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Beaver reintroductions and beaver dam structures are an increasingly utilized ecological tool for rehabilitating degraded streams, yet beaver dams can potentially impact upstream fish migrations. We collected two years of data on Arctic grayling movement through a series of beaver dams in a low gradient mountain stream, utilizing radio‐telemetry techniques, to determine how hydrology, dam characteristics, and fish attributes impeded passage and movement rates of spawning grayling. We compared fish movement between a "normal" flow year and a "low" flow year, determined grayling passage probabilities over dams in relation to a suite of factors, and predicted daily movement rates in relation to the number of dams each fish passed and distance between dams during upstream migration to spawning areas. We found that the average passage probability over unbreached beaver dams was 88%, though we found that it fell below 50% at specific dams. Upstream passage of grayling was affected by three main characteristics: (a) temperature, (b) breach status, and (c) hydrologic linkages that connect sections of stream above and below the dam. Other variables influence passage, but to a lesser degree. Cumulative passage varied with distance upstream and total number of dams passed in low versus normal flow years, while movement rates upstream slowed as fish swam closer to dams. Our findings demonstrate that upstream passage of fish over beaver dams is strongly correlated with hydrologic conditions with moderate controls by dam‐ and fish‐level characteristics. Our results provide a framework that can be applied to reduce barrier effects when and where beaver dams pose a significant threat to the upstream migration of fish populations while maintaining the diverse ecological benefits of beaver activity when dams are not a threat to fish passage. Beaver reintroductions and beaver dam structures are an increasingly utilized ecological tool for rehabilitating degraded streams, yet the impacts of beaver dams on upstream fish migration remain unclear. Our study provides a framework for co‐managing beaver and fish based on hydrology, dam characteristics, and fish attributes. This framework can be applied to reduce barrier effects when and where beaver dams pose a significant threat to the upstream migration of fish populations while maintaining the diverse ecological benefits of beaver activity when dams are not a threat to fish passage. [ABSTRACT FROM AUTHOR]

Abstract Passage performance of upstream-migrating lamprey (Lampetra fluviatilis) was compared between sections of a Crump flow-gauging weir with and without studded tiles, and at a bottom-baffle fishway, on the River Derwent, England. The effects of microhydropower operation on attraction to multiple routes were also studied. Studded tiles were fixed horizontally on the weir face near the right bank, forming a 1 m wide treatment route, neighboured by a tileless control route. A bottom-baffle fishway was present at the right bank, alongside the hydropower tailrace. Two further weir-face control routes at the left bank, in combination with those on the right side, enabled comparison of lamprey attraction relative to the weir flow. Downstream and upstream ends of the right-hand weir-face routes, and of the fishway, downstream ends of the left-hand weir face routes, and the entrance of the hydropower tailrace area were instrumented with PIT antennas (n = 9 total). Of 395 PIT-tagged lamprey, released 0.52 rkm downstream of the weir on 10 separate dates in early winter 2017 (turbine on for 21/43 days of study period), 363 (91.9%) were detected by at least one of the antennas (median [IQR] minimum delay at weir: 15.0 [7.4–21.4] days). All lamprey detected at the left-bank antennas (attraction efficiency AE: 255/395 [64.6%]) were also detected elsewhere. The fishway was ineffective (AE: 343/395 [86.8%]; passage efficiency PE: 5/343 [1.5%]). While lamprey were more attracted towards the control relative to the adjacent tiled route, a higher number of fish traversed the weir using the latter (AE tiled route: 172/395 [43.5%]; PE tiled route: 44/172 [25.6%]; AE control route: 257/395 [65.1%]; PE control route: 22/257 [8.6%]). Lamprey were attracted towards the right half of the channel when the turbine was running, as only n = 88/4190 (2.1% of total attempts) detections were made at the two left-bank control antennas in the turbine-on condition, compared to 2775/13,029 (21.3%) at the same two antennas when the turbine was off. While improved passage efficiency was achieved using surface-mounted studded tiles, further in situ evaluations are needed to optimize their performance. [ABSTRACT FROM AUTHOR]

Abstract Fish are thought to exploit low velocity recirculation zones in the wakes of baffles to take refuge from challenging hydraulic conditions in baffled culverts. Here, we investigate how sediment deposition in the wakes of baffles affects passage and behaviors of juvenile rainbow trout in a baffled experimental flume. High temporal resolution 3D fish tracking provided detailed kinematics of adopted trajectories. Stereoscopic particle image velocimetry permitted a finely resolved description of the flow over a clear baffle configuration and the same configuration with sediment wedges placed in their wakes. Controlled station-holding, suggestive of flow-refuging, only occurred when sediment wedges were blocking the baffles' recirculation region. Also, maximum distances of ascent were higher, and slower ground-speeds were employed in the sediment condition. The results of this study suggest the turbulent recirculatory wakes of the clear bed condition caused postural instabilities and were in many ways detrimental to passage performance. Additional research is required to understand the relationships existing between baffle height, hydrodynamic recirculatory wake metrics, sediment deposition and the behavioral responses of fish interacting with weir baffle wakes. [ABSTRACT FROM AUTHOR]

