Is the growth of salmon farming significant for wild salmon and sea trout 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.