Coastal and Freshwater news

Green-lipped mussel spat
18 November 2016

App helps mussel farmers

An app to detect when populations of blue mussels are settling is helping green-lipped mussel farmers figure out the best time to avoid them.

Pest blue mussels are a major problem in the industry; Cawthron senior scientist Dr Barrie Forrest says blue mussel biofouling has been impacting the green-lipped mussel industry in the top of the south since mussel farming began in the Sounds in the mid-1970s.

“The settlement of blue mussels on spat and crop lines reduces the space available for green-lipped mussels, and can smother mussel spat and crop,” he says. The extra weight can also affect farm infrastructure and slough green-lipped mussels from crop lines when they’re lifted out of the water.

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“The industry goes to a considerable effort to try and manage these types of impacts.”

In fact, he’s calculated that blue mussels cost the Marlborough mussel industry more than $23m a year; 10 per cent of its annual regional revenue.

“The blue mussel is one of the biggest threats to the green-lipped mussel industry,” says Cawthron marine ecologist Dr Javier Atalah, who developed the web app using open-source software.

The Marine Farming Association has been collecting data on blue mussels at 50 sites around New Zealand for more than 40 years, thanks largely to the efforts of Marlborough marine biologist Jim Jenkins.

“That’s pretty impressive for an ecological study; you never get to see such long-term work done on biofouling pests,” Dr Atalah says. “It was quite visionary in the 1970s to deploy pieces of rope hanging from a buoy or raft, and then they would count every spat or baby mussel, both blue and green. I approached Jim and he was super happy to share everything. He opened his laptop and showed me 200 spreadsheets.”

Jenkins started his mussel work in 1972 in Kenepuru Sound. “We knew the blue was the commercial species of Spain so felt we really should be watching it,” he says. “Then we realised we could never get a blue that would be sellable and by then we realised they were a fouling organism and were increasing the biomass on the mussel lines.”

The app developed by Dr Atalah and Dr Forrest to detect when populations of blue mussels are settling, and to help green-lipped mussel farmers figure out the best time to avoid them

“The app developed I hope will have good financial gain for the mussel farmers if they can keep up with the complexities of the environment out in the Sounds.”

The farmers had been using the data for checking certain trends, but hadn’t done any in-depth analysis. Dr Atalah and Dr Forrest embarked on a comprehensive study to collate the data and look for patterns using more modern statistical tools, such as incorporating salinity, surface temperature, and data on long-term oceanographic processes.

The data confirmed a lot of anecdotal beliefs, found new trends, and corrected others that had been false. One outcome is confirmation that blue mussels are becoming more prevalent over time, but Dr Atalah said further research would help to identify why. “Farmers are improving management practices, and hopefully blue mussel prevalence will be reduced.”

Since the app’s release a year ago, farmers have been digesting the data and learning how to incorporate the knowledge into their farming practices.

“It shows the value of long-term monitoring in terms of gaining insights into the impacts and management of a marine pest,” Dr Forrest says.