A Māori-inspired restoration has turned around the declining mussel population located in one of the historically most productive harbours in the world to restore a once thriving industry.

Numbers of mussels hit a record low in 2019, registering just 80,000 kuku – green-lipped mussels – across Ōhiwa Harbour in Aotearoa/New Zealand's Bay of Plenty area.

Kuku numbers struggled to survive against an overwhelming population of the pātangaroa 11-armed starfish that was consuming the mussels at an unsustainable rate.

The carnivorous seastars dominate shallow seabeds to the exclusion of other sessile organisms.

However, nearly six years has passed since the mussel decline and the numbers have exponentially grown to around 45 million mussels across the 11 hectares of the harbour floor.

Marine scientist Professor Kura Paul-Burke has credited the Aotearoa project to the Te Rūnanga o Ngāti Awa – one of the traditional Māori iwi tribes.

Professor Paul-Burke attributed the recovery success rate to studying the past of Mātauranga Māori – a term that refers to the Indigenous traditional knowledge of the harbour's first inhabitants.

The growth has risen from the 80,000 mussels in 2019 to 470,000 by the end of 2020 after the first seastar removal trials began onto 800,000 mussels in 2021 after further restoration efforts to 16 million that were identified on the sea floor by 2023 before reaching 45 million at the beginning of this year.

The first female Māori professor of marine science, who comes from both Ngāti Awa and Ngāti Whakahemo tribal descent, said from a Mātauranga Māori perspective, the Ngāti Awa iwi were the first source for their kuku knowledge, having a special relationship with their own bay.

"Nobody knows their harbour, their estuary, their ocean better than the home people, the people that have lived there consecutive generations for many years," she told Radio New Zealand.

Though the project could not also be achieved without the support of the University of Waikato marine scientist and her colleagues, in addition to the Bay of Plenty Regional Council and the seven partners of the Ōhiwa Harbour Implementation Forum.

The university researchers that had to manage the growing seastar population also created a biodegradable taura kuku – or mussel spat lines – out of dead cabbage tree leaves to reduce plastic pollution but also to seed the mussel beds.

Part of the project involved speaking with local Kaumātua Elders to identify where they once collected mussels in their youth that allowed the researchers to traverse back up to three generations of local knowledge.

Looking to the past was fundamental to understand the present and to inform the future, Professor Paul-Burke noted.

"Mātauranga Māori uses intergenerational knowledge from the past as a baseline," she said.

"So, it takes us further back to give us a much more broader picture of the harbour and all the species within it."

Professor Paul-Burke also said Mātauranga knowledge proved to be innovative and could be implemented alongside mainstream marine science policy, planning and restoration.

"Our world is declining... we all know it, we can see it, we can feel it," she said.

"Wouldn't it make sense to use both of our hands to help solve a contemporary environmental problem rather than having one hand tied behind our back?"

The project has been a step-by-step journey, she said, carefully managing through the removal of seastars, hands-on restorative efforts and ongoing monitoring.

But the professor also warned that while the mussel beds reached an "exciting milestone" and were becoming more resilient, there was still work to be done.

"We still have to do seastar management because the seastars are still ever present and they're in higher numbers than you'd want for a balanced population," she said.

Equally important to securing the future of the mussels was to retain the rahui – the prohibition against the current activity in order to protect the resource.

New Zealand's Ministry for Primary Industries has since placed a temporary two-year harvesting closure over the mussel beds, giving them time to stabilise and expand further.