Salmon and other migratory species ascending to the Teno river are counted with sonars at Polmak, c. 55 km upstream from the river mouth. Sonar monitoring is started annually on late-May early-June after the highest spring flood has decreased. Monitoring continues annually at least to the end of August.
At the monitoring site in Polmak the river is c. 120 m wide and 1-6 m deep. Two sonar units are used, one in each shore. The river is slightly narrowed by using guiding fences which leaves c. 100 m to be monitored with sonars.
Estimation of salmon numbers in the Teno is complicated by two other similar sized fish species, sea trout and pink salmon migrating past the monitoring site. With pink salmon this problem exists only during odd-years (e.g. 2021, 2023, etc.). The species proportions at the monitoring site are nowadays estimated based on underwater video data collected from the sonar window.
The final estimate of the total salmon run is available at early winter during November-December when all different datasets have been analyzed.
Salmon and other migratory species ascending to the Tornio River are counted with sonars at Kattilakoski, c. 100km upstream from the river mouth. Sonar monitoring is started annually on mid-May and it continues at least to the end of August.
At the monitoring site in Kattilakoski the river is c. 180 m wide. Two sonar units are installed on the river, one unit at each bank, providing us maximum of 160 m coverage. The river is slightly narrowed by using guiding fences so that the whole river can be covered with two sonar units.
Distinguishing salmon from other species is based on fish sizes and observation period. The final estimate of the total salmon run is available at early winter during November-December when all different datasets have been analyzed.
Salmon and other migratory species ascending to the Simo River are counted with sonars at Kiusankoski, c. 4,5 km upstream from the river mouth. Sonar monitoring is started annually on early-May and it continues at least to the end of August.
At the monitoring site in Kiusankoski the river is c. 80 m wide. The river is narrowed to 40 meters by using guiding fences. This enables one sonar unit to cover the whole river.
Distinguishing salmon from other species is based on fish sizes and observation period. Especially problematic at River Simo is differentiating small 1SW salmon from other similar sized fish species. The final estimate of the total salmon run is available at early winter during November-December when all different datasets have been analyzed.
