Farming oysters in the open ocean

New technologies on trial in Ōpōtiki as part of Ngā Punga o te Moana open ocean aquaculture research programme

June 2023


Open ocean oyster farming is one step closer to becoming commercially viable thanks to a trial of new farming structures. Cawthron Institute researchers are leading the five-year MBIE-funded Ngā Punga o te Moana research programme. They are collaborating on this trial with Moana New Zealand, Stainless Concepts and Whakatōhea Mussels Ltd who have deployed the new trial structures on their marine farm off the coast of Ōpōtiki.

Open ocean farming will be necessary to support the growth of Aotearoa New Zealand’s aquaculture industry ambitions and its resilience in the face of increasing environmental pressures, including climate change. 

Laura Biessy in the laboratory at Cawthron Institute

As waters warm and the farming space available in-shore fills up, we’ll need to extend further off-shore and this will require new methods of farming and new technologies.

The challenge:

Ngā Punga o te Moana research programme partners Whakatōhea Mussels are the only company commercially growing mussels offshore in Aotearoa New Zealand. There is no one currently farming oysters in this high energy environment.

Our researchers classify open ocean farming as any marine location where the farm will be exposed to high wind and waves and strong currents – it’s not so much about the distance offshore as it is about the level of energy at the site.

Oysters are a pillar species in Aotearoa New Zealand’s aquaculture industry with high value and potential for growth, however they are vulnerable to the effects of viruses, bacteria and heat stress caused by warming waters. Farming oysters further offshore would be a great solution.

Programme researchers worked with Nelson-based firm Stainless Concepts to design a new structure, known as a sub-unit, that will be fixed to traditional long-line style systems. These subunits have been specifically designed to withstand high-energy conditions.

The site selected for the trial is Whakatōhea Mussels marine farm, about 11km from the coast of Ōpōtiki where the ocean is 50m deep.

The oysters are suspended at about 9m below the surface to avoid surface wave energy.

Deployment – Early May

8000 6mm oyster spat were deployed into two new subunits. Researchers counted and weighed oysters to distribute into 15 baskets, with the spat contained in mesh sleeves inside the baskets. 

The rest of the subunit, and all of the baskets in the second subunit, were left empty. This is because a key objective of the trial is to see how the structures perform in the environment. It’s also because the remaining empty baskets will be required when the oysters need to be split and stocking densities changed. 

Sleeve change – Early June

The oysters were removed from their 3mm mesh sleeves and transferred to a larger mesh sleeve of 6mm before being placed back into the subunit.

The next check on the oysters will need to be brought forward due to their fast growth rate, at which point they’ll be graded and split into smaller stocking densities. 

Growth rate

The growth rate over the first month of the trial has been good, with one sleeve weighing nearly 10x its original weight.


There was some minor fouling on the sleeves, but not enough to restrict waterflow to the oysters and plenty of space in the sleeves for them to move around.

Animal health

The oysters were clean with no mortalities.


Pending the results of the full trial, this approach shows good promise. We’ll be running further overlapping trials to test and refine the technology, with input from industry partners. 

A core goal of the programme is to develop the technology and methodology required for commercial open ocean farming of shellfish in Aotearoa New Zealand and this is a confidence building step in that direction.

Cawthron_AQ_Cawthron Breeding
Image: Top – Deploying the new trial subunits at Whakatōhea Mussels’ marine farm. Bottom – Cawthron Institute researchers sorting juvenile oysters.
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