Movements of adult Atlantic salmon through a reservoir above a hydroelectric dam: Loch Faskally

Movements of adult Atlantic salmon were determined as they migrated through Loch Faskally, a 4-km long hydroelectric reservoir in North-east Scotland. The horizontal and vertical movements of four salmon were monitored for pe riods of 4-7 days using depth-sensing acoustic transmitters in June-July 19 95. Each fish began sustained directed upstream movements within 5.5 h afte r release at swimming speeds of 0.15-0.40 bl s(-1). Three fish reached the head of the loch after 7.25-17 h, but then returned downstream. The four fi sh remained in the upper half of the loch for 15-51 days, making localized movements. Mean depths of fish were 3.7-4.0 m (max 20.7 m). Two fish were r ecorded at significantly shallower depths at night than during the day. Dep arture from the loch coincided with periods of high water flow into the res ervoir. In May-July 1996, 17 radio-tagged salmon entered Loch Faskally and reached the head of the loch in 3 h-5.8 days (mean 39 h). The durations of stay in the loch varied from 3 h 50 min to 67.4 days (mean 10.9 days). Only two radio-tagged salmon left the loch under conditions of high water flow into the loch. (C) 1999 The Fisheries Society of the British Isles.