Fish migration in the Byske River
Every year, salmon make their long migration from the southern Baltic Sea back to their home river and the spawning grounds where they will reproduce. The migration in the rivers starts in the spring and continues throughout the summer until the salmon spawning season in the autumn. Here in Fällfors, 28 kilometres upstream in the Byskeälven from the sea, Skellefteå municipality has a fish counter to monitor the migration of salmon and trout for monitoring purposes.
In the old fishway on the south side of the river, a fish counter will be installed during the season to count fish passing upstream and downstream. This counter is of the so-called optical type and consists of a scanning unit, control unit and photo tunnel.
The counter is mounted at an opening in a concrete wall through which the upstream fish have to pass. The fish are guided through a funnel-like grating into the counter and through the scanning unit, which consists of two plates facing each other where passing objects are detected by infrared light. When something passes the scanner plates, the light beams are refracted and the direction, size, shape and speed of the object are recorded in the counter's control unit along with the date and time of the passage. In addition to recording passing objects, the counter also measures the temperature of the water every three hours.
After the scanner unit is the photo tunnel where a camera is placed. When a fish passes the counter, a short video sequence is recorded. The video footage provides a good opportunity to study the individual fish in detail. The film sequences not only allow the fish to be identified with a high degree of certainty, but also to study details such as sex, degree of spawning maturity, state of health and external markings such as a cut-off adipose fin (indicating that the fish has been farmed) or possible damage from fishing gear or predators.
The northern fishway also has a fish counter of the same type, but this lacks a camera, which does not allow species or other characteristics to be distinguished.
Please note that the fish count data presented on the web during the season is preliminary and uninterpreted data. Some adjustments may be made after review at the end of the season.
The Salmon Observatory is located in Fällfors by the Byske River. The Salmon Observatory is an underground room where you can look out into the fishway through large windows. Here you can see when the salmon pass on their way up to their spawning grounds. Through monitors on the walls you can also see the salmon passing through the southern fishway, which is directly adjacent on the other side of the river. The salmon observatory opens in June and is free to visit