Effect of geometrical and hydraulic parameters on the behaviour of migrating fish at hydropower facilities To protect migrating fish from harmful turbine passages, bar racks and bypasses can be effective mitigation measures. The number of fish that are protected by facilities like these can be increased if the behaviour of fish is considered during its design process. The effect of hydraulic and geometrical aspects of bar racks was tested by means of ecohydraulic studies with eels, graylings, perches, salmons and roaches. The combination of behavioural studies and flow examination offers the possibility to gain insight into parameter‐behaviour interactions. These studies proved that apart from the approach velocity the bar rack spacing is the most influential parameter with regard to the screening effect of the bar rack as well as the searching behaviour of fish. [ABSTRACT FROM AUTHOR]

Highlights • Few fishway assessment studies compare performance of multiple fishway designs. • Use of vertical slot and lock-style fishways was simultaneously compared. • Small bodied species caused differences in composition among fishway and river samples. • Use of either fishways by fish was not influenced by hydrology or water quality. • Evaluating fishway performance requires both site and landscape-scale analysis. Abstract Engineering solutions that aim to restore hydrological connectivity in river systems fragmented by dams and weirs frequently include the installation of fish passage facilities (i.e. fishways). Assessment of fish passage performance is often limited to single fishway designs and with a focus on species of commercial or conservation significance, meaning that conclusions regarding fishway success may not apply to all species that require access to fragmented habitats. We simultaneously compared the population structure and fish assemblage composition at two fishways (vertical slot and fish lock designs) at weirs in a subtropical coastal river system. We used hydrological and physico-chemical water quality data to explore if fishway performance was linked to particular environmental conditions. At both fishways, fish assemblage composition differed between fishway exit and downstream river samples, yet differences between exit and river samples were not associated with hydrological variables related to the size and frequency of weir drown-out events or water quality. Population structure of the most abundant species (sea mullet, Mugil cephalus ; 61% of fish samples) also differed significantly among fishway exit and river habitats. A low-level structure spanning the river channel downstream of one weir was not associated with differences in fish assemblage composition indicating that access to the fishway entrance (and therefore fishway use) was not hindered by in-stream obstructions. Eight and seven species (predominantly small-bodied species that migrate within freshwater systems) were exclusively sampled in downstream river locations at the vertical slot and fish lock fishways, respectively, indicating that neither design was fully capable of facilitating the passage of the local fish fauna. Further assessment over a broader range of hydrological conditions will be necessary to determine if use of either fishway by fish is affected by low flows. Coupled with evidence produced from landscape-scale analysis of spatial and temporal variation in fish assemblage structure and dispersal patterns of diadromous species associated with river flow regime highlight that hydrological connectivity may be maintained by natural weir drown-out events. This study highlights that factors controlling hydrological connectivity for riverine biota need to be integrated among co-occurring anthropogenic impacts to identify and overcome constraints to effective conservation management in rivers subject to water resource development. [ABSTRACT FROM AUTHOR]

Hydropower dams can negatively affect upstream and downstream migratory fish populations in many ways, such as blocking access to upstream habitats and causing injuries or mortality during downstream passage. For downstream passage at projects in the USA, federal regulators and agencies responsible for oversight of hydropower facilities typically require assessment studies and mitigation to address negative effects, with a primary goal of minimising fish impingement and turbine entrainment and mortality. So as to assess the effects of downstream passage of fish populations at a unique, small hydro project on the Mississippi River, impingement and entrainment rates, Oberymeyer gate passage, spillway gate passage, turbine survival, and total downstream passage survival were estimated. It was determined that 85% of fish passing downstream at the project would be small enough to pass through the bar spacing of the trash racks and 15% would be physically excluded. When 55% of river flow enters the turbine intake channel, the total project survival rates were estimated to be 77.3% with an Obermeyer gate bypass rate of 10 and 96.6% with a gate bypass rate of 90%. Therefore, any effects on local fish populations resulting from the operation of the project are expected to be negligible and inconsequential on the basis of expected survival rates for the range and probability of river flows occurring at the project. We evaluated total project survival for fish moving downstream past a small hydropower facility located on the Upper Mississippi River in Minnesota, USA. Survival rates were developed from a desktop model that incorporated estimates of spillway and gate passage, intake trash-rack impingement, and turbine entrainment and survival. The results indicated that it was unlikely that the operation of the project was affecting local fish populations. [ABSTRACT FROM AUTHOR]

Knowing the kinds of physical stress experienced by fish passing through hydropower turbines can help optimise technologies and improve fish passage. This paper assesses the hydraulic conditions experienced through three different low-head turbines (a very low head (VLH), Archimedes screw and horizontal Kaplan turbine), taken using an autonomous sensor. In total, 127 Sensor Fish deployments were undertaken across all three turbines, generating 82 valid datasets. Decompression was rare at the VLH and screw turbines and rarely fell more than 10 kPa below atmospheric pressure. In contrast, the Kaplan was capable of generating pressures as low as 55.5 kPa (~45 kPa below atmospheric pressure), over shorter periods of time. More severe ratios of pressure changes could, therefore, be expected for both surface- and depth-acclimated fish at the Kaplan than at the other turbines. Strike was another possible source of fish injury (detected in 69–100% of deployments), and although strike severity was highest at the Kaplan, strike was more likely to be encountered at the screw and VLH than the Kaplan turbine. Shear occurred only near the blades of the Kaplan, and not at severe levels. The results demonstrated that low-head hydropower facilities are not without their risks for downstream migrating fish. Hydraulic and physical conditions through three different low-head turbines (very low head (VLH), Archimedes screw and horizontal Kaplan) were assessed using an autonomous sensor. All turbines displayed conditions that could injure fish migrating downstream. Strike events were common at the VLH and screw turbine, and decompression, strike and shear observed at the Kaplan turbine. [ABSTRACT FROM AUTHOR]

