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

Abstract

Summary Ecological theory and field studies suggest that lateral floodplain connectivity and habitat heterogeneity provided by side channels impart favourable habitat conditions for lotic fishes, especially fluvial fishes dependent on large patches of shallow, slow velocity habitats for some portion of their life cycle. However, anthropogenic modification of large, temperate floodplain rivers has led to extensive channel simplification and side‐channel loss. Highly modified rivers consist of simplified channels in contracted, less dynamic floodplains. Most research examining the seasonal importance of side channels for fish assemblages in large rivers has been carried out in heavily modified rivers, where side‐channel extents are substantially reduced from pre‐settlement times, and has often overlooked small‐bodied fishes. Inferences about the ecological importance of side channels for small‐bodied fishes in large rivers can be ascertained only from investigations of large rivers with largely intact floodplains. The Yellowstone River, our study area, is a rare example of one such river. We targeted small‐bodied fishes and compared their habitat use in side and main channels in two geomorphically distinct types of river bends during early and late snowmelt runoff, and autumn base flow. Species compositions of side and main channels differed throughout hydroperiods concurrent with the seasonal redistribution of the availability of shallow, slow current‐velocity habitats. More species of fish used side channels than main channels during runoff. Additionally, catch rates of small fishes were generally greater in side channels than in main channels and quantitative assemblage compositions differed between channel types during runoff, but not during base flow. Presence of and access to diverse habitats facilitated the development and persistence of diverse fish assemblages in our study area. Physical dissimilarities between side and main channels may have differentially structured the side‐ and main‐channel fish assemblages during runoff. Patches of shallow, slow current‐velocity (SSCV) habitats in side channels were larger and had slightly slower water velocities than SSCV habitat patches in main channels during runoff, but not during base flow. Our findings establish a baseline importance of side channels to riverine fishes in a large, temperate river without heavy anthropogenic modification. Establishing this baseline contributes to basic fluvial ecology and provides empirical justification for restoration efforts that reconnect large rivers with their floodplains.

Fish community response to habitat variables in two restored side channels of the lower Platte River, Nebraska

“…Our findings contradict what we expected to occur with species diversity in regard to discharge in a restored side channel within a large, low‐gradient warm‐water river. We hypothesized that lower discharges and warmer water temperatures in the main channel would restrict available habitats in floodplain environments, similar to previous studies that have examined trends in fish usage among main‐stem and floodplain habitats (Heiler, Hein, Schiemer, & Bornette, ; Reinhold, Bramblett, Zale, Roberts, & Poole, ; Ward & Stanford, ). However, we hypothesize that the presence of deep pools (>1 m) and the influence of groundwater in the east side channel are likely creating suitable, or possibly refuge, habitat for many species including several native riverine fish species (e.g., flathead catfish, longnose gar, suckermouth minnow, brassy minnow, and silver chub); several of the species observed in the east side channel when discharge was low and temperatures were warm (e.g., bigmouth buffalo, brassy minnow, shoal chub, silver chub, and suckermouth minnow) were listed as declining in the Platte River by Peters and Schainost () and Steffensen, Shuman, and Stukel ().…”

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

“…Relationships with substrate and instream habitat structures were important for a few species in this study, but shallow areas with reduced flow appear to serve as a major driver of habitat use for small‐bodied fishes in this floodplain river system. The significance of SSCV habitats for small‐bodied fishes has been reported in other large floodplain river systems that have experienced a wide range of anthropogenic disturbances (Love, Phelps, Tripp, & Herzog, ; Nannini, Goodrich, Dettmers, Soluk, & Wahl, ; Reinhold et al, ). However, the availability of SSCV habitats is dependent on flow (Bowen et al, ; Reinhold et al, ), and these conditions may be entirely absent in regulated floodplain river systems as a result of water development.…”

“…The significance of SSCV habitats for small‐bodied fishes has been reported in other large floodplain river systems that have experienced a wide range of anthropogenic disturbances (Love, Phelps, Tripp, & Herzog, ; Nannini, Goodrich, Dettmers, Soluk, & Wahl, ; Reinhold et al, ). However, the availability of SSCV habitats is dependent on flow (Bowen et al, ; Reinhold et al, ), and these conditions may be entirely absent in regulated floodplain river systems as a result of water development. The lack of SSCV areas in other large river systems has prompted their artificial development for the benefit of native fishes.…”

“…In concert, shallow habitats with slow current velocities warm quickly and can extend the growth season for fishes (Ward & Stanford, 1995). The importance of SSCV habitats for small-bodied fishes has been demonstrated in small unimpounded streams (Watkins, Doherty, & Copp, 1997) and in a large unimpounded river (Reinhold, Bramblett, Zale, Roberts, & Poole, 2016 Relationships describing the occurrence and relative abundance of fishes were variable with regard to substrate type. In general, the occurrence of a fish species was positively related to large substrate, whereas relative abundance was negatively related to large substrate.…”

“…Our study further suggests that fish assem- et al, 2016). However, the availability of SSCV habitats is dependent on flow (Bowen et al, 2003;Reinhold et al, 2016), and these conditions may be entirely absent in regulated floodplain river systems as a result of water development. The lack of SSCV areas in other large river systems has prompted their artificial development for the benefit of native fishes.…”