| Summary: | Hydropower facilities are obstacles in the rivers, which mostly are impassable for fish. The loss of longitudinally connectivity in many rivers prevents salmon fulfilling their reproductive cycle, leading to worldwide reduction of the Atlantic salmon population. Three hydropower stations today exploit the river Daugava, Latvia. This has resulted in extirpation of the native Atlantic salmon population. To investigate the possibilities of reintroducing salmon, a telemetry study with trap- and transport-approach was carried out. Eighteen Atlantic salmon were caught near the river mouth of River Daugava and tagged. Two groups were transported past the most downstream obstacle in River Ogre to two different release sites, R1 and R2 (n = 8 and 6), and a third group, R3 (n = 4) group and was released in Riga reservoir, above Riga HES, in River Daugava. All salmon released in River Ogre migrated downstream, eventually ending up in River Daugava. In total seven salmon passed downstream through the turbines of Riga HES, whereof the recapture success downstream Riga HES was 71%, and the survival rate of turbine passage was at least 60%. This indicates there is a high fishing pressure on salmon in Daugava. The majority in the first group (R1), passed through the turbines of Riga HES, likely due to the high discharge event. However, none in the second group (R2) did. Half of the fish in the third group (R3) released in River Daugava either went downstream passing the turbines of Riga HES or moved upstream standing below the next hydropower station Kegums HES. Six individuals remain missing, presumably because of poaching and/or lack of feedback reporting. After passing downstream from the River Ogre to the Daugava River, about 13% and 17% of groups R1 and R2, respectively, migrated upstream to reach Kegums HES, the furthest possible migration point in River Daugava. The results from this study give valuable information of the possibilities of reintroducing the wild Atlantic salmon to Daugava. Fishing pressure might be a ...
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