Movement of three non‐salmonid fish species through a low‐gradient vertical‐slot fishway

Well‐designed fishways have assisted in restoring migrations and rehabilitating riverine fish species in all continents. The performance of fishways varies greatly with their type, design and operating regime, and with the species involved. Vertical‐slot fishways are widely used to overcome low‐level barriers, especially for non‐salmonids. Important issues remain in the design of fishways to meet performance and cost criteria, including the relationship between fishway bed gradient and the fish that ascend, and whether resting pools are needed. Models of species' movement patterns can inform fishway designers about likely fish response to various design options, and can lead to improved efficiency and effectiveness. Models of general movement patterns of three potamodromous non‐salmonid fishes in the Murray River, Australia, were developed from empirical data in a low‐gradient vertical‐slot fishway. The models integrate data on times of entry and exit, ascent rates, and whether fish continued to ascend during the night. These fish species did not favour resting pools. Ascent rates of fish ≥120 mm were more closely related to fish behaviour than to length; for a given fishway height, reducing bed slope by increasing the number of pools may slow the ascent of such fish, whereas enlarging pool volumes increases costs. Copyright © 2010 John Wiley & Sons, Ltd.     

An assessment of the effectiveness of a vertical‐slot fishway for non‐salmonid fish at a tidal barrier on a large tropical/subtropical river

Fishways for salmon in temperate rivers have often been successful, but salmonid‐type fishways for non‐salmonid species in tropical and subtropical rivers have frequently failed. This study assessed the effectiveness of modifying a salmonid‐type pool‐and‐weir fishway into a vertical‐slot design on a tidal barrage on the subtropical Fitzroy River, in Queensland, north‐eastern Australia. In 38 paired samples of the top and bottom of the fishway, over 16 months, 29 fish species and over 23 000 fish were collected at a maximum rate of 3400 per day. This study shows much greater potential for success with a vertical‐slot fishway as relatively few fish negotiated the original pool‐and‐weir design. Common species using the vertical‐slot fishway included blue‐catfish (Arius graeffei [Ariidae]), bony herring (Nematalosa erebi [Clupeidae]), striped mullet (Mugil cephalus [Mugilidae]), barramundi (Lates calcarifer [Centropomidae]), and long‐finned eels (Anguilla reinhardtii [Anguillidae]). Freshwater shrimp (Macrobrachium australiense [Palaemonidae]), juvenile crabs (Varuna litterata [Grapsidae]) and long‐finned elvers did not ascend the full length of the fishway and specific fishways for these species are recommended. Fish between 25 and 640 mm in length ascended the fishway, although the passage of smaller size classes of immature fish was restricted and this may be important for the sustainability of these migratory populations. The barramundi (200–640 mm) which ascended the fishway were all immature fish. However, during a period of low river flows enlarging the width of the vertical‐slot from 0.15 to 0.45 m only encouraged a small number of larger fish (890 mm maximum length) to enter. The strong diel movement patterns of many species will need to be considered in future fishway design. Blue‐catfish could ascend the fishway in 2 h, but many fish remained in the fishway and this behaviour may cause crowding and a reduction in fishway capacity. Further work is needed to assess the proportion of fish finding the fishway entrance. However, the findings suggest that vertical‐slot fishways with lower water velocities and turbulence than salmonid fishways have great potential to pass the diverse migratory fish fauna of subtropical and tropical rivers. Copyright © 1999 John Wiley & Sons, Ltd.     

Do fish locks have potential in tropical rivers?

