subantarctic

Antipodes Island is part of New Zealand’s World Heritage subantarctic region and hosts special biodiversity values and significant species endemism. Invasive house mice were the only introduced mammal and detrimentally impacted invertebrate and native bird communities. Eradication of mice from Antipodes Island was undertaken in 2016 and confirmed in 2018. We present the monitoring used to confirm eradication of mice and the ecological outcomes measured over the 6 years since the eradication.

Feral goats (Capra aegagrus hircus) were eradicated from Auckland Island, a National Nature Reserve and World Heritage site, between 1989 and 1991. Goats had established on the main Auckland Island following several releases in the 19th century. The population, amongst the most southerly ever recorded, was restricted to the northernmost areas of the island, with environmental conditions appearing unfavourable for southward spread, and the population stable at c. 100 individuals during scientific studies in the 1970s and 1980s.

Feral sheep were eradicated from Campbell Island (Motu Ihupuku) – a National Reserve, Nature Reserve and UNESCO World Heritage Site in subantarctic New Zealand – in three distinct stages from 1970 to 1991. The sheep derived from farming attempts on the island, starting in 1895 and abandoned by 1931. The potential genetic and commercial value of the isolated sheep population meant proposed eradication plans were not wholly supported.

New Zealand manages five island groups in the Southern Ocean New Zealand subantarctic region: The Snares (Tini Heke), Bounty Islands, Antipodes Islands, Auckland Islands (Motu Maha or Maungahuka) and Campbell Island / Motu Ihupuku. Charted by Europeans in the late 18th and early 19th centuries, their preservation commenced in the early 20th century and restoration in the late 20th century.

We analysed biomass allocation of Pleurophyllum speciosum (Asteraceae) and Anisotome latifolia (Apiaceae) to explore the 'megaherb' phenomenon, the apparent importance of large-leaved, colourful forbs on southern oceanic offshore islands. The two species had similar shoot dry weights, with high leaf:stem ratios. Even within the megaherb form there are differences in shoot allocations, with Pleurophyllum investing more biomass in rhizome than foliage, compared with Anisotome.

The diets of feral pigs and feral goats shot on the main Auckland Island in 1989 are described from analyses of stomach and rumen contents. Feral goats ate at least 50 species of plants, but only three, Metrosideros umbellata, Chionochloa antarctica, and Durvillea antarctica made up over 50% by dried weight of the food eaten. Feral pigs ate a mixed plant and animal diet, of which plants made up 61% of the diet, with the megaherb Anisotome antipoda being the largest dietary item at 38% by dried weight.

Sheep introduced to Campbell Island in 1895 for farming reached numbers of over 8000 in 1916 then declined to 1000 by 1961 (exponential growth rate r = -0.05 p.a.). Numbers increased to around 3000 from 1961 to 1969 (r = 0.14 p.a.). The island was divided into halves by a fence in 1970, and all sheep north of it were killed. The southern population continued to grow from 1970 to 1984 (r = 0.053 p.a.). The southern half of the island was cleared of sheep in 1984 except for about 800 fenced off on a peninsula.

Marked sites established around Port Ross in 1973 were re-examined in 1983 to measure changes in the vegetation and assess the impact of goats and pigs. Goats had not increased in numbers, nor extended beyond their earlier range, but they were seen higher on the Hooker Hills. Pigs were scarce, but their sign was seen throughout. Photopoints and numerical methods both showed that Chionochloa antarctica tussock was eliminated or greatly reduced where goats and pigs occurred together, and where only pigs were present it was reduced slightly.

New Zealand’s subantarctic Antipodes Islands are of international significance for breeding seabirds. However, penguin populations on the islands are declining. Uncertainty about the extent of this decline has been accentuated by a lack of accurate information on the population size and nest distribution of the penguin species, and the absence of an appropriate methodology for their long-term monitoring. We surveyed the nest abundance and distribution of eastern rockhopper penguins (Eudyptes filholi) and erect-crested penguins (E.