Mortality levels on Scottish fish farms last year broke previous records, new government data has revealed. The worst hit company was Norwegian-owned Mowi, which blamed “El Nino” and record sea temperatures for the deaths.

According to data published by the Fish Health Inspectorate (FHI), the mortalities on Scottish Salmon farms, at 17.4 million, exceeded the 17.2 million of 2022’s record-breaking year. Close to half those mortalities took place on farms owned by Mowi. Bakkafrost accounted for 26.5% and Scottish Sea Farms 14.6%.

The data included both salmon and trout, and covered all sizes of fish, from several kg to just 5g.

Not only did Mowi account for 46.6% of mortalities, but the global fish farm giant is behind the single most badly-affected sea-based salmon farm, Seaforth, which saw nearly a million deaths.

It also owns Inchmore Hatchery,  the farm with the worst freshwater mortality rate,  which suffered more than 2 million deaths. Across all its farms, the company reported 8.1 million mortalities in 2023, up from 5.1 million in 2022; 3.0 million in 2021 and 1.4 million in 2020.

Mowi also published its quarterly financial report yesterday, which revealed the huge impact of the losses in terms of harvest volume and loss of profits. Mowi Scotland suffered a rare operating loss of €0.10 per kilo on its fish in the last quarter of 2023.

READ MORE: Salmon farm mortalities worst ever: Moratorium calls grow

The Herald:

Across the industry in Scotland, the report noted, harvest volumes were down by 18%, and this was attributed to “lower-than-expected feed consumption, in combination with continued biological issues and connected water quality issues, were the main reasons for reduced volumes.”

The report also stated that in Scotland “biological and financial performance” at Mowi’s farms was “negatively impacted by severe gill health issues in the wake of El Niño and all-time high seawater temperatures”. The poor gill health was attributed to "amoebic gill disease and jellyfish".

But it was not only the heat that was the problem. The October storms had an impact by preventing routine treatment of amoebic gill disease.

READ MORE: Scottish salmon: What dead fish I saw tells us about sector

The report noted that the rising sea temperatures and changing environmental conditions call for "more robust salmon and a shorter production cycle in sea in order to, amongst other things, avoid a second summer and autumn in sea."

Ben Hadfield, COO of Mowi Scotland said: “The much-discussed rise in sea temperatures which brought about a harmful jellyfish species not normally present on Scotland’s west coast had resulted in elevated mortality of small fish. To overcome the wide-ranging challenges that climate change brings, Mowi Scotland has announced its post-smolt plan that reduces time at sea during summer months, as well as the development of a bespoke salmon egg and broodstock facility that will ensure our salmon stock is most adaptable to the local, natural environment.”

Mowi CEO Ivan Vindheim added: “Biology improved towards the end of the quarter and year for Mowi Scotland. Lower seawater temperatures and better water quality which has continued into the new year and our mortality levels and production rates are now back to normal in Scotland which should pave the way for improved biological and financial metrics in the coming months.”

Scotland's three farms with the worst mortality levels in 2023 – Seaforth, Gravir and Grey Horse Channel - are all Aquaculture Stewardship Council certified and on the Western Isles. Between them they had over 1.7 million deaths.  The fifth worst mortality event, Geasgill, was one the Herald visited in August 2023 – witnessing boats removing large quantities of dead fish from pens.

READ MORE: Why tiny jellyfish are such a big threat to salmon farming

The Herald: Geasgill salmon farmGeasgill salmon farm (Image: Scamon Scotland)


Though much blame is put on issues at sea, the industry is clearly also struggling at a freshwater level. The scale of the loss at Mowi's Inchmore hatchery makes it the most deadly salmon farm in Scotland since reports began in 2015, having recorded a total of over 4.5 million.

The Fish Health Inspectorate report listed the causes behind the mortalities as "poor genetics" and "event mortality". 

Rachel Mulrenan, Scotland director at Wildfish, said: "These latest figures cement an undeniable truth – mortalities on salmon farms are rising, and the Scottish salmon farming industry seems unable to stop this trend. High mortality on salmon farms reflects an environmental disaster, as well as being an animal welfare scandal."

Anti-salmon farming activist, Don Staniford of Scamon Scotland, said: “It’s only a matter of time before banks pull the plug on the welfare nightmare that is Scottish salmon. A lethal industry riddled with 50% mortalities - from hatch to 'catch' - is ethically bankrupt. 2023 will be looked back on as the year when Scottish salmon died.”

The Herald: Anti salmon farm activist Don StanifordAnti salmon farm activist Don Staniford (Image: Vicky Allan)

Highlands and Islands MSP Ariane Burgess said: “Yet again, the latest salmon farm mortality figures are higher than the year before.

“17.4 million salmon died prematurely in fish farms last year. That means 17.4 million farmed fish could not be sold as food. That is an outrageous waste of life, not to mention the waste of money, marine space, and energy that it takes to farm fish. 

“The Rural Economy Parliamentary Committee recommended that no expansion should be permitted at sites with high levels of mortality. 

“Yet the industry continues to expand. It’s past time to get this under control. Last January I signed a letter to the Cabinet Secretary for Rural Affairs, supporting calls for a moratorium on industry expansion until the fish death rate is brought under control. 

“This year I’m repeating that call.”

Tavish Scott, chief executive of Salmon Scotland said: “Scottish salmon is a global success story which is frequently voted the best in the world. As well as providing vital jobs and wealth for the Scottish economy it is integral to Scotland’s identity at home and abroad.

“While consumer demand for nutritious salmon continues to grow, these figures confirm what member companies have been saying: that record breaking seawater temperatures and challenging environmental conditions have made it a really tough year for production in many parts of the world.

“We all recognise the impact climate change will have on farming operations globally and through continuous improvement we will continue to produce healthy, low-carbon salmon for decades to come.”