Monitoring Juvenile Atlantic Salmon and Sea Trout in the River Sävarån, Northern Sweden

Abstract

Downstream migrations of Atlantic salmon (Salmo salar) and sea trout (S. trutta) smolts were monitored in the in northern Sweden to evaluate the river’s potential as a national index river for salmonid populations in the Baltic region, and to acquire information for stock conservation plans. A rotary screw trap was installed and operated from 2005 to 2008. Recapture rates of tagged smolts were high (from 8% to 31%), which allowed smolt abundances to be estimated. Between 2,600 and 3,900 salmon and 500–1,500 trout emigrated from the river each year. Genetic analyses made it possible to identify the origin of salmon and trout smolts and to determine whether they originated from the Sävarån stock or from stocks in neighbouring rivers. In 2005 and 2006, most of the salmon were from the Sävarån stock, which previously had been thought to be extinct. By contrast, 58% and 52% of the salmon analysed in 2007 and 2008, respectively, originated from stocks other than Sävarån. The density of salmon and trout 0+ parr (i.e. recruitment success) based on electro-fishing was a poor predictor of smolt abundance 2 to 3 years later. The smolt trap data combined with genetic analyses provided valuable information to develop stock conservation plans.