Anadromy comprises a successful life-cycle adaptation for salmonids, with marine migration providing improved feeding opportunities and thus improved growth. These rewards are balanced against costs from increased energy expenditure and mortality risk. Anthropogenic-induced environmental changes that reduce benefits and/or increase costs of migration e.g., aquaculture and hydropower, may therefore result in adaptations disfavouring anadromy. We tagged brown trout (Salmo trutta) smolts (N = 175) and veteran migrants (N = 342), from five adjacent riverine populations located in Sognefjorden, the longest Norwegian fjord-system supporting anadromous brown trout populations (209 km). Over four years, 138 acoustic telemetry receivers were deployed to track migrations of tagged individuals from freshwater and throughout Sognefjorden. Detected movements were used to fit migration models and multi-state mark-recapture models of survival and movement for each life-stage. Seaward migration distance was modelled to examine the fitness consequences from alternate migration strategies, with these models used to simulate the extent of fjord-use by individuals and accompanying growth, fecundity and survival consequences. We compared these findings with mark-recapture data collected prior to aquaculture and hydropower development.

R studio, 4.2.0

MARK, 6.2

Leiv Rosseland and Bjørn Olav Rosseland- Professor emeritus in Ecotoxicology, Norwegian University of Life Sciences Kristensen T, Urke H, Haugen T, Rustadbakken A, Alfredsen JA, Alfredsen K, et al. Sea trout (Salmo trutta) from River Lærdalselva, W Norway: A comparison of growth and migratory patterns in older and recent studies (In Norwegian). NIVA Report: 6122; 2011.