When news leaked that two salmon farms on the Isle of Harris in the Outer Hebrides had lost more than one million fish in mass die-offs over the course of a year and a half because of rising sea temperatures, for critics it was yet another example of the industry’s poor welfare and environmental record.
Salmon farming has been under the intense glare of media publicity for decades. The charge sheet includes allowing sea lice and other diseases to proliferate among farmed fish and spread to their wild cousins; the overuse of antibiotics and other chemicals that impact Scotland’s delicate marine ecology; and even the shooting of seals that are accused of pilfering the salmon as tasty treats.
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Some marine conservationists say that, over the years, salmon farming has improved. Yet rising sea temperatures, which produce blooms of micro-jellyfish and plankton that sting and block gills and bring about the onset of amoebic gill disease, are completely outside of any company’s control. As climate change continues to ramp up, the mass mortalities are a dark omen for the industry’s future.
These large-scale die-offs appear to be becoming more frequent. In November 2022, Fishfarmingexpert reported that 2.8 million individual salmon died in September of that year, amounting to nearly 5% of all the fish farmed in Scotland and the worst month for deaths since records began in 2018. Another report found that 10 Scottish salmon farms had suffered 50% mortality rates in 2023, with four of them alone losing nearly two million fish in total. While salmon farming has weathered many storms, could climate change be the wolf that blows the house down?
Learning from the past?
Fish farming has a long and rich history. The Chinese were keeping carp in ponds more than 3,000 years ago, and the Romans were cultivating oysters and fish in Mediterranean lagoons some 500 years later. By the 1200s, we were farming mussels in Britain, while salmon farming began in the 1960s but only took off as a major industry two decades later.
“Back then, it did a lot of things wrong,” says Dawn Purchase, aquaculture programme manager for the Marine Conservation Society (MCS). “It used a lot of antibiotics, and it was a steep learning curve in terms of feed use, management and welfare. It got itself a bad reputation as an industry, which was well deserved.” But a lot has changed since then, Purchase argues, and the MCS now rates organic farmed salmon as a “Good Choice” in its well-renowned Good Fish Guide.
Salmon farmed inorganically only rates as “Okay”, and both fare badly for their impact on the environment. Salmon farming is now a massive industry estimated to be worth around £766 million to the Scottish economy every year and is the UK’s biggest food export. In 2023, Scottish fish farms produced more than 150,000 tonnes of salmon, enough for every person in the country to eat more than 2kg.
It can be argued that, globally, aquaculture is critical to human food security. “Aquaculture has to be part of our future if we are to carry on eating fish,” says Purchase. “Wild-catch fisheries are either over exploited or at maximum capacity, and our ability to produce terrestrial protein will be limited as land is lost to development.”
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Off the menu
Before farming became such big business, there was a time when eating salmon was a luxury, but today you can pick up a couple of fillets weighing nearly 500g, with both environmental and welfare accreditation, for less than £5. It is far from being the most expensive protein product in the shops and offers a substantially lower carbon footprint than beef, for example. But is its ubiquity itself a problem? A number of chefs and restaurants have turned against farmed salmon, partly because of the quality of the product itself and partly because of environmental or welfare concerns.
A campaign website, Off the table – coordinated by independent charity WildFish – lists more than 200 restaurants, cafés, chefs, fishmongers and food writers who won’t serve or sell farmed Atlantic salmon. Their numbers include the Science Museums in both London and Manchester, all the Tate galleries and 60 pubs owned by the brewer Butcombe.
And then there’s the health aspect. Fish – any fish, but especially oily fish such as salmon – is regarded as being better in our diet than red meat and chicken. Salmon is rich in omega-3 fatty acids, which play a critical role in maintaining both heart and mental health, and even your metabolism and therefore your weight. A 200g serving of farmed Atlantic salmon contains your weekly omega-3 requirements. But then there are the contaminants. Studies have discovered high levels of dioxins, polychlorinated biphenyls (PCBs) and organochlorine pesticides in farmed salmon, which could be a risk to human health.
Scientists, for example, reported in 2005 that carcinogenic chemicals occurred at higher rates in European farmed salmon than those from other parts of the world and would pose “elevated cancer and non-cancer health risks when consumed at modest rates”.
Salmon Scotland, which represents all of the country’s salmon-farm companies, points out that levels of dioxins and PCBs are well below the thresholds set by international health watchdogs. “Scottish salmon farmers only source the highest quality fishmeal and fish oils, and are increasing the use of alternatives to marine ingredients that further reduces the risk of contaminants,” says head of technical Dr Iain Berrill.
