Effects of fall-to-winter changes in habitat and frazil ice on the movements and habitat use of juvenile rainbow trout in a Wyoming tailwater

Overwinter declines in the abundance of small rainbow trout Oncorhynchus mykiss have been observed in a section of the Big Horn River that lies downstream from Boysen Reservoir, where reservoir releases prevent surface ice formation. To provide insight into the possible causes of these declines in abundance, radiotelemetry was used to determine movement and microhabitat use of juvenile (20–25 cm total length) rainbow trout during the fall and winter of 1995–1996. Throughout the fall and winter, both stocked (hatchery) and naturally spawned (wild) fish were generally found in main-channel pools with cover that reduced current velocities to less than 2 cm/s near the bottom and with nearby (