Growth and Genetic Variation of Atlantic Salmon (Salmo salar) from Different Sections of the River Alta, North Norway

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Abstract
Growth of young Atlantic salmon (Salmo salar) from three different sections of the River Alta was correlated with estimated growth differences among adult salmon caught in corresponding sections of the river. Young salmon grew most quickly each of the three years investigated in the upper section of the river; further downriver, presmolts had a significantly lower growth rate. Growth calculations based on scale samples from adults indicated corresponding river growth patterns from the three sections. Salmon caught in the upper section of the river had significantly lower smolt age (mean 3.92 yr) and better presmolt growth than salmon caught further downriver (mean smolt age in the middle and lower sections was 4.35 and 4.19 yr, respectively). Correlations between growth differences in young and adult salmon suggest that presmolts that have lived their first years in the upper section of the river apparently return there after having been at sea. Genetic analyses of presmolts indicate that local populations exist. Allele frequency differences at three electrophoretically detectable protein loci give independent support for the existence of genetically differentiated local populations within the River Alta.