Lines of sugar kelp were installed at the Scottish Sea Farms site last October, with salmon due to be stocked during June 2024.
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A new pilot project to combine salmon and kelp farming has been launched on the Scottish west coast.
The pilot involves a collaboration between Scottish Sea Farms and seaweed grower Guy Grieve, a former operator of the Ethical Shellfish Company, whose new venture Atlantic Garden aims to produce commercial quantities of sugar kelp for garden compost.
The year-long project is taking place at a fallow Scottish Sea Farms site on Loch Spelve in the Sound of Mull, Scotland.
Seaweed lines were installed at the site last October and, according to the project partners, these have already shown promising growth over the winter. The four 750m lines were seeded by Dutch supplier Hortimare, and were installed on the raised net pen grid with the help of Inverlussa Marine Services.
As the next stage of the project, during June, four 90-meter pens will be stocked with salmon.
"We plan to stock the farm with 7kg fish, from Fishnish in the Sound of Mull, so this will only be a four or five-month cycle, not the full 18 months," said Scotttish Sea Farms Area Support Manager for Mull Andrew MacLeannan in a press release.
"Loch Spelve is sheltered so ideal for seaweed, which doesn’t like strong currents, but the environmental conditions have been challenging for salmon production in the past, particularly for gill health," he added.
The integration of kelp with salmon is expected to provide mutual benefits, a concept supported by multi-trophic aquaculture projects elsewhere, the partners said.
The project will monitor water samples daily to assess the trial's success from a salmon farming perspective, focusing on plankton levels that can impact gill health.
The pilot is also expected to yield up to 30 tonnes of biomass for Atlantic Garden's compost.
"We should get 8-10 kilos per metre of seeded line but this is a pilot so we don’t know what to expect yet. I look forward to what we learn from this trial and what our next steps will be," Grieve said.
Scottish Sea Farms sought permission from Crown Estate Scotland for the trial and says it is now in talks to amend the farming lease to allow for longer-term seaweed cultivation.
The project is part of a broader effort to integrate seaweed farming with salmon production, a practice already adopted by some salmon farming companies in Norway, including Lerøy and SalMar, which co-own Scottish Sea Farms.
Anne Anderson, Head of Sustainability and Development at Scottish Sea Farms, pointed out the benefits of seaweed to the marine environment, in absorbing carbon and oxygenating water.
"And some of the organic nutrients, nitrogen and phosphorous, from salmon farming are absorbed to help nourish the kelp. It will be interesting to see if we get more seaweed growth once we put the salmon in," Anderson added.
"We all recognized that seaweed is beneficial for the environment in different ways and agreed to look at it more closely," said Grieve. Atlantic Garden is also supporting the Scottish Coastal Clean-up campaign, donating 20p from every bag of seaweed compost sold.
In an earlier trial, Scottish Sea Farms successfully grew seaweed within salmon pens to replace artificial hides for cleaner fish. The project, at Scallastle, also in the Sound of Mull, resulted in improved health and welfare for both the salmon and wild wrasse, a species of cleaner fish, the company said.