Movements of adult Atlantic salmon (Salmo salar L.) in relation to hydroelectric schemes in Scotland
The movements of adult Atlantic salmon (Salmo salar L.) were investigated in relation to hydroelectric schemes in Scotland. Salmon were tagged with radio- and acoustic transmitters and released into the River Tummel, Perthshire, and River Conon, Ross-shire, and their subsequent movements recorded. Thirty-nine salmon were monitored in the vicinity of Pitlochry Dam on the R. Tummel. All fish that approached the dam successfully ascended a fish pass located here. Pass efficiency was estimated at 100%. Movements through the fish pass were related to water temperature and ambient light level. The three-dimensional movements of four salmon were recorded as they moved through a hydroelectric reservoir, Loch Faskally. Fish migrated to the head of the reservoir in under 48hours. Gross swim speeds were in the region 0.4 to 0.8mh-1. Swimming depths were similar to mean loch depth. Two fish were recorded at shallower mean depths during the night than during the day. A total of 54 salmon were radio-tagged on the River Conon to determine the effects of a series of hydroelectric obstructions on upstream migration. Fish were either unable or unwilling to pass beyond each of the obstructions: only 20.7% of fish migrated beyond six obstacles, thus reaching their spawning grounds. Salmon were recorded moving through a 2.5km long pipeline into a separate tributary of the river. The muscle activity of three salmon were recorded, using electromyogram (EMG) telemetry, as they ascended Conon Falls fish ladder. The results show that fish are required to make use of anaerobic white muscle in order to ascend the structure. The highest mean levels of activity were recorded when fish were delayed in the ladder overnight. This finding is of great significance when designing new fish passes.