Highlights • Horizontal and vertical wedge-wire screens induced different hydrodynamics. • A vertical bar configuration created higher sweeping flow toward the bypass. • Chub avoidance to the screens was high resulting in low guidance overall. • A horizontal bar configuration under low discharge performed best. Abstract Physical screens are commonly installed to prevent downstream moving fish from entering dangerous areas (e.g. intakes to hydropower turbines, irrigation canals, and fish farms), and divert them to preferred alternative routes (e.g. bypass systems). In northern temperate regions, assessments of the functioning of screens have largely focused on diadromous species (e.g. salmon and eel), while ignoring those with other life history characteristics. Recent developments in physical screens include the usage of horizontally aligned bars as opposed to traditional vertical ones, but a direct comparison in terms of guidance remains untested. To address this and aid in the development of successful screens for the wider fish community, this study compared the efficacy of wedge-wire screens with horizontally and vertically oriented bars to block and divert downstream moving groups of five chub (Squalius cephalus) to a bypass channel installed in a recirculating flume under two discharge regimes. Hydrodynamics differed between horizontal and vertical screens under both flows; the vertical configuration created a higher velocity gradient towards the bypass. Total guidance (the number of bypass entries as a percentage of the number of approaches) was generally low (mean = 17.3% for all treatments), the highest being recorded for the horizontal screen under low discharge (25.3%). Rejections and holding station events, both proxies for fish exhibiting avoidance of the hydrodynamic conditions created by the screen, were lowest under this treatment. Horizontal performed better than vertical screens in guiding fish to the bypass under low but not high discharge. The results confirm that screen functioning is dependent on hydrodynamic conditions as well as the fish's behavioural response. [ABSTRACT FROM AUTHOR]

Knowledge of the spatial distributions and dispersal characteristics of invasive species is necessary for managing the spread of highly mobile species, such as invasive bigheaded carps (Bighead Carp [Hypophthalmichthys nobilis] and Silver Carp [H. molitrix]). Management of invasive bigheaded carps in the Illinois River has focused on using human-made barriers and harvest to limit dispersal towards the Laurentian Great Lakes. Acoustic telemetry data were used to parameterize multistate models to examine the spatial dynamics of bigheaded carps in the Illinois River to (1) evaluate the effects of existing dams on movement, (2) identify how individuals distribute among pools, and (3) gauge the effects of reductions in movement towards the invasion front. Multistate models estimated that movement was generally less likely among upper river pools (Starved Rock, Marseilles, and Dresden Island) than the lower river (La Grange and Peoria) which matched the pattern of gated versus wicket style dams. Simulations using estimated movement probabilities indicated that Bighead Carp accumulate in La Grange Pool while Silver Carp accumulate in Alton Pool. Fewer Bighead Carp reached the upper river compared to Silver Carp during simulations. Reducing upstream movement probabilities (e.g., reduced propagule pressure) by ≥ 75% into any of the upper river pools could reduce upper river abundance with similar results regardless of location. Given bigheaded carp reproduction in the upper Illinois River is presently limited, reduced movement towards the invasion front coupled with removal of individuals reaching these areas could limit potential future dispersal towards the Great Lakes. [ABSTRACT FROM AUTHOR]

Understanding the influence of river hydrology and connectivity on the migration and recruitment of diadromous fishes is fundamental for species management and conservation. We investigated the downstream catadromous spawning migration of adult female congolli (Pseudaphritis urvillii) using acoustic telemetry, and subsequent juvenile recruitment, in the lower reaches of the River Murray, Australia, in 2009–2011. The years 2009 and 2010 were characterised by diminished freshwater flow, closure of tidal barrages, and disconnection of freshwater and estuarine habitats; however, a navigation lock was operated to facilitate downstream fish passage in 2010. In both years, >70% of individuals tagged upstream undertook downstream migrations, in association with day-of-the-year (June–July) and moonphase (full), and accumulated upstream of the tidal barrages. In 2009, fish were unable to pass the barrages and remained upstream, but in 2010, an estimated >15 000 individuals passed through the navigation lock, including 40% of individuals tagged upstream. These transitioned rapidly (<24 h) through the estuary and into the ocean. In association, abundances of upstream migrant juveniles in spring–summer 2010–2011 were up to 180 times greater than in spring–summer 2009–2010. Our study illustrates the potential impact of tidal barriers on migrations and population dynamics of catadromous fish, and the importance of understanding species-specific migration ecology. This study investigated the downstream catadromous spawning migrations of congolli (Pseudaphritis urvillii), and subsequent juvenile recruitment, in the River Murray, Australia. During a period of freshwater scarcity, complete closure of tidal barrages obstructed migrations from freshwater habitats. In the subsequent spawning season, operation of a navigation lock facilitated passage past the barrages, and access to marine spawning habitats. In association, recruitment increased significantly. This illustrated the potential impact of tidal barriers on migrations and population dynamics of catadromous fish. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • 2 vertical slot (VSF) and 3 multi slot (MSF) fishways were assessed with 3D CFD. • MSF needs a lower discharge to operate than VSF, while keeping similar flow depths. • Velocity, turbulent kinetic energy, and Reynolds shear stress in the MSF are much lower. • MSF could be less selective and a better option for a multiple-species fishway. Abstract Adequately designed fishways mitigate the negative effects of barriers in rivers, restoring longitudinal connectivity. To do so, they must present suitable hydraulic conditions, with velocity and turbulence fields adequate for multiple fish species. In the present study, numerical modelling was used to compare the hydrodynamics of two widely used vertical slot fishways (VSF) configurations and three multi slot fishway (MSF) configurations. The MSF configuration needs a lower discharge to operate than the VSF, while keeping similar flow depths, which is vital in regions where water availability is limited, such as most Mediterranean regions. By reducing the discharge, the velocity, turbulent kinetic energy, and Reynolds shear stress values in the studied MSF configurations are much lower than the values for VSF configurations. Thus, besides requiring smaller discharges than similar VSF geometries, the MSF additionally could be less selective for fish species, particularly smaller-sized individuals, and individuals with weaker swimming capacities, and a better option for a multiple-species fishway. [ABSTRACT FROM AUTHOR]

