Abstract
The bull trout (Salvelinus confluentus) is listed as a threatened species and is native to the Kootenai River, Idaho and Montana, USA, and British Columbia (BC), Canada. Little is known about its life history and movements downstream of Kootenai Falls, Montana. Between 1998 and 2006, 19 bull trout were monitored in the Kootenai River with radio and sonic transmitters. Two bull trout life history patterns were found; 16 bull trout were likely fluvial, and two were adfluvial. Evidence of spawning was found for only about 33% of the bull trout tracked; of those, 50% were annual spawners and 50% alternate-year spawners. Temperature of the Kootenai River during spawning migration of six bull trout that made spawning migrations ranged from 7.1°C to 15.0°C and averaged 11.4°C. Telemetry data indicated nine bull trout concentrated below Kootenai Falls during the spawning season, but it is not known if they spawned. Two tagged bull trout were located in Kootenay Lake, BC. One fish returned to the river and moved a total of 228 km from Kootenay Lake through Idaho and to Kootenai Falls. Bull trout also used several tributary streams outside of the spawning season, possibly as a thermal refuge.
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