The Impact of Dam Removal on Native Fish
Small Dam Removal in the Clearwater River, MT
A major issue in stream and river restoration is the removal of barriers and dams on the landscape. Many small dams that were initially constructed for water diversion and irrigation have reached the end of their useful life, and are being considered for removal or restructuring because of ecological concerns, as well as the safety concerns and costs of continued operation or repair of older structures. For example, in the last 20 years, over 500 dams, primarily smaller dams, have been removed in the United States (Poff and Hart, 2002; Stanley and Doyle 2003).
In many cases, these barriers are problematic for migrating species, especially two species of concern in Montana, westslope cutthroat trout (Oncorhynchus clarki lewisi) and bull trout (Salvelinus confluentus). Implicated in the decline of both of these native Montana species is fragmentation and loss of river and tributary habitat (Montana Fish Wildlife and Parks 2005). In western Montana, dams are a major landscape feature impeding movement of native fish. Despite these documented negative impacts to native fishes, fish passage barriers can also act to benefit fish communities by impeding the expansion of introduced species, such as lake trout and northern pike. Many of these introduced species prey upon and competition with native species resulting in their decline. As we move forward with restoration plans for these river sections we need to explicitly evaluate the impact of the successful spread and establishment of exotic species on the landscape, as well as, the benefits to native species.
Aubree Benson, a graduate student in Wildlife Biology is investigating these issues in the Clearwater River. This is a collaborative project with Montana Fish Wildlife and Parks, the Forest Service, and the university. She will be working to both (1) develop and implement a decision framework and evaluating the risks and benefits of dam removal on the Clearwater River native fish community and (2) examine different strategies to examine whether there is a way to replace low head dams with structures that may pass bull trout and westslope cutthroat trout, but not other exotic species whose distributions are currently limited by dams (e.g., northern pike). Aubree Benson performing a snorkel survey at Emily A dam on the Clearwater River to determine which species may pass when dams are removed. Aubree Benson tracking bull trout with radio-tags to determine how they use the Clearwater River and what impact these small dams are having on movement patterns.