Salmon Farming

Is the growth of salmon farming significant for wild salmon stocks?

Farmed salmon production in the North Atlantic area has increased dramatically, particularly in Norway, but also on the west coasts of Ireland and the Scottish Highlands.

A number of problems have resulted, which include:

• High concentrations of sea lice, which multiply in the confined conditions of sea rearing cages. As explained earlier, migrating sea trout and salmon smolts can be very vulnerable to attack by these lice. In some rivers, wild stocks have virtually collapsed.
• Escapes of farmed fish, which are known to be able to interbreed with wild fish. Since stocks in individual rivers are locally adapted to optimise their survival, this interbreeding has been shown to reduce the fitness of wild stocks for their local environment.
• Pollution of the water environment, by uneaten food, fish faeces, or medications used to treat farmed salmon in their cages.
• The risk of the spread of disease or parasitic infestation, such as Infectious Salmon Anaemia and Gyrodactylus salaris.

Can anything be done to counter these problems?

Codes of best environmental practice are being developed and improved. These include use of the principle of integrated sea lice control, through co-ordinated fallowing within sea lochs and bays to break the cycle of sea louse survival, followed by co-ordinated treatment to prevent cross infestation. Legislation to enforce these codes is essential. The Scottish Executive set up the 'Tripartite Working Group' in 1999 which involves fish farming and wild fish intersts. A sub-group – Restoration – chaired by the Trust's Director has the remit to conserve and improve wild fish stocks. The Trust's Biologist spends much of his time acting as the sub-group's coordinator of these activities on the west coast of Scotland.

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