A two-generation experiment comparing the fitness and life history traits of native, ranched, non-native, farmed, and hybrid Atlantic salmon under natural conditions

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In recent years there has been widespread stocking of Atlantic salmon rivers using juvenile salmon derived from non-native broodstock. Stocking has also been undertaken using surplus juveniles from the Atlantic salmon farming industry. In addition, farmed salmon enter rivers due to escapes from smolt rearing units and from sea cages. The increase of Atlantic salmon Salmo salar culture has meant that large-scale escapes are now inevitable and frequent occurrences. For example, farmed salmon escapes in Scotland in 2000 totalled 491,980 fish (Intrafish 2000), five times the total wild catch, with escapees potentially outnumbering wild adult salmon returning to many Scottish rivers. In Norway, where escapes generally exceed one million fish per year, which is more than four times the natural spawning runs, overall about one-third of salmon entering rivers are escaped fish with over 80% in some rivers (NASCO 2000).