Abstract

Tornionjoki salmon and sea trout are closely monitored annually with multiple methods. Despite extensive data collection, some fundamental knowledge of the Tornionjoki salmon and sea trout relevant for modern adaptive salmon management is still lacking. Specifically, the in-river migratory behavior and survival of both pre- and post-spawning salmon and sea trout, as well as the distribution of spawning sites, are not well known. In addition, recent observations of sick and dying salmon in the Tornionjoki system, and declining returns reported from many rivers in connection with these observations, are concerning. More knowledge about how the disease symptoms affect behavior and survival of the Tornionjoki salmon is therefore needed. In-river migrations of Tonionjoki salmon and sea trout have been studied in cooperation between Luke and Swedish University of Agricultural Science (SLU) by means of radio telemetry in 2018‒2019. Radiotagging of salmon was carried out at the estuary from June to July (n = 227) and in the river in spring (May-June, n = 10) and autumn (August-October, n = 38). Sea trout were tagged in the river in spring (May-June, n = 33) and autumn (August-October, n = 59). Samples for age and genetic analysis were taken from all tagged individual, and the visual condition of the fish was classified in conjunction with the tagging. In both study years, a majority (61% in 2018; 83% in 2019) of the salmon tagged at the estuary returned to the sea by the end of July, i.e before spawning. Of the salmon that entered and stayed in the river until spawning, most of them were located below the Kattilakoski echo sounding place (c. 100 km from the sea) during spawning time. The salmon caught and tagged in the river showed a highly varying post-release behavior. In both study years, all salmon tagged in the spring moved downstream and descended to the sea or died during downstream movement. In contrast, all salmon tagged in autumn stayed in the river over the spawning time. Most of them stayed near the tagging site during the autumn, but some of them moved a long distance upstream after release. The tagged sea trout can be divided into two groups based on their migration pattern: (1) immature trout which moved into the lowermost river for overwintering and returned back to the sea in next spring, and (2) mature trout which ascended the river for spawning. The second group can be further divided into trout which entered the lowermost river in autumn and overwinter there before continuing to the spawning areas next spring, and trout which entered the river in springtime and continued to the spawning areas within the same season. In spawning time, autumn 2019, tagged trout were located in the main stem Tornionjoki and Muonionjoki, as well as in the tributaries Naamijoki, Äkäsjoki, Parkajoki and Merasjoki.

Published in

Natural Resources Institute Finland (LUKE)
2020, number: 2020:78
ISBN: 978-952-380-073-1, eISBN: 978-952-380-074-8
Publisher: Natural Resources Institute Finland

SLU Authors

• Hellström, Gustav

  • Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences
    

• Söderberg, Linda

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    

• Palm, Stefan

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Zoology


Permanent link to this page (URI)

https://res.slu.se/id/publ/109864