3 July 2025
Kia ora koutou
In this update – new CAN restrictions on anchoring and fishing at Hauturu o Toi Little Barrier Island; and we take a deep dive into the creation of new treatment tools.
Ban on anchoring at Hauturu Little Barrier Island
New biosecurity rules are in place at Hauturu o Toi Little Barrier Island, making it illegal to anchor anywhere around the island without a permit from Biosecurity New Zealand.
The rules are set out in a Controlled Area Notice issued today and are in response to the discovery of exotic caulerpa in a number of small patches on the island’s north and east coasts.
As well as the anchoring ban, the CAN prohibits any form of fishing in the Controlled Area that contacts the seabed such as netting, dredging, bottom trawling or lobster potting. Drift fishing, spear fishing and hand gathering are still allowed.
Equipment used within the CAN area – for example, fishing/diving gear, needs to be inspected before leaving the area and any seaweed found on the equipment must be removed, stored securely and disposed of on shore.
The CAN is to help prevent spread of the pest around the island or further afield.
We know that exotic caulerpa can be inadvertently relocated when small pieces are caught on anchors, anchor chains, and fishing/dive equipment. Stopping anchoring and seabed-contact fishing activities around the whole coastline will greatly reduce this risk.
Ngāti Manuhiri has placed a rāhui over the same area with the same restrictions.
Protecting Hauturu is important as it is a significant environmental area. It is New Zealand’s first ever nature reserve and one of the most significant conservation areas in the world.
Since the discovery of caulerpa there in early May, Biosecurity New Zealand has worked closely with Ngāti Manuhiri, Auckland Council, the Department of Conservation, Auckland University and Revive our Gulf on operations in response to the finds.
Work has involved surveillance for the pest seaweed and rapid treatment using chlorine pellets under benthic (seafloor) mats. So far, 17 small areas of exotic caulerpa have been treated.
Full information about the Hauturu Little Barrier Island CAN, including a map.
The Hauturu CAN is the fifth CAN in place in the upper North Island. All five CANs, including Hauturu, expire on 30 September 2025 and will be reviewed before this date.
An underwater look at two new caulerpa management tools
Two tools to fight exotic caulerpa have been undergoing trials at sea in recent months to test their effectiveness in the field. The results so far are very encouraging.
The ‘Rehabitat’ chlorine enclosure, developed by Commercial Dive Specialists, builds on a known effective treatment – applying chlorine under benthic mats (which are essentially mats on the seafloor with chlorine underneath).
The innovative new device is a large (75 square metres), inflatable unit that uses negative pressure to suction to the seabed, containing chlorine to the area under treatment. Separate modules can be tethered together to quickly treat very large areas of dense caulerpa.
Advanced Aquarium Technologies’ light array takes the lab-proven method of using UV-C light to irradiate exotic caulerpa and scales it up to destroy large areas of the seaweed pest in the field.
We captured these exciting new technologies at work and talked with their developers in these two videos.
Video - Rehabitat chlorine treatment enclosure
Video - UV-C light treatment
Reports on the results of the two treatment trials are expected in coming weeks.
Successful community caulerpa effort in Northland
Hapū involvement and a locally-based approach has been key to the success of a caulerpa surveillance and treatment programme in Northland.
Northland Regional Council contracted the community organisation Conquer Caulerpa Charitable Trust to deliver high-resolution surveillance, targeted treatment and feasibility assessment for further response efforts in the Bay of Islands.
The Conquer Caulerpa Charitable Trust (CCCT) was established by Nga Hapū o Ngati Kuta ki Te Rawhiti and the Trust acts on behalf of Nga Hapū o Ngati Kuta in the response to exotic caulerpa in the Bay of Islands.
CCCT engaged the Māori-owned and operated Northland-based Northern Divers NZ to carry out all underwater dive operations and the four-person team was able to run an efficient and cost-effective surveillance model.
Northland-based Northern Divers caulerpa rapid response dive team at Waitangi before heading out in their boat (from left) - Corey Dalley-Takaia (Kaeo), company managing director Stephen Te Tai (Whangārei), Shanon Scott (Pakaraka), Tureiti Heta (Whangārei).
The team carried out surveillance in a number of locations around the Bay of Islands, identifying new areas of exotic caulerpa at Paroa Bay, Otiao Bay, and the Waewaetorea Channel.
The response to these new infestations was also carried out by the CCCT team and involved high-resolution monitoring, targeted treatment using benthic mats and chlorine, and follow-up surveillance.
In addition to this work, the team evaluated treatment methods and their suitability for future deployment in newly detected or recurring infestation areas.
CCCT focused on operational effectiveness while also placing strong emphasis on cultural considerations. Engagement was carried out with local hapū through community liaison activities and included close guidance from Nga Hapu o Ngati Kuta ki Te Rawhiti.
From a logistical perspective, using a local dive team allowed for rapid mobilisation, reduced costs and access to community support. This included subsidised vessel hire, low-cost accommodation and in-kind contributions from stakeholders partnered with the Trust’s kaupapa.
Nāku noa, nā
The exotic caulerpa response team
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For more information about exotic caulerpa seaweeds in New Zealand visit the Ministry for Primary Industries Biosecurity New Zealand website.