‘You don’t get a second chance at these things’ – caulerpa dredging underway

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    Operations now underway to suction dredge invasive exotic caulerpa at Aotea Great Barrier Island have been widely welcomed, but the government has also drawn criticism for its slow response.

    A team from NIWA, the Cawthron Institute, and suction dredge firm Bay Underwater arrived at Aotea to start work at three locations – Schooner Bay, Shoal Bay and Pūriri Bay – in Tryphena Harbour on Monday. Initial work is expected to take two to three weeks.

    Biosecurity New Zealand’s deputy director-general, Stuart Anderson, says the treatment crew will work from three vessels moored in the harbour.

    “Divers will use a large vacuum device to suck up visible caulerpa from the seabed and then store it securely on board a vessel so that any material cannot escape back into the water,” he says.

    “We expect about 10 tonnes of exotic caulerpa to be removed from the area and then it will be disposed of on the island.

    “We’re working with residents and mana whenua to determine the best approach and location for this.”

    Meanwhile, a rāhui [restriction] has been placed in areas one nautical mile from both Thompsons Point and Onetangi Bay in Waiheke where exotic caulerpa has also been detected within a 400-hectare area.

    While welcoming the trial, Massey University Emeritus Professor Barry Scott said the remote island community of Aotea had felt abandoned since the invasive seaweed was found at Aotea’s Okupe Harbour in July 2021.

    “Apart from the establishment of Controlled Area Notices (CANs) over three western harbours on Aotea, and a small scale salt trial, no further ‘in the sea’ effort has been made by Biosecurity New Zealand since then to control the spread of this exotic seaweed,” said Scott. • Liza Hamilton

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