The recent increase in river restoration projects is altering habitat connectivity for many aquatic species, increasing the chance that previously isolated populations will come into secondary contact. Anadromous and landlocked alewife (Alosa pseudoharengus) are currently undergoing secondary contact as a result of a fishway installation at Rogers Lake in Old Lyme, Connecticut. To determine the degree of prezygotic isolation and potential for hybridization between alewife life history forms, we constructed spawning time distributions for two anadromous and three landlocked alewife populations using otolith‐derived age estimates. In addition, we analyzed long‐term data from anadromous alewife migratory spawning runs to look for trends in arrival date and spawning time. Our results indicated that anadromous alewife spawned earlier and over a shorter duration than landlocked alewife, but 3%–13% of landlocked alewife spawning overlapped with the anadromous alewife spawning period. The degree of spawning time overlap was primarily driven by annual and population‐level variation in the timing of spawning by landlocked alewife, whereas the timing and duration of spawning for anadromous alewife were found to be relatively invariant among years in our study system. For alewife and many other anadromous fish species, the increase in fish passage river restoration projects in the coming decades will re‐establish habitat connectivity and may bring isolated populations into contact. Hybridization between life history forms may occur when prezygotic isolating mechanisms are minimal, leading to potentially rapid ecological and evolutionary changes in restored habitats. [ABSTRACT FROM AUTHOR]

The United States and Canada have begun renegotiating the Columbia River Treaty, which is an international model for transboundary water governance. This paper identifies six institutional factors that will affect negotiations pertaining to fish passage during the renegotiation of the treaty: geographical advantage, issue linkage, a basin commission, the duration of agreements, negotiating autonomy and side payments. These factors and the methods used to determine them can be applied to other transboundary river basins where basin states have a history of transboundary resource governance. This analysis also serves as a policy-relevant resource for Columbia River Treaty negotiators and stakeholders. [ABSTRACT FROM AUTHOR]

Abstract: To examine the role of longitudinal connectivity on the spatial and temporal dynamics of mountain whitefish (Prosopium williamsoni), we quantified movement and population dynamics following installation of the Landsburg Dam fishway, Cedar River, WA, USA. Mountain whitefish is widely distributed, poorly studied and not the focus of restoration. Before the fishway, mountain whitefish were not observed above the dam. Here, we focus on snorkel counts collected at reach and mesohabitat (e.g. pools) scales over 11 summers on the 20‐km above‐dam segment following restoration. A camera within the ladder provided number, size and movement timing, thereby informing on behaviour and recolonisation. Segment‐scale abundance increased following fish passage reaching an asymptote in 7 years, and mountain whitefish were detected throughout the main stem in 10 years. Annual movement through the ladder increased over time and was positively correlated with instream abundance and discharge, but negatively correlated with water temperature. About 60% of fish movements occurred in spring and early summer, potentially for foraging opportunities. Reach‐scale abundance peaked between 7 and 10 km from the dam; deep, cool (~10.6 to 11.6°C) conditions characterised these reaches. At the mesohabitat scale, mountain whitefish detection increased with depth and velocity after accounting for distance from the dam. Our results show how restoring longitudinal connectivity allowed this nontarget species to colonise newly available habitat. Their response supports the critical roles of longitudinal connectivity and environmental conditions, that manifest at different spatial scales, in dictating how freshwater fish respond to habitat disturbance. [ABSTRACT FROM AUTHOR]

Abstract: Traditional box culvert designs lead to development of high velocity zones in the culvert barrel that often impede upstream migration of fish. Herein, three‐dimensional Reynolds‐averaged Navier‐Stokes (RANS)‐ and Large eddy simulation (LES)‐based computational fluid dynamics (CFDs) simulations were performed to compare the effectiveness of smooth, asymmetrically roughened, and corner‐baffled barrels, in creating low‐velocity zones (LVZs) and providing opportunity for upstream passage of small‐bodied fish. The results revealed distinctive benefits provided by the asymmetrically roughened and corner‐baffled barrels relative to the smooth barrel. Cross‐sectional asymmetry, corners, and obstructions are important factors that contribute to the generation of LVZs conducive to fish passage, albeit contiguity of LVZs is required, particularly for weak swimmers. The study demonstrates the adequacy and effectiveness of CFD models to complement traditional laboratory studies in understanding basic mechanisms beneficial to fish passage and to provide insights into future designs. [ABSTRACT FROM AUTHOR]

