FREQUENCY OF OCCURRENCE OF REARED ATLANTIC SALMON IN SCOTTISH SALMON FISHERIES

Marine salmon farming in Scotland is restricted to sheltered inshore l ocations in four main geographical areas - the western coast, the West ern Isles, the Orkney Islands, and the Shetland Islands. Rivers suppor ting runs of wild salmon are present on the western, northern, and eas tern coasts of mainland Scotland and in the Western Isles. Since 1981, coastal fisheries and rivers have been monitored using a variety of m ethods to detect the presence of reared salmon, including those that h ave escaped from sea-cages. On the east coast and in the eastern river s, reared salmon have not been detectable or have been detected only a t low frequencies in catches - even in years when they were frequent a mong western coastal catches and when the progeny of females containin g synthetic flesh colourant were widespread and sometimes frequent in western rivers. The eastern Scottish rivers are one of the principal w orld sources of early-running salmon and therefore include an importan t component of the phenotypic (and probably genetic) diversity associa ted with Atlantic salmon. In a European context, the eastern Scottish rivers constitute one of the greatest continuous units of wild salmon production that can be shown to have remained substantially free of es caped farmed salmon. (C) 1997 International Council for the Exploratio n of the Sea.