ECOLOGICAL FUNCTIONS OF FISH BYPASS CHANNELS IN STREAMS: MIGRATION CORRIDOR AND HABITAT FOR RHEOPHILIC SPECIES

The introduction of weirs into stream ecosystems resulted in modifications of serial continuity and in the decline of riverine fish species. Successful river restoration requires information on the ecological functionality of fish bypass channels that are considered an ecological improvement according to the European Water Framework Directive. In this study, we compared the functionality of three nature‐oriented fish passes as compensatory habitats and migration corridors for fishes. Fish passes differed significantly from upstream and downstream reaches of the weirs, revealing higher current speed, lower water depth, smaller channel width and greater habitat variability. Following these structural differences, they provided key habitats for juvenile, small and rheophilic fishes that are typically underrepresented in highly modified water bodies. All fish passes were used as migration corridors, with increased fish movements during high discharge and at spawning periods. Because river stretches with high variability of current speed and water depth are scarce in highly modified water bodies, fish passes can play an important role as compensatory habitats and should thus be considered more intensively in habitat assessments and river restoration. Ideally, fish bypasses should mirror the natural discharge dynamics and consider all occurring fish species and sizes. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydropower Development,Riverine Connectivity,and Non‐sport Fish Species: criteria for Hydraulic Design of Fishways

Hydropower barriers are among the most conspicuous anthropogenic alterations to natural riverine connectivity, resulting in species‐specific effects linked to dispersal abilities, especially swimming performance. They may present a particular problem for small‐bodied ‘non‐sport fish’, such as those that characterize the freshwater communities of temperate regions in the Southern Hemisphere. Recent studies have suggested that nature‐like fishways could ensure passage of diverse fish assemblages through hydropower barriers. Through experiments performed in a swim tunnel, we present, for the first time, fishway design criteria for two non‐sport species endemic to Chile, a country experiencing rapid hydropower development. In`cremental velocity tests showed that Cheirodon galusdae and juveniles of Basilichthys microlepidotus were capable of very similar standardized critical swimming speeds of 69.7 and 69.6 cm s^?1, respectively. When expressed in units of body lengths, C. galusdae was capable of very high critical speeds of 16.2 bl s^?1, whereas for B. microlepidotus, this was 7.6 bl s^?1. However, fixed velocity tests revealed that the swimming endurance of the latter species was slightly higher. Dimensionless analysis showed a clear relationship between fatigue time and fish Froude number, similar to that already described for subcarangiforms. Based on these results, we present fishway design curves indicating a transition from sustained to prolonged swimming at a fishway length of 15 m. Our results show that the swimming capacity of these species is well‐suited to the mean flow velocity field described for nature‐like fishways. However, more work is required to understand the effects of turbulence on the passage of non‐sport species. Copyright © 2016 John Wiley & Sons, Ltd.     

Norden multimesh gill net for fish sampling in lotic environments

Reliable data on species composition, length‐frequency distribution and relative density of freshwater fish are difficult to obtain for some stream habitats. Present methods, with electro‐fishing being the most important one, are not useful where the conditions are unfavourable, as in deep, turbulent or turbid waters. A new sampling method focusing on fish in stream habitats is presented in this study. The novel gill net is a development of the European standardized fish sampling method Norden (standardized multimesh survey net). The net was tested in both lotic (up to 0.5 m s^?1) and lentic habitats. The results were compared to fish trap data. The novel net produced consistent data on the number of fish species and length frequency of the catch. It was straightforward to handle and is considered to be useful for sampling fish in flowing waters. Further studies are required to evaluate the performance of the net at high stream velocities, and to establish the effort (number of nets) required for good sample precision.     

Changes in fish communities of the Shoalhaven River 20 years after construction of Tallowa Dam,Australia

This study was undertaken as part of a long‐term investigation of the ability of high‐level fishways to rehabilitate fish communities upstream of high dams. Effects of Tallowa Dam on fish of the Shoalhaven River system were studied by comparing species abundances, population size‐structures and the structure of fish communities above and below the dam. Fish were sampled twice yearly for two years at 12 sites throughout the catchment. Species richness was greater downstream of the dam, with 21 species, compared to 16 species upstream of the dam. Ten diadromous species are believed to be extinct above the dam because of obstructed fish passage. Another four migratory species capable of climbing the wall have reduced abundances upstream. Accumulations of fish, particularly juveniles, directly below the dam were evident for nine species. Fish communities upstream and downstream of the dam differed significantly, identifying the dam as a significant discontinuity in the available fish habitats within the system. Historical evidence suggests that before the dam was built, fish communities from the tidal limit to at least 130 m elevation were largely continuous. This study has demonstrated that Tallowa Dam is a major barrier to fish migration and has had adverse effects on the biodiversity of the system. The creation of Lake Yarrunga by Tallowa Dam has resulted in distinctive fish communities in riverine and lacustrine habitats. Populations of five species that occur both upstream and downstream of the dam have developed differences in their size structures. The fish community downstream of the dam also differs from its historical condition because of the virtual disappearance of Australian grayling (Prototroctes maraena) and the establishment of non‐native species. A high‐level fishway is now being designed for the dam to restore fish passage. Data from this study will serve as a baseline against which to assess the effectiveness of the fishway in rehabilitating fish communities of the river system. Copyright © 2002 John Wiley & Sons, Ltd.     

