Revealing trends in densities of juvenile Atlantic salmon, Salmo salar L.,in the subarctic River Teno using cluster analysis on long-term sampling data

The density of juvenile Atlantic salmon, Salmo salar L., was monitored at 5 7 sites representing different habitats in the River Teno and two of its ma jor tributaries from 1979 to 1995. Cluster analyses were used to combine si tes with similar densities and to study trends in densities within clusters . It was found that management measures have played an important role in ma intaining salmon stocks and there was some evidence of increasing juvenile salmon densities. Parr densities decreased significantly in one cluster con taining 45% of the sites studied in the River Utsjoki, whereas densities in creased significantly in one cluster in the River Teno and in one cluster i n the River Inarijoki containing 38% of the sites in these rivers. Fry dens ities increased significantly in two clusters containing 16% of all the sit es studied in the three rivers. In general, the mean densities in successiv e years in the clusters were independent. The results demonstrate the value of long-term monitoring in ecological investigations.