This study evaluated attraction and passage of native fish through an automated fish lock on the tropical Fitzroy River in north‐eastern Australia. In 69 samples (24 h each) taken at the exit and entrance of the fish lock, 17 fish species and 13 402 individuals were collected, at a maximum rate of 3317 fish per day. During low river flows, the fish lock transferred a broad size range of fish (35–710 mm long), though migratory biomass was small. Removal of a vertical fish‐crowding device did not affect the passage rate. Netting studies and observations of fish migrating below the weir suggested that the entrance was poorly located during high flows and another fishway near the spillway would enhance fish passage. The fish lock was inoperative for 48% of the time, due to mechanical and software failure, and a narrow operational range unsuited to the variable hydrology. Nevertheless, these design issues are site specific and reflect that fish lock technology is in its infancy in Australia. The operational reliability of the fish lock is now greatly improved but further work is needed to optimize the automatic cycling. To accommodate the inherently variable hydrology of lowland tropical/sub‐tropical rivers into fishway design, we highlight important research needs for fishways and migratory fish communities. Fish locks are often considered a less favourable fish passage option but with the operational reliability issues partially resolved, they appear to have considerable potential for tropical river systems with low minimum flows and low biomass; with further research and design, they may have wider application. Copyright © 2007 John Wiley & Sons, Ltd.     

Monitoring upstream fish passage through a Mississippi River lock and dam reveals species differences in lock chamber usage and supports a fish passage model which describes velocity‐dependent passage through spillway gates

Nearly 200 fish were released below Lock and Dam 2 (LD2) in the Upper Mississippi River and tracked to determine both whether and how they passed through this structure, and if passage could be explained using a computational fish passage model (FPM) which combines hydraulics with fish swimming performance. Fish were either captured and released downstream of LD2 in Pool 3 or captured in Pool 2 (upstream of LD2) and displaced below LD2. Tagged fish were tracked using 13 archival receivers located across LD2. Approximately 90% of all fish approached LD2 many times with the displaced species likely attempting to home. Of 112 common carp, 26% passed through LD2 with 15% (most) going through the lock and 6% through the spillway gates. Similar values were seen for bigmouth buffalo. In contrast, although 42% of 31 channel catfish passed through the lock, only 3% went through the gates. Finally, of 22 walleye, only 14% passed through the lock and none through the gates. Ninety percent of all documented passages through the spillway gates occurred when the gates were out of the water and water velocities through these gates were at their lowest levels, an attribute described and predicted by the FPM at LD2. This study strongly suggests that fish passage through spillway gates of LDs is determined by water velocity and can be predicted with a FPM, whereas passage through locks is determined by species‐specific behavioural preferences. Both attributes could be exploited to reduce passage of invasive carp at certain locations.     

Turbulent flow field comparison and related suitability for fish passage of a standard and a simplified low‐gradient vertical slot fishway

Fishways are hydraulic structures that allow passage of fish across obstructions in rivers. Vertical slot fishways—VSFs—are considered the most efficient and least selective type of technical fishway solutions, especially due to their ability to remain effective even when significant upstream and/or downstream water level fluctuations occur. The scope of the present study is to perform numerical simulations in order to investigate and compare the hydraulic turbulent flow field in a standard and a simplified version of the most common VSF design. Implications in relation to fish swimming behaviour and fish passage performance are discussed. Different water depths (as well as discharges) were investigated, using a bed slope of 5%, as a reference for low‐gradient VSFs with a very limited selectivity that can be used in multispecies rivers in grayling‐barbel regions. Results show that maximum values of velocity, turbulent kinetic energy, and Reynolds stresses are higher in the standard design. However, corresponding to slot geometry and orientation, the direction of the main jet in the simplified design is more inclined towards the left side of the pool. This causes the eddy to split into 2 smaller ones; the minimum eddy dimension is reduced from 0.4–0.5 to 0.2–0.3 m. These dimensions are detrimental for fish passage efficiency, being more comparable with fish length (0.15–0.40 m), thus affecting migrating fish stability and orientation. Furthermore, the standard design provides a more straightforward upstream path and wider areas of low flow velocities and turbulence, useful for fish resting. Therefore, it is recommended that the standard design should be preferred over its simplified version, even if its construction costs are around 10–15% higher than the simplified one.     

