Movements of and habitat use by fluvial bull trout in the Blackfoot River, Montana
habitat, trout, survey, migration, spawning, adult, pool
Journal or Book Title
Transactions of the American Fisheries Society
The seasonal movements and habitat use by fluvial bull trout (Salvelinus confluentus)in the Blackfoot River drainage, western Montana, were investigated by using radiotelemetry andsnorkel surveys from May 1994 to October 1995. Twenty-four bull trout made upriver migrations(mean distance, 63 21 km), 33% of which were related to spawning. In June of both years fishbegan migrations, which appeared to be cued by an increase in maximum daily watertemperature (to 17.7 degrees C in 1995) and a decrease in discharge from peak runoff. Largerfish began moving at cooler temperatures and earlier dates than smaller fish. Migrations occurrednocturnally and were generally rapid (grand mean, 4.4 2.2 km/d). Daily rates of migration werecorrelated with maximum daily temperatures. Spawning bull trout ascended tributaries in lateJune to early July, 67 10 d before spawning. Nonspawning fish entered the lower portions ofthese tributaries after spawning fish and remained in them 28 18 d before returning downriver inlate August. While in Monture Creek, a major spawning tributary for the Blackfoot River, adult bulltrout used deep pools and were positively associated with habitat units containing mountainwhitefish (Prosopium williamsoni). Eighty-six percent of migrants returned downriver to within 20m of sites occupied in the spring. In 1994, two nonmigrating fish in the Blackfoot River used theconfluence of a cold tributary, but no such behaviour was observed in 1995. Results suggestedthat water temperature influenced the movement of fluvial bull trout and that tributary habitat wasimportant for both spawning and nonspawning fish. Results also demonstrated the large spatialscale and diversity of habitats required to sustain fluvial bull trout populations.