Population Structure and Movement Patterns of Adfluvial Bull Trout (Salvelinus confluentus) in the North Fork Boise River Basin, Idaho

Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Biology



Major Advisor

Peter Koetsier


Bull trout (Salvelinus confluentus) were captured using four methods in distinctly different hydrologic conditions across the North Fork Boise River Basin in Southwestern Idaho. Trapping occurred between the months of April and October in years 1999 and 2000. Over 1,100 bull trout representing age classes 0+ - 9+ were sampled. Bull trout were found to move primarily at night and movement was related to temperature and flow fluctuations. Growth in bull trout appears to be greatest in age classes 2+ - 3+ fish that show movement in the river system. A possible relationship between year class strength of captured bull trout and annual flow and precipitation levels was observed. The North Fork Boise River adult (total length > 300 mm) post spawning population estimate was calculated to be 969 (s = 228) bull trout. The study results indicate that accessibility to migratory corridors and environmental conditions such as temperature and stream discharge play a major role in the movement and persistence of this population of fish.

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