With the explosive growth of global energy demand coupled with effects of climate change, there is a significant shift towards green energy generation in recent years. Of the various renewable energy resources available, micro-hydro-power and pico-hydro-power remain very popular in both developed and developing countries. Since 2006, significant growth has spurted in the use of artificial free-surface vortices to generate low and ultra-low-head hydropower following the development of the so-called gravitational water vortex hydropower plant. The technology works on the principle of harnessing hydroelectric power from the high angular velocity experienced in the core of a whirlpool generated in a vortex chamber. In this article, a state-of-the-art review is undertaken on the vortex hydropower technology including a historical review of the technology, the underlying hydraulic principles of such devices, overview of research and technologies that have been deployed to date together with an evaluation of their performance and key findings. Currently, there are 19-22 known live vortex hydropower technologies operating internationally with key academic and commercial research activity in Europe and Asia. The average efficiency from these sites was found to be in the region of 53% which is lower than conventional propeller turbines but higher than waterwheel systems. It was found that the vortex plant, due to its ability to sustain relatively high efficiencies at low heads and small to medium flow rates, addresses a gap in the current turbine application chart. Its key advantage lies in the high-power densities produced compared with conventional technologies. The system also demonstrates potential to be able to function as a fish passage; however, stronger validation is required to prove this for a range of turbine systems. Finally, the authors propose a number of areas that should be investigated that should provide immediate improvements to the turbine in terms of performance. [ABSTRACT FROM AUTHOR]

Highlights • Vertical slot fishways enable lateral fish movement in the Lower Mekong Basin (LMB). • Submerged 150 mm-orifice fishways also enable lateral fish movement in the LMB. • These fishways are similarly effective to one another, during the day and night. • However, they pass different species to each other during the day. • Fishway design choice will depend on the species being prioritised for restoration. Abstract River infrastructure poses a serious threat to diverse and productive fish stocks in many tropical river-floodplain systems; particularly the Lower Mekong River, where the fisheries are vital for food security. Dams and weirs block fish migration pathways and prevent access to feeding, spawning or nursery habitat. Fishways are becoming increasingly important for mitigating the effects of barriers; however, knowledge regarding their effectiveness for the biodiverse tropical river systems is still scant. This study examined the effectiveness of differing low-cost fishway designs for rehabilitating degraded floodplain fisheries in the Lower Mekong Basin (LMB) in Laos: (1) vertical slot; (2) submerged orifice — 150 mm square opening; and (3) submerged orifice — 300 mm square opening. Day and night in situ field experiments were undertaken to compare the abundance, biomass, species richness and size range of fish able to pass through each design with relatively low drops between pools (i.e. 150 mm each) and low water velocities (i.e. 1.71 ms−1). Passage of a total of 73 species was supported by the fishway designs at a similar abundance, biomass, species richness and size range of fish, during both the day and night; although, the vertical slot design supported a different suite of fish species to that of the other two designs during the day. This suggests that each of these fishway designs could be successfully used to support the rehabilitation of fisheries in the LMB and potentially other large tropical river systems with relatively diverse migratory fish communities and variable hydrological characteristics. However, the vertical slot provides greater design and operational flexibility over the submerged orifice designs particularly in tropical systems with inherently variable hydrology. The final fishway design choice ultimately depends on the fish species and size classes being prioritised for restoration and the unique hydrological characteristics of the site. [ABSTRACT FROM AUTHOR]

For some applications, fish passage through culverts may be enhanced by adding weir baffles along the culvert invert. In an effort to evaluate the effectiveness of computation techniques as a design tool for baffled-culvert design, turbulent free-surface flow conditions through a weir-baffled-lined culvert were simulated numerically using a three-dimensional numerical model utilizing three different turbulence models: k-, renormalized group k-, and large Eddy simulation. Experimental data from a small prototype-scale baffled-lined culvert, measured using particle image velocimetry, were used to assess the ability of these turbulence models to predict the turbulent flow characteristics for various culvert slopes and discharges. All computer simulations struggled in the regions of high shear and reverse flow, independent of the specific turbulence model used. Comparisons between the measured and computed flow field velocity and turbulent kinetic energy data, however, found that the renormalized group k- model provided the best approximation of the flow field, which included undulating supercritical flow profiles with recirculating eddies downstream of each baffle. Despite the limitations found in this study, computational fluid flow modeling represents a reasonable design tool-baffled-culvert design. [ABSTRACT FROM AUTHOR]

The ability of fish to swim upstream through regions of swiftly flowing water is ultimately dependent on their physiological capacity. Swimming performance, the relationship between swim speed and time-to-fatigue, has been used to design fishways and identify barriers to fish movement. However, existing numerical models do not all capture the variability in swimming abilities nor the turbulent, unsteady, and three-dimensional aspect of natural flows. This deficiency is particularly problematic for fish species whose behavior is poorly understood (i.e., invasive fish) and at sites with complex flow patterns. Here, we combine species-specific swimming performance with high resolution abstractions of fluid flow in a new agent-based framework to model fatigue of upstream swimming fish under turbulent flow conditions. Our model simulates fish paths, in the absence of information on their behavioral tendencies, based on a rules-set aimed at fish swimming as far upstream as possible before complete exhaustion by selecting the path of least fatigue. We demonstrate how this model functions by examining theoretical passage of invasive silver carp, Hypopthalmichthys molitrix, and bighead carp, H. nobilis, as well a native fish, the lake sturgeon, Acipenser fulvescens, through a typical Mississippi River lock-and-dam (Lock-and-Dam #8 near Genoa, WI). The model then tests whether passage could be reduced by altering spillway gate operations. Model results suggest that passage of all three species is low under current gate operations and that passage of both carp species could be further reduced by about half through minor changes in spillway gate operation without apparent impacts on navigation, scour, or lake sturgeon passage. Model results are qualitatively consistent with observed passage rates monitored by other studies at similar lock-and-dams and are consistent with the possibility that the model likely overestimates passage rates by relying on physiological data only. This approach could be exported to other applications and fish species to help manage and control fish migration and dispersal, especially for fish whose behavior and ecology are poorly understood and not presently quantifiable. [ABSTRACT FROM AUTHOR]

