Possum with kereru egg. Photo - Nga Manu Images

Local and Global Eradication Projects

Our project centres on the eradication of predators from Rakiura – not the control of predator numbers. Even though both sometimes use the same tools, eradication permanently removes all identified pest species with ongoing surveillance and management of reinvasion risks.

A predator removal project of this complexity, on an island of this scale, has never been attempted before. This means we will learn new techniques and innovations that could be applied not only in Aotearoa towards a predator free New Zealand but also for restoration projects around the world.

Did you know?

Islands make up just 5.3% of Earth’s land area, and since AD1500, they have lost 75% of all known bird, mammal, amphibian, and reptile species due to extinction. Right now, they are home to 36% of our most critically endangered species.

(Source: Holmes et al., 2019.)

Eradication projects are highly complex, and many have long periods of control work before fully committing to a focused intensive eradication effort. The eradication process typically involves five stages: Feasibility, Knock-down, Mop-up, Verify, Biosecurity. 

Re-invasion risk and post-project biosecurity are key considerations for the feasibility of every eradication project. A strong biosecurity programme, which has been tailored to the specific needs of the individual island, is essential to preventing re-invasion – and avoiding another costly eradication operation in the future. 

Learn more about the difference between control and eradication here.

Read on to find out what we can learn about eradication projects in New Zealand and around the world.

New Zealand Island Eradication Projects

Aotearoa New Zealand has worked on some amazing eradication projects, and is constantly building knowledge and capability for taking on these large projects.

The learnings from these projects are hugely important for us here at Predator Free Rakiura. Rakiura/Stewart Island is inhabited, and 160,000 hectares. It will be New Zealand's largest island eradication project if successful. We are getting ready to move into the feasibility stage where trials will be used to come up with an innovative planned approach to predator eradication.

Read on to find out about:

New Zealand's capability building for rodent removal. Image source: Veronika Frank, New Zealand Department of Conservation.

Rangitoto-Motutapu Islands 

3,881 hectares combined, uninhabited. Predator free since 2011.

Rangitoto Island at dawn. Image: Chris Gin | Creative Commons

Predators: 3 species of rats, stoats, mice, feral cats, hedgehogs, rabbits

Methods used:

  • Feasibility study and consultation
  • Knock-down – aerial poison baiting
  • Mop-up – trapping and spotlighting
  • Verify – sign search, dogs, and trapping
  • Biosecurity – protocols in place

 What did they learn?

  • This was a complex project as it involved eradication of 8 species at once.
  • The feasibility study allowed proper planning and rapid delivery.
  • Lots of time was spent planning to ensure the Auckland stakeholders were happy.
  • Intense pressure was maintained at the ‘mop-up’ stage, hunting survivors (particularly cats and hedgehogs). Lots of effort went into verifying eradication.
  • Timing is critical – you cannot give predators time to adapt and learn how to avoid bait and traps.
  • The project was completed in a shorter time frame and at less cost than anticipated, highlighting the effectiveness of targeting multiple species in one operation.
  • One operation also meant less impact and subsequent cost on external stakeholders such as tourism, farming and education camp operators. 

Ahuahu-Great Mercury Island 

1872 hectares, inhabited by a small population on a working farm. Predator free since 2016.

Ahuahu Island. Source: New Zealand Department of Conservation

Predators: rats & feral cats

Methods used:

  • Feasibility study and consultation
  • Stock removal and biosecurity systems put in place
  • Knock-down – aerial poison baiting
  • Mop-up – trapping and spotlighting cats
  • Verify – sign search, dogs, and trapping
  • Biosecurity – consultation and education to engage visitors.

What did they learn?

  • It took a huge amount of effort and money to move stock and manage the pasture while the stock was away.
  • The project proved a good public/private partnership delivers a successful eradication outcome.
  • Although a permit is required to visit the island, boating access is generally unrestricted, which emphasises the need for raising awareness and gaining social license to manage the ongoing challenges of biosecurity with the local community. Adequate surveillance and response capability is required to sustain outcomes in this situation.

Antipodes-Moutere Mahue Island

2000 hectares, uninhabited. Predator free since 2018.

