| Summary: | In this collaborative project between the Natural Resources Institute (Luke) and the Swedish Agricultural University (SLU), the migratory behaviour and survival of Tornionjoki (Torneälv in Swedish) salmon and sea trout were studied between 2018‒2021 by the means of radiote-lemetry. Altogether, 227 and 92 salmon were tagged at the Tornionjoki estuary and in the river, respectively. 114 sea trout were tagged in the river. Scale samples and fin clips for age-ing and genetic identification were taken from all the tagged specimens. The external condi-tion of the tagged specimen was also documented (wounds, skin colour, degree of haemor-rhage etc.). Moreover, a separate follow-up of the external condition of salmon caught in trap nets was conducted in 2020‒2021 at sea near the river mouth. The post-release behaviour of salmon tagged at the estuary was markedly different from that normally expected: a large majority (61% and 83% in 2018 and 2019, respectively) of the salmon which ascended the river after tagging aborted their riverine migration on the lower river and returned to the sea during the summer (i.e., before spawning season). Those salmon which stayed in the river until spawning time predominantly stayed on the lowermost 100 km of the river. More varying migration patterns were observed among the salmon tagged in the river. All specimens caught and tagged during the early summer of 2018 and 2019 started to drift downstream after their release and none of them was alive in the river at spawning time. However, about half of the specimens tagged in the river in early summer 2020 and 2021 continued their upstream migration and were alive in the river at spawning time. Salmon tagged in late summer 2018‒2020 stayed alive in the river and almost half of them also moved further upstream by spawning time. A large majority of salmon overwintered in the river after spawning and returned to the sea in spring. The majority of the salmon caught in the estuary had various external damages (wounds, scale losses, fin damages, ...
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