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In‐stream habitat enhancement is a common remedial action in rivers where degradation/lack of suitable fish habitat can be diagnosed. However, post‐project monitoring to assess the response of the biota to modification is rare particularly during winter. We conducted in situmonitoring during the winters of 2004–2006 in the regulated Dalåa River, central Norway, in order to determine if winter habitat requirements of Atlantic salmon (Salmo salarL.) parr were realized in an enhanced (substrate and mesohabitat modification) reach. In total, 140 parr were marked with passive integrated transponder (PIT) tags and the fish were followed by carrying out active tracking surveys under variable ice conditions throughout the winter. Highest emigration (44%) occurred before ice formation started. Emigration was reduced after ice formed and was largely offset by parr re‐entering the enhanced area. Dispersal into the non‐enhanced, small substrate control area was observed only when the study reach was ice covered, and no parr were subsequently encountered in the control section after ice had melted. In the enhanced area, declining water temperature and surface ice conditions did not affect the spatial distribution of the resident salmon parr at the studied scale. Areas with ‘solid’ anchor ice precluded access for salmon parr whilst areas with ‘patchy’ anchor were used throughout the winter. Our results indicate that surface ice creates conditions that allow salmon parr to use stream habitats that otherwise provide only a limited amount of in‐stream cover. Ice processes should be taken into consideration when habitat enhancement projects are carried out and subsequently assessed for effectiveness. Copyright © 2008 John Wiley & Sons, Ltd.

The fat and protein content, and thus energy resources of young (parr) Atlantic salmon (Salmo salar) were examined in a temperate river. Juvenile salmon exhibited distinct seasonal patterns of energy storage and use. The lowest levels of energy were found towards the end of winter (mean mass specific energy about 4.3 kJ·g−1). There was a rapid accumulation of fat in spring/early summer in spite of low‐water temperatures (highest mean content of mass specific energy of about 5.0 kJ·g−1in June). By early autumn (August) there was a rapid depletion of fat and energy resources. The decline in specific energy during late summer was of the same magnitude as the corresponding winter decline. Furthermore, total fat and protein content, and thus energy resources of juveniles below a hydroelectric power plant (hydrostation (HS)) differed from those at a (lower) reference station (RS). The younger fish exhibited higher gains, but also larger losses of energy resources compared to corresponding values at the RS. Specifically during the summer, young of year (YOY) had 31% lower total energy content at the regulated site (mean 1.27 kJ per individual) than the RS (mean 1.84 kJ). Higher mortality may occur at the site most affected by the hydroelectric plant, where energy resources on average were higher, but where depletion was also most severe. Copyright © 2006 John Wiley & Sons, Ltd.

The spawning migration and local homing of adult brown trout was analysed using radio telemetry in a regulated river in central Norway. Twenty‐eight large (37–64 cm) brown trout (Salmo truttaL.) were tracked before, during and after spawning in the River Nea, a watercourse with several obstructions, including an outlet tunnel from a power station and a regulated stretch (26 km) with 45 weirs.