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

Abstract

Fish and microhabitat data were collected at 542 prepositioned electrofishing sites (surface area of each site = 4 m2) 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.

Resource selection and species interactions between native and non‐native fishes in a simulated stream system

“…Field surveys have demonstrated that juvenile largescale sucker use areas with slow current velocities (Branigan et al, 2018), and slow current velocity habitats are generally associated with the presence of pumpkinseed (Wydoski & Whitney, 2003). Although backwater habitats in the Kootenai River are scarce, they provide important habitat for smallbodied native fishes, including juvenile largescale sucker (Branigan et al, 2018). Given the pumpkinseed's affinity for lentic environments and the evidence surrounding their use of low-velocity habitats, backwaters likely provide suitable habitat for pumpkinseed in et al, 2018;Smith et al, 2016).…”

“…Although backwater habitats in the Kootenai River are scarce, they provide important habitat for smallbodied native fishes, including juvenile largescale sucker (Branigan et al, 2018). Given the pumpkinseed's affinity for lentic environments and the evidence surrounding their use of low-velocity habitats, backwaters likely provide suitable habitat for pumpkinseed in et al, 2018;Smith et al, 2016).…”

“…Fish were immobilised using low power output (<1800 W) to minimise stress and injury. Captured fish were visually assessed to select size ranges for each species that reflected those observed in association with engineered habitats in the Kootenai River (Table 1; Branigan et al, 2018; Smith et al, 2016; Watkins et al, 2015). All test fish were immediately transported to the Fisheries Wet Laboratory at the University of Idaho to begin acclimation.…”

“…To reduce the effect of observers, each experimental tank was out- Each trial began by placing an individual fish near the downstream barrier of each experimental tank at 07:00 h. A single fish was used to mimic low native fish densities observed in the Kootenai River (Branigan et al, 2018;Watkins et al, 2015). Eight replicate trials were conducted for each species in allopatry using naïve fish subjected to different wood treatments.…”

“…Our study examined two fish species native to the Kootenai River, mountain whitefish Prosopium williamsoni (Girard) and largescale sucker Catostomus macrocheilus (Girard), and one non‐native species, pumpkinseed Lepomis gibbosus (Linnaeus), in a simulated stream system. These species are frequently sampled within rehabilitated areas of the Kootenai River, and their habitat associations have been described in relation to habitat rehabilitation (Branigan et al, 2018; Smith et al, 2016; Watkins et al, 2015). More broadly, catostomids and coregonids are native and ecologically important to lotic systems throughout the northern hemisphere.…”