Migration of juvenile Atlantic salmon Salmo salar in small tributaries of the subarctic River Teno, northern Finland

Downstream migration of Atlantic salmon Salmo salar smelt and up and downst ream migration of salmon parr were studied in two small tributaries of the large subarctic River Teno, northern Finland. The tributaries are not spawn ing areas for salmon, but juveniles enter them from the main stem of the ri ver. The tributaries produced notable numbers of smelt, 300-700 a year, equ ivalent to approximately 70 smelt per km of river (1.0-1.2 smelt per 100 m( 2)). Substantial upstream migration of salmon parr, 100-200 specimens a yea r, was also detected, although the number of downstream migrants usually ex ceeded that of the upstream migrants. Most of the migrants in both directio ns were 1 + or 2 + ages, the older parr migrating earlier in the summer tha n the younger ones. Environmental factors, water temperature and water leve l, had some influence on the migration of both parr and smelt. Salmon parr show active exploratory behaviour in addition to the traditionally assumed sedentary, territorial behaviour. The importance of identifying all habitat s used by salmon during their life-cycle is emphasized. (C) 1998 Elsevier S cience B.V. All rights reserved.