Fish Assemblage Structure in Side Channels of the Kootenai River, Idaho

Since disconnection of the Kootenai River from its historic floodplain, off-channel habitats, though scarce, have been of high importance to the fish assemblage.  In particular, side channels in the “braided reach” of the Kootenai River are thought to provide important habitat diversity and refugia for many fishes.  While the importance of side channels in the Kootenai River to the fish assemblage has not been assessed, the functional diversity they offer makes them an important component of the lower Kootenai River ecosystem.  To evaluate fish assemblage structure we used boat-mounted electrofishing to sample fishes in 118 sites on 14 sampling events from July 2012 to January 2013 in side- and main-channel habitats.  We compared catch rates and assemblage structure of fishes between habitats.  Lastly, we used depletion methods to estimate population sizes in side-channel and main-channel habitats at a variety of discharges to evaluate whether catch-per-unit-effort from electrofishing is an adequate representation of fish abundance, and thus useful for drawing inferences from comparisons made between side- and main-channel habitats in the Kootenai River.  The results of this research will provide insight on the relative importance of off-channel habitats for fishes in the braided reach of the Kootenai River.