Scottish Sea Farms has joined a seaweed growing venture in a scheme that combines salmon and kelp farming on Loch Spelve in the Sound of Mull. The aim of the year-long pilot is to enrich and replenish the marine environment while minimising any impact from farming activities.
The farm, which had been fallowed, was chosen as a suitable testing ground in the collaboration between Scottish Sea Farms and businessman and writer Guy Grieve, who ran the Ethical Shellfish Company from Mull. Grieve now plans to produce commercial quantities of sugar kelp to be used in garden compost.
The seaweed lines, installed last October, produced encouraging growth over the winter. This month, four 90-metre pens will be stocked with salmon. The mutual benefits of growing salmon and kelp in the same waters have been shown in multi-trophic aquaculture projects elsewhere, said Scottish Sea Farms Head of Sustainability and Development Anne Anderson.
"Seaweed is so beneficial in so many ways for the marine environment," said Anderson. "As a plant, it absorbs carbon dioxide, while releasing oxygen. And some of the organic nutrients, nitrogen and phosphorous, from salmon farming are absorbed to help nourish the kelp."
Scottish Sea Farms sought permission from Crown Estate Scotland for the trial. Talks are now underway to amend the farming lease to cultivate seaweed for the longer term.
Salmon farmers in Norway, including Lerøy and SalMar which co-own Scottish Sea Farms, have hosted seaweed farming businesses adjacent to some of their farms.
In an earlier trial, Scottish Sea Farms pioneered seaweed settlement within salmon pens to replace artificial hides for cleaner fish. The project, at Scallastle, resulted in improved health and welfare for both the salmon and wild wrasse, a species of cleaner fish.
In Loch Spelve, Area Support Manager for Mull Andrew MacLeannan worked with Grieve to install four 750 metres of seaweed lines (a total of three kilometres) and tied the lines to the raised salmon pen grid.
"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," MacLeannan said. "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.
"'We will be looking to see if the seaweed trial has been successful from a salmon farming point of view by taking daily water samples, before and after the salmon are stocked, and checking for levels of plankton, which can impact the gills."
Grieve, who runs Atlantic Garden, supplying seaweed-rich compost to gardeners, wanted to start producing seaweed at scale in Scotland to complement the seaweed gathered from harbours. He plans to keep the crop in the water until the summer to harvest as much biomass as possible, up to 30 tonnes if possible.
"'We should get eight to 10 kilos per metre of seeded line but this is a pilot so we don't know what to expect yet," said Grieve. "I look forward to what we learn from this trial and what our next steps will be."