Influence of navigational lock and dam structures on adjacent fish communities in a major river system

We assessed the effects of a series of navigational lock and dam (L/D) structures on the composition of their adjacent fish communities. The Allegheny and Monongahela Rivers of southwestern Pennsylvania contain 14 lock and dam installations, eight and six respectively, which transform their river corridors into a series of contiguous pools. We selected two targeted fish assemblages, large‐bodied fishes (>250 mm TL) susceptible to gill‐netting and small‐bodied benthic species captured by trawling, for assessment upstream and downstream of each L/D installation. Gill nets were fished for approximately 16 h/net, while trawls were performed across three parallel 2‐min hauls. A total of 56 samples were collected over the spring/summers, 2004–2008. Species richness, abundance and the Jaccard Coefficient of Community Similarity (JCS) were calculated for each targeted fish community. Small‐bodied species, particularly darters, were depauperate upstream L/D while abundant and diverse downstream L/D on the Allegheny River. However, Monongahela River upstream and downstream L/D communities were similar. Jaccard Coefficient of Similarity values were comparable for both targeted fish assemblages on the Monongahela River, but differed markedly among Allegheny sites. While JCS values of large‐bodied fish assemblages of both rivers were strongly correlated with lockage frequency, this pattern was not replicated among small‐bodied assemblages. The near doubling of yearly lockages on the Monongahela River compared with the Allegheny may account for the similarity of its upstream and downstream ichthyofauna. Serial L/D navigational facilities on a large river may alter biotic connectivity patterns through physical isolation of adjacent fish communities. Copyright © 2010 John Wiley & Sons, Ltd.     

Meta‐analyses,Metrics and Motivation: Mixed Messages in the Fish Passage Debate

Over recent years, there has been increasing challenge to the accepted wisdom that the environmental impacts of river engineering can be adequately mitigated through the installation of infrastructure, such as fish passes. This has led to a debate on the value of fish passage with some arguing that increased research and development will advance solutions for a variety of structures that are suitable for multiple species and transferable to different regions. Others suggest that policies and management strategies should reflect the realization that current mitigation technology frequently fails and can itself have negative impacts. Meta‐analyses of the results of studies on fish passage effectiveness have led to the challenge of conventional views by highlighting lower than expected efficiencies, wide variation between and within fish pass designs, and bias towards consideration of a limited number of commercially important species mainly from northern temperate regions. Results of meta‐analyses can also be controversial, and difficulties can arise when nuances associated with individual studies are lost and when metrics used are not standardized. Intrinsic variation in fish passage efficiency between and within species due to differences in patterns of movement and motivation may not be considered, and in many situations, current metrics are not appropriate. Quantification of variation in trends in fish passage efficiency over time and with spatial scale is lacking and should be the focus of future reviews. It is time to accept that fish passage does not provide a universally effective mitigation solution, particularly when designs and strategies are transferred to other regions and species for which they were not originally designed. Admitting to cases of failure is an essential first step to advancing water resources planning and regulation based on well‐informed decision‐making processes. Copyright © 2016 John Wiley & Sons, Ltd.     

Partial dam removal restores passage for a threatened salmonid

Dams represent one of the major forms of river alteration. As these structures reach the end of their lifespan, they often require extensive refurbishments or removal. A small‐scale water supply dam in Banff National Park (Alberta, Canada) was partially removed, creating a breach that allowed water to scour a new passage resembling a nature‐like fishway. We investigated the permeability of the partially removed dam as a means of validating the conservation benefits of the partial dam removal. We quantified the proportion of bull trout (Salvelinus confluentus), a threatened species in Canada, that approached and passed the fishway using radio telemetry receiver stations. The proportion of bull trout that approached the fishway was low (37.0%; N = 27 of 73), but was consistent with upstream reference sites (33%; N = 20 of 60). For those that did approach, the proportion of bull trout that passed yielded a high passage efficiency (77.8%; N = 21 of 27 that approached). The probability that a fish passed the fishway was related to water depth and time of day. Bull trout were more likely to pass when water depths were high (>0.40 m), and at night. Passage duration ranged from 5‐mins to 13‐days, suggesting that this resident species used the fishway for a variety of purposes (e.g., station holding and foraging) and not just transiting. Some individuals underwent large‐scale movements 2‐km upstream (15.1%; N = 11 of 73), or 2‐km downstream (2.7%; N = 2 of 73) following a successful passage event. This study provides new insight on how, in some instances, a breach in a dam can function as a nature‐like fishway, accommodating year‐round stream flows and providing hydraulic conditions suitable for fish passage without costly engineering or construction.     

