Understanding the Dynamics, Cues and Implications of Bull Trout Movement in the Walla Walla Basin

Bull trout (Salvelinus confluentus) exhibit a complex and diverse life history, giving rise to migratory and resident individuals that are essential for long term population persistence and viability.  To best manage and recover these populations we must maintain the connectivity between suitable habitats and facilitate the expression of all life histories.   To inform recovery planning and prioritize efforts and limited resources, we need an understanding of the environmental requirements and limitations of migratory bull trout across space and time.  Here we investigate the consequences of a highly altered and over allocated river system using passive in-stream antennas (PIA) and a large population of tagged bull trout.  Since 2002, we have built an infrastructure of 11 PIAs encompassing more than 160 rkm in the Walla Walla Basin and mainstem Columbia River.  Data gathered from this effort has been used to determine population estimates, survival, and connectivity between core areas.  We have observed a range of movement patterns in terms of direction, distance, rate, and timing.  Juvenile fish were detected moving year round, and often dispersed downstream farther than adults.  Adult fish showed distinct seasonal spawning migrations and most were detected making annual spawning runs in sequential years.  Fish have also been recorded overwintering in the Columbia River and returning 120 rkm to the spawning area.  We have also documented avian predation, irrigation diversion use, and migration delay at fish ladders. The results of this study will be useful in understanding the how river management can be used to promote range-wide species recovery and assist managers in identifying the limiting factors of other species with similar migratory requirements (e.g., salmon, steelhead, and lamprey).