11. The farming of Atlantic salmon is based on a method of marine culture first developed in Norway. In Scotland, salmon culture is dominated by multinational corporations and production levels there rose from near zero in the early 1970s to 64,000 tonnes in 1994. In that year there were 119 salmon-producing companies in Scotland operating on 262 sites and employing over 1,200 staff; the ova and smolt industry comprised 68 companies, employing almost 400 staff on 147 sites and produced over 23 million smolts in 1994. In Europe, and indeed, the world, the largest producer is Norway with an output in 1994 of 209,000 tonnes. Other production areas in Europe are the west coast of Ireland, the Faroe Islands and, to a small extent, France and Spain. As production levels have increased so the service industries have become equipped to provide more sophisticated fish feeds, farm equipment, disease treatments, transport, processing facilities and quality-control procedures.
12. There are two distinct phases to salmon farming. First, the freshwater phase which embraces the spawning cycle of egg production and hatching and the feeding of fry until the fish turn into smolts. Large fish farming companies may produce their own smolts but many will be supplied by specialist smolt producers. In the second phase, these smolts, now physiologically adapted to a life in sea water, develop further in the sea. Growth is rapid in this phase and a proportion complete growth to a point where reproduction is possible in one year. These fish are known as grilse. Fish that grow through two or more winters are called salmon. Grilse are usually separated from the rest of the population for slaughter. This is done by grading after 12-18 months at sea and most of the remaining salmon are kept for up to a further year. Selected adult fish will be retained as broodstock.
13. Severe weather places strong constraints on what can be done at sea. Sites are usually chosen to minimise exposure to rough weather conditions whilst providing an adequate flux of clean water. Other natural hazards (e.g. predators) have to be considered and the farms themselves should not have an adverse impact on the environment (see paragraph 16).