Densities of the juvenile Atlantic salmon (Salmo salar L.) in the subarctic Teno River watercourse, northern Finland

Changes in juvenile wild Atlantic salmon densities in the subarctic Teno River watercourse, northern Finland, have been studied and recorded since 1979 at 57 sites representing different biotypes. Densities were very low in the first few years, after which there was substantial variation. The lowest and highest mean densities of fry at a site in the Teno River were 0.2 and 135 fish per 100 m2, respectively; respective values for parr were 0.9 and 50 fish per 100 m2. The lowest and highest values in the Utsjoki, a river in northern Finland, were 0.1 and 136 fish per 100 m2 for fry and 2.3 and 71 fish per 100 m2 for parr. The highest densities of fry and parr ever recorded in the Teno River were 424 and 106 fish per 100 m2, respectively. The annual densities of fry and parr were interdependent only in a few cases. Different densities in some other northern rivers relative to those in the Teno watercourse might reflect the different fishing culture, but also the stocking of juveniles can increase densities, thus, hampering the interpretation. The densities of the juvenile salmon fluctuated within sampling sites and between years, primarily as a result of fluctuations in the spawning stock, which is strongly affected by changes in the in-river fishing effort. Fluctuations in the juvenile salmon densities are obviously not affected by predation as the proportion of other species in the juvenile salmon's habitat is low. Parr densities in the Teno River catchment are on average clearly lower than those found in rivers which lack a diverse net fishery. Several fishing regulations set after the year 1984 have functioned only partly. Juvenile densities have not crashed despite the increased in-river exploitation by rod and reel anglers but densities of the juvenile salmon have not either increased.