Do Beaver Dams Impede the Movement of Trout?

Dams created by North American beavers Castor canadensis (hereafter, “beavers”) have numerous effects on stream habitat use by trout. Many of these changes to the stream are seen as positive, and many stream restoration projects seek either to reintroduce beavers or to mimic the habitat that they create. The extent to which beaver dams act as movement barriers to salmonids and whether successful dam passage differs among species are topics of frequent speculation and warrant further research. We investigated beaver dam passage by three trout species in two northern Utah streams. We captured 1,375 trout above and below 21 beaver dams and fitted them with PIT tags to establish whether fish passed the dams and to identify downstream and upstream passage; 187 individual trout were observed to make 481 passes of the 21 beaver dams. Native Bonneville Cutthroat Trout Oncorhynchus clarkii utah passed dams more frequently than nonnative Brown Trout Salmo trutta and nonnative Brook Trout Salvelinus fontinalis . We determined that spawn timing affected seasonal changes in dam passage for each species. Physical characteristics of dams, such as height and upstream location, affected the passage of each species. Movement behaviors of each trout species were also evaluated to help explain the observed patterns of dam passage. Our results suggest that beaver dams are not acting as movement barriers for Bonneville Cutthroat Trout or Brook Trout but may be impeding the movements of invasive Brown Trout.