FishPath (NO)

Sun, 01 Mar 2026 00:00:00 +0000

In the River Mandalselva, we are evaluating the efficiency of a newly improved mechanical behavioural barrier designed to guide smolts away from the turbine intake and towards a safe bypass route. Using high-resolution fish tracking, we aim to determine whether smolts are successfully guided to the bypass or whether some descend and pass underneath the guidance rack, as observed for an earlier design (Kjæråsen et al., 2022). A total of 32 acoustic receivers deployed around the guidance rack will provide detailed swim tracks for +100 tagged Atlantic salmon smolts during the migration period from May to June 2026.

Background

Hydropower facilities represent a major obstacle to river connectivity and fish migrations worldwide. Infrastructure associated with hydropower can cause direct injury and mortality during turbine and spillway passage, and indirectly affect fish by restricting access to critical habitats, prolonging migration, and increasing vulnerability to predators.

Although bypass solutions often exist to reduce these impacts, they are not always effective. Migrating fish generally follow the main river flow, which at hydropower facilities is diverted into turbine intakes. Consequently, fish may be attracted to intake areas and fail to follow safe passage routes, increasing the risk of injury or mortality.

Multiple mitigation measures have therefore been developed to prevent fish from entering intake areas. Physical barriers in front of water intakes have proven effective for small and medium sized hydropower facilities, but are costly and technically difficult at large facilities due to high water flows. These limitations have prompted the development of mechanical behavioral barriers with larger bar spacings, designed to guide fish towards safe bypass routes while minimizing head losses.

While these fish guidance solutions are promising, their effectiveness depends strongly on how fish respond to the structures. For example, Kjæråsen et al. (2022) found that although Atlantic salmon smolts have been assumed to be surface-oriented, some individuals descended and passed underneath a guidance rack in the River Mandalselva. This behaviour would likely have gone unnoticed without detailed movement data from high-resolution fish tracking.

High-resolution Fish tracking

To properly evaluate fish guidance solutions, it is crucial to understand not only whether fish are guided successfully, but also how they move and interact with structures in three dimensions. High-resolution acoustic telemetry allows researchers to obtain fine-scale movement patterns that cannot be detected using traditional monitoring methods.

In this project, high-resolution fish tracking is used to evaluate the efficiency of a newly improved fish guidance rack (a modified angle-bar rack) in the River Mandalselva. Building on earlier work by Kjæråsen et al. (2022), this research will help determine whether the updated design improves fish guidance and reduces the number of smolts passing underneath the rack. These results will provide valuable insights into how guidance structures can be optimized to better protect migrating smolts near hydropower facilities.

Project Partners

This is part of FishPath lead by Dr. Ana Silva (NINA, Norway).

Dr. Ana Silva, NINA, Norway
Dr. Torbjørn Forseth, NINA, Norway

FishPath | 3D Fish Telemetry

FishPath (NO)

Background

High-resolution Fish tracking

Project Partners