Effects of river scale flow regimes and local scale habitat properties on fish community attributes

Abstract

Community attributes result from processes operating at various spatial scales. The hierarchic organisation of rivers and the prevailing hypotheses about the variables that affect fish communities make lotic ecosystems particularly suitable to study processes taking place across spatial scales. The general goal of this study was to investigate how river flow regime and local habitat properties explain and predict fish community attributes in unregulated and regulated rivers. Our objectives were: (1) to identify the hydrological indices that best describe the flow regimes of river segments subjected to different regulation types (unregulated, run-of-the-river, storage, and peaking), and; (2) to estimate the relative importance of hydrological indices (river scale), and water depth, water velocity, and substrate composition (local scale) in explaining and predicting local fish community attributes (species richness, total density, and total biomass). We surveyed 880 sites (*300 m 2 ) in 25 rivers (14 unregulated and 11 regulated) located in six physiographic regions of Canada. Based on a discriminant function analysis, nine hydrological indices were selected to represent river flow regime. Models of fish community attributes were developed using linear mixed-models (LMM) by nesting sites within rivers and regions. A few hydrological indices along with habitat properties predicted fish community attributes at the site scale (0.43\ cross-validation R 2 CV \0:66). Specific hydrological indices and local habitat properties can be managed to preserve fish community attributes in regulated rivers. Combining variables associated with different scales in a LMM was a powerful and efficient way to model fish community attributes and produced reliable predictive models.

Using fish guilds to assess community responses to temperature and flow regimes in unregulated and regulated Canadian rivers

“…Hydro-peaking rivers additionally provoke frequent and rapid flow peaks that are timed to match daily consumption needs, causing significant flow alteration (Zimmerman et al, 2010) and subsequent ecological impacts (Bond, Jones & Haxton, 2015;Macnaughton et al, 2015b;Senay et al, 2016). All unregulated and regulated rivers segments were analysed together to assess the effect of contrasting river flow and thermal regimes on fish guild models.…”

Run-of-River hydropower and salmonids: potential effects and perspective on future research

“…For example, even small, but repeated, flow fluctuations were found to decrease the feeding time, growth, and survival of fish (Young et al 2011). In addition, small but frequent anthropogenic fluctuations in flow have also been found to reduce fish density and biomass when compared to infrequent but large fluctuations generated by storage-reservoir hydropower in Canada (Senay et al 2016). These findings may be particularly relevant for RoR hydropower systems, which can create more frequent pulses in flow compared to reservoir-storage hydropower due to the lack of water storage in headponds and wider-magnitude fluctuations during low-flow seasons.…”

“…Data from an unregulated montane stream in the US Pacific Northwest show that natural fluctuations in stage rarely exceeded 5 cm·h −1 (Hunter 1992, cited in Bell et al 2008, while frequent declines in river stage of 80-90 cm over 10 min were reported downstream of a reservoir-storage dam in Norway (Hvidsten 1985). Fish stranding or isolation in side channels may in turn lead to negative effects on survival, biomass, density, or fitness, as reported in studies from reservoir-storage systems (Young et al 2011;Nagrodski et al 2012;Senay et al 2016). Given the limited research that has specifically sought to understand the consequences of anthropogenic flow fluctuations in RoR hydropower systems, large uncertainties remain about how their effects differ from those documented downstream of reservoir-storage systems where most peer-reviewed research has occurred.…”

“…Such changes in physical habitats can lead to impacts on riverine ecosystems by reducing water quality and altering the abundance, richness, and composition of periphyton, invertebrate, and fish assemblages (Santucci et al 2005;Mueller et al 2011;Anderson et al 2014). In contrast, the flow regime in reaches downstream of RoR powerhouses is expected to be the most similar to the NFR, since water diverted for power generation is returned to rivers after passing through turbines (Poff and Hart 2002;Kibler and Tullos 2013;Senay et al 2016). Nonetheless, the return of water at the tailrace may have a hydraulic impact on benthic macroinvertebrate composition (Anderson et al 2015) or fish as a result of dissolved gas supersaturation (Weitkamp and Katz 1980).…”

“…The limited peerreviewed literature that we found specific to RoR hydropower strongly suggests that impacts to salmonids and other fishes are probable under certain conditions, which is supported by better studied impacts of other forms of flow regulation. However, we caution that the knowledge developed from other types of flow regulation may not be directly applicable to RoR hydropower (Senay et al 2016). As such, research specific to how RoR hydropower operations alter the NFR and how these alterations impact fish populations and river ecosystems is needed to confirm the pathways and mechanisms we outline in this paper.…”