Kuku (mussel) restoration

Kuku or green lipped mussel beds were once extensive in the harbour’s main channels. Whether due to overharvesting, deteriorating water quality or other factors, these beds had almost disappeared by the end of last century. Concern about the future of kuku led to Professor Kura Paul-Burke (Ngāti Awa, Ngāti Whakahemo) to begin monitoring them in 2007. Her work was subsequently supported by the Ōhiwa Strategy partners and the Sustainable Seas National Science Challenge.

 

There were a couple of small beds still left at first but Kura found that these were disappearing rapidly. The culprit at this stage was found to be waves of eleven armed seastars (also native) moving through the beds and devouring all the kuku as they went. Further investigation identified a further offender – the much smaller (and also native) cushion star was eating the very small juvenile kuku. A number of techniques were tried to firstly increase the kuku numbers and secondly to deal with the seastars. The Mussel Restoration Trial was a project sponsored by the Bay of Plenty Regional Council on behalf of the Ōhiwa Harbour Strategy partners from 2018 to 2020.

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Following the trial project Kura secured funding for the Awhi Mai Awhi Atu research project through the Sustainable Seas National Science Challenge. The project was co-developed with hapū/iwi of Ōhiwa Harbour and brought together mātauranga Māori (knowledge), Western science and local kaitiakitanga to progress the recovery of the harbour’s once abundant green-lipped mussel (kūtai, kuku) beds. Awhi Mai Awhi Atu can be translated as 'Care for me and I will care for you. Embrace me and I will embrace you'. The Awhi Mai Awhi Atu project ran from 2020 to 2023.

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During the early Mussel Restoration Trial 2018 to 2020 the researchers, in collaboration with local hapū, had already successfully experimented with cages made from pirita (supple jack) and mānuka to protect mussels from seastars. Spat lines that were installed to catch mussel spat were very successful. Usually these mussel spat lines are predominantly made of plastic. At Ōhiwa, however, the practicality of using natural fibre lines to help restore kuku/mussel beds was investigated. At a wānanga in August 2020 renowned expert weaver Roka Ngarimu-Cameron from Hāwai east of Ōpōtiki and her students engaged in weaving lines from natural fibres. Lines from harakeke (flax), tī kouka (cabbage tree) and kiekie were woven and deployed into the harbour. The trial showed that tī kouka lasted the longest, up to 5 months. No less than 2,000 kuku were counted per line, that’s about 50kg! ​​

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Four mussel restoration stations were installed and have been successful at recruiting spat and growing mussels. The spat lines at these stations are suspended above the bed of the harbour, preventing predation by the seastars. These mussels will continue to help the regeneration of three new mussel beds on the harbour floor. 

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Awhi Mai Awhi Atu key events: 

• In 2019, there were 80,000 mussels across the whole harbour 

• In 2020, following pātangaroa (11-armed seastar) removal management trials there were 470,000 kuku (mussels) across the whole harbour 

• By 2021, after continued mātauranga-led restoration efforts there were 800,000 kuku (mussels) in Ōhiwa harbour

• In 2022, a feasibility study for removing eleven-armed seastars was carried out. Diver removal was effective at catching larger sized eleven-armed seastars. Trapping was more effective at catching smaller animals with 30 traps collecting 550 eleven-armed seastars and 18,900 cushion stars over an 18-day period

• On a maintenance dive in 2023, it was identified that the kuku (mussel) population had grown to 16 million mussels on the seafloor 

• In December 2024, following a new survey conducted by Professor Kura Paul-Burke and her team, there are now 45 million multi-generational mussels that have regenerated from the original restored mussel bed. The mussel bed size had also increased from 3.5 hectares in July 2023 to 11 hectares in December 2024

 

The latest, incredible increase of kuku, or green-lipped mussels confirms Ōhiwa Harbour as the most successful mussel restoration effort across the country. The survey also showed that kuku are now beginning to grow up: 60 per cent are babies, 24 per cent teenagers, and 16 per cent adults. Back in July 2023 90 per cent of the mussel population were babies. This exciting and hopeful discovery showed that prioritising mātauranga Māori alongside marine science, had managed to restore mussel numbers from a drop to only 80,000 in 2019 across the whole harbour, and appeared to reverse the decline.

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The majority of the mussels are still juveniles (baby and teenage sized) and will require protection from human harvesting to be able to grow to adults, reproduce and help stabilise the new bed. A section 186A temporary two year harvesting closure, or rāhui, has been installed by the Ministry of Fisheries on request by Ngāti Awa in late 2024. No mussels can be taken from an area beginning near the Ōhope Road end and extending to the east towards the harbour mouth. 

 

The Awhi Mai Awhi Atu project led by Kura and funded by the Sustainable Seas National Science Challenge concluded in June 2023. Generously, Kura continues to advise the Ōhiwa Harbour Strategy partners on mussel restoration in the harbour. Currently, further funding options are being considered. 

 

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Further information

Watch Turning the Tide | Episode 2: Mātauranga-Led Restoration on RNZ. The six-part series was made by Tauihu Media and funded by the Sustainable Seas National Science Challenge.

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Learn more about Kura Paul-Burke and her mātauranga Māori approach in the New Zealand Geographic and on the Sustainable Seas Science Challenge website.

 

Go on a virtual field trip with Kura Paul-Burke, students from Kutarere School and Shelley at LEARNZ. 

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