“This is a massive project,” says Stephen Horn, of a plan to eradicate introduced pests from Auckland Island/Maukahuka. The manager of the Department of Conservation’s national eradication team says that’s something a feasibility project, published in 2021, unearthed – “that the scale is enormous, and it’s complex”.
The scale and complexity translates into eight years and $80 million. It’s a project now being actively fundraised for by NZ Nature Fund, which signed an agreement with the department (DoC) in September.
In New Zealand’s subantarctic region, goats were culled from Auckland Island in 1991, mice and rabbits from nearby Enderby in 1993, rats were eradicated from Campbell Island in 2001, and mice from Antipodes Island in 2014. Removing the last pig, cat and mouse from Auckland Island would be the “last piece of the puzzle” for a pest-free subantarctics, Invercargill-based Horn says.
Such a feat would be a significant achievement for DoC, Horn says, and carry international importance. Aside from its status as a multi-species eradication, to date, the world’s largest successful extermination of mice was on an Australian subantarctic island, Macquarie. Auckland Island is nearly four times larger.
Auckland Island, the largest in an eponymous group of islands, is located 465km south of Bluff. The rugged, wind-and-rain-swept island, featuring imposing cliffs on its western flank, is New Zealand’s fifth-biggest island, with a coastline measuring 374km. At 459 square kilometres in area, it’s about three-quarters the size of Lake Taupō.
Given Auckland Island’s isolation in the highly productive Southern Ocean it’s a biodiversity hotspot, recognised as a UNESCO World Heritage site. There’s also a rich cultural heritage, with evidence of Polynesian occupation on Enderby Island, part of the Auckland Islands group, dating back to the 13th century. The pest project is supported by Ngāi Tahu ki Murihiku.
However, for the past 200 years, pigs, mice and cats have inflicted enormous ecological damage, diminishing Auckland Island’s native biodiversity.
To say it’s a challenging environment seems an understatement.
“The weather’s pretty poor most of the time,” Horn says. “The terrain’s not too bad, but the whole western coast is steep cliffs, basically straight down into the sea, up to 600 metres, with strong westerly winds most of the time.
“You pretty much can’t go around the western side in a boat. And even when it’s calm, you get cap cloud hugging the tops and around that coast.”
The scrub’s “pretty horrendous”, he says. When you’re in contact with scrub and vegetation, you get soaked anytime it’s wet.
DoC’s feasibility study included two big summers of research, and pilot programmes to test the responses of the target species.
Aerial hunters with thermal cameras hunted for pigs in different vegetation – on the tops versus scrub versus forest canopy. “Then we ground-hunted to verify … how many we got rid of proportionally by the helicopter, [and] how many were left for the ground hunters.”
Aerial drops of cereal pellet poison bait for mice are usually done in winter, but the Auckland Island weather meant it was done in summer – when tussock grasslands were “seeding” or “masting”, and mice were breeding.
“We were interested to know whether mice would eat the bait when they had lots of other available food in those tussock seeding events as well,” Horn says.
A non-toxic version of the cereal pellet, with an ultraviolet fluorescent marker in it, was spread by helicopter. Mice were trapped afterwards. If they glowed under UV light they’d eaten the bait.
All but two of the mice glowed – with the exceptions weighing under 10 grams.
“It told us that, well, there’s two juveniles that have probably just emerged out of a nest and jumped into a trap before they’ve had a chance to eat bait. So it reinforces the need to do the second application, which is the best-practice approach for eradications.”
Population estimates were between 750 and 1500 for pigs and cats, pulsing up and down between seasons and years – “not really dense populations”, Horn says.
Mice, on the other hand, have massive population fluctuations, from barely detectable to millions.
Information gleaned from the summer trials gave the DoC team confidence about the level of effort required for the eradication, and the best sequence in which to stage it.
For the record, the sequence is: pigs, mice, and then cats.
The feasibility report said: “Pigs must be eradicated first to make the attempts on mice and cats possible (pigs will create gaps in bait coverage for mice and interfere with traps and baits for cats). The mouse eradication method complements that for cats. Too long a delay after the pig eradication risks vegetation regrowth that could make cat hunting unfeasible.”
Surveillance and detection will rely on a camera network spaced every 500m, or about 2000 cameras. (That’s based on the smallest “home range” for collared cats of about 120 hectares.)
While Covid-19 slowed momentum on the project (Horn was on the island when the first lockdown began), one benefit of the pandemic-enforced pause has been the advancement in camera technology.
“We’ve now got cameras that we can use AI on that can connect to satellites. They’re just in small-scale testing at the moment, but those cameras can be trained, with our database of images, to detect cats and then tell us in almost real time that they’ve detected a cat.”
Initially, the plan was to check the cameras manually every two weeks. “That gives you much more likelihood to shrink the duration of the project.”
The first two years will involve the installation of base facilities for helicopters, and 20 to 30 people, for four years of intense operations. “It’ll take about a year for the pig operation, and then about six months to deliver the mouse operation, the baiting operation, and then straight into the cats for approximately 18 months,” Horn says.
“Then, of course, there’s quite a bit of time associated with demobilisation, removal of facilities that aren’t required long term.”
The feasibility study said eradicating pigs, mice and cats “will immediately halt the destruction of indigenous fauna and flora to enable recovery and protection of over 500 native species”.
The pest-free area in the subantarctic islands would increase from 30,000ha to 76,000ha. “This will secure the region as predator-free and reduce the extinction risk for more than 100 endemic species,” the study said.
Horn says 25 sea birds breed on the Auckland Islands, and they’ll be big beneficiaries of the pest eradication.
“We see the likes of white-capped mollymawk, which are about 100,000 pairs breeding on Disappointment Island, the little rock to the west of the main Auckland Island. And there’s about 5000 pairs breeding on the main island, because they only survive in the very steepest places that pigs can’t get to.
“Gibson’s wandering albatross, which is endemic to the site, breed on Adams Island to the south, which is pest-free.
“If you’re in Carnley Harbour, you’ve got this immense bird song cacophony on one side of you, and on the other side it’s deathly quiet. So it’s really quite stark.
“And then you get up onto the tops, and there’s a plateau that’s turned over by pigs, where it should be herb field and tussock grasslands.”
The portent of Auckland Island’s future – should the money for the project be found – can be found in other parts of the subantarctics.
Since the eradication of rats and the removal of livestock from Campbell Island, there’s a veritable sea of pink and purple flowers on the tops, Horn says.
“And the same with Enderby, to the north of Auckland Island, where rabbits and mice and cattle were removed in 1993. That terrain that was billiard table was returned to be these expanses of yellow and purple flowers of herb fields that come up to your knees.”
DoC has learnt incrementally from decades of pest eradication in the subantarctics, he says, developing its capability and innovation at every stage. Its planning has to be thorough.
“You get one shot, right? And the outcome is very clear. So if you leave some mice behind, or if you miss some cats, it won’t be long before the outcomes are reversed. So you have to get it right.”
The scale of the project sounds daunting, Horn says. “But when you break it down in the way we have, you can see how to approach it, and that it is achievable. We’ve invested a lot of effort and time, and DoC’s put a lot of money and effort into understanding this project really well, to build that confidence.”
That still-to-be-found $80m is a one-off investment that, Horn says, will achieve a permanent outcome that’s pretty much self-sustaining.
“These are extraordinary projects. When you look at them, they take extraordinary effort, extraordinary innovation, and also in terms of the funding, it’s an extraordinary event as well.”
