Microhabitat use of native fishes in the Kootenai River: A fine-scale evaluation of large-scale habitat rehabilitation efforts

Fish and microhabitat data were collected at 542 prepositioned electrofishing sites (surface area of each site = 4 m(2)) in the Kootenai River, Idaho, during 2014 and 2015 to evaluate small-scale habitat use by fishes, as it relates to large-scale habitat rehabilitation efforts. Samples were collected from a 12-km braided segment of river that had received localized habitat rehabilitation treatments since 2011. Fish and microhabitat data were collected to investigate habitat drivers related to the occurrence and relative abundance of fishes. Each sampling location was selected at random and characterized as "treated" (i.e., rehabilitated) or "untreated" based on proximity to habitat treatments. Fishes sampled from backwaters composed 71% of the overall catch and 84% of the catch from locally untreated areas of the river. Species-specific regression models suggested that water depth and current velocity influenced the occurrence and abundance of fishes. In particular, shallow habitats with low current velocities were important for small-bodied native fishes and likely serve as important rearing areas for juvenile fish. These habitat conditions typically characterize backwater and channel-margin habitats that are vulnerable to anthropogenic perturbation. Prioritizing process-based rehabilitation of these areas in large, regulated rivers would allow natural channel-forming processes for the benefit of native fishes.