Intake Approach and Dam Passage by Downstream‐migrating Atlantic Salmon Kelts

Studying fish behaviour at hydropower dams is needed to facilitate the design and improvement of fish passage solutions, but few studies have focused on Atlantic salmon kelts. Here, we used radio telemetry (n = 40, size range = 50–81 cm) and acoustic sonar to study kelt movements in the forebay as well as their dam passage survival and subsequent migration success past multiple dams. We also compare radio telemetry and acoustic sonar observations of fish behaviour and used acoustic sonar to measure the depth distribution of fish approaching the turbine intake zone. Passage success at the dam was 41%, and mortality was largely associated with turbine passage (62%). The two fish that passed via the spill gates survived and continued their downstream migration. At the dam, all but one radio‐tagged kelt approached the intake zone shortly after arrival to the forebay, and sonar data showed that approaching fish were predominantly surface oriented (72%, 88% and 96% of the observations were less than 1, 2 and 3 m deep, respectively). Turbine passage rate from the intake zone was higher at night than at day, indicating that the lack of visual cues may reduce the barrier effect of the 70‐mm conventional trash rack. Turbine passage rate also increased with increasing hydropower generation. The percentage of observed upstream movements away from the intake zone compared with the total number of observations was considerably greater in the radio telemetry data (41%) than in the sonar data (4%). Only one fish survived passage of all eight hydropower dams to reach the lake. This low‐passage survival underscores the need for remedial measures to increase the survival of migrating kelts, and the fish's surface orientation as well as their rapid approach to the intake rack should be taken into account when designing such measures. Copyright © 2017 John Wiley & Sons, Ltd.     

仿自然通道及鱼道池室结构布置研究

为了提高仿自然通道及鱼道设计水平,以某水电站仿自然通道工程为案例,根据其过鱼需求,提出了池室结构布置方案,并通过数值模拟及物理模型试验对其平面及三维池室流态进行了分析。结果表明:通过在仿自然通道或鱼道内部采用收缩段、侧壁设置消能墩、底部辅以条形消能墩的新型结构可使池室内部流场实现纵向分层和横向分区,可供不同游泳能力的鱼类通过。该池室结构在流速流态控制等方面较普通仿自然通道和技术型鱼道均具有优势,适合多种鱼类通过,具有推广价值。     

Offstream movements of fish during drought in a regulated lowland river

Access to offstream habitats is vital for many freshwater fish, but details of their lateral movements are scarce. We describe the movements of fish between the channel of the River Murray and six perennially inundated wetlands in South Australia from August to November 2006. At this time there were unprecedented low flows in the river owing to the combined effects of river regulation, drought and over‐allocation to upstream users. Some 210 000 fish from 18 species (14 native, 4 alien) were recorded, including two uncommon native species listed by conservation agencies. Movements of juveniles and adults varied among wetlands despite the shared river reach and the proximity of the wetlands to each other, but showed no consistent directionality. This may reflect the prevailing low‐flow conditions, the virtually permanent connections between the wetlands and channel maintained by weirs, levees and barrages, and the dominance of ‘generalist’ species. We speculate that movements facilitate efficient resource utilization and nutrient exchange between homogenized river and wetland habitats in the absence of the flood‐pulse. We anticipate directional movements will become apparent when flows are increased, so that our data could provide a comparative baseline for future studies. As modifications to natural flow paths may impede access to/from wetlands by fish and other aquatic fauna, provisions for access should be incorporated into flow‐control structures, used locally to manipulate wetland hydrology. Copyright © 2010 John Wiley & Sons, Ltd.     

