IMPORTANCE OF ONTOGENIC HABITAT SHIFTS TO JUVENILE OUTPUT AND LIFE-HISTORY OF ATLANTIC SALMON IN A LARGE SUB-ARCTIC RIVER - AN APPROACH BASED ON ANALYSIS OF SCALE CHARACTERISTICS

Juvenile and adult scale characteristics were used to compare two juve nile groups of Atlantic salmon in a large subarctic river in northern Scandinavia: individuals that have migrated from the main stem into sm all tributaries and those which remain in the main stem. Body size and scale measurements indicated enhanced growth in migratory parr as com pared to their resident main stem counterparts. Analysis of adult salm on scale characteristics using maximum likelihood estimators revealed that 20% of the adults had been in the tributaries before the end of t heir second year of life, and more than 30% more had moved into the tr ibutaries 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. I n addition, when smell ages and ages at maturity were compared, older female smelts often resulted in smaller spawners and younger smelts, l arger spawners. Small female spawners were more likely to survive to b ecome repeat spawners. (C) 1997 The Fisheries Society of the British I sles.