# River-Wide Habitat Availability for Fish Habitat Guilds: Implications for In-Stream Flow Protection
## 4 Discussion  
Assessment of habitat suitability at a river-wide spatial scale and at different river discharges provided insight into the dynamic nature of habitat availability that may influence fish community composition along river systems [6; 27]. Suitable habitat conditions were available in each river segment of the Niobrara River for each fish guild. The relative proportion of habitat was influenced by the magnitude of discharge. For instance, the lobate margin guild had no less than 30% of channel area considered suitable habitat across all river segments at the greatest discharge levels modeled but had less than 17% of the channel area considered suitable habitat at low discharges. The percentage of habitat needed to support the current fish community is unknown. However, the availability and distribution of suitable habitat in the Niobrara River may serve as a conservation baseline for habitat needs to keep the fish community intact [19]. Suitable habitat availability for each fish habitat guild generally increased with increasing discharges. The increase in habitat availability with increasing discharge may be particularly relevant for habitat types that may completely disappear under certain discharge conditions. For instance, riffle and slackwater areas may become greatly diminished at extreme low discharge levels [28]. Our results suggested that habitat availability in segment 1 might be limited for the riffle guild during low discharges. Shallow water habitats used by riffle guild fishes are likely reduced in segment 1 due to limited constraining of river water in the wide and braided channel. In contrast, habitat availability for the riffle guild is consistent across discharges in segment 3 where channel geomorphology (i.e., single channel with defined banks) constrains river water and maintains habitats needed by fishes in the riffle guild. Changes in habitat availability across discharge levels and segments due to geomorphic changes in valley width along the length of the river may influence the composition of the Niobrara River fish community [17; 29]. Furthermore, if water availability within the Niobrara River changes substantially either through increased human use or changing climate patterns the current structure of fish habitat guilds may be altered as habitat abundance and distribution is tightly linked to discharge patterns. Discrepancies existed between habitat availability and fish habitat guild structure along the Niobrara River. Fish habitat guilds were not represented proportionately with suitable habitat availability and suggest a mechanism other than habitat alone may influence the presence and abundance of fish guilds. The observed discrepancies between suitable habitat and fish habitat guild composition may result from changes in natural biologic variability due to species mobility and life-history shifts in habitat use [30]. Seasonal migration patterns and multiple life stages present in the river that may not be captured by single survey observations that did not differentiate among life-stage specific habitats. Additionally, species interactions (i.e., competition or predation), may also influence establishment of species throughout available habitats [31]. For instance, non-native species within the Niobrara River have been implicated in shaping macroinvertebrate and fish community structures [32; 33]. River discharge guidelines used to protect riverine fishes may benefit from reflecting the intra- and inter-annual variability in discharge that occurred without human modification [34]. Anthropogenic use of river systems, however, has modified river discharge and altered the spatial and temporal dynamics of river systems [1; 35]. Elimination of hydrologic variability--including droughts or floods--alters the evolutionary trajectories of fish communities as well as reduces a system's ability to limit invasion by non-native species [36; 37].