PNNL

Abstract

We captured and radio tagged six adult bull trout Salvelinus confluentus in a spawning tributary of the East River basin, Idaho. These fish were tracked for a year to determine the type of migration they endured to reach their over-wintering and spawning locations. Our tracking efforts revealed that these bull trout were adfluvial as four of the six fish migrated to Lake Pend Oreille, Idaho, following spawning. To reach this lake these fish migrated at least 12 km out of the East River basin into the Priest River, 34 km down the Priest River into the Pend Oreille River and then turned upstream and migrated 36 km to reach Lake Pend Oreille. Three of the six bull trout returned to the East River basin the following spring. These movement patterns are uniquely complex and extensive for outlet spawning bull trout. This work illustrates the type of outlet spawning migrations adfluvial bull trout can have and suggest that we may need to extend our thinking of how to expand bull trout populations into historically occupied habitats. Eliminating barriers downstream of lakes could potentially contribute to and increase bull trout populations considerably.