17 May 2024
Kia ora koutou
In this update we report on the detection of a new location of exotic caulerpa at the northern tip of the Coromandel Peninsula and cover developments in the Exotic Caulerpa Accelerated Programme.
Detection in Fantail Bay, Coromandel Peninsula
Small patches of exotic caulerpa have been discovered in Fantail Bay on the north-western coast, near the top of the Coromandel Peninsula.
It’s disappointing to find exotic caulerpa in another new area but it is not unexpected given it can be moved by people over long distances on vessels and marine equipment. The locations we’re finding caulerpa are typically in bays where vessels anchor.
Fantail Bay is a remote location with a Department of Conservation campground and is popular with divers and fishers.
Divers carrying out reef restoration work in the area found a number of small 10x10cm patches at a depth of 8-10 metres. NIWA taxonomists were able to confirm the find as exotic caulerpa from photographs.
Biosecurity New Zealand will work with partners and people associated with the area to determine the most appropriate actions following this discovery.
Exotic caulerpa is currently found at seven other upper North Island locations - Aotea Great Barrier Island, Ahuahu Great Mercury Island, Waiheke Island, Kawau Island, Rakino Island, the Mokohinau Islands and Te Rāwhiti Inlet in Northland.
Out at sea? See weed? Bag it. Bin it.
The new detection at Fantail Bay, along with discoveries last month at the Mokohinau Islands and Rakino Island, serves as a reminder to boaties and fishers that they need to help avoid spreading this invasive seaweed.
While we know it can spread naturally, particularly from large areas of infestation, we also know that being caught up on vessels and equipment is the main way it is moved over distances.
If you’re out boating, before you move locations – when you pull up anchor or fishing gear, check it for any attached seaweed. If you find seaweed, remove it, securely contain it in a bag or other container and dispose of it in bins back on shore.
Also – if you think you’ve seen exotic caulerpa, let us know. Record the location, take a photo if possible, and call us on 0800 80 99 66, or report it online at report.mpi.govt.nz
Updates from the accelerated programme
Great progress is being made in the key projects of our Exotic Caulerpa Accelerated Programme to rapidly develop new technologies for finding and removing caulerpa.
This programme is the result of a Government allocation of $5 million announced in February this year.
Iris Shoal removal
Operations at sea off Iris Shoal near Kawau Island are now complete. This project set out to trial and refine a removal method using a hand-held diver controlled suction dredge. The team of NIWA, Bay Underwater and partners Ngāti Manuhiri managed to remove exotic caulerpa from 1.27 hectares of the seabed and safely dispose of the material at a local landfill.
Cage of exotic caulerpa emptied at landfill. Photo: Anne Murrow, Biosecurity New Zealand
Improvements were made to the process and equipment as the project progressed, with the aim of finding the best means of tackling exotic caulerpa in a dynamic marine environment with strong tides and currents and in deep waters. Removal of exotic caulerpa from a large area using this method has not been attempted overseas before in such difficult sea conditions.
One improvement made was building a new dredge head for easier manoeuvrability called the “dust buster”.
NIWA is currently conducting post-treatment monitoring of the dredged area to check if any exotic caulerpa remains.
The information gained from this project will form part of a suite of information available in future to inform exotic caulerpa management.
Omakiwi Cove large-scale suction dredging
At Omakiwi Cove in the Bay of Islands, dredging is well underway using new trommels and ‘stinger pipes’ (which return sand and spoil to the seafloor) fitted on the mechanical suction dredge.
Exotic caulerpa in the trommel, which has separated it from the seabed material suctioned from the sea floor. Photo: Northland Regional Council
The innovative new approach has produced good results so far, with over 120 1.3-tonne bags of exotic caulerpa removed in the last week. Each trommel can fill a bag in 8-10 minutes.
Bags of caulerpa set for disposal. Photo: Sid Wales, Biosecurity New Zealand
Johnson Bros, the contractors running this work, supported by Northland Regional Council and Ngāti Kuta and Patukeha, continue to work hard to improve the removal effort at Omakiwi Cove and we’re confident further efficiency gains can be made.
At this stage, we have reasonable confidence the pace of removal can be accelerated with the current technology.
Improved Surveillance Systems project
NIWA and sub-contractor Commercial Dive Services are about to start testing advanced towed (TOV) and remote operated (ROV) camera systems with artificial intelligence to scan imagery and spot caulerpa in near real time. Ngāti Pāoa (Waiheke Island) is working in partnership with NIWA on this project.
The second part of the Improved Surveillance Systems project is the creation of a data solution tool that will create a standardised data collection, reporting, storage, and display solution to centralise exotic caulerpa surveillance data and inform future management decisions. Auckland Council is leading this part of the project, and the work is well advanced.
Aotea perimeter management
We expect work to start in the water next week in this Auckland Council-led project testing how best to manage the perimeters of identified priority areas of exotic caulerpa. What we learn from this trial will inform how we can best slow the spread of ‘creeping’ expansion in areas of infestation. Divers will remove exotic caulerpa using a hand-held suction dredge at the Man o’ War Passage (Port Fitzroy), Motuhaku Island (Port Abercrombie) and Katherine Bay.
Ahuahu Great Mercury Island re-survey
This project, to re-survey Ahuahu and understand how the incursion there is behaving is now almost complete with much of the island’s coastline now searched for the presence of exotic caulerpa. Final dive surveillance will take place at the end of the month when results will be collated and reported.
Nāku noa, nā
The 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.