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 downstream migration of salmon parr were studied in two small tributaries of the large subarctic River Teno, northern Finland. The tributaries are not spawning areas for salmon, but juveniles enter them from the main stem of the river. The tributaries produced notable numbers of smelt, 300-700 a year, equivalent 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 year, was also detected, although the number of downstream migrants usually exceeded that of the upstream migrants. Most of the migrants in both directions were 1 + or 2 + ages, the older parr migrating earlier in the summer than the younger ones. Environmental factors, water temperature and water level, 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 habitats used by salmon during their life-cycle is emphasized. (C) 1998 Elsevier Science B.V. All rights reserved.