A different ball game
Welfare concerns have been at the top of the list of issues surrounding salmon farming; sea lice infect farmed salmon to a greater extent than wild fish, and there are other diseases known to proliferate when thousands of salmon are contained in a sea pen. High mortality rates caused by micro-jellyfish blooms, however, are a more recent concern.
Salmon Scotland argues that published figures for sea lice on salmon farms are at their lowest levels since public reporting began, and that the mortality events of 2022 and 2023 were not repeated in 2024. It says a huge amount of work is going into understanding the movements of micro-jellyfish, and combined with lower sea temperatures this year, “monthly survival rates have been some of the highest in five years”.
Companies are also working on growing smolts – the early stages of a salmon’s life cycle – to a larger size before they are put into sea pens. “These ‘one-summer salmon’ will reduce the amount of time salmon spend at sea before reaching harvest weight, which will maximise fish health and welfare, survival and environmental benefits,” Berrell says.
There’s growing scientific knowledge about fish – their capacity to suffer pain and their psychological needs are more complex than was imagined when salmon farming first began. “Fish welfare has become a whole different ball game because we’re starting to understand more about their mental needs,” says Sean Black, the RSPCA’s senior scientific officer for aquaculture.
Monitoring welfare
Under the RSPCA’s certification scheme for salmon farming – RSPCA Assured – its welfare policy has 1,200 individual standards covering everything from health and husbandry practices and treatment of diseases to stocking densities and slaughter guidelines. Farms are inspected once a year, though they’re given advance warning of a visit. According to the RSPCA, over 90% of farmed salmon is produced under the scheme.
That doesn’t mean that problems don’t occur. Last year, the conservation charity WildFish obtained footage of a fish farm in Invasion Bay, Scotland, which showed serious welfare issues, including fish missing eyes and chunks of flesh.
At the same time, WildFish released a report claiming the three leading certification schemes – not just RSPCA Assured, but the Aquaculture Stewardship Council (ASC) and the Soil Association’s organic standards, too – had demonstrably failed to improve the environmental and welfare performances of open-net salmon farming.
“The RSPCA Assured standard sets no maximum mortality threshold limits on certified farms,” the report says. “Consequently, Scottish salmon farms reporting as many as 74% of its fish dying in a single month can continue to sell the remaining fish as RSPCA Assured-certified ‘high welfare’ farmed salmon.”
The report highlights numerous instances of mass mortalities at individual salmon farms in which hundreds of thousands of fish died, yet resulted in no action from the certification schemes. RSPCA Assured does not contest any of the details in the report but said in a statement (published in an appendix to the report) that these incidents were down to environmental conditions outside of the farms’ control.
“It is sadly a reality of salmon farming that from time to time there may be external environmental factors which can change rapidly beyond anyone’s control, such as changes in weather, climate patterns and tidal conditions, which can result in fish mortalities,” the response reads.
More than half of all farmed Scottish salmon is exported, with France the single biggest market, and exports are continuing to increase; the French market nearly doubled in the first half of 2024. Brexit has provided further challenges, with all consignments requiring physical paperwork when the industry says they should be moving to a digital system.
Future of farming
Some people argue that a move towards close-containment – either at land or sea – is inevitable in the future to mitigate against environmental impacts, but proposals for a land-based farm in Grimsby is mired in a court battle after an animal welfare group was granted a judicial review of the plans.
In any case, are these systems really any better – if not potentially worse? Salmon Scotland argues that because of the investment in infrastructure that would be required, stocking densities would be higher than they are at sea. This was also highlighted by Animal Equality, the NGO that is opposing the Grimsby scheme.
Dawn Purchase doesn’t expect to see the Scottish salmon farming industry disappearing any time soon, but she says it does need to tackle the sustainability of the fish meal and fish oils fed to the salmon. Though the industry has successfully integrated the use of byproducts – so-called trimmings – from the fish processing industry into fish meal, she says it doesn’t currently go far enough.
“We would like to see all the fish used for meal and oil sustainably managed,” she says. “At the moment, they are [only] responsibly managed, but responsible management will not ensure the long-term viability of these fisheries and secure their role in oceanic ecosystems.”
Scottish salmon farmers argue they receive greater scrutiny of their welfare record and environmental impact than other forms of animal husbandry. On the other hand, taking place as it does beneath the waters of Scotland’s bays and sea lochs, it is also, by its nature, more hidden from view, and there is little doubt that as long as there is an industry of such magnitude, exposés – such as that into the mass mortalities in the Outer Hebrides – will continue to hit the headlines.
Main image: Fish farm in Loch Awe, Arygll and Bute/Getty
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