Frequency of occurrence of reared Atlantic salmon in Scottish salmon fisheries

Abstract

Marine salmon farming in Scotland is restricted to sheltered inshore locations in four main geographical areas — the western coast, the Western Isles, the Orkney Islands, and the Shetland Islands. Rivers supporting runs of wild salmon are present on the western, northern, and eastern coasts of mainland Scotland and in the Western Isles. Since 1981, coastal fisheries and rivers have been monitored using a variety of methods to detect the presence of reared salmon, including those that have escaped from sea-cages. On the east coast and in the eastern rivers, reared salmon have not been detectable or have been detected only at low frequencies in catches — even in years when they were frequent among western coastal catches and when the progeny of females containing synthetic flesh colourant were widespread and sometimes frequent in western rivers. The eastern Scottish rivers are one of the principal world sources of early-running salmon and therefore include an important component of the phenotypic (and probably genetic) diversity associated 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 escaped farmed salmon.