AEI 8:77-88 (2016)  -  DOI: https://doi.org/10.3354/aei00165

Area use and movement patterns of wild and escaped farmed Atlantic salmon before and during spawning in a large Norwegian river

Karina Moe1,2, Tor F. Næsje1,*, Thrond O. Haugen2, Eva M. Ulvan1, Tonje Aronsen1, Tomas Sandnes3, Eva B. Thorstad1

1Norwegian Institute for Nature Research (NINA), PO Box 5685 Sluppen, 7485 Trondheim, Norway
2Norwegian University of Life Sciences (NMBU), PO Box 5003 NMBU, 1432 Ås, Norway
3Aqua Kompetanse AS, 7770 Flatanger, Norway
*Corresponding author:

ABSTRACT: We compared the within-river movements and distribution of wild and escaped farmed Atlantic salmon Salmo salar before and during spawning in the Namsen river system of Central Norway. A total of 74 wild and 43 escaped farmed salmon were captured at sea, tagged with radio transmitters and released. Based on our examinations, most, if not all salmon (farmed and wild) entering the River Namsen were sexually mature. Farmed salmon entering the river system had a higher probability than wild individuals of reaching the migration barrier in the upper part of the river, 70 km from the sea. During the pre-spawning and spawning periods, farmed salmon were located mainly in the upper parts (50 to 70 km from the sea), whereas wild salmon were evenly distributed along the entire river during both periods. Consequently, the probability of farmed × wild inter-breeding varied among river sections. Our finding that the distribution of escaped farmed salmon may differ from that of wild salmon and among river sections in the pre-spawning and spawning periods—and that it may also vary over time—must be taken into consideration when (1) designing monitoring programs aimed at estimating the proportion of escaped farmed salmon in rivers and (2) when interpreting monitoring results. Furthermore, targeted fishing in the river aimed at reducing the number of farmed salmon prior to spawning may be more effective in upper rivers sections, and below major migration barriers.


KEY WORDS: Radio telemetry · Farmed escapees · Within-river movements · Pre spawning · Spawning period · Introgression risk · River Namsen


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Cite this article as: Moe K, Næsje TF, Haugen TO, Ulvan EM, Aronsen T, Sandnes T, Thorstad EB (2016) Area use and movement patterns of wild and escaped farmed Atlantic salmon before and during spawning in a large Norwegian river. Aquacult Environ Interact 8:77-88. https://doi.org/10.3354/aei00165

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