Biosecurity New Zealand is updating controls on anchoring and fishing at Aotea Great Barrier Island to help prevent the spread of exotic caulerpa seaweed.

Caulerpa can form large underwater fields, altering the natural ecosystem, and has been found in the Hauraki Gulf at Aotea Great Barrier Island, Ahuahu Great Mercury Island, off Kawau Island and Waiheke Island, and in Northland at Te Rāwhiti Inlet.

Biosecurity New Zealand Deputy Director-General Stuart Anderson says the current Controlled Area Notice (CAN) covering both Aotea Great Barrier Island and Ahuahu Great Mercury Island expires tonight and will be replaced with new conditions tomorrow.

“In recent weeks we’ve talked with affected people from Mana Whenua, local authorities, fishing industry and local communities about the most appropriate measures.

“The update to the CAN reflects those discussions and manages the risk of human spread of caulerpa, while minimising the impacts on local people as much as possible.”

For Aotea Great Barrier Island, the new CAN includes:

• The controlled area is extended further north to Port Fitzroy.
• Anchoring restrictions will remain.
• Less risky forms of fishing that don’t come into contact with the seabed, for example drift fishing from a boat or kayak, spear fishing, shore-based long-lining (e.g. using a kontiki or drone) and line fishing will be permitted.

The area under control at Ahuahu Great Mercury remains the same, but changes made to fishing methods at Aotea Great Barrier Island also apply here.

"We'll work with our partners to get the information out and this week we launched a new summer campaign to inform boaties, fishers and divers about some simple actions they can take when at sea to avoid spreading caulerpa,” says Mr Anderson.

“Caulerpa can travel short distances naturally as small pieces adrift in the water, but it is spread primarily by people, snared in boating and fishing gear. We’re asking boaties to check their anchor, anchor chain, and any gear that’s been in the water before they move on to a different location.

“If any seaweed is found attached this equipment, they should remove it and securely bag it or contain it and take it ashore for safe disposal on land – for example in a rubbish bin or compost."

Biosecurity New Zealand, in partnership with Mana Whenua for the affected areas, local government and the Department of Conservation, has worked hard over the past two and a half years to contain the difficult pest while exploring all possible options for its control.

"We have two trials underway to use suction dredging to remove caulerpa at mass. Those trials will continue into early next year.

“From the outset, independent scientific experts told us that eradication (full and permanent removal) of this pest is highly unlikely given the large size of the incursion in New Zealand and the lack of any control tool internationally that would work at this scale.

"However, we remain committed to identifying and trialling potential techniques that could help remove new and small outbreaks or knock back larger populations to try to reduce further spread."

Mr Anderson said the existing CAN for Te Rāwhiti Inlet in Northland remains unchanged and expires at the end of June 2024. The CAN for Aotea/Ahuahu ends at the same time and settings will be reviewed at that point.

Anyone planning boating or fishing at Aotea or Ahuahu this summer can visit www.biosecurity.govt.nz/caulerpa for precise boundaries of the zones and actions required.

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