The latest report on New Zealand amphibians’ conservation status has confirmed higher numbers of Archey’s frogs than previously known, although they’re still at risk of extinction.
An independent panel of experts has assessed all 20 frog species and sub-species found in New Zealand, and one newt. Four species have declined in status, and none have improved, the experts found.
The Department of Conservation’s (DOC) lead on the assessment panel, Dr Rhys Burns says Hamilton’s frogs and one subspecies of Hochstetter’s frog are in serious trouble, while Archey’s frogs have higher numbers than previously thought, but are still declining mainly due to the impact of introduced mammals.
“The current Archey’s adult frog population, previously estimated as between 5,000 and 20,000, has been revised to over 100,000 individuals,” said Dr Burns.
“Surveys of Archey’s frog in central-southern Coromandel and Whareorino (western King Country) over the past few years have identified higher numbers than previously known. However, their conservation status remains At Risk – Declining, primarily due to predation by rats and mice.”
Hamilton’s frog, mainly found on Te Pākeka/Maud Island, Takapourewa/Stephen’s Island and a few smaller translocated populations at other sites, was moved into Threatened – Nationally Critical. Monitoring indicates a decline in the size of the largest population found on Te Pākeka Island.
The actual cause of the decline isn’t known, but possibilities include climate impact, predation from mice and weka, direct or secondary poisoning from two brodifacoum operations in 2014 and 2019 to eradicate two mouse incursions on the island, the impact of a frog fungus recently found on the island, or a combination of these factors.
DOC says it will take all these possibilities into account for future frog management planning on Te Pākeka.
Climate change impact was added to the assessment for the first time – an acknowledgement that climate pressures are 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,” said Dr Burns.
“Long periods of high temperatures and dry periods temporarily dry out streams and areas of water seepage that Hochstetter’s frogs rely on. Large storms affect Hochstetter’s frogs that use stream habitat, by increasing water flows, siltation, and in extreme situations, landslides.”
He says DOC recently saw the devastating impact of severe weather on the already-fragile Hochstetter’s frog population.
“Following the severe rainfall events of January 2023, a major slip in Otawa, near Te Puke, destroyed the habitat of the ‘Otawa’ Hochstetter’s frogs, resulting in an estimated loss of 30-40 per cent of the frog population in one night.”
“‘Otawa’ Hochstetter’s frogs were assessed as Threatened – Nationally Critical in this and previous assessments, so the loss was a huge blow. DOC is doing pest control at this site to try to support the recovery of this population.”
Other Hochstetter’s frog populations were assessed as threatened or declining largely due to the impact of predation by introduced mammals.
Dr Burns says frogs are 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 said.
“We hope more organisations – whether they’re iwi, other agencies, businesses or community groups – consider researching and surveying frogs.
“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.”
Read the report: Conservation status of amphibians in Aotearoa New Zealand, 2024.
