Intra and interhabitat migration in junvenile brown trout and Atlantic salmon in restored tributaries of the Vindelriver

Sammanfattning: Several techniques are used to sample juvenile salmonids in lotic environments. Electrofishing is by far the most commonly used method on the Scandinavian peninsula. As restoration of stream habitat is becoming increasingly popular, electrofishing is consequently being used to assess the effects of restoration on juvenile brown trout and Atlantic salmon. Electrofishing requires a number of assumptions regarding the movements of the target species. This study scrutinized a few of those assumptions to find out whether current electrofishing-based monitoring methods are appropriate in restored tributaries to the Vindel river in Northern Sweden. By sampling juvenile trout and salmon in two different tributaries, providing them with PIT-tags and releasing them into specific locations of the streams the within-stream-movements of the fish were studied. PIT-tag antennas were used to monitor any potential outward migration from the streams. Several of the tagged fish were detected to migrate out of the electrofishing reaches they were originally caught in. Body length of the fish did, to a small extent, differ between individuals with different migration patterns. Salmon showed a more concentrated period of outmigration compared to trout. One of the tributaries had a considerably larger outmigration from the stream compared to the other. These findings are discussed in relation to future electrofishing-based monitoring.