Since 2012, mass mortality events (MMEs) affecting farmed salmon have become more frequent and severe, leading to the deaths of millions of fish in certain aquafarms, as detailed by a study published in Scientific Reports.

Why does this matter? Fish are a vital source of nutrition for billions of people. Aquaculture is critical to supplying this nutrition and is now the leading source of fish production globally.

The scale of MMEs impacting the aquaculture sector not only threatens global food security but is concerning from an economic and animal welfare perspective. Although the study’s findings are concerning, innovative technology firms have presented solutions to help the aquaculture sector combat the rise of MMEs.

For example, WellFish, an aquaculture diagnostics start-up, provides rapid fish health assessment using blood-based clinical chemistry analysis. Its technology utilises blood biomarkers and artificial intelligence to evaluate fish health, enabling aquaculture operators to enhance the well-being of their stocks and optimise production.

The solution potentially allows salmon aquafarms to reduce the frequency and scale of MMEs through improved monitoring standards. Solutions such as WellFish are crucial aids to the fastest-growing food production system in the world, with salmon consumption increasing three-fold since 1980.

However, mass production fosters an increased risk of mortality – between 2012 and 2022, an estimated 865 million salmon perished in the six major salmon-producing markets. In Scotland, 17 million salmon died last year, the most ever recorded, while 17% of Norwegian-farmed salmon died suddenly in 2023.

The rising number and severity of MMEs in salmon populations are linked to various catalysts. For example, environmental influences, including higher ocean temperatures, compound problems like disease, sea lice, and harmful algae blooms that afflict the industry.

Environmental factors are often not the only drivers – combinations of natural events, human oversight, and unsafe practices create conditions for significant MMEs. For instance, the overuse of antibiotics can lead to bacterial resistance, while thermal delousing may compromise fish health.

If not managed correctly, salmon aquaculture can also affect the surrounding marine ecosystem. Nets that define the pen perimeters may be coated with copper oxide, which can pollute the water. Furthermore, salmon escaping from captivity can interbreed with and weaken the gene pool of the wild population, including endangered species like the wild Atlantic salmon.

Despite the ecological and welfare issues associated with certain forms of salmon aquaculture, simple operational adjustments can mitigate the worst effects. Measures such as reducing the density of salmon in pens can improve fish welfare and reduce the spread of disease and lice – RSPCA standards recommend a target ratio of 15kg of fish per m3.

Other welfare practices include regular cleaning and general maintenance of nets, sea lice shields, and environmental monitoring equipment able to monitor shifts in water temperature or oxygen levels.

The salmon industry could also take pointers from the practices pursued by other aquaculture sectors. Tilabras produce thousands of tonnes of fresh tilapia annually and manage the stock through their entire lifecycle from egg to harvest. Here, the tilapia are fed on locally-produced plant-based feed rather than fishmeal and the stock has ample room to swim in.

The technological and operational solutions now available to the salmon aquaculture industry can improve fish health monitoring, welfare conditions, and disease prevention, working towards a reduction in the frequency and scale of MMEs even as ocean temperatures rise.

Why does this matter? As fish farming operations grow worldwide, and governments simultaneously look to reduce greenhouse gas emissions and target other environmental issues, the aquaculture sector is under pressure to expand sustainably.

The Scottish Salmon Producers Organisation’s (SSPO’s) Sustainability Charter sets out the Scottish salmon industry’s plans to do just this – with 41 specific actions to increase standards in both environmental impact and animal welfare.

From an environmental perspective, alongside targeting net-zero emissions by 2045, the sector – worth £885m to the Scottish economy – will work to use 100% renewable energy, source 100% of fish feed from sustainable sources with full traceability of ingredients, and reach 100% recyclable packaging. Scottish salmon farmers have also committed to improve fish pen structures to prevent escapes, and to work with government and regulators on trialling new technology. This includes innovations to capture waste from marine farms.

In terms of social sustainability, firms will provide sustainable homes in the Highlands for workers to tackle the lack of affordable housing in the region. Electric vehicle charging points will also be installed for communities, and the sector has committed to providing future high-quality jobs through investing in skills and recruitment.

The salmon farming sector in Scotland has not been without its issues. In 2018 an NGO report highlighted concerns over fish welfare in Scottish farms, with environmental campaigners accusing the industry of breaking sea lice, mortality and escape limits. Late last year Mowi was criticised after 700,000 of its salmon died over three months. SSPO put the lower 2019 survival rate figures down to planktonic blooms and increased water temperatures.

Scottish regulators have clamped down on the sector in recent years – though rules were temporarily relaxed earlier in 2020 due to Covid-19. Specific loch-based farms have also been highlighted as environmentally problematic, and a plan to develop a salmon farm in the Wester Ross Marine Protected Area has recently been opposed due to its potential environmental impact.

This has prompted operators to look to new locations, including farms further out to sea. Norskott Havbruk is in discussion with authorities about developing Scotland’s first open ocean fish farm. Meanwhile Loch Long Salmon is looking to establish semi-closed farms in the country, where deep water is pumped into an impermeable bag containing the salmon. To tackle lice, Scottish farmers have been experimenting with sea-lice eating wrasse fish to cut down on medicine use, and University of Edinburgh researchers are also looking to tackle the problem with selective breeding.

Elsewhere, other countries and firms are seeking to improve the sustainability of salmon aquaculture. Canada, for example, is pushing the industry to move away from net pen aquaculture towards alternatives, and semi-closed farms are also being trialled in the country. Norway is building fully electric salmon farms, while also piloting schemes to use facilities’ waste to create biofuels for aviation.

More generally, these initiatives will act to boost a sector that’s already seen as relatively sustainable in the context of global protein producers. Salmon farmers score highly in the Coller FAIRR Protein Index, which ranks all protein producing firms based on ESG factors, with Mowi leading the list.

Source: BBC