Mussel Ropes

May 2021

Western science and mātauranga restoring mussel beds at Ōhiwa Bay.

For nearly two decades marine scientist Associate Professor Kura Paul-Burke has been working with four iwi (including her own) and three regional councils to restore the mussel beds at Ōhiwa Bay. Blending Western science and mātauranga they’re trying to identify  sustainable, simple solutions – and it’s working. 

In 2003 iwi Whakatōhea had concerns about the depletion of mussels in the Ōhiwa Bay and contacted local councils. Iwi and councils with a stake in the wellbeing of the bay came together to find answers to the disappearing mussels and as critically, how to restore the mussel beds. A rahui on harvesting was put down for 8 years while baseline surveys and mapping was carried out with iwi. Mātauranga Māori based on intergenerational transmission of knowledge was used to locate and map the beds. The findings were concerning, with four of the key beds reduced from populations of millions of mussels to around 80,000. 

Initial thoughts were that the area was over harvested, however the mussels continued to diminish despite the rahui. The causes of the depletion are complex to pinpoint, but human impacts, including sedimentation from run-off were certain contributors.

Nearly 2 decades later, 4 local iwi, 3 councils and other entities continue to work together with experts, including  marine scientist and tangata whenua Associate Professor Kura Paul-Burke (Ngāti Awa, Ngāti Whakahemo). Further research uncovered a contemporary tohu – the abundance of sea stars were significantly reducing the mussel beds through predation. 

Kura points to 17 years of research into the explosion of Crown of Thorn sea star populations in Australia – after 17 years, researchers there still have no definitive answers, although there is a strong hypothesis that run-off is increasing the survival rates of juvenile sea stars.

Mahi to protect and regenerate the Ōhiwa beds began with the determination to grow the mussel population on the bottom of the harbour and protect them from the sea stars. The mahi was underpinned by mātauranga and the first trials were with ‘predator exclusion cages’ made of rebar and netting and others with traditional materials. 

Re-populating the mussel beds became the issue as with all the mahi being funded by the stakeholders, funding for commercial spat was not viable. Commercial aquaculture operations tend to buy in mussel spat harvested from up North. 

Conversations were held with a local aquaculture company, Whakatōhea Mussels who were generous in sharing their knowledge around commercial approaches to mussel farming, including the use of nylon and plastic based ropes that are ‘seeded’ with spat. Kura knew mussels were present and breeding in the harbour (from those growing on buoys and under boats) so capturing the spat on lines became a focus.  

Kura was determined to find a sustainable alternative to the plastic based spat lines – she didn’t want to contribute further to the microplastic pollution of the moana, and speaks of the importance of protecting the moana for the upcoming generations, “What is more important than our mokopuna?”. 

This mahi has formed the basis of the Awhi Mai Awhi Atu Project – an investigation into traditional materials and techniques to create sustainable spat lines. Kura brought in master weaver Whaea Roka Hurihia. Whaea Roka and her students developed a series of ropes from kuku, harakeke and tī kouka (cabbage tree). The lines used are shorter than commercial lines, as the harbour is shallow. The prototypes were trialled in phase 1 alongside standard nylon aquaculture spat lines.

Results have been promising in the first year. The cabbage tree lines had weathered well and supported around 20,000 mussels – approximately 50 kilos. However, the lines eventually broke where they were attached to the buoys in the strong currents. Subsequently, in September 2020, a second lot of new rope trials were initiated. Each line has a core of pirita (supplejack) for strength with either tī kouka, pīngao or neinei woven around it. They’re also creating bushier ropes to support larger populations of spat.

Late in 2020 the research team discovered encouraging signs of success with three new mussel beds having established themselves outside of the current four research stations set up by Kura’s team where the first-generation trials took place in 2019.

These results have applications for further environmental, conservation and restoration work for the future.

Showdown Productions Ltd.   Rural Delivery Series 16 2021