Downstream migration of Salmo salar and S. trutta smolts in two regulated northern Swedish rivers

The downstream migration of Atlantic salmon and anadromous brown trout smolts was studied in two flow controlled northern Swedish rivers. The annual mean flow in Umeälven and Piteälven is c. 430 m3/s and c. 150 m3/s, respectively. Water power constructions located in the lower parts of these rivers may hinder or kill downstream migrating fish. Naturally produced salmon smolts in these rivers have two alternatives for passage of the water power constructions when they undertake their seasonally timed seaward migration in may-june: a) passing the turbines, or b) pass through the spill-way over the dam. Existing power-stations in Stornorrfors (Umeälven) use Francis turbines while Sikfors (Piteälven) use Kaplan turbines. In spring 2002 and 2003 a total of 90 Atlantic salmon and 56 brown trout two-year old hatchery-reared smolts were radio tagged with internal esophageal, individually coded radio transmitters (ATS). Trout were significantly larger (average length: 23.8 cm) than salmon (19.7 cm) (t-test, p