Video monitoring of the River Neidenelva salmon and sea-trout migrations in 2006-2011

An underwater video monitoring study for counting adult salmon and sea-trout numbers was conducted in 2006-2011 in the Skoltefossen rapids at the River Neidenelva. The main aim of the study was to evaluate the effectivity of the Skoltefossen fish ladder and the significance of natural migration routes (straight through the waterfall) for salmon migration.

The fish ladder was found as an important migration route for small sized salmon (one-sea-winter, 1SW) and sea-trout, and annually c. 2000-4400 salmon and c. 400-700 sea-trout individuals ascended via the fish ladder. Larger salmon individuals (multi-sea-winter, MSW) were found to ascend more frequently straight through the waterfall itself, close to the southern shoreline of the Skoltefossen rapid. Changes in discharge was observed to affect the migration activity of salmon at Skoltefossen, high discharge peaks caused significant migration depressions in both the fish ladder and at waterfall itself.

Overall, the river stretch below the Skoltefossen waterfall is one of the key areas regarding the management of the River Neidenelva salmon populations. Alternative management measures for enhancing the salmon production are presented.