An Archey's frog Photo: Supplied / Amanda Haigh
A huge increase in critically endangered Archey's frog numbers has been confirmed, as the Department of Conservation updates its conservation statuses for amphibians.
It has also shown the successful eradication of a pesky introduced newt near Waihi, after a decade of hard work following its escape from a nearby home.
A panel of experts has assessed all 21 species of amphibian found in the wild - 20 frogs and this one newt - and found four species have declined in status, and the others have remained stable.
Dr Rhys Burns - DOC's lead on the assessment panel - said Archey's frogs existed in higher numbers than previously thought, mostly thanks to a survey in Coromandel commissioned by mining company OceanaGold, which intends to mine under the frogs' habitat.
"The current Archey's adult frog population, previously estimated as between 5000 and 20,000, has been revised to over 100,000 individuals," Burns said.
But the population was still declining, mainly due to the impact of introduced mammals like rats and mice.
The other stronghold for this population was at Whareorino, where pest control had been quite successful. However, as rats declined, mice rose, and mice were able to target the young frogs as prey.
An Archey's frog amongst fern leaves. Photo: Supplied / Amanda Haigh
Climate change impact was added to the assessment for the first time - an acknowledgement that climate pressures were increasing for most frog species.
"Changes in rainfall and temperature dry the forest understorey where land-based frogs such as Archey's and Hamilton's live," Burns said.
There was also an instance of a major slip in Otawa near Te Puke, which took out the side of a hill and buried a stream, bringing tonnes of earth and vegetation down on the Hochstetter's frogs within.
It caused in an estimated 30-40 percent loss of the population in one night.
But in a case where a decline was actually a success story, an introduced species had reached eradication, Burns said.
Introduced to an area near Waihi in 2013, the population of Italian Alpine Newts was far from home.
"They escaped from someone who had them - we don't quite know how they got into the country, but anyway, this individual had them - and we've been spending the last ten years with MPI and some pretty amazing contractors to actually eradicate them over about 11 hectares," he said.
The newts could be quite destructive to the habitat of other protected species, found in concentrations of up to 50 per square metre at the population's height.
Rhys said frogs were challenging to survey. "They range from the size of a thumbnail to the length of a thumb, and often live in remote places. It's resource-hungry work.
He hoped more organisations would take on research and survey work.
"The more high-quality information we have, the better we can protect these taonga species. Our frogs are unique to New Zealand, so if they go from here, they're gone from everywhere."
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