辅助鱼类过闸的诱驱鱼灯光试验研究

为提高船闸的过鱼效率,参照葛洲坝1号船闸建立试验模型,以草鱼、鲢鱼、鳙鱼为试验对象,观察不同光色和闪光模式下的诱驱鱼效果,并选择合适的灯光开展诱驱鱼进出闸室试验。结果表明:红、黄、白、蓝、绿5种光色的诱鱼灯中,红色诱鱼效果最好;单闪、双闪和变闪3种闪光灯中,双闪驱鱼效果最好;通过在闸室内布置并运行红色诱鱼灯和双闪闪光灯,可有效提高船闸过鱼效率约10%,最高达16.7%。研究成果可为中低水头的水利枢纽船闸过鱼提供依据。     

Bidirectional connectivity via fish ladders in a large Neotropical river

The conservation of migratory fish species worldwide has been threatened by the loss of longitudinal connectivity caused by dams intercepting large rivers. One environmental management strategy for reestablishing connectivity is providing passage through fish ladders. However, ladders in Neotropical rivers have been described as ascending one‐way routes. We analysed the movements of Prochilodus lineatus through a fish ladder at a large dam—Porto Primavera—in the heavily impounded Upper Paraná River, Brazil, to determine whether the ladder connected habitats downstream and upstream of the dam, in both directions. A total of 1,419 specimens of P. lineatus were PIT‐tagged above and below the dam, and continuously monitored for 4 years. We documented bidirectional movements of P. lineatus through the fish ladder. Many individuals repeated these movements annually; one individual as many as six times. It was estimated that the cumulative probability that P. lineatus would return from downstream after descending through the ladder was 0.38, 0.50, and 0.56 in 1, 2, and 3 years, respectively. Correspondingly, return probabilities from upstream were 0.15, 0.22, and 0.26 in 1–3 years, respectively. Although return probabilities from upstream were roughly half, our results suggest the Porto Primavera fish ladder contributes to habitat connectivity, bidirectional passage, and preservation of P. lineatus. These results deviate from the perception that fishways are ineffective in Neotropical rivers. We suggest that fishways can restore the bidirectional connectivity denied to some Neotropical species, and until the services of dams are no longer needed, environmental management through fish ladders could continue to be considered as an integral part of broader conservation strategy designed to preserve native fauna.     

USING AN EXPERIMENTAL IN SITU FISHWAY TO PROVIDE KEY DESIGN CRITERIA FOR LATERAL FISH PASSAGE IN TROPICAL RIVERS: A CASE STUDY FROM THE MEKONG RIVER,CENTRAL LAO PDR

Fish passage through an experimental vertical‐slot fishway was assessed at a floodplain regulator on the Mekong River in Central Laos between April and July 2009. Experiments were conducted to investigate the influence of fishway floor slope (1v:15h or 1v:7.5h) on fish passage success with a view to developing a series of optimal design criteria for the construction of vertical‐slot fishways at other barriers to fish passage in the Lower Mekong Basin. A total of 14 661 fish from 73 species were captured during the experiments. Catches were dominated by riverine (white) (n = 51; 69% of total) and floodplain (black) species (n = 15; 20%) which represented 19 families in total. The work demonstrated that fish were actively attempting upstream passage from the Mekong River to an adjacent floodplain and displayed strong migratory behaviour during river level rises. Migratory activity was greatest during sharp rises in water level but reduced substantially when river level fell. Fish community composition varied greatly among the two fishway floor slopes and the control group. More fish species were collected from control samples, but the most fish and species were collected when the fishway was configured on a moderate hydraulic slope (1v:15h). A range of size classes were also collected from control and moderate‐slope groups, but steeper‐gradient catches were dominated by larger fish. This study demonstrated that vertical‐slot fishways could provide passage for a biodiverse fish community where fish move laterally onto floodplains. The construction of fishways which consider the local fish ecology and hydrology may therefore represent a valuable management tool to help restore important movement pathways for tropical freshwater fish. Copyright © 2011 John Wiley & Sons, Ltd.     

