16 December 2024
Kia ora koutou
In this update – a new controlled area is in place at Waiheke Island; a caulerpa decline is confirmed in some areas; and a new area of exotic caulerpa has been found at Kawau Island.
CAN in place at Waiheke Island
New biosecurity controls are in place over an area of Waiheke Island waters to prevent the spread of the invasive seaweed exotic caulerpa.
Within this zone (see map below), people will still be able to anchor but must follow equipment cleaning directions before they leave the controlled area.
The law requires boaties to check their anchor, anchor chain and any equipment used in the water for attached seaweed or plant material. This includes, for example, diving and fishing gear, wetsuits and fins.
Any seaweed found must be removed, bagged or securely contained, and taken ashore for disposal in a rubbish bin. If secure containment isn’t possible, it can be put back into the waters it came from. The important thing is that it is not taken to other waters outside the controlled area. The equipment should be washed down with fresh or seawater and, where possible, left to dry before being used in another area.
Launching vessels, including amphibious Sealegs-type craft is permitted, as is motoring or sailing through the waters of the controlled area.
The controls at Waiheke are not as restrictive as those for the Aotea and Te Rāwhiti CAN zones because the caulerpa is less dense at Waiheke.
Map showing the Waiheke Island controlled area which extends from the western point of Mawhitipana Bay, north including Nani Island, northwest to 500m off Thompson Point and finishing at Waihihi Point on the eastern side of Onetangi Bay. It includes the marine waters up to and including the high-tide mark and to a depth of 22 metres.
The CAN also restricts some types of fishing activities that risk spreading caulerpa.
You must not fish in the area using any method that makes contact with the seabed and can potentially snag and relocate caulerpa. This means no netting, dredging, bottom trawling or potting.
Line fishing from the shore or drift fishing from a vessel, spear fishing and hand gathering, and shore-based longlining – for example from a knotiki or drone – are all allowed.
Biosecurity New Zealand has engaged with a range of partners and groups on a proposal to introduce a CAN in the area for some months. This has included Ngāti Paoa, the Local Board, Auckland Council, the Waiheke Marine Project, the local tourism sector and representatives of Auckland yachting and boating clubs. All agreed some controls were necessary.
Tighter restrictions, including, potentially, a ban on anchoring, were initially considered. However, in a new development, a decline or reduction event has been confirmed at Waiheke. As a result, a less stringent CAN is now considered appropriate.
CANs are an important tool to help prevent the spread of exotic caulerpa. This pest seaweed can spread over long distances as small pieces, caught on anchors, anchor chains and other equipment including fishing and diving gear. It’s interesting to note that most of the locations it has been found in are popular anchorages.
Decline event in exotic caulerpa
Following multiple reports of a reduction in caulerpa cover at several locations in the Hauraki Gulf, we commissioned NIWA to determine the extent of this and the potential cause. Monitoring work was undertaken at Waiheke and at a number of locations at Aotea.
NIWA's preliminary report shows that there have been large reductions in the cover of exotic caulerpa at some sites, notably in Onetangi Bay, Waiheke Island and Okupu Blind Bay at Aotea.
The biggest areas of decline have occurred in caulerpa on soft sediment or sandy seabed. However, it is still present in large amounts in rocky and intertidal areas and in deeper waters.
As well as Okupu and Waiheke Island, the team surveyed parts of Rangitawhiri/Tryphena Harbour and Schooner Bay at Aotea. These results were more variable with some declines in caulerpa cover but still significant amounts on rocky reefs and substrate.
The dive team checked areas that had been previously surveyed to enable a cross-checking of data, as well as some of the reported locations of suspected decline.
While this development is good news, we need to be cautious about interpreting it, and exotic caulerpa continues to present a significant challenge. We need more research to understand the significance of the decline and what has caused it.
Environmental factors and reproductive cycles could be involved, but the NIWA team believe varying water temperatures are not likely to be the cause as winter sea temperatures have not changed significantly in the three years since exotic caulerpa was detected here.
NIWA will be undertaking some surveillance work in Te Rāwhiti Inlet in the Bay of Islands to understand if any decline has also occurred there.
New area of exotic caulerpa confirmed at Kawau Island
Exotic caulerpa has been confirmed at a second location at Kawau Island in the Hauraki Gulf.
There is an existing area of exotic caulerpa at Iris Shoal, to the north-west of the island.
NIWA divers surveyed Bostaquet Bay on the south coast of the island following reports of suspected caulerpa by University of Auckland divers.
The dive team examined six locations in the bay covering areas of seabed from 5-24 metres deep and across a range of substrates including sand, gravel, shell, reef and muddy sand.
Exotic caulerpa was confirmed in five out of those six locations, showing up in small, sparse patches but distributed across a wide area.
A team with representatives from mana whenua, Biosecurity New Zealand, Department of Conservation, Auckland Council and Revive our Gulf has formed to organise further surveys to help understand the extent of the infestation and to consider next steps. This could include removal with existing tools such as benthic mats.
Boaties are asked to, where possible, avoid anchoring and fishing in Bostaquet Bay as exotic caulerpa can be spread as fragments snagged on anchors, anchor chains and fishing or diving gear.
In any area, before moving location, check the anchor, chain and fishing or diving equipment for attached seaweed. Remove it, bag it and dispose of it ashore.
Helping boaties know where biosecurity restrictions are
Now there’s an easy way for boaties to find out about biosecurity restrictions in our ocean, lakes and rivers and help stop spread of invasive species.
Biosecurity New Zealand has published an interactive map of restricted areas that will be updated when required. You can find it here or by scanning the QR code below.
Nāku noa, nā
The exotic caulerpa response team
Receiving these updates
If you would like to subscribe to these regular updates, please sign up here.
To unsubscribe, please click the link below.
For more information about exotic caulerpa seaweeds in New Zealand visit the Ministry for Primary Industries Biosecurity New Zealand website.