Passage and reproductive activity of fishes in the Igarapava fish ladder,Grande River,Southeastern Brazil

We sampled fishes within the vertical‐slot Igarapava fish ladder (IFL), Grande River, southeastern Brazil, and immediately downstream IFL in 12 field trips from February 2000 to December 2002. A total of 1145 fishes belonging to 13 families and 39 species were captured. The most abundant species captured within the IFL, in order of abundance were: Pimelodus maculatus, Metynnis maculatus, Astyanax altiparanae, Hypostomus spp., Leporinus octofasciatus, Salminus hilarii, Leporinus elongatus, Leporinus friderici, Schizodon nasutus and Prochilodus lineatus. Size distribution of the most abundant fishes captured downstream or within the IFL was similar indicating no constraints to adult fish to ascend the IFL. Except P. maculatus, the number of migratory species captured in the IFL and downstream the IFL were very low. Some of the so‐called sedentary species were collected in the IFL indicating that they possess an innate behaviour to migrate. Juveniles of P. lineatus and P. maculatus were captured ascending the IFL implying a dispersal behaviour. Gonadal analyses of the fishes captured in the reproductive season showed that the overall number of reproductive active fishes (which included fish in maturation, mature and spawned/spent) surpassed those non‐active. Thus, the IFL offers upstream passage for juveniles, some of the so‐called sedentary species, as well as fishes in reproductive migration. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Effects of flow on the fish communities of a regulated California river: implications for managing native fishes

We assessed the importance of flow regime to the success of native and non‐native fish species by analysing winter/spring seining data collected from 1987 to 1997 on the resident fish communities of the lower Tuolumne River, California. The data were analysed using regression models to predict the percentage of non‐native fish at a site. The regression models included various combinations of the variables longitudinal location of the site, mean April/May stream discharge in the year of sampling, and mean April/May stream discharge in the previous year. Comparison of the models indicated that the best model included longitudinal location and stream discharge in the previous year. This model is consistent with the hypothesis that flow in the previous year differentially affects reproductive success of native and non‐native species and thus the resulting community sampled in the following winter/spring. A detrended correspondence analysis of percentage abundance species data identified a co‐occurring group of native species and a co‐occurring group of non‐native species with the non‐native red shiner (Cyprinella lutrensis) grouping separately. The differing reproductive strategies of the species were consistent with the hypothesis concerning spawning success. Our results indicate that flow regime is an important determinant of the reproductive success of native and non‐native fish species in regulated rivers. Manipulations of flow regime are a potentially powerful tool for managing native fish species, but should be considered in combination with other restoration efforts and in the context of ecosystem restoration. Copyright © 2002 John Wiley & Sons, Ltd.     

Optimum fish passage and guidance designs are based in the hydrogeomorphology of natural rivers

Understanding hydrodynamic cues used by outmigrating juvenile salmon (emigrants) to guide fine‐scale swim path selection is critical to successful fish guidance and passage at man‐made structures. We show how these cues can be inferred from channel features and complex flow fields of natural rivers through which emigrants pass. We then describe a new cue, ‘total hydraulic strain’, integrating properties of flow acceleration and turbulence through the spatial gradients in velocity to create a single flow field distortion metric amenable to the analysis of fish movement at the scale of large man‐made structures. We explain how total hydraulic strain, together with the magnitude of velocity, provide sufficient information for any fish to distinguish between the two categories of channel features with their mechanosensory system. We demonstrate that total hydraulic strain, velocity magnitude and hydrostatic pressure can be integrated into rule‐sets (the Strain–Velocity–Pressure (SVP) Hypothesis) to explain emigrant swim path selection near dams. To confirm the reasonableness of the SVP Hypothesis, we describe how its separate elements can be detected by different components of the fish mechanosensory system. We evaluate the SVP Hypothesis by (1) using it to explain the traces made by acoustically tagged emigrants overlaid on coincident total hydraulic strain and velocity magnitude fields, (2) using it to explain different passage efficiencies of competing bypass designs and (3) testing it via stepwise discriminant analysis to infer the relationship between hydrodynamic pattern and emigrant orientation. We conclude the SVP Hypothesis is a reasonable and useful approximation of the strategy used by emigrants to select their swim path through complex flow fields sufficient to serve as the basis of guidance and bypass system design. Published in 2008 by John Wiley & Sons, Ltd.     

