As 2019 ends, so does the feasibility stage of the Maukahuka Pest Free Auckland Island project. This ambitious project proposes to eradicate pigs, mice and cats from Auckland Island (46,000 ha), the largest island in New Zealand’s World Heritage listed Subantarctic region. This is a significant project for Predator Free 2050 and success would complete a pest-free New Zealand Subantarctic. So, what have we learnt and where to next?
Winter 2019 saw the Maukahuka team heading back to Auckland Island. The summer trials had left some questions unanswered and raised others: How would the mouse population respond to the tussock seeding / mast of the summer? What is it like operating in the field while dealing with the subantarctic winter? How do pigs and cats cope with these conditions? Are the proposed cat baits palatable to feral cats?
The Deas Head trail camera grid from the summer was fired up again to investigate this last question. DOC scientists are working on a bait that targets cats and mustelids that can be aerially distributed – a tool vital to landscape-scale conservation efforts across New Zealand. Cameras were baited with one of four non-toxic tasty treats: chicken sausages, rabbit sausages, a delicious sounding ‘meat glue block’ and a fishmeal pellet.
Over four weeks, 13 cats were detected and all consumed baits, with the meat-based products almost always consumed by the first cat to encounter them. This is a hugely promising result. The next stage in the process to register this bait for use in toxic trials. Manaaki Whenua/Landcare Research have started work on pen trials and field trials will potentially run on Auckland Island next winter.
The rest of the team headed to the south of the island to Camp Cove in Carnley Harbour to prepare the area for the further bait trials in 2020. They installed a shelter to protect staff and gear from the elements and cut a network of tracks to support a grid of trail cameras. Eight cats were caught and collared to provide information about their behaviour and to monitor the population through the bait trial. Three cats were also added to the monitored population at Deas Head.
Information from the satellite collars fitted to cats last summer have shown distinct seasonal changes in habitat use and vast differences in home range size. A small female at the north of the island has a home range of 116 hectares of rātā forest, while one male is roaming 6,959 hectares of the tops above Carnley Harbour in the south.
While at Camp Cove, the team visited Masked Island. This little dot of 5.6 hectares sits 118 metres offshore, theoretically within swimming distance of the pests on the main island. To find out more about Masked Island and what the team discovered, check out the Masked Island Story Map here.
Mouse tracking tunnels and trapping both at South West Cape, Falla Peninsula and Deas Head had higher capture rates than the summer, showing the mouse population booming post tussock mast. The higher numbers of mice in the tops are clearly drawing cats up into alpine areas. More cats were caught on camera there than in summer and scats full of mouse fur and bones were found. It’s possible that the bumper crop of mice was responsible for the higher number of juvenile cats encountered compared to the summer.
The eradication of pigs, cats and mice will need every tool in the box and some yet to be designed. Automated feeders and bait dumps were installed across the island to see how attractive they are to the pigs and cats in the winter. While pigs had not been drawn by a ready supply of kibbled corn in the summer, this time plenty of pigs were snapped enjoying the free food. Food dumps (fish and sheep carcasses) were successfully tested for cats and drew in pigs and giant petrels as well. Sound lures proved tempting too, with trail cameras catching cats searching the cavity in which the speakers were placed, projecting the sound of a sooty shearwater apparently living there.
An automatic lure dispenser from ZIP was also tested to see if cats like anchovy mayonnaise (they do). Long-term lures will be important to tools like an island wide grid of trail cameras during the cat eradication, so this is another promising development. A few thermal trail cameras from The Cacophony Project were also tested, to see if they can assist with cutting down on the number of false triggers.
Elsewhere on the island Stephen Bradley captured startling images of a cat feeding on an almost-fledged white-capped mollymawk. An archaeologist and a building expert visited proposed base sites to inform future infrastructure work. Ngāi Tahu kaumatua Stewart Bull and Melvin Cain spent a week visiting sites around the island and helped install a new shelter providing much needed storage space at Deas Head.
Stewart Bull summed up his visit: “[The island was] more harsh than I dreamt because my experience is with Rakiura and Fiordland. It was more extreme than anything I know. [It was] quite an eye opener for me, it’s really enthused me to get on board and try to enthuse others… I want to be talking to others because accepting kaitiakitanga is an obligation, to tap out of kaitiakitanga is not an option. I really appreciated the opportunity to go there and to put myself in that place and space, you have to do that to really understand the challenge.”
Back on the mainland, the team were working on a report on the project’s feasibility. Building on the results from the summer and winter trials, this has been produced with the support of DOC’s Island Eradication Advisory Group. The study concludes that it is technically possible to remove all three pests from the island with a few necessary technology developments.
Development of the tools needed is underway. As well as the cat bait research, the team is working on a modification to existing helicopter bait buckets to improve their suitability for applying bait at the low rates required by the mouse eradication (half that normally used, due to the logistics of just getting bait to the island for starters).
If initiated, the project will start developing and building the thermal cameras needed for the pig eradication. Trail cameras is another key area for research. With the current technology it would take one person a whole year to analyse a month’s worth of data from an island-wide network. By providing large data sets gathered in the summer and winter to technology firms and researchers, it is hoped that software can be developed that reliably filters out falsely triggered images (e.g. no animal in the picture). The dream is a camera that can identify a cat and sends an alert to the base, but we’ll settle for not having to trawl through thousands of photos of tussock blowing in the wind.
So, what next? Planning will continue in more detail and over the next year DOC and Ngāi Tahu will look at funding options and partnerships to take the project forward. If the project gets the go ahead to move into the operational phase, late 2020 will see the start of infrastructure installation on the island. It is estimated that three summers will be needed to prepare and install three field bases with boat sheds and helicopter hangars and a network of bivvys and tracks across the island to support the work of returning Auckland Island to the wildlife haven it once was.
Maukahuka Pest Free Auckland Island is a collaboration between DOC and Ngāi Tahu, exploring the feasibility of removing pigs, cats and mice from Auckland Island – the last island in New Zealand’s Subantarctic with mammalian pests. To learn more about the project visit Maukahuka.
Read another article by Rose here.