The hidden harm from salmon farming

In addition to parasites, pathogens, chemical residues, and other treatments can persist in cages. Fallow sites are expected to undergo complete removal of fish and nets to limit pathogen carryover. Campaigners, however, say the Aird site “continued functioning as a reservoir of disease and flesh-eating lice.”

Unsustainable

Abigail Penny, executive director of Animal Equality UK, said: “Just like farmed salmon, vast numbers of wild fish become trapped inside these underwater cages, exposing them to the same harsh and harmful practices. 

“They too face exposure to parasitic sea lice, disease, predation, and toxic chemicals, yet the number of wild fish dying in these cages remains undisclosed. Because of reporting loopholes, the true scale of death on Scottish salmon farms is still unknown. 

“The industry does not reveal how many farmed fish are culled, die in transport, or perish within the first six weeks of entering sea cages. The public has a right to know what is happening beneath the water.” 

She added: “Wild fish already suffer in unimaginable numbers at the hands of the salmon farming industry – trawled from the sea to become feed for carnivorous salmon, or taken as ‘cleanerfish’ to eat the lice off of the farmed fish. There is so much hidden harm within salmon farming, it is fundamentally unsustainable.”

Studies show that wild fish routinely enter salmon farms around the world, sometimes by the tens or hundreds of thousands.

Dwindling

In Canada, ‘incidental catch’ – wild fish from within the fish farms that are caught during harvest, movement between or within facilities, or removed from the nets – are publicly reported by the salmon industry, although no data is provided for the wild fish trapped in cages throughout the entire farming cycle. 

According to Canadian NGO Watershed Watch Salmon Society, wild fish entering salmon farms may be negatively impacted in a number of ways, including being eaten by farm salmon, infected with pathogens and/or parasites from farm fish and contaminated with pesticides, medications and other toxins through eating fish farm feed.

In late 2024, the Scottish Parliament’s Rural Affairs and Islands Committee conducted a nine-month inquiry into the Scottish salmon farming industry, following a similar inquiry in 2018, prompted due to environmental concerns posed by the industry. 

The committee referenced concerns about the industry’s potential impact on dwindling wild salmon and trout populations, due to the possible spread of deadly pathogens or parasites. This latest footage suggests wild aquatic animal species may be affected by the industry in other ways that are currently under-researched.

Concerning

The Ecologist contacted Tesco, Scottish Sea Farms, Cooke Aquaculture, Bakkafrost and Mowi for comment. A spokesperson for Cooke Aquaculture said: “In regards to your enquiry, Salmon Scotland will be responding on behalf of the sector.”

The spokesperson from Salmon Scotland stated: “Scottish salmon farmers operate to some of the highest health, welfare, and environmental standards in the world, with sea lice levels now among the lowest on record.

“A small number of wild fish may occasionally pass through farms in the open sea, but there is no evidence this affects the welfare of either farmed or wild fish, and using footage from a single site to make sweeping claims about an entire sector is misleading.

“Farms must meet strict fallow and environmental standards, and where issues arise they are investigated and addressed through a robust regulatory system.”

A Tesco spokesperson said: “As soon as we were made aware of this concerning footage, we immediately suspended the farm to carry out an investigation with our supplier. Any failure to meet our high welfare standards is unacceptable and we take swift action where necessary.”

This Author

Brendan Montague is an editor of The Ecologist.