ScholarWorks at University of Montana

Stream connectivity in the Clark Fork watershed: Balancing fish passage, sport fisheries, and native fish conservation

Montana’s wild trout fisheries and native aquatic communities depend on connectivity of aquatic habitats. For fish, connectivity (the means to move freely between streams or stream reaches) allows spawning migrations, seasonal movements and complex life history strategies to persist. However, management strategies that prioritize conservation of native fish populations (including genetic integrity) require a balance between connectivity, selective movement and, in some instances, isolation. In western Montana rivers, rainbow trout (Oncorhynchus mykiss, the predominant introduced sport fish), as well as migratory forms of native bull trout (Salvelinus confluentus) and westslope cutthroat trout (Oncorhynchus clarki lewisi), require connectivity between rivers and their tributaries in order to thrive. In other instances, physically segregating genetically ‘pure’ stream-resident trout populations (particularly westslope cutthroat trout) is essential to isolate them from hybridization with non-native salmonids and other threats. Balancing the need for both connectivity and isolation creates a paradoxical management situation. Here, I will describe the middle Clark Fork River basin in this context, summarize fisheries management plans, and provide examples of recent fish passage improvements and sustained population isolates.