Instream barriers (e.g. dams, weirs and road crossings) fragment aquatic habitat and prevent the upstream movement of fish, impairing the ability of fishes to complete critical life stages, access critical habitat and for dispersal among local populations. Mitigation efforts have improved aquatic connectivity to some degree, but it has been challenging to quantify the overall improvement in connectivity without long-term and costly field assessments. The development of spatially explicit habitat connectivity indices make it possible to evaluate current stream connectivity, and quantify the improvement prior mitigation projects have had on connectivity. We combined a list of instream barrier mitigation projects completed in five watersheds in the Toronto (Ontario, Canada) area from 1987-2016 (mitigated barriers) and a previously established inventory of all known instream barriers in 2016 (current barriers). The cumulative improvement to connectivity was measured for potadromous (remain in tributaries) and diadromous (move between tributaries and lake) fish species using the dendritic connectivity index. Aquatic connectivity improved for diadromous species between 0 and 14.5% and for potadromous species between 0.1 and 4.4% in the five studied watersheds. Some variation in improvement among the watersheds can likely be attributed to differences in mitigation strategies among the watersheds and a historical emphasis on mitigating instream barriers to benefit migratory salmonid species. [ABSTRACT FROM AUTHOR]

Abstract: The construction of fishways for upstream and downstream connectivity is the preferred mitigation measure for hydropower dams and other riverine barriers. Yet empirical evidence for effective design criteria for many species is missing. We therefore assembled a group of international fishway designers and combined their knowledge with available empirical data using a formal expert elicitation protocol and Bayesian networks. The expert elicitation method we use minimizes biases typically associated with such approaches. Demonstrating our application with a case‐study on the temperate Southern Hemisphere, we use the resulting probabilistic models to predict the following, given alternative design parameters: (i) the effectiveness of technical fishways for upstream movement of migratory fish; (ii) habitat quality in nature‐like bypasses for resident fish; and (iii) rates of mortality during downstream passage of all fish through turbines and spillways. The Fish Passage Network (Fish‐Net) predicts that fishways for native species could be near 0% or near 100% efficient depending on their design, suggesting great scope for adequate mitigation. Sensitivity analyses revealed the most important parameters as follows: (i) design of attraction and entrance features of technical fishways for upstream migration; (ii) habitat preferences of resident fish in nature‐like bypasses; and (iii) susceptibility of fish to barotrauma and blade strike during turbine passage. Numerical modelling predicted that mortality rates of small‐bodied fish (50–100 mm TL) due to blade strike may be higher for Kaplan than Francis turbines. Our findings can be used to support environmentally sustainable decisions in the planning, design and monitoring stages of hydropower development. [ABSTRACT FROM AUTHOR]

Culverts are instream structures that act as hydrological barriers to fish movement by altering water turbulence, increasing water velocities and disrupting connectivity. Hydrological barriers like culverts have led to the fragmentation and decline of freshwater fish populations worldwide. Culvert remediation strategies such as bed roughening have proved effective at increasing the likelihood of fish passage in a variety of fish species. However, little is known about whether culvert roughening is efficacious for Australian small bodied fishes and if so, whether bed roughening is comparably beneficial to all species that may utilise remediated culverts. This study assessed the effect of roughened bed substrates on the swimming performance and behaviour of four small bodied or juvenile Australian fishes ( Hypseleotris compressa and Melanotaenia duboulayi , and juvenile Tandanus tandanus and Maccullochella peelii ) that exist in sympatry over parts of their distribution. Results showed that bed roughening increased water turbulence and the size of low velocity regions within fluid flow and that all fish species displayed the same positive behavioural preferences for these zones. However, the effect of bed roughening on swimming endurance and traversability was found to only benefit Mel. duboulayi and Mac. peelii. Roughening decreased endurance and traversability in T. tandanus , and had no effect on performance in H. compressa . These data indicate that sympatric species may respond differently to culvert remediation actions, highlighting the need for a holistic approach to culvert remediation and a comprehensive understanding of all species’ requirements within the affected environment. [ABSTRACT FROM AUTHOR]

