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Marine Ecology Progress Series

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MEPS 535:185-195 (2015)  -  DOI:

Survival and progression rates of anadromous brown trout kelts Salmo trutta during downstream migration in freshwater and at sea

Kim Aarestrup1,*, Henrik Baktoft1, Eva B. Thorstad2, Jon C. Svendsen1,3, Johan Höjesjö4, Anders Koed1

1National Institute of Aquatic Resources, Technical University of Denmark, Vejlsøvej 39, 8600 Silkeborg, Denmark
2Norwegian Institute for Nature Research, 7485 Trondheim, Norway
3Interdisciplinary Centre of Marine and Environmental Research, University of Porto, 4050-123 Porto, Portugal
4Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, 40530 Gothenburg, Sweden
*Corresponding author:

ABSTRACT: The marine migration of post-spawning anadromous fish remains poorly understood. The present study examined survival and progression rates of anadromous brown trout Salmo trutta L. after spawning (kelts) during downriver, fjord, and sea migration. Kelts (n = 49) were captured in the Danish River Gudenaa, tagged with acoustic transmitters and subsequently recorded by automatic receivers. Kelts spent on average 25 d moving down the 45 km river and through the brackish fjord. The fish entered the Kattegat Sea between 14 April and 30 May. Eighteen of the 49 kelts disappeared in the river and fjord during outward migration, likely due to mortality. Survival was not significantly related to gill Na+/K+-ATPase activity, suggesting that physiological adaptation to saltwater may be less critical for adults compared to juveniles (smolts). Of the 31 fish that entered the Kattegat Sea, 45% survived and returned to the fjord. The duration of the entire marine migration, from leaving to entering the river, was on average 163 d. The fish returned from the Kattegat Sea to the fjord between 22 July and 21 October. Upon return, the fish spent 1-90 d passing through Randers Fjord, with most individuals completing the reach within 4 d, suggesting that the kelts spent limited time foraging after returning to the fjord. The total survival during the entire marine migration, including the fjord, was a minimum of 29%. Our study provides data that are important for management of anadromous brown trout, and the high survival highlights that kelts may represent a valuable resource for both population reproduction and recreational fisheries.

KEY WORDS: Anadromous · Migration speed · Survival · Migration · Fishing mortality · Acoustic telemetry · Salmon · Swimming

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Cite this article as: Aarestrup K, Baktoft H, Thorstad EB, Svendsen JC, Höjesjö J, Koed A (2015) Survival and progression rates of anadromous brown trout kelts Salmo trutta during downstream migration in freshwater and at sea. Mar Ecol Prog Ser 535:185-195.

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