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

Abstract

Summary Hydropower currently accounts for 63% of Canada's total electricity generation and is bound to increase with the energy demands of a growing population. With damming and flow regulation known as major threats to aquatic biodiversity and river and floodplain habitats, an improved understanding of the specific impacts of river regulation is needed for the proper management of these systems. Although interactions among river flow and thermal regimes have been described in the literature, their concurrent influence on fish guild responses has yet to be analysed for temperate rivers. Such an analysis may be used to identify the ecological traits linked with the flow and thermal variables reflecting river regulation. Extensive field surveys were conducted across 25 unregulated and regulated rivers to estimate fish species density and biomass. Fish guild models were developed to characterise morphologic, trophic, reproductive, habitat preferences and behavioural traits, as well as phylogenetic associations. To characterise ecologically relevant components of the flow and thermal regimes of rivers, we calculated indices based on the magnitude, frequency, duration, timing and rate of change in each driver. Model relationships between fish biomass and density estimates were then run using redundancy analyses (RDA) on each type of guild and dominant patterns of flow and thermal variability. Variables representing the magnitude of summer temperatures and intra‐annual flow variability were consistently selected as independent drivers of fish guild responses (>86% of RDA models), clearly showing the importance of integrating thermal regimes in current river hydro‐ecological studies. Fish guild density and biomass were significantly explained (R2Adj = 25–44%) and predicted (R2CV = 35–76%) by flow and thermal variables characterising regimes across unregulated and regulated rivers, whereas total fish density and biomass were not. Fish guild models based on trait–environmental relationships performed better than those based on phylogeny. Our results also showed that the models describing habitat and trophic guilds had the greatest explanatory power (R2Adj = 0.44 and R2Adj = 0.41 respectively). This study identified differences in guild trait–environment relationships across rivers and the guilds most susceptible to changes in flow and temperature conditions resulting from river regulation. In particular, more constant summer temperatures and lower flow variability favoured habitat and trophic guilds over morphologic, reproductive and behavioural guilds. Our results showed that maintaining particular aspects of the flow and thermal regime may be important for ensuring the presence of certain guilds in temperate rivers.

Living in flowing water increases resistance to ultraviolet B radiation

“…Human modifications such as the construction of dams will compound climate effects and also cause interactions between flow and other drivers such as temperature (Macnaughton et al, 2016). We show that decreased flow, as well as changes in temperature (Ghanizadeh Kazerouni et al, 2016) can make fish more vulnerable to the negative effects of UV-B.…”

Multiscale Investigation of Water Chemistry Effects on Fish Guild Species Richness in Regulated and Nonregulated Rivers of India's Western Ghats: Implications for Restoration

“…Water chemistry criteria could also be linked to estimation of flow release thresholds from barrages (Macnaughton et al. ). Such criteria could be prioritized in decision‐making processes to mitigate the impacts of dams on sensitive species.…”

Evaluating transferability of flow–ecology relationships across space, time and taxonomy

“…Theoretical and experimental studies point to the strength of guilds over taxonomy in predicting flow responses (Macnaughton et al., ; Merritt et al., ). We found no significant differences between transferring within species identity versus transferring across guild members for informing a species’ flow–ecology relationship, which supports the use of guilds in transferring flow–ecological knowledge across different species.…”

“…Flow variability and seasonality are also important flow regime features to consider (Mims & Olden, 2012;Naiman et al, 2008;Stewart-Koster et al, 2014) and responses to these features are likely to transfer in manners different from flow magnitude relationships. Additionally, species' responses to thermal regimes for supporting environmental flows need to be better characterised (Macnaughton et al, 2016;Olden & Naiman, 2010). These factors may explain the relatively low correlations in our flow-ecology models (Table 2).…”

“…Lytle, Merritt, Tonkin, Olden, and Reynolds () categorised riparian vegetation into five flow‐response guilds to study the network connectivity of plant communities in natural and altered flow regimes and illustrate the destabilisation of these communities with increasing levels of drought. Guilds such as habitat preference and trophic position also strongly characterised the flow response of freshwater fishes across 25 natural and regulated rivers in Canada (Macnaughton et al., ). Dunbar et al.…”