An Introduction to Subantarctic New Zealand

If you read the blog I posted before I left, you’ll recognise this map:

subantarctic_map

When I mention the subantarctic to people, they often comment on how much ice I’m going to see – which would be true if I was heading down to South Georgia. But New Zealand’s subantarctic islands are actually much closer to New Zealand than Antarctica, and sit between the Subtropical and Antarctic convergences. This means our subantarctic islands are warmer and wetter than those further south, and they lack any permanent ice. In this region – the roaring forties and furious fifties – the weather is defined by wind and rain, and our subantarctic islands boast some absolutely unique plant life because of it.

This post is a brief introduction to the islands – some, like the SnaresAucklandCampbell, and Macquarie I had visited before, others I hadn’t. Each is unique and has its own character and history – but this will just be a quick introduction. Macquarie Island is Australian, all the others are part of New Zealand – and while the Chatham Islands aren’t technically subantarctic, they’re often included due to the amazing biodiversity that occurs there. So let’s dive in!

 

The Snares/Tini Heke eaw_2913web

The closest group to mainland New Zealand, the Snares lie 100km southwest of Stewart Island/Rakiura. Those who visit the Snares typically focus on the largest island, North East Island, which is blanketed in a forest of silvery Oleria lyalli and Brachyglottis stewartiae, the latter blooming with large bright yellow flowers during summer. The islands themselves are 100 million year old muscovite granite, uplifted from the ocean floor and eroded by the wild Southern Ocean. The Snares boast a pristine status that has never seen invasive pests establish there, and as such are home to millions of seabirds – the endemic Snares Crested penguin breeds nowhere else on earth. The burrows of Sooty Shearwaters honeycomb the earth beneath the forest, as well as those of several other burrowing seabird species such as Common diving petrels and Mottled petrels. Four species of albatross and three species of prion also breed on the island. The Snares are home to three endemic land-birds as well, with unique subspecies of Fernbird, Snipe, and an all-black Tomtit. Other conspicuous fauna are New Zealand Sea lions and Fur seals, both of which breed on the rocky coast.

 

Auckland Islands/Motu Maha

eaw_5665web

The Auckland archipelago is the largest of our subantarctic groups – in fact, all of New Zealand’s other subantarctic islands could easily fit inside the main Auckland Island! It also boasts the greatest species richness. Four hundred and sixty kilometres south of Bluff, the Auckland Islands are the remains of two eroded volcanic craters that erupted between 25 and 10 million years ago, over a basement of 100 million year old granite. They’re the tallest of our subantarctic islands, with Mt Dick on Adams island sitting 705m above sea level, and the cliffs on the battered western coastline soaring in places to 400m. Auckland Island itself has three introduced pest animals: cats, pigs, and mice. Enderby Island, forming the northern part of Port Ross, used to house feral cattle, rabbits, and mice, but these have all been eradicated. The other large islands in the group – Adams and Disappointment – are both pest free. Auckland Island is blanketed in Southern Rata forest which turns into Dracophyllum scrublands and tussock grasslands at higher elevations. It’s the breeding stronghold for the critically endangered New Zealand Sea lion, and Southern Right Whales frequent Port Ross to calve and mate during winter. Seabirds also breed in great numbers throughout the archipelago, although those on the main island are hampered by the presence of pest animals. Gibson’s wandering albatross is endemic to the Auckland Islands, and most of the population resides on pest-free Adams Island, the southernmost point in the archipelago. 

 

Campbell Island/Moutere Ihupuku

eaw_3411web

Campbell Island is the most southerly of New Zealand’s subantarctic islands, sitting 700km from the South Island at 52° 33′ south. It’s the second largest group, also formed by an ancient shield volcano that erupted between 6 and 11 million years ago. While the western side of this volcano has eroded away completely, the eastern side forms the bulk of Campbell Island, sitting on a basement rock of 450 million year old mica schist overlaid by sandstone and spectacular white limestone, which is exposed on the cliffs of Northwest Bay. Like Auckland Island, the eastern coast is deeply scored by fjords that are the result of past glaciation, and Perseverance Harbour nearly entirely bisects the island. Campbell Island is home to the endemic Campbell albatross, and the largest proportion of the Southern Royal albatross population, as well as a few stray Antipodean albatross and the circumpolar Light-mantled albatross. Yellow-eyed penguins have a stronghold on Campbell Island, and Eastern Rockhopper penguins also breed here, although their numbers have suffered a massive decline – from tens of thousands to mere hundreds left today. Many other seabird species breed, and there are also small populations of New Zealand Sea lion, Fur seal, and Southern Elephant seals. Campbell has no true trees except a ‘lonely’ Sitka spruce that was reputedly planted by Lord Ranfurly in the early 1900’s, and is covered in tussock and dracophyllum. In summer a riot of megaherb species turn the gold tussock into a lush green garden of magenta, indigo, and flaming yellow blooms. 

