摘要：Survival and behavioural effects of handling and transport related to a fishway in a natural waterfall was examined for radio-tagged sea trout (Salmo trutta, n = 39) during their upstream migration to spawning grounds. Main aims were to examine (1) if handling and transport impacted their subsequent survival, (2) whether they remained above the waterfall and resumed upstream migration, or migrated downstream again below the waterfall, and (3) if migration behaviour differed between fish tagged with small and large external transmitters. A high survival rate (at least 97% of the fish), fast upstream movement after release above the waterfall (average 6 km during the 6 first days), no recorded downstream movements during the entire study period, and wide-ranging migration before the spawning period (average 25–27 km upstream of the release sites), indicated that handling, tagging and transport of the sea trout did not greatly impact their subsequent survival and behaviour. The results did not differ between two release sites (0 and 9 km upstream from the waterfall) and did not depend on fish body size or sex. Fish with large, external radio transmitters had covered a shorter distance before spawning than fish with small transmitters. Our results indicate that the use of external transmitters may reduce the migration distance and affect the distribution of fish during the spawning period. Hence, we recommend using as small external transmitters as possible in watersheds where fish have to negotiate waterfalls and river stretches with strong currents. A low determination coefficient of the model (r2 = 0.22) indicates that other factors than the external transmitters largely affect the migration distance among individuals.
