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Boaties And Fishers Can Help Stop The Spread Of Exotic Seaweed

Biosecurity New Zealand is reminding boaties and fishers to clean their anchors and fishing gear and reduce the risk of introducing or spreading any exotic seaweeds after a small clump of suspected Caulerpa brachypus was spotted on a Bay of Islands beach.

Biosecurity New Zealand director of readiness and response John Walsh said a local resident who had been at a beach at Te Rāwhiti, near Russell, did the right thing by taking a photograph of the 20cm seaweed clump they found and sending it in for visual identification.

“We did provisionally identify the seaweed as Caulerpa brachypus based on the photograph, but unfortunately the seaweed was no longer there when the person returned, and no more has been found on the beach, so we have been unable at this stage to collect a sample for confirmation testing. We do have a small team up there today doing beach-based surveillance.”

“We know that exotic Caulerpa can be spread through breaking into little pieces and can potentially spread over large distances by rafting on floating debris. This can happen by wave action, or when anchors and fishing gear are moved into or through weed beds, which is why keeping your boat and equipment clean is the best thing you can do to avoid spreading marine pests and diseases, including exotic Caulerpa.

“We have the strictest biofouling requirements for vessels in the world, as shown over the last summer cruise season, to help protect our marine ecosystems but it’s important everyone plays their part.

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“If people think they’ve found this species of Caulerpa, they should not move it elsewhere but let us know. We thank the person who notified us in this instance.”

John Walsh says Biosecurity New Zealand had spoken to the Northland Regional Council and local iwi and will work closely with them and others to determine next steps in Te Rawhiti, including having divers in the water later next week looking for any further signs of Caulerpa brachypus, weather permitting.

“Exotic Caulerpa was first found at Aotea Great Barrier Island in July 2021, and then, later, at Ahuahu Great Mercury Island. It is very difficult to remove as it travels and grows easily, and there are limited treatment options.

“To minimise the spread, a controlled area notice (CAN) remains in place on 3 affected harbours at Great Barrier Island and over an area of the south western coastline of Ahuahu Great Mercury Island, which bans activities likely to result in its movement (fishing and boating). Mana whenua for the islands have imposed a rāhui on the same areas.

“At the original finds, we worked closely with Aotea and Ahuahu mana whenua and the local communities, along with Auckland Council, the Waikato Regional Council, and the Department of Conservation to collectively decide a course of action.

“If we establish through surveying that exotic Caulerpa is in Te Rāwhiti, then a CAN may be an appropriate response, but we will work with the community and seek advice from experts here and overseas.

“We continue to investigate possible treatment options for Caulerpa and are seeking advice regarding suction techniques and whether they could be viable in our conditions.”

John Walsh said Caulerpa was included in Biosecurity New Zealand’s national marine high-risk site surveillance programme, which surveys locations where there is a high volume of vessel traffic every six months. Whāngarei Harbour and Ōpua Marina/Waikare inlet in Northland are locations in this programme.

People can report suspected finds to Biosecurity New Zealand on 0800 80 99 66 or by completing the online reporting form at

Help stop the spread

  1. Check your gear – anchors and chains especially. If you see any seaweed on your equipment, chuck it straight back.
  2. Know where Caulerpa is
  3. Know the rules about anchoring and fishing there

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