Comparing and contrasting shear forces and hydrodynamics of Industrial Larval Mussel tank design and operation



Aquaculture is one of the world's fastest growing primary industries and demand for aquaculture products is expected to continue growing as the world's population grows and wild-catch levels remain relatively static. Globally, aquaculture will soon produce more seafood than wild fisheries.

The New Zealand aquaculture industry, although relatively small on a global scale has positioned itself at the high-end of the market, exporting premium seafood products around the world. Sanford Limited is New Zealand's largest producer and exporter of aqua-cultured products, with Greenshell mussels representing the largest by volume and value.

Greenshell™ mussels (Perna canaliculus) are unique to New Zealand and are one of New Zealand's most iconic seafood offerings. Mussel aquaculture is one of the world's most efficient forms of food production and is considered a highly sustainable method of producing high protein foods.

The Government's Aquaculture strategy and five-year action plan supports sustainable growth of the aquaculture industry – balancing our economic, social, cultural and ecological values.

Historically, most green-lipped mussels in New Zealand are farmed in the same way. Spat (juvenile mussels) are collected from Ninety Mile Beach and elsewhere in New Zealand, where they wash up in their billions attached to clumps of seaweed. After arriving at a mussel farm, spat are transferred to nursery ropes and grown on the ropes in seawater until about 6 months of age. At this point, they are removed and reseeded onto longlines (stretches of rope up to several kilometres long) that are suspended between buoys.

Mussels are grown for a further 9–12 months before they are harvested. Mussel barges, which harvest the mussels, are mechanised and contain equipment for removing mussels from lines, then declumping, washing, sorting and packing.

Until now, New Zealand's mussel growers have relied on catching wild spat (baby mussels) around our coastline. Supply is unpredictable, yield levels are extremely low and the genetic profile of the mussels are uncontrolled. Through partnership with the New Zealand Government in the form of a primary growth partnership, we have developed a facility capable of selectively breeding Greenshell™ mussels and producing spat on a regular and controlled basis so our growers have the spat they need. SPATNZ (Shellfish Production and Technology New Zealand) operates this hatchery and research facility and its aim is to produce innovations to advance New Zealand's mussel aquaculture industry and deliver benefits for New Zealand's economy.

Preferred Project option 1 - Larval tank design and operation

One of the greatest challenges in the SPATnz project is to produce batches of larvae year-round. Mussels are naturally seasonal, and the technical challenges involved make it all the more difficult to consistency rear the highly sensitive larvae. We have observed differences in survival of larval rearing in various tank designs. At certain times of year we can get total loss of larvae in the commercial scale tank while the smaller scale (non-commercial) tanks continue to perform very well, so it has a big impact on our annual production. The reasons for the variation is unknown and one hypothesis is that the shear forces or hydrodynamics generated by aeration differ between these tanks, and interact with microbial communities and mussel larvae in ways that determine the success or failure of the batch. We are interested in comparing and contrasting the shear forces and hydrodynamic regime in these two tank designs. We are interested in hypotheses about why the difference in tank performance is seasonal.

Alterative Project option 2 - Invasive and unwanted species

Several invasive and unwanted species settle and grow on Greenshell mussel farms to the detriment of the NZ mussel farming industry, the most significant is the unwanted species Mytilus spp (blue mussels). The abundance of blue mussels has increased dramatically in the Marlborough Sounds and other growing areas in the last 10 years. There is a lot of historical data on blue mussel settlement and this has been analysed by Cawthron Institute and an app developed to predict blue mussel settlement. Given the impact of blue mussels on the GSM industry, we seek to understand the future trends and impacts of blue mussels and potentially other unwanted organisms. Will the prevalence increase, decrease or plateau and how will this affect the industry.

Alterative Project option 3 - Economic modelling of GSM selective breeding

A preliminary bio-economic model has been prepared to examine the economic importance of many factors influencing the profitability of mussel farming. The report is based on a spreadsheet model, and "user instructions" are available. We would be interested in a critique of this model and suggested further developments to enhance its utility of accuracy. The model does not currently incorporate changes to product condition over time, and is limited in its consideration of many external potential variables.


Sanford contact:

Andrew Stanley
General Manager Innovation
027 495 9678