Implications of an invasive fish barrier for the long‐term recovery of native fish assemblages in a previously degraded northeastern Illinois River system

Barriers to fish movement have been used to prevent the spread of invasive fishes but may also limit the movements of native fishes. We evaluated the potential consequences of a proposed barrier on the Illinois River Waterway, meant to inhibit the spread of silver and bighead carps, to the continued recovery of native fishes in the Des Plaines River following water quality improvements. We compared changes in upstream cumulative species richness and community structure from 1983 to 2013 in the DuPage River, an adjacent tributary with an impassable dam, to the area upstream of a newly proposed barrier on the Des Plaines River where fish can currently pass through a navigational lock. Fewer species displayed truncated distributions upstream of the passable lock and dam (n = 18) compared with the impassable dam (n = 23). Due to water quality improvements in the Illinois River as a whole, cumulative species richness downstream of both dams steadily increased over time. Richness also increased upstream of the passable dam but plateaued upstream of the impassable dam. Fifteen to 18 species accounted for differences in community structure between areas downstream and upstream of either dam. Most species (78–100%) were found in greater relative abundance downstream of the impassable dam, and only 53% were found in greater relative abundance downstream of the passable dam. The truncation in species richness and abundance at the impassable dam foreshadows the potential consequences of an indiscriminate barrier on native fishes and the continued recovery of native assemblages.     

Effects of bed slope on the flow field of vertical slot fishways

Vertical slot fishways (VSFs) are the most efficient and least selective typology of technical fish passage, due to their ability to remain effective even when significant upstream and/or downstream water level fluctuations occur. Fishway construction costs can be reduced by increasing its bed slope, but this affects the flow field inside the pools, with higher head drops between the basins, as well as turbulence levels and flow velocities, which may affect fish passage. In light of this, a VSF was investigated by 3D numerical simulations to identify the possible effects of the bed slope (using values from 1.67% to 10%) on the flow field and subsequent implications for fish passage. A particular focus was devoted to cyprinind species, but the results can be extended to other species of similar swimming abilities and, therefore, be applicable to multispecies rivers. Flow velocity and turbulence values such as turbulent kinetic energy and Reynolds stresses were analysed from a fish passage perspective in relation to threshold values derived from previous studies. Pool areas where turbulence values are compatible with fish ability and behaviour were quantified. Maps of the location of fish‐friendly zones in the VSF pools were produced and can constitute a reference for practical applications in fishway design. The flow field generated with bed slopes lower than 6.67% is more compatible with fish swimming capabilities, because it exhibits a predominantly 2D behaviour and more suitable hydraulic conditions, whereas at higher slopes, turbulence levels in the pools increase.     

Fishway passage and post‐passage mortality of up‐river migrating sockeye salmon in the Seton River,British Columbia

Adult sockeye salmon (Oncorhynchus nerka) were studied to assess the consequences of a dam and vertical‐slot fishway on mortality during their spawning migration in the Seton–Anderson watershed, British Columbia, Canada. Since previous research suggests fishway passage may be difficult, our main hypothesis was that the dam and fishway have post‐passage consequences that affect subsequent behaviour and survival. Eighty‐seven sockeye were caught at the top of the fishway, implanted with an acoustic telemetry transmitter, non‐lethally biopsied to obtain a small blood sample and released either upstream or downstream of the dam. Indices of physiological stress (i.e. plasma cortisol, glucose, lactate and ions) indicated that fish were not stressed or exhausted after capture from the fishway, and were not unduly stressed by transportation to release sites or net‐pen holding. Of 59 fish released downstream of the dam, 14% did not reach the dam tailrace. Overall passage efficiency at the fishway was 80%. Mortality in two lakes upstream of the dam was greater in fish released downstream of the dam (27%) compared to fish released upstream of the dam (7%; p = 0.04) suggesting that dam passage has consequences that reduce subsequent survival. Cumulative mortality of fish released downstream of the dam (n = 55) resulted in only 49% survival to spawning areas, compared to 93% of fish released upstream of the dam (n = 28). Survival was significantly lower for females (40%) than for males (71%; p = 0.03), a finding that has implications for conservation because spawning success of sockeye salmon populations is governed primarily by females. Copyright © 2010 John Wiley & Sons, Ltd.     

