Why do fish strand? An analysis of ten years of flow reduction monitoring data from the Columbia and Kootenay rivers,Canada

Stranding of fish due to flow reductions has been documented in the near shore of the Columbia and Kootenay Rivers, Canada, and can result in sub‐lethal or lethal effects on fish. Ten years (1999–2009) of monitoring data have been collected at sites below two hydro‐electric dams (Hugh‐L‐Keenleyside and Brilliant Dam) following flow reductions. A generalized linear mixed effects model analysed the probability of a stranding event in relation to environmental and operational variables including the rate of change in the water levels, the duration of shoreline inundation prior to a reduction (wetted history), the river stage, the magnitude of the reduction, distance downstream from the dam, time of day, day of year (season) and whether a site had been physically altered to mitigate stranding. The results demonstrated statistically significant effects on stranding risk from minimum river stage, day of the year and whether a site had been physically re‐contoured. The combination of investigated factors giving the highest probability of stranding was a large magnitude reduction completed in the afternoon in midsummer, at low water levels when the near shore had been inundated for a long period. This research is significant in its approach to assessing years of ecosystem scale monitoring data and using the modelling results to determine ways for these findings to be applied in regulated river management to minimize fish stranding. It also highlighted data gaps that require addressing and provides ecosystem scale results to compare with stranding studies carried out in mesocosms. © 2014 The Authors. River Research and Applications published by John Wiley & Sons Ltd.     

Fish age and size distributions and species composition in a large,hydropeaking Prairie River

Fluctuations in river flows result from diverse natural and/or anthropogenic causes. Hydropeaking, an important anthropogenic flow alteration, results from the rapid increase or decrease of water releases from reservoirs at hydroelectric power stations to meet variable demand for electrical power, thereby altering the flow regime of the river downstream of the hydroelectric power station. Hydropeaking causes short‐term, artificial fluctuations in flow on an hourly, daily, and/or weekly basis. The frequent and regular occurrences of these high and low flow events are fundamentally different from natural flood and drought events and may affect fish fauna. We compared the fish species composition and fish age and size distributions in the Saskatchewan River (Saskatchewan, Canada) downstream of a hydropeaking facility with results from an unaffected Reference Site situated upstream of the reservoir. Lower fish diversity was observed in the 2 downstream sites (Sites 1 and 2, number of species = 11 and 9, respectively) closest to Generating Station in comparison to Site 3 (n = 15) situated further downstream and the upstream reference site (n = 13). There was no difference in the age–length relationship of any of the fish species above and below the Generating Station suggesting that fish grew at the same rates. However, lower numbers of small‐bodied and juvenile fish were caught downstream of the Generating Station suggesting the possibility of increased mortality, decreased habitat suitability, or altered behaviour of small fish downstream of the dam. These data illustrate potential impacts of hydropeaking power stations and has management implications.     

Structure and Ordination of Epiphytic Invertebrate Communities of Four Coastal Wetlands in Green Bay,Lake Michigan

Epiphytic macroinvertebrate communities of four coastal wetlands of Green Bay, Lake Michigan were compared by taxonomic composition, feeding group composition, and environmental influences using Bray-Curtis ordination. Ordination scores from the most sheltered oligotrophic site, Portage Marsh, were distinct from the eutrophic, exposed sites located in middle and lower Green Bay— Seagull Bar, Little Tail Point, and Dead Horse Bay. Epiphyton chlorophyll a, phytoplankton chlorophyll a, and specific conductance strongly correlated to the ordination axes, indicating the trophic gradient within Green Bay was a primary environmental influence. The feeding group compositions at the sites were consistent with the type and abundance of food available. Portage Marsh is a scraper-shredder system, with macroinvertebrates feeding mainly on epiphyton and coarse particulate detritus. Dead Horse Bay and Little Tail Point are collector systems, sustained by phytoplankton and fine particulate organic matter. Seagull Bar is intermediate in trophic position along the ordination axes, but more closely resemble the latter two sites. The type and abundance of food resources available to these invertebrate communities are influenced by wave exposure, light attenuation, nutrient levels, and algae levels of the littoral and pelagial waters. Macroinvertebrate communities were sensitive to shifts in food resources, which generated shifts in trophic structure.     

Environmental Issues and Management for Hydropower Peaking Operations

Many hydropower plants are operated as peak generators or frequency controllers, because they can change their output quickly to follow the fluctuating power demand. When meeting peak load requirements, a power station is turned on at a particular time during the day, generates power at a constant load for a certain number of hours, and is then turned off or set to a different load for another time period, resulting in a high variability inflow discharges. Where reservoir hydro schemes are operated primarily to provide peak load services, there are particular environmental risks that should be considered in any environmental impact assessment. At a minimum these should focus on water quality, fluvial geomorphology, riparian vegetation, macro-invertebrate and fish communities underpinned by a sound hydrological analysis. Frequent temperature changes may occur downstream of a peaking power station; increased seepage-induced erosion of riverbanks due to frequent water level drawdowns; and impacts to macro-invertebrate and fish communities due to rapid and frequent in channel habitat conditions. With a sound understanding of the potential environmental issues, there are strategies that can be employed at the siting and design stage to minimize or mitigate these risks, including but not limited to minimum environmental flows, ramping rules, utilization of a re-regulation storage and localized treatment works.     

Do cyprinid fish use lateral flow-refuges during hydropeaking?

Hydropeaking caused by small-scale hydropower plants creates rapid changes in the intensity, frequency, and persistence of river flows. These changes can induce stress in fish across all life-stages and, may negatively impact fish communities. Rapid increases in the flow velocity may cause fish to avoid unstable habitats, seeking out nearby refuges to reduce their energy expenditure. A lateral flow-refuge constructed from maritime plywood (0.4 m wide × 0.5 m long × 0.4 m high) was installed in the left river bank, 40 m downstream of the Bragado hydropower plant. A multispectral stereo underwater camera trap was installed inside the flow-refuge to monitor fish over one-month period. The camera recorded images continuously both during base and peak flow conditions. Two different peak-flow conditions were detected: peak and high peak-flow conditions. The peak flow conditions correspond to a turbine discharge of 0.67 m³/s (peak), and 2.1 m³/s (high peak) at full load. The base-flow condition corresponded to a discharge of 0.064 m³/s. The fish presence inside the refuge was observed to be significantly higher during the peak condition when compared with the base and high peak conditions. These findings strongly indicate that the flow during the high peak condition prevented fish from using the flow-refuge due to the increase in the current. We hypothesize that this may be due to the increase in the current velocity and increased levels of ambient turbulence near the refuge. An alternate hypothesis is that the spatial distribution of velocities and depths during the high peak condition induced fish to inhabit areas with poor access to the refuge. The results of this study indicate that fish refuges can be used to successfully mitigate hydropeaking, and that their use by fish can depend on the flow regime.