Fish Barrier Assessments in the Bow River Watershed
The historic range of Westslope cutthroat trout (WSCT) in Alberta lies entirely within the Oldman and Bow River watersheds. In recent decades, genetically pure populations have declined to approximately 5% of the historic distribution. Invasive species are among the biggest contributors to the WSCT declines because of hybridization and competition. Natural waterfall barriers that impede upstream fish movements are known to protect headwater populations of WSCT from non-native rainbow trout and brook trout invasions. As a conservation measure, ACA has undertaken a broad-scale inventory and assessment of these barriers to identify barriers protecting crucial populations currently sustaining the species, and find opportunities to expand the WSCT range into secure, unoccupied habitat reaches above barriers. Since 2017, we have developed standard methods to identify, measure, classify, and rank a complex range of fish barriers in the context of invasion risk and conservation potential, and have completed assessments in much of the Oldman River watershed. In 2020, we finalized assessment methods into a field manual that assesses four main mechanisms that impede fish passage over barriers: 1) height/length obstructions to leaping, 2) water velocity obstructions to swimming, 3) water depth obstructions to swimming, and 4) turbulence obstructions to swimming. We have broadened surveys into the Bow River watershed, visiting 50 of approximately 250 locations in that watershed. We will continue barrier surveys through 2021 to comprehensively catalogue all barriers across the WSCT range and help prioritize future range expansion strategies to restore and reconnect WSCT populations.
Alberta Environment and Parks, Fisheries and Oceans Canada
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