The last trip by researchers to hunt for a beetle threatened by a controversial dairy conversion has been unsuccessful.
But they say it may still be too soon to write the species off.
Only 10 specimens of the Eyrewell ground beetle have ever been found – all in the Eyrewell Forest area northeast of Christchurch.
Much about them remains a mystery to scientists, although their story is a tale of two conversions.
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The Eyrewell Forest area is thought to have originally been kānuka shrubland and converted to a regularly-felled pine plantation in 1928. It was returned to Ngāi Tahu – the original landowners – in 2000.
In 2016, it was announced the forest would be converted to 8500 hectares of irrigated pasture, supporting 14,000 dairy cows across 20 farms. Tree felling was completed by 2018.
Lincoln University researchers have been carrying out surveys of the leftover forest since 2013, with work ending last year.
They were unable to find a single Eyrewell beetle.
Ecology professor Nicholas Dickinson has been involved in the beetle hunt since its early days.
“It probably is too early to write the obituary for something we’re not sure we ever had.”
The last specimens were found during large scale searches in 2000, when “tens of thousands” of traps were spread across Eyrewell Forest before the conversion began.
“We found about six.”
The searches might not have painted an accurate picture of the population though, he said.
Most of the surveys were done using pitfall traps, which Dickinson said ended up trapping various insects, including butterflies and weta.
“We had thousands of samples with loads of little bugs in them, so we had the issue of sorting those out to try and pick out a ground beetle the size of a pencil head. Many samples were never analysed.”
He said many traps also had other carnivorous ground beetles in them, which could have eaten the smaller Eyrewell beetle.
“An overseas expert also told us what we were doing was wrong, and this sort of beetle doesn’t readily enter these traps.
“He said the only real way to find them is to crawl around with a head-torch at night, so quite possibly there are lots.”
The other question was whether the beetles were really a species at all.
“They were mostly identified by a small aberration on the penis of the males … but I’m not sure if that’s enough to say it’s a separate species.”
Dickinson said DNA testing would be needed to make sure they were not just a variant of other beetles living nearby.
“We priced it up as something we could do with $50,000.
“But is that the way we should spend $50,000? We could spend it preserving a whole site.”
If the Eyrewell ground beetle was a unique species, Dickinson said he was not optimistic about its chances of surviving the land conversion.
“When conversion started, we got them to protect areas of pine forest in case the beetle is there … but we did not protect the exact locations where beetles were found – we couldn’t, there were grand plans for these farms.”
He said in theory, the beetles could survive in the remaining patches of forest, or in native plant restoration areas.
“But we never found any there, [so] I wouldn’t put any money on it.
“A ground beetle would have to be pretty tough to survive in a paddock.”
The Canterbury landscape had been knocked around more than any other, Dickinson said.
“The conservation story is about protecting what’s left … the Eyrewell beetle is just one part of our hidden biodiversity, and focusing on one species is no use. We need to focus on the assemblage of species.”
Ngāi Tahu Farming had not responded to requests for comment by the time of print.
How is a species declared extinct in New Zealand
The New Zealand Threat Classification System is used to determine the conservation status of a species, and is managed by the Department of Conservation (DOC).
DOC technical adviser Pascale Michel said a panel of experts, usually taxonomists and ecologists, were selected from within the department and from external organisations like museums, Crown Research Institutes, universities, and private consultancies.
They would then assess the conservation status of a species based on estimates of its population state and size (which could be based on the number of mature individuals, number of subpopulations, or area of occupancy), and the trend within 10 years or over three generations.
The assessments were carried out every five years or so, and focused on specific groups, like birds, reptiles, or marine mammals.
“A species is assessed as ‘extinct’ if there is no reasonable doubt – after repeated surveys in known or expected habitats at appropriate times and throughout the taxon’s historic range – that the last individual has died,” Michel said.
“[Species] that are extinct in the wild but occur in captivity or cultivation are not listed in this category – these are listed instead as ‘nationally critical’ with qualifier ‘EW’ or ‘extinct in the wild’.”