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The northern North Island could face a 30 to 50 per cent decline in kai moana and fish stocks if the eradication of the invasive seaweed caulerpa isn’t given more urgency.
Hauraki Gulf Forum executive director Alex Rogers says that caulerpa can rapidly mat the sea floor and this had reduced marine biodiversity by up to 50 per cent in places overseas.
The seaweed was first found at Aotea Great Barrier Island in 2021 and a further 16 hectares was identified in the Bay of Islands in May.
The forum was told last month that the current management approach, led by Biosecurity NZ in coordination with regional councils and NIWA, was to try and slow the seaweed’s spread through a mix of containment, education and research.
Forum executive officer Alex Rogers said that the confirmation of its presence in Northland suggested that a step change in approach was now required.
“In recent weeks, Ngāti Pāoa and Ngāti Rēhua Ngātiwai ki Aotea have written to the Minister for
Biosecurity, Damian O’Connor, urging a switch to an eradication strategy,” Rogers said. “Similar sentiments have been expressed by Revive our Gulf and Legasea.
“The forum has, over the past year, repeatedly expressed its concerns to Biosecurity NZ. As a result of this discussion today, it is proposed that the forum joins with the Northland and Auckland Conservation Boards, and regional councils, to jointly call for a change in approach.
“The present strategy, with a seaweed that can spread at just two millimetres in size, essentially leaves mana whenua, regions and communities in an endless game of marine whack-a-mole. Eventually, it will result in caulerpa everywhere from Cape Reinga to East Cape, including in the inner gulf around Waiheke, Motutapu, and the eastern and north shore beaches.”
Biosecurity NZ’s readiness and response director John Walsh said several methods were being used to kill caulerpa, including dredge spoil, UVC lights, bio controls like kina, suction dredging and coarse salt.
Coarse salt was the preferred option so far, but to treat the 16 hectares of infestation in the Bay of Islands would take 8000 tonnes of salt.
Northland Regional Council councillor Jack Craw said MPI had been slow off the mark, no one was joined up and none of the council’s biosecurity responses looked particularly good.
“We are repeating all the mistakes of the past with kauri dieback. It took us seven years to get that funding,” Craw said.
He said MPI handed pest problems back to regional councils and that there was a failing nationally.
Fellow councillor Geoff Crawford said they needed support and surveillance, but MPI had been slow to respond.
“Northland’s stance is always going to be eradication – there is no other option for us,” Crawford said.
Aotea Great Barrier Environmental Trust representative Kate Waterhouse said eradication would be good, but there was no resourcing to prevent the current spread at Aotea.
“Seabirds are already starving,” Waterhouse said. “There is no regular MPI surveillance of the waters of Aotea; we get an Auckland Council dive team once a year.”
Aotea Great Barrier Environmental Trust representative Barry Scott said residents already felt abandoned.
“We need to be better prepared for the inevitability of this thing spreading,” Scott said.
Waiheke Marine Project representative Miranda Cassidy O’Connell said while Waiheke was lucky not to have caulerpa in its waters, local communities needed to be enabled to prevent the spread.
“We have been asking what happens when we see caulerpa. We don’t have legal permission to do anything if we see it,” O’Connell said.
Forum co-chair Nicola MacDonald recently visited California where divers in Newport Bay were removing caulerpa by hand.
“They recognised that the local community needed to be trained,” she said.
The team in the US were awaiting final surveys to confirm whether their approach had been successful.
