Significant drop in salmon mortality recorded at Mowi Scotland

Mowi Scotland recorded a significant drop in salmon mortality during August.

Mortality was around one third of that recorded in recent years when El Niño conditions caused a marine heat wave in the North Atlantic. El Niño is part of the natural climate phenomenon called the El Niño Southern Oscillation (ENSO) and leads to warmer than average sea surface temperatures.

This marine heat wave led to warmer seawater temperatures causing salmon to suffer gill disease and ultimately led to mortality in 2023 and 2024. This is despite the fact that this period saw fewer incidents of viral, bacterial and parasitic challenges to farmed salmon.

In August 2024, Mowi Scotland recorded its lowest monthly mortality for over eight years and achieved record high feeding and growth rates in the cooler coastal waters.

Ben Hadfield, COO of Mowi’s operations in Scotland, Ireland, Faroes and Canada East, explained: “The decline of El Niño conditions, much cooler summer air temperatures and higher rainfall have all benefited our salmon farming operations. We had expected a slightly easier summer due to the declining marine heat wave evident in 2022 and 2023. This weather, combined with our enhanced mitigation measures such as the high capacity to treat salmon with freshwater and the use of bubble curtains to prevent micro jellyfish and algae entering our farming systems, have so far proved effective.

“To see such a big fall in mortality rates is really encouraging because all our focus as salmon farmers is about caring for the fish. Until this year, the warmer seas have presented a big challenge for salmon farmers and the stock we work so hard to rear.”

Sean Anderson, Production Director at Mowi Scotland, added: “This summer has brought a return towards favourable growing conditions for salmon. We have witnessed much lower levels of problematic species of jellyfish and algae, which historically have caused problems for the salmon. We cannot be complacent, however, the threat posed by jellyfish and algae has not gone away and may well challenge us in September. We will continue to do our utmost to predict, monitor and use the best husbandry measures possible to protect the fish in our care.

“We must and will remain as vigilant as ever over the coming months. Our skilled and passionate farmers have already put several measures in place to reduce the impact the warm autumn season historically poses. It is vitally important as farmers, that we always look at what may lie ahead of us and act early, in all instances, to stay ahead of any challenges that will likely come before temperatures start to decline again as we approach the winter months.”

Mowi Scotland now enters a critical period within its operations, which will include the first movement of salmon from the Loch Etive post smolt programme to seawater farms in Muck and Rum, marking a pivotal milestone within Mowi and the Scottish industry.

Sean continues: “I would like to pass on my thanks to all our dedicated teams across the business, who work around the clock, seven days a week, in hail, driving rain and shine, ensuring our salmon are cared for and are in the best possible health given the challenges we can face.”

Echoing Sean’s thanks to the Mowi Scotland team, Ben added: “Everyone is focussed on the end of year challenges and working hard to ensure the best rearing conditions for our salmon. We don’t normally focus on any one team, but in a rare break in precedent it is only right to single out the team in Loch Erisort who have harvested over ten thousand tonnes from the three sites in Loch Erisort and produced some exceptional salmon this year!”