Trial aims to prevent runaway mussel floats

A Marlborough mussel farm with regular floats. Photo / Supplied

A Tasman-based company has begun a one-year research trial aimed at reducing the number of mussel floats that get lost at sea each year.

Aquaculture float specialist SS Floats has teamed up with the Ministry for Primary Industries (MPI) to devise an improved float and attachment method for longline mussel farming.

MPI is contributing $72,500 towards the $145,000 project through its Sustainable Food & Fibre Futures.

The new design must be able to withstand the unpredictability of open waters better than the existing floats, lead designer for SS Floats Paul Smith said.

"Mussel farming in New Zealand began in sheltered bays in the Marlborough Sounds, so the old design, which has been used for the past 40 years, worked pretty well," Smith said.

"However, the industry's move to more exposed waters has driven our need to come up with a new design."

Currently made of plastic, mussel floats can occasionally come loose due to adverse weather or tidal conditions.

Appropriate buoyancy was a critical element of longline mussel aquaculture and required a delicate balance, Smith said.

"Too much flotation and crops are shaken by wave energy at the surface; too little flotation and lines can sink. Both can result in crop loss."

Smith said he had been contemplating this issue for some time, so quickly had a prototype solution ready to test once funding was approved.

"We've already got trial floats in the water locally, which are working really well," he said.

"We now need to test them in different parts of the country with more exposed waters."

The trial supports the government's Aquaculture Strategy objective to extend marine farming into the open ocean.

Ned Wells, General Manager of the Marine Farming Association, which was supporting the research project, said floats that got loose were generally recovered.

The new design in the water. Photo / Supplied

"Despite that, it's an expensive exercise for companies to go round and collect them," Wells said.

Data collected over the last 10 years showed between 500 and 1500 floats were lost from Top of the South mussel farms each year, with an annual cost of at least $500,000.

MPI director of investment programmes Steve Penno said if the project was successful, it would mean one less source of plastic in the marine environment.

"This could help the mussel industry with another step towards boosting its sustainability, while saving time and money."

The new floats will be tested in the open waters of Golden Bay, Tasman Bay, Pegasus Bay and off the coast of Coromandel.