Thousands of permit applications are filed annually with the U.S. Army Corp of Engineers, requiring significant review efforts to ensure that applications conform to regulations, and that proposed activities avoid, minimize, and compensate for stream and wetland impacts. However, the effectiveness of this approach remains uncertain. We evaluated the effectiveness of those regulatory efforts using newly installed stream-road crossings as a case study because crossings are pervasive on the landscape and many U.S. Army Corp of Engineers jurisdictions have requirements that are aimed at minimizing crossing-induced impacts to fish passage. Specifically, we assessed whether requirements intended to facilitate fish passage were implemented, whether requirements resulted in fish-passable stream-road crossings, and whether the amount of construction-related stream impact that was authorized by permits corresponded to the amount of compensation that was required. Our analysis is devoted solely to stream-road crossings in Georgia that are permitted under nationwide permits, the permit type commonly used to authorize activities in streams throughout the United States. We found that no new crossings conformed entirely to the requirements intended to avoid and minimize impacts to fish passage. The measured total stream impact length in this study was 46.0% higher than the amount of impact proposed in permit applications for perennial streams, and 23.7% higher for intermittent and ephemeral streams. Only 30.6% of the perennial stream length affected in this study received compensation for impacts even though 90.9% of impacts qualified. Collectively, these results indicate that regulations and mitigation policies are not having their intended effects of providing fish passage or preventing net loss of streams in Georgia as required under the Clean Water Act. We recommend that decision makers undertake a more geographically comprehensive evaluation of stream impacts that are authorized by permits to thoroughly evaluate regulatory effectiveness and impacts to fish passage. [ABSTRACT FROM AUTHOR]

Partial-depth guide walls are used to improve passage efficiency and reduce the delay of out-migrating anadromous fish species by guiding fish to a bypass route (i.e. weir, pipe, sluice gate) that circumvents the turbine intakes, where survival is usually lower. Evaluation and monitoring studies, however, indicate a high propensity for some fish to pass underneath, rather than along, the guide walls, compromising their effectiveness. In the present study we evaluated a range of guide wall structures to identify where/if the flow field shifts from sweeping (i.e. flow direction primarily along the wall and towards the bypass) to downward-dominant. Many migratory fish species, particularly juveniles, are known to drift with the flow and/or exhibit rheotactic behaviour during their migration. When these behaviours are present, fish follow the path of the flow field. Hence, maintaining a strong sweeping velocity in relation to the downward velocity along a guide wall is essential to successful fish guidance. Nine experiments were conducted to measure the three-dimensional velocity components upstream of a scale model guide wall set at a wide range of depths and angles to flow. Results demonstrated how each guide wall configuration affected the three-dimensional velocity components, and hence the downward and sweeping velocity, along the full length of the guide wall. In general, the velocities produced in the scale model were sweeping dominant near the water surface and either downward dominant or close to the transitional depth near the bottom of the guide wall. The primary exception to this shift from sweeping do downward flow was for the minimum guide wall angle tested in this study (15°). At 15° the flow pattern was fully sweeping dominant for every cross-section, indicating that a guide wall with a relatively small angle may be more likely to produce conditions favorable to efficient guidance. A critical next step is to evaluate the behaviour of migratory fish as they approach and swim along a guide wall in a controlled laboratory environment. [ABSTRACT FROM AUTHOR]

The development of hydropower and other infrastructure that disrupts river connectivity poses a serious threat to highly endemic and genetically distinct freshwater fish species in temperate parts of the Southern Hemisphere. Such locations have been neglected in previous reviews on fish passage. Fishways have long been constructed to mitigate the impacts of riverine barriers on fish, yet they have often failed for all but the largest, strongest swimming taxa. This is a particular problem in the temperate south, which is home to native species that are non-recreational and generally small-bodied with weak swimming abilities (e.g. Galaxiidae) relative to typical target species for fishway design (e.g. Salmonidae). Using the Eco Evidence method for rapid evidence synthesis, we undertook an assessment of evidence for effective fishway design focusing on species representative of the temperate south, including eel and lamprey. Systematic literature searches resulted in 630 publications. Through a rigorous screening process these were reduced to 46 publications containing 76 evidence items across 19 hypotheses relating to design criteria for upstream and downstream passage. We found an overwhelming lack of evidence for effective fishway design in the temperate south. Particular deficiencies were found with regard to the design of effective facilities for downstream passage. The attraction and entrance of upstream migrating fish into fishways is also relatively under-researched. Given the urgent need for effective fishways in the temperate south, these results justify an approach to fishway design based on a combination of empirical data and expert knowledge. In the meantime, significant resources should be assigned to improve the evidence base through high quality research. The particular deficiencies identified here could guide that research agenda. [ABSTRACT FROM AUTHOR]

Abstract: Damming of rivers disrupts migration of fish and results in lotic habitats being both scarcer and spaced further apart, ultimately affecting riverine fish communities. Nature‐like fishways are often designed as bypass channels, constructed with natural materials that reroute part of the water around weirs and dams, restoring longitudinal connectivity as well as forming nature‐mimicking habitats. We evaluated the potential of such bypasses to function as compensatory lotic habitats by comparing fish fauna in 23 bypasses to adjacent lotic stream habitats in a same‐river pairwise design. Bypasses were narrower, shallower, and less shaded than adjacent stream habitats, but very few significant differences could be detected in the fish communities, indicating the potential of such nature‐like fishways to constitute compensatory lotic habitats for fish. Analyses also indicated how bypass design may be altered to favour or disfavour certain target species. Generally, narrower and shallower bypasses with high gradient favoured brown trout (Salmo trutta), whereas European eel (Anguilla anguilla) were more abundant at sites with lower gradient. Finally, to increase the impact of these compensatory habitats on running water ecosystems, we suggest that the size of bypasses should be maximized in areas where natural stream habitats have been lost. [ABSTRACT FROM AUTHOR]

