Pre-spawning habitat selection of subarctic brown trout (Salmo trutta L.) in the river Vindelälven, Sweden

Sammanfattning: Habitat selection of migratory brown trout at the upper reaches of River Vindelälven, wasstudied in September during the pre-spawning period. The fish migrate from down- orupriver lakes for spawning in the river and data was collected by habitat mapping andradio-telemetry. Habitat selection of fish was analysed with preference curves andstatistical modelling, using the physical variables; depth, stream velocity and streambedsubstrate. Preference curves were derived by comparing fish habitat use with their nearbyavailable environment while the statistical modelling aimed to answer three main questions.1) Do the trout have a specific preference of depth, water velocity and streambed substrate?2) Is there any difference in habitat selection between sexes? 3) Is there a shift in habitatselection over time? The preference curves indicated that trout favored water depths of 1-2m, velocity compositions characterized as glides (c. 0.2-0.4 m s-1), both fine (0.02-2 mm)and large (>200 mm) substrate compositions. The overall habitat selection of fish wassignificantly influenced by all three investigated physical variables. Stream velocity was theonly factor statistically segregating females and males in habitat selection, where malesused higher velocity areas. No shifts in habitat selection over the one month study periodwere found. The complexity of streams and correlations between variables often results indifficulties to evaluate fish habitat preferences and consequently future challenges lies inthe development of models accounting for a wider range of abiotic and biotic factors.