Fish assemblage response to rehabilitation of a sand‐slugged lowland river

The impact of excessive sediment supply on river channels has been described in many areas of the world. Sediment deposition disturbance alters habitat structure by decreasing channel depth, changing substrate composition and burying woody debris. River rehabilitation is occurring worldwide, but information is scant on fish assemblage responses to rehabilitation in sediment‐disturbed lowland rivers. Sediment removal and large woody debris (LWD) replacement were used to experimentally rehabilitate habitat along a 1500 m stretch of the Glenelg River in western Victoria, Australia. Using an asymmetrical before‐after control‐impact (BACI) design, fish were captured before and after the reach was rehabilitated, from two control reaches and from a ‘higher quality’ reference reach. After two years post‐rehabilitation monitoring, the fish assemblage at the rehabilitated reach did not differ from control reaches. Temporal changes in taxa richness and the abundance of Philypnodon grandiceps, Nannoperca spp. and three angling taxa occurred after rehabilitation (winter 2003) compared with the before period (winter 2002), but these effects did not differ between rehabilitated and control locations. Highest taxa richness and abundances occurred at the reference location. High salinity coincided with the timing of rehabilitation works, associated with low river discharges due to drought. The negative effects of other large‐scale disturbances may have impaired the effectiveness of reach‐scale rehabilitation or the effects of rehabilitation may take longer than two years to develop in a lowland river subjected to multiple environmental disturbances. Copyright © 2009 John Wiley & Sons, Ltd.     

Ascent of neotropical migratory fish in the Itaipu Reservoir fish pass

The Piracema Canal is a complex 10‐km fish pass system that climbs 120 m to connect the Paraná River to the Itaipu Reservoir along the Brazil–Paraguay border. The canal was constructed to allow migratory fishes to reach suitable habitats for reproduction and feeding in tributaries upstream from the reservoir. The Piracema Canal attracted 17 of the 19 long‐distance migratory species that have been recorded in the Paraná River Basin and Paraguay–Paraná Basin. However, the incidence of migratory fish decreased from downstream to upstream, with the pattern of decrease depending on species. Overall, 0.5% of the migratory fish that entered the Piracema Canal and segment 1, eventually were able to reach segment 5 and potentially Itaipu Reservoir. Ascension rate was examined relative to various physical attributes of canal segments; maximum water velocity emerged as the most influential variable affecting fish passage. Water velocity may be manipulated by controlling water discharge, and by re‐engineering critical sections of the canal. Because the Itaipu Reservoir flooded a set of falls that separated two distinct biogeographical regions, facilitating fish movements through the Piracema Canal into the Itaipu Reservoir presents a management dilemma that requires deliberation in the context of the fish assemblages rather than on selected migratory species. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of dams in river networks on fish assemblages in non‐impoundment sections of rivers in Michigan and Wisconsin,USA

Regional assessment of cumulative impacts of dams on riverine fish assemblages provides resource managers essential information for dam operation, potential dam removal, river health assessment and overall ecosystem management. Such an assessment is challenging because characteristics of fish assemblages are not only affected by dams, but also influenced by natural variation and human‐induced modification (in addition to dams) in thermal and flow regimes, physicochemical habitats and biological assemblages. This study evaluated the impacts of dams on river fish assemblages in the non‐impoundment sections of rivers in the states of Michigan and Wisconsin using multiple fish assemblage indicators and multiple approaches to distinguish the influences of dams from those of other natural and human‐induced factors. We found that environmental factors that influence fish assemblages in addition to dams should be incorporated when evaluating regional effects of dams on fish assemblages. Without considering such co‐influential factors, the evaluation is inadequate and potentially misleading. The role of dams alone in determining fish assemblages at a regional spatial scale is relatively small (explained less than 20% of variance) compared with the other environmental factors, such as river size, flow and thermal regimes and land uses jointly. However, our results do demonstrate that downstream and upstream dams can substantially modify fish assemblages in the non‐impoundment sections of rivers. After excluding river size and land‐use influences, our results clearly demonstrate that dams have significant impacts on fish biotic‐integrity and habitat‐and‐social‐preference indicators. The influences of the upstream dams, downstream dams, distance to dams, and dam density differ among the fish indicators, which have different implications for maintaining river biotic integrity, protecting biodiversity and managing fisheries. Copyright © 2010 John Wiley & Sons, Ltd.