Targeted dredging to eradicate exotic caulerpa seaweed from Iris Shoal near Kawau Island in Te Moananui-ā-Toi|Hauraki Gulf begins today as part of the Government's response to address the invasive pest.

The suction dredging trial is being delivered in partnership with Ngāti Manuhiri Settlement Trust (the Trust) and Biosecurity New Zealand, including marine specialists from NIWA and Bay Underwater Services NZ Ltd.

“Dredging involves divers using an underwater suction pump to extract caulerpa from the seabed, and this trial will help inform how we remove caulerpa in other areas,” says Nicola MacDonald, Chief Executive of the Trust.

“The programme will be underway for the next three weeks and we hope to remove close to 18 hectares of caulerpa from the seafloor as well as identify other potential sites for dredging.”

Ngāti Manuhiri Kaumatua and Trustee Ringi Brown officiated karakia at the site on Tuesday to affirm Manuhiritanga, ensuring cultural safety of all those involved working to remove the caulerpa.

In 2023, the Trust brought in expert scientists from the United States, who had successfully eradicated caulerpa in California. The Trust facilitated an educational roadshow from Bay of Islands to the Hauraki, where caulerpa had been identified to support whānau, hapū and communities by raising awareness and providing information on how they can combat caulerpa.

“We are hopeful the Exotic Caulerpa Iris Shoal Suction Dredge Trial will give us much needed cut through so we can get closer to eliminating this pest,” says Nicola.

The work is expected to continue until approximately 17 May (weather permitting). During this time the trial site at Iris Shoal will be closed to the public. The Trust, with support of Maritime NZ, will have detection buoys to mark out the area to ensure the suction dredging trial can be executed as effectively as possible in the limited time available.

Caulerpa has also been recently discovered elsewhere in the rohe of Ngāti Manuhiri at Mokohinau Islands. The Trust is coordinating a response group and is also consulting with experts from the University of Auckland to determine the best approach for the delicate reef system around the Islands and hopes to begin treatment in the next week.

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