Year of Award


Document Type

Thesis - Campus Access Only

Degree Type

Master of Science (MS)

Degree Name

Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Chair

Lisa Eby

Commitee Members

Mike Mitchell, Mike Young


barriers, conceptual framework, dams, migratory bull trout, tradeoffs


University of Montana


Dams are well known for their negative ecological impacts on fish populations. Despite these negative impacts, dams are ubiquitous, many dams are aging, and decisions to remove dams are becoming progressively more common. Barriers can be detrimental by inhibiting movement among key habitats, but can also be beneficial by preventing exotic species expansion. Therefore, evaluation of these tradeoffs is critical before making decisions that may affect the long term viability of populations. The disruption of movement corridors due to damming and interactions with nonnative species are two of the primary factors responsible for the decline of migratory bull trout (Salvelinus confluentus). All bull trout in the coterminous United States are currently listed as threatened under the Endangered Species Act. In order to prioritize actions and develop effective conservation strategies for bull trout, managers need a better understanding of how bull trout use available habitats, the ecological effects of barriers on bull trout life history, and the risks of exotic species expansion if barriers are removed. I used radio telemetry to determine the effects of the small Emily-A and Rainy Dams and numerous natural beaver dams on migratory bull trout in the Clearwater River Drainage. I also developed a conceptual framework to evaluate the tradeoffs of both habitat fragmentation and exotic species expansion in context with dam mitigation or removal. To capture and monitor bull trout, and to determine the species composition and relative abundance throughout the drainage, I used a variety of sampling methods including a fish ladder, snorkeling, angling, gill netting and electrofishing. The two man-made dams as well as beaver dams are limiting the production of bull trout in the Clearwater Drainage by blocking or delaying migrations of large migratory fish, particularly during low flow conditions. The data suggests that reestablishing habitat connectivity and protecting and restoring tributaries is likely to increase population growth. Based on our evaluation of the invasion threats at the two man-made dams, we recommend the removal of Emily-A Dam, and the modification of Rainy Dam to restore connectivity for migratory bull trout.

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© Copyright 2009 Aubree Benson