Abstract
Scale analysis indicated that two-sea-winter (2SW) Atlantic salmon (Salmo salar) had a greater growth increment during the first year at sea than 1SW of the same smolt year in the Rivers Narcea and Esva, but no differences were found between sea age-classes in the River Cares. Interannual variation in marine growth was synchronized among rivers. Variation among years was greater than variation between sea age-classes, suggesting that marine growth per se does not determine age at maturity. In the River Narcea, 2SW salmon were larger than 1SW at the end of the first marine period, but differences between sea age-groups were not significant in the other two rivers. Some of this variability could be attributed to differences in size at smolting; for two rivers (Esva and Cares), 1SW salmon had been larger as smolts than 2SW salmon. Length increment during the first marine growth period was inversely correlated with smolt size (age-1 smolts); in spite of that compensatory effect, large smolts tended to maintain their size advantage at the time of formation of the first marine annulus, as indicated by positive correlations between smolt size and length at the first sea winter.

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