Diel Movement Patterns of Adult Migratory Bull Trout in a Large River System

In order to understand the life history requirements of threatened bull trout Salvelinus confluentus detailed and accurate information on migration patterns is necessary. Radiotelemetry was used to monitor movements of adult migratory bull trout at fixed receiver telemetry stations in the Columbia, Entiat, and Methow rivers of the Upper Columbia Bull Trout Recovery Unit in Washington, USA. The diel period of movement past telemetry stations was dependent on season and location within the large river system. During spring migrations to upstream spawning areas, movements in the Columbia River occurred primarily during the day while entry into the Entiat and Methow rivers occurred both day and night. As migrations proceeded upstream in these tributaries, movements shifted primarily to the night, except at impediments such as waterfalls or rapids, where movements occurred mostly during the day. After spawning, bull trout migrated downstream primarily at night until they entered the Columbia River where movements occurred both day and night. These results suggest the movement patterns of adult migratory bull trout can be more variable and complex than commonly reported. This information is critical to understanding and ameliorating potential impacts of management activities on migratory bull trout.