DOC and the owners of Great Mercury Island have eradicated rats and cats to enhance the native wildlife and improve the conservation of 'threatened' and 'at risk' plants.

Great Mercury Island - Pest Free logo.

Great pest-eradication progress has been made on Ahuahu-Great Mercury Island. The island is located off the Eastern Coromandel coast and its beaches are open to the public to explore and enjoy.

DOC, together with the private owners of Great Mercury Island, successfully eradicated rats and cats from the 1872 ha island during winter and spring 2014.

The six month eradication project was a complex task that could not be achieved alone. DOC provided specialist skills in species management, island pest eradication and island biosecurity. This successful partnership just shows that together we can achieve amazing results.

Ahuahu-Great Mercury Island declared pest free – media release 13 May 2016

Why pests needed to be eradicated

This pest eradication has ensured long-term success for native geckos, giant tusked wētā, tuatara, kākā, kākāriki, New Zealand dotterel, tāiko (petrels) and other sea birds, as well as 50 species of native land snails.

The pest-eradication project was crucial as neighbouring islands are pest free and are close enough to Great Mercury Island for pests to swim to them. These neighbouring islands have undergone decades of successful island management and species protection.

Future protection of the island

Pest eradication on Ahuahu-Great Mercury Island is just one part of several heritage protection initiatives on the island.

Restoration plantings, weed management and fencing have been ongoing since 1979. Possible introductions of other threatened native species may also be considered over time.

Our goal for the future is to provide a sanctuary for native species, and have an island that is better for everyone to appreciate and enjoy.

Approaching Huruhi harbour, Great Mercury Island. Photo: Kelly Smith.
Approaching Huruhi harbour, Great Mercury Island

How the rodents were eradicated

Due to the island’s terrain, it was a difficult task to successfully make sure the island is pest free.

Conservation dogs were used to detect the last remaining cats on the island, then checked for rats and mice on a continual, rotational basis.

The application of rat poison pellets, containing Brodifacoum, was done by helicopters with accurate navigational guidance technology. This was the main method of eradication. All stock was removed from the island before the operation and did not return for several months after the poison application was complete. The last of the stock has been returned.

The costs of the operation were shared equally between DOC and the owners of Great Mercury Island.

Peachgrove Bay. Photo: Pete Corson.
Peachgrove Bay

Final steps and early results

The final aerial operation to remove the last of the rats and feral cats was successfully completed on 11 August 2014.

As a result, there are nests and chicks of petrels, shearwaters, little blue penguins, kaka, morepork and New Zealand dotterels. The project showed immediate success – in 2012 there was only one grey-faced petrel chick and in 2014 there were 20.

Having safely and successfully completed the aerial bait applications, we need to make sure we all keep Ahuahu- Great Mercury Island free from pests and you can help us out.

Eastern Coastline. Photo: Greg Martin.
Eastern coastline of the island

You can help

We need your help to keep the islands pest free. The trick is to stop pests getting on your boat and then escaping onto the pest-free island.

Everyone travelling by boat to Great Mercury Island needs to make sure they’re not carrying any stowaways including mice, rats, Argentine ants, rainbow skinks, and cats.

Keep in mind that part of the island is still a working farm and dogs must be kept on a lead at all times, even on the beach.

Tips to help keep your boat free of pests

  • Keep your boat tidy and clean.
  • Don't leave rubbish or fish scraps on board. 
  • Before departure, inspect your boat for signs of rats and mice, eg chewed wiring or holes in gear or bags, and for insects (especially ants).
  • Owners of larger vessels are encouraged to maintain pest control on board. Use glue boards for insects and traps or bait stations for rodents.
  • All food should be packed in sealed containers. Don't just use open shopping bags or cardboard boxes as these are known to harbour pests.
  • Do your loading in daylight hours. Most pests are active at night and will come aboard then.
  • Vessels should stay anchored offshore except for embarking and disembarking passengers. Tenders are OK as long as you inspected them for pests before arrival.

These steps will help keep the Mercury Islands pest-free and could also save you from pest damage on board your boat.

For more information

Whitianga Field Base
Phone: +64 7 869 5639
Fax: +64 4 471 1117
Address: 2/20 Joan Gaskell Drive, Whitianga 3510
Postal Address: PO Box 276, Whitianga 3542

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