Importance of ontogenetic habitat shifts to juvenile output and life history of Atlantic salmon in a large subarctic river: an approach based on analysis of scale characteristics

Juvenile and adult scale characteristics were used to compare two juvenile groups of Atlantic salmon in a large subarctic river in northern Scandinavia: individuals that have migrated from the main stem into small tributaries and those which remain in the main stem. Body size and scale measurements indicated enhanced growth in migratory parr as compared to their resident main stem counterparts. Analysis of adult salmon scale characteristics using maximum likelihood estimators revealed that 20% of the adults had been in the tributaries before the end of their second year of life, and more than 30% more had moved into the tributaries in the third year. Tributary fish matured at a smaller size and younger age (one-sea-winter salmon) than those rearing in the main stem which included a higher proportion of multi-sea-winter salmon. In addition, when smolt ages and ages at maturity were compared, older female smolts often resulted in smaller spawners and younger smolts, larger spawners. Small female spawners were more likely to survive to become repeat spawners.