Fish farms, often accused of causing environmental damage and threatening wild salmon stocks, could be established on dry land under plans backed by the SNP.
The industry has come under the spotlight again in recent weeks after the release of Seaspiracy, a highly critical Netflix documentary made by the team behind the award-winning 2014 film Cowspiracy.
It claimed that the sector generated the same amount of organic waste as the entire population of Scotland, and produced secret footage from a farm in the Highlands showing thousands of dead salmon piled in a tanker.
In response Scottish salmon farmers rejected suggestions that the industry is guilty of animal welfare abuses but pressure has been growing on politicians to overhaul the sector.
Closed containment fish farming is an approach tried elsewhere, including Iceland, Denmark and Nova Scotia, and projects are planned in several other countries, including Sweden and Japan.
Supporters of the approach say using water-recirculating technology to grow salmon on land-based farms has steadily improved in recent years, drawing out waste that can be turned into fertiliser instead of being dumped in the oceans.
Andrew Graham-Stewart, director of Salmon and Trout Conservation Scotland, whose patron is Prince Charles, welcomed the SNP’s election manifesto pledge to explore the potential for a similar approach in Scotland.
Arguing that it may reflect a realisation that Scotland is being left behind, he said: “We support closed containment salmon farming as it does resolve many of the environmental issues associated with conventional open-cage salmon farming. It eliminates interactions with and impacts on wild salmon and sea trout, especially the spread of parasitic sea lice to infest the wild fish.
“Land-based farming means that fish excrement and lethal chemicals are not discharged into the marine environment to the serious detriment of coastal ecosystems and fragile marine habitats.”
But he said closed containment did not resolve concerns about fish welfare and the unsustainable use of wild-caught fish in feed for farmed fish. He also warned that areas at present home to sea-based salmon farms could lose out, with land-based closed containment located “closer to markets rather than in the remote Highlands and Islands”.
Hamish Macdonell, director of strategic engagement at the Scottish Salmon Producers Organisation, said: “Scotland’s salmon producers do use closed containment systems; they have already invested hundreds of millions in technologically advanced land-based systems to grow salmon through their freshwater cycle until they become smolts so they are happy to keep developing this option.
“But using closed containment on land for the full marine phase — growing salmon from smolt to market size — remains commercially unviable. This is partly because of the massive amounts of energy needed to do this.”
He added: “Scottish salmon has a great environmental story to tell with a low carbon footprint and low freshwater use. All of this would be undermined by moving to closed containment on land. Indeed, to grow a salmon in a closed containment facility to an average weight of 5kg would require the equivalent energy as that used by a Scottish family over nine days: it is not a green option nor is it a commercially viable one either.”
Critics point to the experience of some on-land salmon farmers such as Atlantic Sapphire ASA, which reportedly made an operating loss of £33.8 million last year. It operates a 2,400-tonne capacity on-land Atlantic salmon farm in Denmark and a bigger facility in Florida, where it intends to produce 220,000 tonnes annually by 2031.