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Environmental News from New Zealand and Around the World

Milestones for island eradications

In the last month, two significant rodent eradications have been declared a success  - one on South Georgia and the other closer to home, on the sub Antarctic Antipodes Islands.

South Georgia was declared rodent-free in early May with the island now clear of rats and mice.  The project is the world’s biggest to eradicate an invasive species  - the island is about 160-km-long, covering about 350,000 ha, with about 100,000 ha ice and snow free.

Rats and mice were inadvertently introduced to the island 250 years ago by passing ships that called in.  The effect on native bird populations was dramatic, as unused to predators, they laid their eggs on the ground or in burrows, easily accessible to the rodents.

Two species of birds endemic to the island, the South Georgia pipit and pintail, were largely confined to a few tiny islands off the coast, which the rodents could not reach, and penguins and other seabird populations were also threatened.

Aerial and ground based poison was laid over three seasons, ending in 2016. Thousands of peanut butter-coated chew sticks, camera traps and tracking tunnels were checked and  New Zealand dog handlers and three rodent detection dogs spent months on South Georgia walking over hundreds of kilometres across the island looking for any signs of rats and mice  - and finding none.

The project has been heralded as an inspiration for eradications on other large islands around the world.

New Zealand conservation dogs checked South Georgia for signs
of rats and mice. Photo: Oliver Prince/South Georgia Heritage Trust

Meanwhile on the  Antipodes Islands,  750 km southeast of New Zealand, the Department of Conservation officially declared the island free of mice in March this year. The ‘Million Dollar Mouse’ project aimed to eradicate mice , the only mammalian predator, from the islands and set about aerial baiting in the winter of 2016. Two seasons of breeding in were then needed to determine if the islands were mice free. Like on South Georgia, the team used a variety of monitoring methods as well as dogs to check for signs of mice.  

The Antipodes Islands are the only home of the Antipodes Island snipe and the Antipodes Island parakeet, both of which nest on the ground and are set to benefit  greatly from the eradication.

New Zealand seabird relocation

Nearly 100 mottled petrel chick have been moved over 1,000km from their home on Codfish Island to mainland New Zealand -  inland on the Maungaharuru Range in Hawke’s Bay. Like so many of New Zealand’s hill country, the Maungaharuru Range once was home to millions of seabirds.

The relocation in March was the biggest ever attempted and is part of a broader plan to help seabirds repopulate the region.

The mottled petrel (kōrure) will spend four to six weeks at the site where they will be monitored and fed to bring them into optimal condition for fledging.

Kōrure, like many seabirds, were ecologically important as natural recyclers of nutrients from the sea into native bush.

Seabirds usually return to their natal nesting site—where they were born—to breed, often several years after emerging from their burrows and fledging.

Kōrure will spend three to four years at sea before (hopefully) returning to Maungaharuru to nest. Running since 2014, the relocation programme has seen the first kōrure returning to the site. 

Kōrure, like many seabirds, were ecologically important as natural recyclers of nutrients from the sea into native bush.

Korure or mottled petrel is endemic to New Zealand and currently only breeds at a few sites in the south of the country.  Photo: Department of Conservation

Update from Lord Howe Island

The Lord Howe Island Rodent Eradication Project aims to eradicate ship rats (Rattus rattus) and mice (Mus musculus). If successful, Lord Howe Island would be the largest inhabited island in the world where rodents have been eradicated.

Delay to 2019

In March 2018, the Lord Howe Island Board decided to delay the baiting implementation phase of the project to winter 2019. The decision to delay related to delays with receiving permits  and a change in the proposed method to increase bait stations in the settlement area in response to community consultation. The change needed more time and resources during the eradication and more time invested in planning.

The overall baiting approach includes aerial broadcasting over uninhabited parts of the island and a combination of hand broadcasting and bait stations in the settlement area.  The actual treatment method over individual properties is to be discussed and negotiated with individual leaseholders and residents through property management plans.

Fish behaviour towards placebo bait pellets

Professor David Booth, Professor of Marine Ecology at the University of Technology Sydney,  has been studying the potential effects of baits  entering the ocean adjacent to Lord Howe Island during the eradication. The study looked at the response of fish to bait pellets.

Placebo pellets (no toxin) were dropped into the water and fish behaviour towards the pellets observed i.e., whether they ignored, approached, mouthed or swallowed the baits.  About 400 fish were observed where pallets were dropped. About 37% totally ignored the pellets, 36% approached but deflected the pellet, and 25% mouthed the bait and then rejected it. Less than 2% of fish swallowed the bait, all of which were at sites where people hand feed fish (and where no aerial baiting would occur). The study concluded that aerial application of bait would have little or no effect on fish in areas adjacent to aerial baiting operations.