Spatially Dependent Responses of a Large‐River Fish Assemblage to Bank Stabilization and Side Channels

Abstract

The alteration of rivers by anthropogenic bank stabilization to prevent the erosion of economically valuable lands and structures has become commonplace. However, such alteration has ambiguous consequences for fish assemblages, especially in large rivers. Because most large, temperate rivers have impoundments, it can be difficult to separate the influences of bank stabilization structures from those of main‐stem impoundments, especially because both stabilization structures and impoundments can cause side‐channel loss. Few large rivers are free flowing and retain extensive side channels, but the Yellowstone River (our study area) is one such river. We hypothesized that in this river (1) bank stabilization has changed fish assemblage structure by altering habitats, (2) side‐channel availability has influenced fish assemblage structure by providing habitat heterogeneity, and (3) the influences of bank stabilization and side channels on fish assemblages were spatially scale dependent. We developed a spatially explicit framework to test these hypotheses. Fish assemblage structure varied with the extent of bank stabilization and the availability of side channels; however, not all assemblage subsets were influenced. Nevertheless, bank stabilization and side channels had different and sometimes opposite influences on the fish assemblage. The effects of side channels on fish were more consistent and widespread than those of bank stabilization; the catches of more fishes were positively correlated with side‐channel availability than with the extent of bank stabilization. The influences of bank stabilization and side channels on the relative abundances of fish also varied, depending on species and river bend geomorphology. The variation in river morphology probably contributed to the assemblage differences between stabilized and reference river bends; stabilized alluvial pools were deeper than reference alluvial pools, but the depths of stabilized and reference bluff pools did not differ. The strengths of the relationships among fish assemblages, bank stabilization, and side channels were spatially scale dependent; optimum spatial scales ranged from less than 200 m to 3,200 m up‐ and downstream, suggesting that bank stabilization and side channels influenced fish assemblages across multiple spatial scales. Received October 7, 2016; accepted January 23, 2017 Published online July 31, 2017

Comparative use of side and main channels by small‐bodied fish in a large, unimpounded river

“…Goldeyes are considered riverine habitat generalists (Pegg & Pierce, 2002) and occupy side channels in the Missouri River (Moon, Fisher & Krentz, 1998) and upper Mississippi River (Barko & Herzog, 2003) during base flow. However, the depths and velocities of Yellowstone River main channels (Reinhold, 2014) are probably similar to the depths (Moon et al, 1998;Barko & Herzog, 2003) and velocities (Barko & Herzog, 2003) of side channels in these larger rivers.…”

“…Third, side channels probably provided small fish refugia from swift current velocities. The majority of our catch was small cyprinids, which are more reliant on velocity refugia than larger main‐channel fishes such as adult channel catfish or shovelnose sturgeon, which although abundant in our study area (White & Bramblett, ) were rarely captured in our SSCV net sets (Reinhold, ). Although the differences in current velocity between side‐channel and main‐channel SSCV were small in magnitude, catch rates and quantitative assemblage composition followed the patterns in current velocity, and these differences may have contributed to our results.…”

“…Goldeyes are considered riverine habitat generalists (Pegg & Pierce, ) and occupy side channels in the Missouri River (Moon, Fisher & Krentz, ) and upper Mississippi River (Barko & Herzog, ) during base flow. However, the depths and velocities of Yellowstone River main channels (Reinhold, ) are probably similar to the depths (Moon et al ., ; Barko & Herzog, ) and velocities (Barko & Herzog, ) of side channels in these larger rivers. Our findings are consistent with other studies that report that some fishes occur primarily in either side or main channels (Burgess et al ., ), whereas others move laterally between side and main channels (Hohausová, Copp & Jankovskỷ, ; Csoboth & Garvey, ; Burgess et al ., ).…”

“…Side channels were probably more suitable habitat than main channels during runoff because black crappie typically occur in areas with little to no currentvelocity and abundant cover (Warren, 2009). Goldeyes shifted from using both side channels and main channels during runoff to primarily using main channels during base flow, probably because goldeyes are frequently found in fast currents (Pegg & Pierce, 2002;Barko & Herzog, 2003), which occurred primarily in the main channel during base flow (Bowen et al, 2003;Reinhold, 2014). Goldeyes are considered riverine habitat generalists (Pegg & Pierce, 2002) and occupy side channels in the Missouri River (Moon, Fisher & Krentz, 1998) and upper Mississippi River (Barko & Herzog, 2003) during base flow.…”

Riverine turtles select habitats maintained by natural discharge regimes in an unimpounded large river

“…Similarly, riverine fishes also occupy and aggregate in deep, overwintering habitats to avoid ice scour, high water velocities, or predation (Jaeger et al, ; Jaeger et al, ; Mitro & Zale, ; Swales, Lauzier, & Levings, ). Selection for natural bluff pools over altered pools (e.g., riprap alluvial and diversion dam) suggests that the quality or function of altered habitats may be diminished and discernible by riverine biota (Reinhold, Bramblett, Zale, Poole, & Roberts, ).…”