Four decades, one loch, and a question: Did salmon farming leave a mark?
Mowi Scotland has announced findings from a 37-year independent water quality monitoring programme at Loch Arkaig, indicating that salmon farming operations did not alter the nutrient status of the freshwater loch.
The programme, which began in 1987 and was carried out by researchers from the University of Stirling, involved regular monthly water sampling. The results, compiled into a final report following the closure of Mowi’s Loch Arkaig site earlier this year, show that the geometric mean for phosphorus levels remained stable throughout the monitoring period and within the loch’s trophic classification.
“With the recent closure of our Loch Arkaig fish farm, it is only right to look back on our operations extending to almost 40 years, with a particular focus on the nutrient status of the water body, to better understand any potential impact from salmon farming,” said Stephen MacIntyre, Head of Environment at Mowi Scotland.
According to MacIntyre, phosphorus — the principal nutrient controlling trophic status — varied seasonally due to land management practices and rainfall levels, but overall remained consistent. “It is therefore important to invest in monthly sampling and establish a long-running data set to establish a geometric mean,” he said.
The Scottish Environment Protection Agency (SEPA) has classified Loch Arkaig as a water body of “High Ecological Status,” meaning it is considered unaffected or virtually unaffected by human activity.
The Loch Arkaig study is part of a broader continuous monitoring programme that Mowi operates at its other freshwater farming sites at Loch Ness, Loch Lochy, Loch Garry, Loch Shiel, and Loch Awe. Monitoring includes the analysis of total phosphorus and chlorophyll-a concentrations to track any ecological changes.
MacIntyre added: “In addition to complying with all regulatory standards and conservation thresholds, we often go beyond our regulatory requirements by carrying out additional environmental studies.”
The findings align with Mowi’s broader environmental strategy, which includes adapting to new standards under the Aquaculture Stewardship Council’s revised Farm Standard launching this year.
The Loch Arkaig report follows Mowi’s 2024 post-closure study at its former Isle of Ewe marine site, which found that seabed conditions had recovered following the cessation of farming activity.