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Migration of atlantic salmon salmo salar smolts in river orkla of central norway in relation to management of a hydroelectric station


, : Migration of atlantic salmon salmo salar smolts in river orkla of central norway in relation to management of a hydroelectric station. North American Journal of Fisheries Management 6(3): 376-382

The migration pattern of Atlantic salmon (Salmo salar) smolts in River Orkla, central Norway, was studied in 1980 and 1981 before construction of a hydroelectric plant was finished in 1983. Smolts were caught in traps operated from moveable racks fastened to a bridge and lowered by winches. This sampling device worked satisfactorily at a water discharge less than 200 m3/s and a water velocity less than 2.5 m/s. The smolt run started in early May and lasted until about June 10. The migration was initiated by the first peak in water discharge (> 100 m3/s), when the water temperature was 2-3.degree. C. Significantly more smolts migrated when the discharge was increasing, followed by a drop in water temperature, than under the opposite conditions (P < 0.05). The smolts exhibited a predominantly nocturnal migration pattern as 87% were caught between 2200 and 0200 hours. Generally, the salmon smolts followed the main current during the run. River Orkla was to be diverted through a tunnel to turbines for production of hydroelectric power. Mortality of smolts could be reduced if most of the river water were allowed to pass by the tunnel at night during the migration season.

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