The impact of intermediate‐head navigation locks on downstream fish passage

Navigation in inland waterways is increasingly important worldwide and so is inherently the construction and use of navigation locks. However, the impact of navigation locks on downstream migrating fish is rarely documented. In Belgium, the Albert Canal connecting the Meuse River to the Scheldt Estuary may offer migration opportunities for European eel (Anguilla anguilla) and Atlantic salmon (Salmo salar), two critically endangered species. During their downstream migration phase (respectively silver eels and salmon smolts), both species have to pass five intermediate‐head navigation locks before reaching the estuary. Previous research showed that silver eel escapement is largely unsuccessful and that eels are delayed extensively at the navigation lock complexes. To get a better understanding of the mechanisms behind these failures and delays, we tagged and released 62 silver eels and 44 salmon smolts in the vicinity of one navigation lock complex of the canal. This paper reports the mechanisms behind the previously perceived delay, the route choices to pass the complex, and the risks involved. Of the 65% tagged eels and 73% tagged smolts that succeeded to pass the complex, respectively, 20% and 41% needed more than one trial to pass the complex. Moreover, 52% of all trials were via intakes of the lock filling system, at least four smolts (17%) died after intake passing, and about 30% of both intake‐passing smolts and eels stopped migrating after passage. Therefore, intermediate‐head navigation locks are a potential threat to downstream migrating fish, which requires more research to fully investigate its impact.     

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.     

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.     

Predicted impacts of proposed hydroelectric facilities on fish migration routes upstream from the Pantanal wetland (Brazil)

There are 104 hydroelectric facilities proposed to be installed in the watersheds that feed the Pantanal, a vast floodplain wetland located mostly in Brazil. The Pantanal is host to 23 long‐distance migratory fish species that ascend upland tributaries to spawn. A Geographic Information System was used to predict the impact of hydroelectric dams on potential migration routes for these species. Both anthropogenic (hydroelectric dams) and natural barriers were included in the analysis. Natural barriers were identified by river slope. Critical river slopes of 10 and 25%, above which fish were predicted to be incapable of ascending, were modeled as natural barriers. Based on this model, we show that between 2 and 14% of rivers in the Pantanal watershed are naturally blocked to fish migration. An additional 5 to 9% of rivers are currently blocked due to 35 existing hydroelectric facilities. If all proposed dams are built, the area flooded by new reservoirs will triple and the river kilometers blocked will double, blocking 25 to 32% of the river system to fish migration. The Taquari and Cuiabá River sub‐basins will be the most impacted, each having more than 70% of their rivers blocked. The impact of individual proposed facilities on the loss of migration routes is related to their proximity to existing barriers. Fourteen of the proposed dams are upstream from existing barriers and will therefore not further restrict long‐distance fish migration routes while proposed dams are predicted to close an additional 11,000 to 12,000 km of river channels.     

Modelling upstream fish passage in standard box culverts: Interplay between turbulence,fish kinematics,and energetics

Box culverts are common hydraulic structures along rivers and streams, in rural and urban water systems. The expertise in fish‐friendly culvert design is limited, sometimes leading to adverse impact on the catchment ecosystem or to uneconomical structures. Basic dimensional considerations highlight a number of key parameters relevant to any laboratory modelling of upstream fish passage, including the ratio of fish speed fluctuations to fluid velocity fluctuations, the ratios of fish dimensions to turbulent length scale, and the fish species. Alternately, the equation of conservation of momentum may be applied to an individual fish, yielding some deterministic estimate of instantaneous thrust and power expended during fish swimming, including the associated energy consumption. The rate of work required by the fish to deliver thrust is proportional to the cube of the local fluid velocity, and the model results demonstrate the key role of slow‐velocity regions in which fish will minimize their energy consumption when swimming upstream.     

Investigation of turbulent flows using spillway models aiming to aid downstream migration of fish

Dams and other flow control structures constitute obstacles to upstream and downstream aquatic habitats, reducing life-cycle success and even eliminating diadromous and potamodromous fish species from river basins. Providing effective passage past hydroelectric dams is critical for restoring habitat connectivity and sustaining populations of fish species. Surface water release over spillways is effective in diverting fish from turbines and establishing a safe bypass for downstream migrants. Developing an effective passage system over spillways requires both biological knowledge of fish behavior and abilities, as well as hydraulic knowledge of spillway flows to provide hydrodynamic conditions that fish may exploit. The present study experimentally investigates several depths, velocity, and turbulence fields intended to promote the downstream migration of fish over spillways. Instantaneous velocity fields were measured in an open recirculating rectangular water channel. A 90° standard spillway model, as well as a spillway model with a modified upstream face slope of 45°, were tested for two water depths. The results show the presence of a distinct recirculation bubble at the heel of the 90° standard spillway with the shallower water depth. It was concluded that the upstream recirculation bubble may be suppressed by either increasing the water depth or decreasing the upstream face slope. Decreasing the upstream face slope also resulted in a more uniform distribution of acceleration and lower turbulence along the upstream face of the spillway. The modified spillways provide more suitable hydrodynamic conditions for downstream migrants.     

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.     

