The Kiwis behind the world's biggest rodent eradication

Multimedia Journalist·NZ Herald·

2 Jun, 2018 05:00 PM3 mins to read

Department of Conservation ranger Miriam Ritchie, with dogs Will and Ahu at an elephant seal colony on South Georgia. Photo / Oliver Prince

Lying 9000km away in the southern Atlantic Ocean, the rugged and windswept island of South Georgia holds scant meaning for New Zealand.

But New Zealand now means much to it, after our world-renowned island conservation expertise helped the British territory rid itself of rodents for the first time in 200 years.

The remarkable feat has left the conservation world abuzz, while offering valuable lessons for New Zealand's bold bid to be free of pest predators by the middle of this century.

Covering some 108,723ha, the South Georgia Heritage Trust's seven-year project was more than eight times larger than any other rodent eradication area ever tackled anywhere on the planet.

Since they were brought ashore by sealing and whaling vessels from the late 18th century, rats and mice had proved a serious threat to the island's wildlife, including two bird species found nowhere else on Earth.

The techniques in the staged eradication were developed in New Zealand and are widely used here today.

Many Kiwis were directly involved in the project, among them field biologists who helped carry out baseline surveys, planners who assisted in mapping out the entire operation - and Department of Conservation dog handler Miriam Ritchie.

Throughout most of summer and autumn, Ritchie and her faithful dogs Will and Ahu trekked across hundreds of kilometres of the island, searching for any trace of rodents that had survived poison aerial drops from the years before.

That meant sleeping in tents and huts, rising early in the morning for breakfasts of dry and canned food, and setting out across rocky, tussock-covered landscape to check a long list of sites.

One of Department of Conservation ranger Miriam Ritchie's terriers, Will. Photo / Oliver Prince

Perched on the edge of the Antarctic Circle, South Georgia's climate plunged to an average -4.9C in winter, but summer days could reach over 9C.

"It was nowhere near as cold as what I was expecting," said Ritchie, whose 16 years as a DoC dog handler have taken her to New Zealand's own subantarctic islands.

One of Department of Conservation ranger Miriam Ritchie's terriers, Ahu, with a seal pup. Photo / Oliver Prince

"We had some beautiful days when I was wearing just shorts and a singlet, but we always had a pack full of everything we needed, including some serious wet weather gear."

The trip, which put her up close with elephant seals and emperor penguins, ranks in her career highlights.

Department of Conservation ranger Miriam Ritchie's terriers, Ahu and Will, with some seals at South Georgia's Gritviken whaling station. Photo / Miriam Ritchie

"The island was very grand and awesome - there were huge mountain peaks in the background, but it was mostly barren, with no trees or shrubs, and just tussock, moss, lichen and lots of scree."

Dr James Russell, a leading island conservation expert at the University of Auckland, said Kiwis continued to push boundaries in the field, having just cleared mice from Antipodes Island.

Sub-antarctic South Georgia is known for its rugged, tussock-covered landscapes. Photo / Miriam Ritchie

"But there was also an opportunity on South Georgia for the New Zealanders to be involved in trialling a staged approach where the eradication of rodents was broken down in to smaller parts," he said.

"This will likely be critical for achieving a Predator Free New Zealand."

One of Department of Conservation ranger Miriam Ritchie's terriers, Ahu, overlooking a penguin colony on South Georgia. Photo / Miriam Ritchie

In particular, the project had shown glaciers could be used as "barriers to movement" - something that would be key to our mission, said Brent Beaven, DoC's Predator Free 2050 programme manager .