We turned it over to be weighed and saw the egg just starting to emerge from the snail," she said.
Very little was known about the snails when they were taken into captivity and staff were constantly making new discoveries, she said.
"I just love watching their progress each month, weighing them, how their shells develop and all the interesting things they do," she said.
"Powelliphanta augusta are slow growing and long lived, not being sexually mature until they are about eight years old and then laying only around five big eggs annually which can take more than a year to hatch.
"Some of our captive snails are between 25 and 30 years old - in this they're polar opposites to the pest garden snail we introduced to New Zealand which is like a weed, with thousands of offspring each year and a short life."
A rare and threatened species of West Coast snail has been captured on camera. Photo: Supplied/Department of Conservation
DOC senior science advisor Kath Walker said the hard shell that helped the snails retreat also posed some problems with mating and egg-laying.
"Powelliphanta have solved this by having an opening (a genital pore) on the right side of their body just below their head so that the snail only needs to peek out of its shell to do the business," she said.
"It extends its penis out of this pore and into its mate's pore, and its mate does the same, simultaneously exchanging sperm, which they can store until they each fertilise the sperm they've received to create eggs.
"As hermaphrodites, they have both male and female genitalia, so although they usually mate with another to cross fertilise their eggs, as carnivores which have to live at relatively low density, being able to occasionally self-fertilise must help with survival of the species."
Before their habitat was mined, about 4,000 snails were collected and moved to nearby sites. A further 2,000 snails were used to start a captive colony.
The snails were mostly housed individually in containers, on moss and litter, and fed worms appropriate to their size once a month. They were regularly measured and weighed.
In March there were 1,884 snails from hatchlings through to adults and 2,195 eggs in captivity.
DOC had established new populations of the snail in the wild and reintroduced them to new and rehabilitated habitats.
A captive population would be managed until DOC was confident the species would survive in the wild.
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