River restoration and habitat improvements in the sub-arctic river Bognelva – effects on anadromous fish

• Main Author: Bråthen Schedel, Joachim
• Format: Master Thesis
• Language: English
• Published: Norwegian University of Life Sciences, Ås 2011
• Subjects: Elverestaurering; Anadrome fiskearter; VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Catch: 925; VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Other fisheries disciplines: 929; Arktis*; Atlantic salmon; Northern Norway; Salmo salar; Salvelinus alpinus
• Online Access: http://hdl.handle.net/11250/186710

Alterations of watercourses in the form of channelization, dam building and digging of dikes has been ongoing for centuries. This has eliminated much of the vital natural variation found in rivers that is necessary for optimal fish habitat, and thus, a major cause of declines of the fish population in many watercourses. In recent times, these effects have been recognized and efforts to restore these altered rivers have been initiated. I examined the river Bognelva located in northern Norway to test whether restoration measures improved conditions for the salmonid species Trout (Salmo trutta), Atlantic salmon (Salmo salar) and Arctic char (Salvelinus alpinus). Restoration measures included removal of flood banks, improvements of erosion control, opening of old side channels and tributary streams, placement of boulder groups and creation of weirs. The river was divided in sections at restored and un-restored sites and electro fished to investigate whether changes occurred in the number of fish compared to previous counts. Furthermore, a number of environmental variables were registered to test how and why restoration measures may or may not have improved fish habitat as predicted. Trout showed the greatest gain from restoration. The most important cause for this was the re-opening of side channels that proved to be “full” of small (<60 mm) trout. Salmon gained most benefit from flood bank removal and other restoration measures in the main river. Arctic char represented a very low percentage of the catch and therefore were difficult to include in the study of specific restoration measures in this study. Because shallow habitats that represent known “trout habitats” were over represented in the sampling sites, there was likely a bias towards catching more trout. Overall, side channel and tributary re-openings and flood bank removal were the restoration measures that had the most positive effects. Comparing catches from previous years before restoration measures were begun confirmed a large increase in the trout ...