Seasonal Movements and Habitat Use of Rainbow Trout (Oncorhynchus mykiss) in the Susitna River Basin, Southcentral Alaska

Potamodromous Rainbow Trout are an important ecological and recreational resource in Alaska rivers, and increased human development, hydroelectric projects, and climate change threaten their populations. We used aerial telemetry tracking to characterize seasonal movements and habitat use of these fish across a complex 31,221 km² Southcentral Alaska riverscape during 2003-2004 (N=148) and 2013-2014 (N=82). We found that trout overwintered in mainstem habitats near tributary mouths from November-April. After ice-out in May, trout ascended tributaries up to 51 km to spawn, and afterward moved downstream to intercept egg and flesh subsidies provided by spawning salmon in July and August. Trout transitioned back to mainstem overwintering habitats at the onset of autumn when salmon spawning waned. Among tributaries where trout were initially tagged, fidelity back to those streams from overwintering sites to spawn and rear varied. However, we found little difference in overall movements and habitat use for a subset of fish for which sex was determined using genetic analysis. As most trout undertake extensive movements and make use of a variety of seasonal habitats to compete their life histories, it will be critical to take a broad-scale approach to their management in light of anticipated future land use and climate change.