Caulerpa at Omākiwi Cove in the Bay of Islands. Photo / Northland Regional Council
Caulerpa at Omākiwi Cove in the Bay of Islands. Photo / Northland Regional Council
Efforts to eradicate pest seaweed caulerpa are ramping up with the country’s first mainland suction dredging starting soon in the Bay of Islands.
The eradication efforts come ahead of the country’s biggest yacht race and Labour weekend’s summer boating season.
About 170 yachts are expected at Russell from October 20 for the 40th annual Coastal Classic Yacht Race from Auckland to the Bay of Islands. Recreational boaties from around Northland and beyond are expected to converge on the boating mecca.
Coastal Classic race organiser and New Zealand Multihull Yacht Club commodore Adrian Percival said caulerpa was of major concern for the country’s boating community, particularly in the Bay of Islands and Hauraki Gulf. He said there would be race issues if caulerpa was ever found at the event’s finish line in Russell.
The major caulerpa diver-directed suction dredging research trial is part of eradication efforts by Te Rāwhiti hapū Ngāti Kuta and Patuketa, Northland Regional Council (NRC) and the Ministry for Primary Industries (MPI).
NRC marine biosecurity manager Kaeden Leonard says major Bay of Islands caulerpa eradication efforts are ramping up ahead of summer boating season. Photo / Michael Cunningham
NRC marine biosecurity manager and national marine invasions specialist Dr Kaeden Leonard said the mahi was aimed at eradicating caulerpa, ahead of the summer boating season and warmer sea temperatures when the seaweed grew faster.
Leonard said Bay of Islands research results will be used to inform potential future caulerpa suction dredging elsewhere in New Zealand.
The Government-funded $800,000 bespoke suction dredging was based on successful Calilfornian techniques. It is being used in New Zealand for the first time in the Bay of Islands and on Great Barrier Island (Aotea).
It will start early in October and focus on the Bay of Islands’ Omākiwi Cove ground zero where the invasive marine pest super-spreader was first found in May.
Thirty divers from NRC, Niwa, commercial operators and from as far away as from Bay of Plenty Regional Council have since May done more than 100 hours’ surveillance to confirm the invasive seaweed’s Bay of Islands locations. Caulerpa has been found across about 16 hectares. Ongoing surveillance continues in the caulerpa infesation area.
The detailed, largely diver-directed caulerpa dredging will see small suctions effectively vacuum the marine pest off the seafloor.
A diver will work across the sea floor in a fine tooth comb approach, positioning the suction’s vacuuming mouth over caulerpa clumps to minimise the environmental impact. The vacuum mouth will include protection against scallops being inadvertently sucked up. The suction hoses will be operated from a boat or from the shore.
Leonard said the suctioning was highly targeted with a lot of attention paid to minimising environmental impacts. It was not large-scale wholesale dredging of the entire sea floor. Rigorous monitoring to measure any environmental impacts and suctioning’s caulerpa eradication efficacy was part of the trial.
Caulerpa washed up at Omākiwi Cove. Photo / Susan Botting
The Bay of Islands mahi will build Aotearoa’s local knowledge. New Zealand’s internationally unique climate and ecosystems meant it was not known how well overseas techniques will perform locally.
Those behind caulerpa eradication efforts in other parts New Zealand are waiting on the Bay of Islands’ results before potentially taking a similar approach, including NRC, Auckland Council, Bay of Plenty Regional Council and Waikato Regional Council.
Leonard said divers would check suction dredging sites about a week after they had been vacuumed. Further dredging could be carried out if some of the pest’s horizontal roots remained. Chlorine mats would also be considered too in a toolbox of caulerpa eradication approaches.
The first caulerpa chlorine mat eradication trial was put down on a small satellite patch of caulerpa in the Bay of Islands’ Albert Channel in June.
Leonard said the chlorine mat, which was in place for a month, killed the targeted caulerpa.
He said positive results from the single trial site had been extended with 20 chlorine mats - in place for a week at a time - also killing all treated caulerpa patches inside the area where the Government has now banned anchoring and fishing because of the invasive smothering pest.
Bay of Islands' Omākiwi Cove, pictured, was an important Bay of Islands boat anchoring spot until caulerpa arrived. Photo / Susan Botting
More than 1000 hectares are now shut to diving, fishing – including spearfishing, drift fishing, net fishing, crayfishing, kina and other shellfishing in New Zealand’s biggest single pest caulerpa ban of its type. The closure comes after the Government’s controlled area notice (CAN) and Te Rāwhiti hapū Ngāti Kuta and Patuketa rāhui in place since June 12.
The closed area covers the equivalent of 1535 rugby fields. It was put in place, along with the rāhui, after the discovery of caulerpa in New Zealand’s first mainland find in May this year.
Coastal Classic race organiser Percival said caulerpa care would be part of participants’ pre-race briefing. They would also be informed about yachts not being able to anchor or fish in the 1075ha Bay of Islands caulerpa ban area.
■ Local Democracy Reporting is Public Interest Journalism funded through NZ On Air