 

Antipodes Island/Moutere Mahue

eaw_6166web

The Antipodes are our most remote subantarctic islands, 870km away from the South Island. They’re the youngest of the volcanic subantarctic islands, with volcanic basalts dated to between one and five million years old. The Antipodes are covered by tussock grasslands interspersed with prickly shield ferns, four Coprosma species, and various megaherbs. Home to the Antipodes albatross, the islands are also home to a plethora of other seabird species including Erect-crested and Eastern Rockhopper penguins, Soft-plumaged petrel, Subantarctic diving petrel and White-chinned petrel, among others. Two endemic parakeet species also live on the island – the all-green Antipodes parakeet which is the largest of New Zealand’s parakeet species, and the Reischek’s parakeet, which looks similar to the mainland Red-crowned parakeet. The invertebrate fauna of the Antipodes has a high proportion of endemics as well – over a quarter of the 150 known species! Unfortunately the extinction of two endemic invertebrates has been attributed to the presence of mice on the island – a problem which has hopefully been removed by the Million Dollar Mouse project in the winter of 2016. With post-eradication monitoring planned for 2018, we’ll soon know whether or not the undertaking was successful – but things are looking good! The removal of mice from the island will be the largest single-species eradication so far, and will do wonders for not only the invertebrate life, but also the birds and vegetation.

 

Bounty Islands/Moutere Hauriri

eaw_7237web

The Bounty Islands are literally rocks in the ocean, protruding lumps of 180 million year old Jurassic granite that are more closely related to rocks found in Western Antarctica than anywhere in New Zealand. They’re the smallest and most northerly group, covering only 135ha and sitting at 47° 45′ S. With a highest point of only 88m above sea level, the islands can disappear underwater completely in a wild storm. Despite their relatively inhospitable nature, they’re an absolute haven for seabirds, and are home to the rarest shag species in the world – the endemic Bounty Island shag, which has a population estimate of little over 1000 birds, based on a survey in 2013.  Around 40,000 Salvin’s albatross breed here, as well as Erect-crested penguins, Snares Cape petrels, Fulmar prions, and the pervasive Southern black-backed gull. New Zealand Fur seals also breed here in their tens of thousands. There is one known species of vascular plant on the Bounties – Cook’s Scurvy Grass, discovered there in 2004. Apart from a few lichen species, the islands are otherwise barren, coated in thick white guano. Despite this, there are several invertebrate species that live on these islands – including flightless beetles, weta, moths and spiders. 

 

Chatham Islands/Rekohu Wharekauri

chatham_albatross_pyramid_eaw_9850-edit6x4web

Well to the north at 44° S, the Chatham islands aren’t remotely subantarctic, and are inhabited by people. However the biodiversity of the group and the large number of endemic species make them a sought-after destination for birders visiting this part of the world. Over 140 million years ago, the Chathams were connected to the then much larger continent of Zealandia. Erosion and tectonic movement during the Cretaceous, between 135 and 65 million years ago, isolated the islands from the mainland entirely, and they currently sit 800km to the east of the central South Island. Despite extinctions resulting from European settlement, the islands still retain a large endemic complement. Some, like the Chatham albatross, are restricted only to certain islands within the group. Other endemics include the extraordinarily rare Taiko (Magenta Petrel) and Chatham Petrel, Chatham Island Pigeon, Oystercatcher, Snipe and Warbler – and the Black Robin, whose population in 1980 consisted of only 5 birds – and only one breeding female. As of 2013, the population was approximately 250 birds strong – an amazing conservation success story driven by the tireless work of Don Merton, one of New Zealand’s legendary conservationists.

 

Macquarie Island

macquarie_island_eaw_8530-edit6x4web

Macquarie Island belongs to Australia, and is administered by the Tasmania Parks and Wildlife Service. It’s the only one of the subantarctic islands in our region that has a permanently occupied research base, the Australian Antarctic Division ANARE station that sits on the isthmus at the northern end of the island. Of this group of subantarctic islands, Macquarie is the furthest south at 54° 30′ S, and lies the closest to the Antarctic convergence. Approximately 700,000 years ago the oceanic crust was uplifted, creating the long ridge of the island from rock that was formed around 20 million years ago on the ocean floor. Macquarie island hosts 20 breeding seabird species, including the endemic Royal penguin and Macquarie Island Shag. King penguins breed in large colonies along the coastline, and Eastern Rockhoppers and Gentoo penguins are also present. Four seal species also breed on the island – Antarctic, Subantarctic, and New Zealand Fur seals, and Southern Elephant seals. In 2012, all of the pest animal species were successfully eradicated from Macquarie, ending the multitude of problems that populations of cats, rabbits, rats, and mice were causing for the island.