涵洞式鱼道设计现状与展望

在工程设计和施工时,为减少截流对鱼类生态环境影响,需要考虑特有鱼类洄游通道的要求而设置专门的鱼道。通过对国内外涵洞式鱼道相关资料的收集整理和分析,针对国内外的发展现状,较详细地介绍了涵洞式鱼道的发展过程、鱼道隔板类型和水力特性及其优缺点,分析了涵洞式鱼道的设计方法和要点,包括收集信息、选址、隔板类型和水力计算等,并对国内外鱼道的建设和发展进行了展望。特别是国外在涵洞式鱼道领域的研究方法和成功经验,可为我国在该领域的后续工作提供良好的借鉴。     

国内外过鱼设施运行效果评估与监测技术研究综述

梳理了国内外过鱼设施运行效果监测评估的发展历程,总结了运行效果评估的主要内容和监测技术,探讨了有关过鱼设施的设计、运行与管理等效果评估方法。通过对比国内外过鱼设施运行效果主要监测技术方法及应用情况,结合国内已开展的过鱼设施运行效果监测评估实践,分析了国外过鱼设施规定和相关实践对我国过鱼设施设计、运行与管理的借鉴作用,讨论了我国已建过鱼设施的运行效果和作用,进而指出过鱼设施运行效果评估研究的发展方向,提出加强过鱼设施监测技术方法研究、适时开展过鱼设施监测和运行效果评估、编制过鱼设施运行效果监测技术规范等建议。     

Underwater video monitoring of fish passage in the Mekong River at Sadam Channel,Khone Falls,Laos

This paper describes the first measurement of fish passage in the Mekong River at Khone Falls. The site was in the Sadam Channel, which was modified in 2013 to improve fish passage and mitigate closure of Sahong Channel for the Don Sahong hydropower project. Underwater cameras recorded 149 hr of discontinuous video from January 18 to 26, 2015, which showed a major upstream migration by small cyprinid fish. Daily catch surveys in the same channel showed most fish migrated on days when video records were almost complete. We used stratified hourly sampling to review 17% of the available video and counted 14,783 fish and identified 16 taxa. The most abundant species were Labiobarbus leptocheilus, Henicorhynchus lobatus, and Henicorhynchus siamensis, and these fishes migrated almost exclusively during daylight. We calculated passage rates for West Sadam Channel from video samples and extrapolated those results to Sadam Channel, by assuming equivalent passage rates for both East and West Sadam Channels. This assumption was based on observations that fish were evenly distributed between both banks below the confluence, and they migrated close to each bank, so we assumed that there was an even split at the confluence and neither channel was preferred for upstream passage. Although channel modification improved fish passage efficiency, we estimated that artisanal fishers caught 79% of migrating fish in Sadam Channel, so fishing pressure remains the greatest risk to successful fish passage. Active fisheries management will be necessary to sustain and further improve passage efficiency in future.     

过鱼设施进口及吸引流设计

利用过鱼设施效果评价模型,分析得到过鱼设施进口吸引流是影响过鱼设施效果的关键因素。通过研究我国过鱼设施现状,指出我国过鱼设施在进口吸引流设计方面存在的不足。结合水利水电工程特性,从过鱼设施吸引流和竞争流的角度出发,给出了过鱼设施位置、进口位置、进口朝向、进口吸引流流量和流速等关键问题的设计思路,并提出了过鱼设施进口概化模型。     

Abundance of native fishes,wild‐introduced salmonids and escaped farmed rainbow trout in a Patagonian reservoir

The introduction of salmonids in Patagonia has resulted in significant impacts on its lakes, as well as a major impact on streams, in which native fishes seem to have been displaced almost completely by rainbow trout (Oncorhynchus mykiss). Another perspective is that the introduced salmonid species have resulted in wild fish populations that sustain an economically important sport fishery. The wide distribution and high abundance of escaped farmed rainbow trout, and a clear decrease in the abundance of native and successfully introduced salmonid species in Alicura Reservoir were all observed, based on comparison of recent data and data from 1993 to 1995 corresponding to littoral gillnet captures. Thus, both native fish and introduced salmonid populations seem to have been drastically reduced in the presence of farmed fish escapees. The results of the present study regarding fish escapes deserve major consideration when making decisions about fish cage culture activities for other Patagonian reservoirs.     

