Boaties asked to help in biosecurity response to pest seaweed

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22 December 2021, New Zealand: Biosecurity New Zealand is asking boaties planning a voyage to Aotea Great Barrier Island this summer to be aware there are restrictions in place affecting water activities in some parts of the island.

The Ministry for Primary Industries’ (MPI’s) biosecurity branch is working with Aotea mana whenua and the local community in response to the discovery of an invasive seaweed in 3 of the island’s harbours.

The pest, 2 species of caulerpa called Caulerpa brachypus and Caulerpa parvifolia, can grow into dense mats, and potentially affect native ecosystems, including local fish and shellfish.

Biosecurity New Zealand’s director of readiness and response, John Walsh, says to prevent the spread of caulerpa while the team plans the most appropriate management approach, legal controls have been placed over 3 harbours – Tryphena, Whangaparapara, and Blind Bay.

Aotea mana whenua have imposed a rāhui over the same areas.

“Under our Controlled Area Notice, it is illegal to take any marine life at all from the affected areas. This includes fish, shellfish, crays and any seaweed. In addition, it is illegal to leave any of the areas if you have anchored there without a permit from Biosecurity New Zealand.”

Mr Walsh says caulerpa breaks up easily, especially when anchors are dragged through a patch.

“Fragments can then be easily carried to new areas on the water currents or on the anchor and establish there.

“The permit will require the anchor and chain to be free of any seaweed and thoroughly cleaned before departure. This will have to be verified by photograph.”

Conviction on charges of failing to comply with the legal controls could result in a fine of up to $50,000 or up to 3 months imprisonment for an individual.

Biosecurity New Zealand has staff on Aotea Great Barrier Island who will be there throughout the summer. They will spend much of their time on the water in the Controlled Areas, speaking with visitors about the rules and supporting a team of local caulerpa ambassadors.

Mr Walsh says managing caulerpa is challenging, particularly where it is present in large amounts.

“We have recently had a group of marine scientists, engineers and mātauranga Māori experts meet to discuss the situation and provide us with advice on innovative control methods we might adopt. We expect a report from them shortly.

“In the meantime, we have carried out some limited management measures in Whangaparapara and Tryphena, applying large amounts of coarse salt to the caulerpa and covering it with hessian and tarpaulins. This appears to have been effective in the areas where it was trialled,” he says.

“We know that the areas of caulerpa have grown in recent months and this means we are now re-planning our options. However, along with our response partners, we remain focused on the elimination of this seaweed, if at all possible.”

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