Hydropower plants commonly impede the downstream migration of Atlantic salmon (Salmo salar) kelts. Thus, understanding the effects of hydraulic conditions on kelt behavior and passage performance at dams associated with these hydro facilities is crucial for developing effective mitigation measures.
The results of such a study recently were published online at Science of the Total Environment journal. The authors represent the Norwegian Institute for Nature Research, Vattenfall Research and Development, Swedish University of Agricultural Sciences and Karlstad University.
In this study, the authors investigated the influence of hydraulic conditions on kelt passage performance and swimming behavior at a Norwegian hydropower plant. They combined biological data from 48 kelts collected via acoustic telemetry with hydraulic data modelled using computational fluid dynamics. They assessed kelt passage performance using metrics such as time-to-pass, total number of detections and total number of detections per day. Additionally, the authors analyzed swimming depths and speeds in relation to the hydraulic conditions created by different dam operating conditions.
The researchers found that the dam operation schedule impacted the kelts’ ability to find a route past the dam. Although kelts could have passed the dam throughout the study period via a submerged pipe installed at the dam (which had seemingly sufficient discharge for the kelts to find), 98% of the kelts studied instead waited for a spill gate to open partway through the study period. The swimming depth analysis indicated diel variation, with kelts swimming nearer to the water surface during the night. The researchers found that swimming speed increased with increasing kelt body length, particularly under high-turbulence kinetic energy and during the day. Furthermore, kelts swam faster as water velocity increased but slowed down again as turbulence intensity increased.
These findings reveal the effects of hydraulic conditions and dam operations on the migration behaviour of Atlantic salmon kelts. This provides valuable insights for developing strategies to optimize dam operations and improve fish passage performance, including the need to spill enough water to increase passage success, and will contribute to sustainable management of Atlantic salmon populations in regulated rivers.
Last year, Hydro Review reported on research from the University of Maine that showed when Atlantic salmon are stopped by dams during their upstream spawning migration, they can deplete needed fat stores.
