When you pick up a pack of Scottish salmon in a supermarket or fishmonger, most people don’t realise that the fish they are buying is farmed. While it is possible to buy wild salmon caught elsewhere in the world, all salmon from within the UK is farmed (and there is no longer a requirement for it to be labelled as such). Salmon farming began at a small scale with crofters raising salmon in sea pens in the 1960s, but has grown into a massive commercial sector with an estimated 75 million fish raised in over 200 farms across Scotland. Where salmon was once a luxury product, it is now incredibly popular with an astounding 1 million meals containing it eaten every day in the UK. But what is the impact of this consumption?
What is a salmon farm?
Salmon are raised in hatcheries before progressing to land based tanks or freshwater lakes until they are old enough to move to what is known as an open-net farm. Here the salmon are raised in a large netted area or pen situated within lakes or coastal waters where water freely flows between the farm and the surrounding water.
Salmon usually live in these farms for around 18-24 months until they reach the correct size for harvesting, and there can be several million fish in a single cage and a number of these cages in a single location.
Who owns the farms?
A common misconception is that the companies producing this salmon – often with local sounding names such as Loch Duart, Wester Ross Salmon and Scottish Sea Farms – are Scottish companies. But this is sadly no longer the case since consolidation began alongside expansion of the industry in the 1990s. A majority of the industry is owned by just six corporations, all of whom are based abroad and the last independent farm was bought by Norwegian giant Mowi a few years ago. Ailsa McLellan, who lives near this farm saw the impact of this move on local employment; “The biggest change has been a drive towards automation with the associated loss of jobs.” When looking at employment in the salmon farming industry, there is evidence that other factors have not been taken into account in these figures, including the related loss of employment in other fields.
Salmon feed
A key challenge of fish farming is what the fish are fed on. Research suggests that 460,000 tonnes of wild fish (mostly herring, anchovies and sardines) are caught every year to be fed to farmed salmon in Scotland, and it takes significantly more than a kilo of wild fish to produce one kilo of salmon. Campaigners suggest that we should instead be eating a portion of this wild caught fish as a much more efficient way to gain the nutrients that oily fish offer. Attempts to reduce the amount of wild fish used in feed have in turn seen an increase in feed from sources like soya and palm oil, which come with other environmental impacts such as deforestation.
Disease and death
The crowded nature of fish in the farms makes them susceptible to outbreaks of sea lice, a parasite that feeds on the skin and the blood of the salmon, sometimes even causing death to the fish; “Infestation by more than ten or so lice usually has fatal consequences for the wild fish – they are eaten alive,” Andrew Graham-Stewart from WildFish explains. In addition, there is growing evidence that the presence of lice in farmed populations is also resulting in increased rates of sea lice among wild populations. Andrew continues; “The sea lice larvae disperse from the open cages into the wider coastal environment where they latch onto any passing juvenile wild salmon or sea trout.”
Farms are required to record the number of sea lice, but conservation organisations have expressed concern about the reliability and accuracy of these self-reported numbers and the lack of action taken against farms who exceed the limits. There is also concern that the lice appear to be building resistance to the chemical treatments used to treat infestations and that these chemicals have impacts on the wider ecosystem. “There is extensive use of lethal chemicals by the industry, which are released or dumped into the sea after a treatment operation,” Andrew Graham-Stewart explains.
In 2023, the industry reported a 27.7% mortality rate (with some farms reporting over 50%), and while in 2024 there was a reduction in this rate, this still resulted in a 17.7% mortality rate including a single farm losing over a million fish. While some of these mortalities are from lice and disease, rising sea temperatures are also having an impact, raising questions about the long term resilience of the industry in Scotland to climate change.
Local ecosystem
In a salmon farm, the faeces – along with the uneaten fish food – can cause significant damage to the surrounding environment, including algae blooms caused by increased levels of nutrients in the local ecosystem. Escapees from farms can also impact on wild populations by spreading disease, competing for food and breeding with wild populations, with more than 200,000 salmon escaping in 2020 alone.
Ailsa McLellan has lived beside Loch Broom for 23 years, home to a Mowi farm, and has seen the impact on the location. “The most tangible impacts are the amount of litter that has washed up on the shores, polystyrene, rope, etc.,” she explains; “Like any industrial set up the site is very noisy, with generators and compressors running to oxygenate the fish in the summer, and all-night lighting to manipulate fish maturity.”
Certification
The two key certification schemes for salmon are Soil Association Organic and RSPCA Assured.
RSPCA Assured sets limits on stocking density and handling, in 2020, over two thirds of Scottish salmon farms were RSPCA certified demonstrating that certified farms still suffer from the aforementioned issues. The scheme has come under a lot of criticism from organisations such as Wild Farmed who have voiced concerns about the scheme being greenwashing.
The first organic standard for salmon was developed by the Soil Association in 2006, and there are currently 14 seawater sites in receipt of organic certification. The standards include restrictions on feed – organically certified, GMO free and fish meal and oil produced from aquaculture trimmings where possible – a lower stocking density, and mortality rates above certain levels to be reported/investigated.
However, the basic farming method remains the same, with the fish being raised in open-net farms, and certain chemical treatments still being permitted to control parasites. At the start of 2024, more than 30 organisations signed an open letter to the Soil Association asking them to remove their certification from open-net salmon and trout farms citing issues such as high mortality rate, permitted chemical use and the use of cleaner fish.
The Soil Association have acknowledged that there is work to be done: “The big question we’re asking now is whether our standards are enough to address the increasingly alarming concerns being raised about the long-term sustainability and viability of salmon farming in Scotland,” Sarah Compson from the Soil Association standards team wrote in a recent blog. They are in the middle of reviewing their standards and considering how to recognise and regulate the wider environmental impacts that reach beyond these farms, but it remains to be seen what the outcome of this process will be.
Alternatives
If farmed salmon is off the menu, what should we eat instead? The Off The Table campaign encourages chefs and restaurants to stop serving farmed salmon. Jan Wilson from the Michelin starred Wilsons in Bristol explains why they don’t serve salmon; “When we were shown the condition of what the fish were living in and how deformed they were, it was pretty disgusting.” The restaurant instead chooses to serve fish like trout or their own cured mackerel.
There are some good alternatives to be had, including sardines, British shellfish and Cornish hake. And if you are going to eat salmon, make it an occasional treat and look for wild-caught salmon through a traceable supply chain offered by places like Sole of Discretion.
This feature is part of our WL Sustainable Food Series, by Steph Wetherell, which includes guides on fruit, veg, bread, meat, and more.
You are so right. Having watched films like Seaspiracy one gets up close and personal with these lovely sentient animals so badly treated. Just seen as a commodity with a shocking death rate, that’s before they are all killed for people to eat. The growing of alternative foods to rear them like soya or palm oil come with their own problems. As you also mention the enormous amount of wild fish that are dragged out of the sea as feed, makes the whole industry suspect, saying nothing about choosing which shade of pink you want your Salmon to be or the pollution caused by their excrement or uneaten feed below the nets they are kept in? Good article to make one think.
Very informative, especially the information regarding industry owners which I didn’t know. Thanks for writing.