Influence of Inter-Basin Transport on Genetic Composition of Bull Trout in the Baker River Basin

Upstream passage of anadromous salmonids has been successfully accomplished by trapping and hauling fish above dams.  In the Baker River basin, a trap-and-haul system provides upstream fish passage above two high head dams, the lower forming Lake Shannon, and the upper forming Baker Lake.  In both basins, downstream passage is facilitated by a floating surface collector located at the downstream end of each reservoir.  Whereas the upstream passage facilities were designed for anadromous salmon, between 10 and 57 bull trout have been captured annually in the lower Baker fish trap since the mid-1990s.  Bull trout life histories include both resident and migratory expressions.  Many populations exhibit inter-basin movements and coastal populations may support anadromous or amphidromous expression.  Until recently, the genetic origins of bull trout transported and released upstream into Baker Lake were unknown.  As such it was not possible to differentiate between bull trout with genetic ties to the Baker basin and those from neighboring basin populations less likely to be using the basin for reproduction.  In support of developing population-specific transport protocols, geographic origins were determined for bull trout collected throughout the Baker River basin by genotyping fish and assigning them to source populations.  GeneClass analysis of tissue samples identified genetically distinct bull trout populations that included Sulphur Creek in Lake Shannon, two distinct populations in tributaries to Baker Lake, and two populations outside the Baker River basin from the Sauk River and Illabot Creek.  Analysis of bull trout collected in the lower Baker River fish trap indicated that 61% of the bull trout captured and released into the upper reservoir had originated outside of the Baker basin.  Despite years of mixing these populations, genetic integrity among Baker Basin populations remains high with little evidence of interbreeding in either reservoir.  GeneClass analysis of juvenile bull trout collected in Sulphur Creek and the upper Baker River indicated that few fish from populations other than Sulphur Creek had spawned in Sulphur Creek, and an even smaller proportion of fish from populations outside the upper Baker River had spawned in the upper Baker River, the largest tributary to Baker Lake.  The information gathered as part of this study is being used to develop new protocols for transporting and releasing bull trout at the Baker Project.