Life‐history traits of three Ambassid fishes (Chanda nama,Parambassis lala and Parambassis ranga) from the Mathabhanga River,southwestern Bangladesh

The present study provides the first indication of the life‐history traits, including, population structure, growth pattern, condition factor, form factor (a_3.0), size at first sexual maturity (L_m), natural mortality (M_W) and optimum catchable length (L_opt), of three Ambassid (Chanda nama, Parambassis lala and Parambassis ranga) fishes from the Mathabhanga River in southwest Bangladesh. A total of 370 individuals were occasionally collected from August 2017 to July 2018 with cast nets, gill nets, square lift nets, and conical‐ and box‐traps. The total length (TL) ranged from 2.4 to 7.5 cm for C. nama, 1.9–3.8 cm for P. lala and 1.8–6.5 cm for P. ranga. The length‐frequency distributions (LFDs) showed the 4.0–5.0 cm TL size group for C. nama and the 3.0–4.0 cm TL size group were numerically dominant for P. lala and P. ranga. The length–weight relationships (LWRs) indicated isometric growth for C. nama, and positive allometric growth for P. lala and P. ranga. All the LWR values were very significant (p < .001), with all r² values > .950. Based on the Spearman rank correlation test, body weight (BW) versus Fulton's‐condition factor (K_F) was extremely correlated (p < .001), indicating a better wellbeing for these species. The a_3.0 value was 0.0082, 0.0138 and 0.0104 for C. nama, P. lala and P. ranga, respectively. Based on the maximum length (L_max), the L_m was 4.4 cm TL for C. nama, 2.5 cm TL for P. lala, and 4.0 cm TL for P. ranga. Based on the asymptotic length (L_∞), the L_m was 4.88 cm TL for C. nama, 2.63 cm TL for P. lala, and 4.28 cm TL for P. ranga. The M_W value was 2.2, 3.3 and 2.7/year for C. nama, P. lala and P. ranga, respectively. The optimum catchable length (L_opt) was 5.36 cm TL for C. nama, 2.75 cm TL for P. lala and 4.65 cm TL for P. ranga. The findings of the present study should be very useful for effective and sustainable management of these fishes in the Mathabhanga River and the connecting ecosystems.     

Taxonomic and functional distinctness of the fish assemblages differing among different types of reservoirs in south-eastern Brazil

The dynamics of fish assemblages in reservoirs depend on factors such as the morphometry of the catchment, habitat structure, and the uses of the reservoir. In the Paraíba do Sul (PSR) basin in southeastern Brazil, there are several types of reservoirs, some on the main channel, some are cascade reservoirs originated from a diversion of the waters of the PSR, and others are isolated reservoirs from tributaries. This study aimed to evaluate the influences of these three types of reservoirs on the taxonomic and functional distinctness of the fish assemblages. It was hypothesized that reservoirs on the main channel (more inflowing waters and habitat availability) have higher taxonomic and functional distinctness compared to cascade reservoirs, which in turn, have greater distinctness than isolated reservoirs. In addition, we expect assemblage structure to differ among these types of reservoirs because of the close relationship with local environmental conditions and habitat structure. Thirty measurements (26 quantitative and 4 categorical) from 34 fish species representing functional traits associated with locomotion, feeding, life strategy, and habitat use were taken. Fish assemblages differed among the three types of reservoirs, which was probably associated with different environmental and local habitat conditions. Higher taxonomic and functional distinctness were found for the isolated reservoirs, and lower for reservoirs on the main channel. This suggests that the fish fauna in this latter type of reservoir were probably composed of phylogenetically close and morphologically similar species. It is likely that limitation of the available resources induces fish to partition the available niches to coexist, favoring assemblages with species adapted to different functions. Our results demonstrate that assessing fish functional and taxonomic distinctness can be used to advance understanding of fish communities from reservoirs in Neotropical regions.     

Coping with hydrogeomorphic variations in a prairie river: resiliency in young‐of‐the‐year fishes

Young‐of‐the‐year (YOY) fish in sand‐bed rivers of grassland ecoregions frequently encounter dynamic habitat conditions produced by highly variable flow and resulting changes in geomorphic complexity of the river. How these vulnerable life history stages cope with changes in habitat condition and location is largely unknown. Therefore, we examined biodiversity and abundance of YOY fish (larvae and juveniles) at two spatiotemporal scales in response to dynamic flow conditions in the Kansas River. During the summer of 2004, we collected and identified 13 745 YOY fish from various moderate to zero‐flow habitats. Patterns of community structure through time were compared with the river's hydrogeomorphic characteristics, as determined by aerial photographs and measurements of instream flow rate and other water quality characteristics. Our initial hypothesis was that species richness and total YOY abundance would be maximized in larger and longer‐lived slackwater habitats. In contrast, our data suggest that dominant fishes in these highly dynamic ecosystems have adapted to hydrological variations with a more generalist lifestyle by either: (i) temporarily using higher flow habitats (except possibly the thalweg) to cope with intermittent loss of prime habitat; or (ii) extending spawning through favourable and demanding conditions. In contrast to current theories, our results suggest that conditions for YOY success are optimized in dynamic prairie rivers during the intermediate flows that maximize habitat heterogeneity and availability. Copyright © 2007 John Wiley & Sons, Ltd.