KEY POINTS:
A pig population introduced to Auckland Island as a food source for castaways is facing slaughter as the Department of Conservation weighs up how it could be eradicated.
DoC staff have fitted transmitters on 20 pigs on the subantarctic island, 450km south of New Zealand, to establish their movements over the next few months.
The exercise involved releasing a pig-hunting dog, flown in by helicopter, to hold down the pigs while a veterinarian knocked them out so transmitters could be fitted using harnesses.
DoC may also remove the island's cats.
Peter McClelland, programme manager outlying islands, said tracking sought to show pig movements to the coast in winter, making the pigs easier to target if a mass kill went ahead over a three-year period.
Since being introduced in 1840, up to 1000 pigs have roamed the 50,000ha island. They have ploughed over large areas of tussock land to get to edible roots and native earthworms.
Mr McClelland said nearly 200 years of pigs on the island had led to major changes in the vegetation, with the more palatable species of plant being restricted to rocky outcrops or cliffs that the pigs could not access.
The pigs had also disturbed historic sites as they looked for food and had impacted on a range of ground-nesting birds.
"They have been recorded eating the eggs and young of many species and will eagerly dig up any burrow-nesting birds that may have fortuitously escaped the cats."
Mr McClelland said pigs had on at least two occasions been seen eating mollymawk chicks and had destroyed all the accessible nests at the southwest cape colony.
The department was also looking at removing cats at the same time.
Both pigs and cats were likely to be having a detrimental impact on yellow-eyed penguins which were still found scattered around the main island, and albatrosses, which appeared to be trying to recolonise the main islands of the Auckland group.
Mr McClelland said only pigs, cats and mice remained as introduced mammals on Auckland Island, the largest of eight main islands. Goats were removed in 1989.
Cattle, rabbits and mice on Enderby and nearby Rose Islands were eradicated in 1991.
Mr McClelland said cats were probably taken to the Auckland Islands in 1850 during the attempted settlement at Hardwicke and had proven voracious predators.
Land and sea birds, including several endemic species, inhabited the group but many were totally absent from Auckland Island.
It was expected they would recolonise the island if the pigs and cats were removed.
DoC was considered a world leader in island eradications, having removed more than a dozen different species from more than 50 islands.
Mr McClelland was instrumental in the rat eradication from Campbell Island - the world's largest eradication - and had travelled overseas to advise other countries how to remove pests.