The behaviour of returning Salmo salar (Linnaeus, 1758) approaching, and attempting to pass low-head weirs remains relatively unknown. A radio telemetry array was created at a low-head weir to enable the behaviour of S. salar ( n = 120) to be observed as they approached and attempted to pass the barrier. The majority of fish successfully passed the barrier on their first or second attempt, some individuals required 11 attempts prior to successful passage occurring. Mean delay at the barrier per fish was 47.8 h (±SD 132.0 h), range 15 min to 31 days. Passage success on a fish's initial attempt was significantly predicted by the amount of searching a fish undertook, fork length, and fat content. Fish were more likely to have a successful first passage attempt if it was smaller with a low fat content and exerted a greater effort in searching for a passage channel. Small-scale barriers cause delays and increased energy expenditure in migrating fish. Barriers may be creating an anthropogenic selection pressure for traits which enable passage success. The impact of a delay at a barrier and increased energy expenditure on reproduction and gonad development remains unknown but is likely to be negatively impacted by instream anthropogenic structures. [ABSTRACT FROM AUTHOR]

This study compared the critical swimming speed ( Ucrit) and endurance performance of three Australian freshwater fish species in different swim-test apparatus. Estimates of Ucrit measured in a large recirculating flume were greater for all species compared with estimates from a smaller model of the same recirculating flume. Large differences were also observed for estimates of endurance swimming performance between these recirculating flumes and a free-surface swim tunnel. Differences in estimates of performance may be attributable to variation in flow conditions within different types of swim chambers. Variation in estimates of swimming performance between different types of flumes complicates the application of laboratory-based measures to the design of fish passage infrastructure. [ABSTRACT FROM AUTHOR]

Fragmentation is a major threat to the integrity of stream ecosystems and maintaining connectivity is a primary goal for conservation to promote natural system functioning. In human dominated systems with extensive anthropogenic fragmentation, resource managers are faced with prioritizing restoration actions to provide the most cost-effective conservation strategies. Road crossings, particularly poorly designed culverts, limit fish passage and thus population connectivity and access to seasonally important resources. Culvert assessment protocols, such as the one developed by the North Atlantic Aquatic Connectivity Collaborative (NAACC), are useful tools for managers to evaluate culvert passability and prioritize restoration actions across broad spatial extents, however the justification of such protocols requires empirical field based investigations. In this study we collected Brook Trout genetic samples from 28 headwater streams, of which 17 were separated by a culverted road crossing and 11 were included as a comparison to natural genetic structuring. The objectives of this research were to 1) determine what effect culverts had on the genetics of Brook Trout populations, 2) evaluate the ability of the NAACC culvert assessment protocol to predict genetic patterns and 3) identify the culvert characteristics that best explained genetic variability. We found significant increases in genetic differentiation at sites with culverts compared to those without, but no differences in genetic diversity metrics. Although the NAACC classifications did not predict the extent of genetic differentiation, the openness ratio of culverts (cross sectional area/length) was significantly correlated, suggesting it may need to receive a higher weighting in assessment protocols. Our results highlight the necessity to match appropriate prioritization strategies with desired management objectives in order to design the most effective conservation actions. [ABSTRACT FROM AUTHOR]

Spillway passage is one of the commonly accepted dam passage alternatives for downstream-migrating salmonids and other species. Fish passing in spill near the water surface may have improved chances of survival over fish that pass deeper in the water column near spillway structures. In this study, an autonomous sensor device (Sensor Fish) was deployed in 2005 to evaluate fish passage conditions through the Removable Spillway Weir (RSW) at Ice Harbor Dam on the Snake River in south-central Washington State. The Sensor Fish deployment was undertaken concurrently with a separate live fish injury and survival study. Conditions at the RSW–Spillway Chute Transition and Deflector region were found to be potentially detrimental to fish. As a result, the spillway slope and deflector radius were modified, and the efficacy of the modifications was evaluated in 2015 using Sensor Fish and a concurrent live fish study. The frequency of severe acceleration events (acceleration ≥ 95 G) during passage decreased significantly (from 51% to 35%; p -value = 0.049), and collisions with structures decreased from 47% to 27% ( p -value = 0.015). Pressures observed in the Spillway–Deflector region and pressure rates of change decreased as well. Overall, the modifications resulted in hydraulic conditions that contributed to improved fish passage conditions and increased fish survival. [ABSTRACT FROM AUTHOR]

Sampling fish by trapping can lead to biased conclusions about a population. We used catch data to assess differences between two types of traps for adult sea lamprey (Petromyzon marinus), submerged-funnel traps and studded-tile traps, which are angled ramps with trickle flow leading out of the water. The studded-tile trap at one river caught about 50% more females than the funnel trap. It caught males that had a smaller body size and females with a lower gonado-somatic index (GSI). The likelihood of catching lamprey in the studded-tile trap increased after they had been caught once. This was not the case for the funnel traps, which are used for mark−recapture-based population assessment of invasive sea lamprey in the Great Lakes. The apparent trap response caused by studded-tile traps may have been caused by a behavioral bias, i.e., the traps consistently attracting a subset of the population. Use of the studded-tile trap for population assessment should only be considered after more is known about its recapture bias. The differences between lamprey caught in the two trap types suggests that a variety of trapping methods needs to be employed in order to get a representative sample from a fish population.