Fur seals, Antipodes Island. Image: Su Yin Khoo | Creative Commons

Predators: mice

Methods:

  • Feasibility study
  • Knock-down – aerial poison baiting
  • not required for rodent eradication. Checks are made two years later to see if the eradication operation worked
  • Verify - two years later via sign search and dogs
  • Biosecurity protocols in place include permitted access, quarantine checks, and island surveillance.

What did they learn?

  • The project was partially funded by a successful public crowd-funding campaign called ‘Million Dollar Mouse’.
  • The physical constraints of the remote location meant the logistics were challenging. Helicopters and all resources had to be shipped 800km from NZ mainland to the site and offloaded. Extensive temporary infrastructure was required including a helicopter hangar and accommodation shelters.

Global Island Eradication Projects

There are many things we can learn from island eradication projects around the globe. Check out some of the key learnings from the global projects below: 

South Georgia Island, Atlantic Ocean, British Territory 

375,000 hectares, uninhabited. Declared predator free in 2018.

Image source: Government of South Georgia & South Sandwich Islands

At the time, this was the largest rodent eradication in the world.

Predators: rats and mice.

Methods used:

  • Feasibility study and consultation - the team made use of the island’s natural glacier barriers and divided the area into nine discrete areas that could be tackled over several years. The glacial barriers had also helped in preventing predators from taking over the whole island; for example, only mice were found on one peninsula (~10,000ha), not rats.
  • Knock-down – aerial poison
  • Mop-up – not required for rodent eradication. Checks are made two years later to see if the eradication operation worked
  • Verification – sign search and dogs
  • Biosecurity protocols in place including checks and quarantine for tourist vessels.

What did they learn?

  • It may be difficult to tackle future invasions if the glaciers retreat due to climate change.
  • Natural barriers are now being used in other eradication projects, such as this local project in South Westland.

Lord Howe Island, Australia - 1,455 hectares, inhabited by a population of 350 residents.

Declared predator free in 2019, but a recent reinvasion due to biosecurity lapses has seen a huge incursion response underway to try and salvage the situation.

Lord Howe Island. Image source: Lord Howe Island Tourism Association.

At the time, this was the largest rodent eradication on a permanently inhabited island.

Predators: rats and mice.

Methods used:

  • Feasibility study and consultation
  • Preparations – removal of most stock and management for others, waste management facility changes, temporary captive management of two bird species.
  • Knock-down – aerial poison across uninhabited areas and bait stations 10m x 10m grid plus hand-spread baiting through community areas.
  • Mop-up – not required
  • Verify – sign search and dogs
  • Biosecurity - dog checks and surveillance on island.

What did they learn?

  • It took 17 years from project inception to completion.
  • Unfortunately, a reinvasion has put the outcome at risk probably due to insufficient mainland biosecurity prior to goods and people going to the island.
  • The intense baiting grid required substantial management resources and a large workforce.
  • Care must be taken to avoid compromising eradication protocols in order to gain access to private properties.
  • A small percentage of rats in the settlement area avoided bait stations completely. This was attributed to 30+ years of baiting rats with sustained control which resulted in a longer project duration and more expense.
  • Eradication operations on inhabited islands are significantly more complex, and in turn, significantly more costly. Managing stock added significant cost and complexity.
  • Eradication projects must be community-led, even though this means the project is likely to take years to get to the operational stage.

Marion Island, South Africa 

29,000 hectares, uninhabited.

Marion Island. Image Source: Birdlife South Africa - Otto Whitehead.

Declared free of feral cats in 1992.

Predators: Feral cats (note: operational planning for a project to eradicate mice is currently underway).

Methods used:

  • Feasibility study
  • Preliminary trials – (1977-1985) including biological control, trapping, baiting, and hunting
  • Knock-down – hunting and trapping
  • Mop-up – (1986-1991) trapping and baiting
  • Verify – sign search and dogs
  • Biosecurity - remote island with quarantine procedures and limited access

What did they learn?

  • There are three aspects of cat biology to consider in any eradication project: the rate of population increase, the cats’ home range, and their response to control methods.
  • A cat population can double every 8 months, so short deadlines are best to achieve eradication.
  • Avoid creating bait- or trap-wary survivors at the end of the first phase as this makes the next phase much harder.
  • Operations must be designed to account for animals with the smallest home range and unusual behaviour. Design for the last animals not the first.

As well as learnings from eradication projects there are lots of learnings we can gain from scientific innovations in current predator control. Find out more about some of the latest trials and scientific innovations here