Aspects of erosion of restored trout spawning beds in two streams in Northern Sweden
Many rivers and streams in northern Sweden have been channelized due to timber floating. This has severely degraded the spawning habitats for salmon and trout, and therefore a common action when restoring channelized rivers is to establish new spawning beds by adding gravel to the streambed. However...
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| Format: | Text |
| Language: | Swedish English |
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2021
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| Online Access: | https://stud.epsilon.slu.se/16545/1/granlund_m_210323.pdf |
| Summary: | Many rivers and streams in northern Sweden have been channelized due to timber floating. This has severely degraded the spawning habitats for salmon and trout, and therefore a common action when restoring channelized rivers is to establish new spawning beds by adding gravel to the streambed. However, little is known about the longevity of these spawning beds, and erosion caused by both water discharge and spawning fish may move gravel/pebbles out the spawning bed, gradually decreasing their functionality. In this thesis, I studied erosion of eight spawning beds (approx. 5 x 2 m), constructed in two different streams, Storkvarnbäcken and Mattjokkbäcken, in northern Sweden. In total, 643 pebbles were tagged with half-duplex passive integrated transponder tags and placed on newly constructed spawning beds, which made it possible to study their movement over multiple years by scanning the spawning beds with PIT-tag reader/antennas. The overall objectives for this study were to quantify and describe erosion process of constructed spawning beds. More specifically, I investigated the effect of streambed slope and pebble size on the distance substrate were moved by erosion processes, and on the likelihood of substrate remaining on the spawning bed. Further, I evaluated different methods used to position PIT-tagged pebbles in boreal streams (conventional GPS, High Precision GPS, and Laser distance meter), and specifically investigated precision and accuracy of commonly used GPS-systems integrated in PIT-tag reader units. Overall, recovery of PIT-tagged pebbles by scanning spawning beds with PIT-tag antennas were high despite multiple years between the deployment of pebbles and the scanning. 85 % of pebbles were found in Storkvarnbäcken 8 years after deployment, and 60 % were found in Mattjokkbäcken 6 years after deployment. There was a big difference between the two study streams in the proportion of recovered pebbles that had remained on the spawning beds (82% remaining in Storkvarnbäcken, and 45% in Mattjokkbäcken), ... |
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