Stream restorations and their impacts for brown trout and salmon in FRESHABIT LIFE IP-projects

• Main Authors: Hynninen, Mikko, Vehanen, Teppo
• Other Authors: orcid:0000-0003-3441-6787, 4100111210, Luonnonvarakeskus
• Format: Report
• Language: English
• Published: Natural Resources Institute Finland (Luke)
• Subjects: Restoration; Trout; Salmon; FRESHABIT; biodiversity; Naamijoki; Tornionjoki; Salmo salar; Lapland
• Online Access: https://jukuri.luke.fi/handle/10024/551846

Several river restorations were conducted in FRESHABIT LIFE- EU project during 2016–2021. These included a single catchment-scale restoration in Naamijoki, a tributary of Tornionjoki located in South-Western Lapland. Multiple on-site stream restorations with the aim of enhancing the natural reproduction of brown trout (Salmo trutta) and land locked salmon (Salmo salar) were conducted on four rivers: Ostrobothnian Isojoki and Karvianjoki, Ala-Koitajoki in North Carelia and Karjaanjoki in Southern Finland. Information about the restoration measures and results of monitoring electrofishing surveys were collected. These were then analysed together with open water quality and weather or river discharge data to assess the effects of the restorations to the target populations. Results showed that in Isojoki restorations together with migration barrier removal had increased the YOY brown trout (young of the year) production on several sites. However, the effect was not seen in older trout densities. For catchment scale restoration in Naamijoki, using water- and sediment retention increasing protective structures, no effect on trout densities was observed during the relatively short monitoring period. In Ala-Koitajoki the results of a treatment-control design with water moss (Fontinentalis sp.) suggested that there might be benefits in water moss transplantations for YOY salmon survival. However, this could not be verified statistically. In Karjaanjoki increasing trends could be seen in YOY densities after restorations, but the lack of adequate monitoring before the restorations hindered conclusions. In Karvianjoki YOY densities showed some decrease after restorations while densities of older trout increased. This could be a result of increased area of deeper pools and hiding places which have altered the sites better suitable for older trout and decreased the catchability of YOY trout. This study underlined the importance of adequate monitoring planning, with long enough before- and after-restoration electrofishing ...