Bay of Islands boat anchoring ban unlikely to expand despite caulerpa spread

Urupukapuka Island's Otehei Bay is a popular tourist destination that will soon be surveyed for the presence of caulerpa. Photo / NZME

A Bay of Islands boat anchoring ban is unlikely to be extended despite exotic invasive caulerpa now being found outside its 1058ha restricted area.

The equivalent of 1525 rugby fields around the eastern Bay of Islands mainland at Te Rāwhiti is currently locked up to boat anchoring, most fishing, and kaimoana gathering under a government-controlled area notice.

But invasive exotic caulerpa has now spread north to infest the iconic picture postcard Ipipiri Islands for the first time – across the equivalent of 180 rugby fields (24ha) outside the current anchoring ban area.

At least six of the Bay of Islands tourist hotspot’s seven main islands – Urupukapuka, Moturua, Motukiekie, Poroporo, Okahu and Waewaetorea - and some areas in between now have confirmed caulerpa.

Motuarohia or Roberton Island has been previously surveyed. Caulerpa was not found at the time of the survey.

Biosecurity New Zealand deputy director general Stuart Anderson (left) with a Te Rāwhiti caulerpa response leader Rana Rewha (Ngāti Kuta) at a high powered local hui about the invasive pest seaweed Photo / Susan Botting

Biosecurity New Zealand deputy director general Stuart Anderson said there was no current plan to widen the Bay of Islands notice because of the seaweed pest’s new locations.

His comment comes despite the Ipipiri Islands being among New Zealand’s most popular local and international boating anchorages. Boating has been identified as a major cause of spread for exotic invasive caulerpa.

“The detections of further sites in the Bay of Islands outside the [notice] area are obviously disappointing, but unfortunately not unexpected. We are dealing with a challenging pest that readily spreads on vessels and in water currents,” Anderson said.

“For this reason, our current management approach continues to be containing spread while focusing on developing the new treatment approaches. This work continues at pace.”

Poroporo Island in the Bay of Islands has now been confirmed as a location infested with invasive caulerpa seaweed Photo / Susan Botting

Anderson’s comments come four months before a review of the Bay of Islands’ existing area notice, which expires in September. It has been in place since May 2023.

He said there were no plans to remove it at that time, given the pest was now beyond its borders.

He said local preference since the areas of new caulerpa infestation had been found around the Ipipiri Islands was for a more regional approach, rather than piecemeal extension of the existing area notice.

“The preferred approach has instead been on surveillance of anchorages and removal of small patches where possible to slow the spread – along with continued education of boaties on how they can avoid moving it,” Anderson said.

Urupukapuka Bay on the island of the same name draws hundreds of campers each year but has now been invaded by exotic caulerpa which covers the equivalent of more than a dozen rugby fields Photo / Susan Botting

The Bay of Islands has one of fourarea notices in New Zealand, with 12,860ha shut for a mix of anchoring, some fishing and kaimoana gathering – along with Aotea/Great Barrier Island (10,060ha closed), Waiheke Island (1150ha closed) and Ahuahu Great Mercury Island (592ha closed).

Anderson said the Bay of Islands’ Te Rāwhiti notice review would be done at the same time as New Zealand’s three others, to ensure the most appropriate measures were in place.

He said advice was being prepared for Biosecurity New Zealand’s chief technical officer who made area notice decisions.

“Criteria are followed when assessing the case for implementing and updating [notices]. These include the size of the infestation, location value (cultural/economic/amenity) and volume of vessel traffic.

A number of the new Ipipiri locations have been identified as high value boating anchorages.

“In the case of the Bay of Islands, the existing [notice] contains the largest known areas of exotic caulerpa. Other confirmed areas in Northland are generally small patches.”

Iconic Bay of islands seascapes such as this at Roberton Island now live with the constant spectre of caulerpa invasive seaweed invasion changing life forever Photo / Susan Botting

Ministry for Primary Industries figures provided to Local Democracy Reporting show there are now 16.65ha, or the equivalent of almost 24 rugby fields, of caulerpa confirmed at Urupukapuka Island with infestations including in Urupukapuka Bay where hundreds camp annually, Entico/Otaia Bay, Cable Bay and its northern boundary with Waewatorea Channel.

Urupukapuka Island’s Otehei Bay tourism epicentre is scheduled for survey before the end of the month.

There are also about 123 rugby field equivalents of caulerpa between Moturua and Motukiekie Islands, with separately a further 32 rugby fields around Motukiekie Island.

Poroporo Island has the equivalent of about one rugby field of caulerpa. Waewaetorea and Okahu Islands’ caulerpa presence is scheduled to be checked before the end of the month.

Anderson said the exact area of caulerpa inside the Bay of Islands area notice could not currently be estimated.

This was due to varying densities of the invasive seaweed across its area. It was also because caulerpa growth was dynamic.

He said there had been a noticeable reduction in Omākiwi Cove caulerpa since recent storms.

Area notices were only one way of preventing caulerpa spread. Boaties and fishers also played their part, Anderson said.

Boaties travelling within and between major traditional boating spots including Northland and Aotea/Great Barrier Island are regularly flouting anchoring ban rules.

■ LDR is local body journalism co-funded by RNZ and NZ On Air.