Migratory and route-seeking behaviour of ascending Atlantic salmon in the regulated River Tuloma

Fifty-two radio-tagged salmon were released below and above the Lower Tuloma hydroelectric plant at the outlet of the River Tuloma, Kola Peninsula. Their route seeking behaviour between the spillway, tailrace and fish pass was monitored below the dam. Fish released above the dam were tracked with emphasis on studying the migration speed, spatial distribution, and fishing mortality in the ca. 50-km long Lower Tuloma reservoir. Fish that reached the outlet of the main spawning tributary, River Petcha, at the upper end of the reservoir, were monitored for their behaviour when confronted with a nearly impassable waterfall and an adjacent fish pass. In general, salmon were observed to be rather reluctant to enter both fish passes, occasionally even backing out after entering the pass. Fish preferred to seek their way in stronger current, i.e., the tailrace and spillway discharges below the Lower Tuloma dam, and the natural channel with waterfall at the mouth of the River Petcha. Nineteen fish reached the River Petcha, the mean duration of the migration being 39 h ( range: 23-70 h). Fishing mortality appeared to be reasonably high as 20 radiotags (39%) were returned by fishermen. In the scope of the salmon restoration project, the results give ground for consideration of possible improvements in the efficiency of the existing fish passes.