The river Vecht fish community after rehabilitation measures: a comparison to the historical situation by using the river Biebrza as a geographical reference

Setting ecological goals for restoring fish communities in larger rivers is hampered by a lack of knowledge of the natural reference conditions. The lowland river Vecht has become highly regulated since 1850. Since the 1970s, measures have been taken to improve water quality followed by the construction of fishways along weirs in the 1990s to rehabilitate migration. We aim to assess the degree of deviation of the current fish community in the river from its pre‐regulation state. The assessment is based on a comparison with the less impacted river Biebrza in Poland as a geographical reference, involving a semi‐quantitative stepwise reconstruction based on available historic evidence. Electrofishing was used to describe the current quantitative species compositions of the fish communities in the rivers Vecht and Biebrza and historical records of the Vecht region were used to crosscheck the reconstructed fish community around 1850 after correcting for zoogeographical differences. Despite various rehabilitation measures, the deviation from the natural reference is still large. Currently, perch Perca fluviatilis and bream Abramis brama are much more abundant, and bleak Alburnus alburnus, white bream Blicca bjoerkna and most rheophilic species are far less abundant, than before. The main reasons for this deviation appears to be the present quality of the habitats and, for some species, the poor connectivity with the sea as well as with small tributaries. The approach used should be widely applicable to derive natural references, assess rehabilitation success or improve the ecological assessment of integrity as imposed by the European Water Framework Directive. Copyright © 2008 John Wiley & Sons, Ltd.     

Evaluation of nature‐like fishways for re‐establishing connectivity in fragmented salmonid populations in the River Emån

We evaluated the function of two nature‐like fishways for re‐establishing connectivity for anadromous salmonids in the regulated River Emån. Between 90 and 100% of the salmonids that entered the fishways actually passed through them, with median speeds of 180–190 m h^?1. Only 50% of the anadromous brown trout that passed the first fishway also passed the second one, indicating that the fish might have had problems locating the upstream fishway. The fishways were also observed to function as a passage for downstream post‐spawning migrants. The densities of brown trout yearlings upstream of the fishways were higher in 2002, after the fishways were built, than during pre‐fishway years. In control sites in other parts of the river as well as in a nearby river, no changes in yearling densities were observed. Thus, the fishways are working for upstream spawners, albeit at a recolonization rate that is slower than expected. Copyright © 2005 John Wiley & Sons, Ltd.     

Evaluating a light‐louver system for behavioural guidance of age‐0 white sturgeon

Water diversions for hydropower and other applications are some of the most disruptive alterations affecting fish populations in lotic systems. Although many different strategies have been developed to reduce lethal encounters with such infrastructure, few studies have evaluated different forms of behavioural guidance concurrently. Here, we combine an LED‐based light guidance device (LGD) equipped with adjustable wavelength and strobing output with a reverse‐configured louver rack to assess the effectiveness of this two‐part behavioural guidance system on downstream movement through a bypass by age‐0 white sturgeon (Acipenser transmontanus). Several combinations of LGD and louver settings were tested under both simulated day and night (low light) conditions in a laboratory setting. In the absence of the LGD, louver slat spacings of 10 or 20 cm were most effective at achieving downstream bypasses with greater success rates (~ two‐fold greater) under night conditions than under day conditions. Incorporating the LGD operating at the most attractive setting (green light strobing at 20 Hz) with the louver spacings of 10 or 20 cm achieved the highest rates of bypass usage (100% and 97%, respectively) under both day and night conditions while the control treatment (no LGD or louver) resulted in the lowest bypass rate (46%) among fish that moved downstream. Collectively, these results demonstrate that complementary cues can enhance the behavioural guidance of fishes and highlight the importance of continuing to explore the use of multiple strategies to mitigate entrainment for high priority fish species.     

BichiCAM,an Underwater Automated Video Tracking System for the Study of Migratory Dynamics of Benthic Diadromous Species in Streams

Conventional methods for surveying diadromous fish migration from marine coastal waters to freshwater habitats are mainly based on electrofishing, a non‐optimal technique for the study of fish migrations in rivers, and fishermen catch data. Underwater video has been recognized for a long time as a good alternative, but those approaches usually require intensive labour for retrieving the information from the video sequences. To overcome these problems, an underwater video system specifically designed for field work (low‐weight, low‐cost and autonomous) named BichiCAM has been developed for automatically counting, measuring and tracking fish observed in video sequences. The efficiency and precision of the BichiCAM system were tested by filming Sicyopterus lagocephalus juveniles passing through the camera field of vision in the Saint‐Etienne River, Reunion Island, Western Indian Ocean. The BichiCAM system accurately measured fish length of the observed individuals when lens distortion of the camera was corrected, and the error percentages on the measurements presented a standard deviation of 5.1% of the total length. The BichiCAM system provides a powerful tool that will not only facilitate research on migrating fishes and invertebrates' communities but also allow studies of the effectiveness of fishways associated to dams or the impacts of fishery activities. Copyright © 2015 John Wiley & Sons, Ltd.     

Migratory fishes of Brazil: Life history and fish passage needs

Many of the most important commercial and recreational species of the megadiverse Brazilian freshwater fishes migrate in rivers among essential habitats during all life stages. These movements, however, have been severely blocked by hundreds of hydroelectric dams and reservoirs and they will be even more obstructed due to hundreds of new developments. Fishways have been used in many countries to allow fish to pass around dams. Fishway construction is booming in Brazil, but poor understanding of migrations by Brazilian fishes has led legislators, scientists, and the public to several misconceptions about the rules of fishways in fisheries conservation. First, is a belief that fishways are only needed to facilitate upstream spawning migrations. Also, it has been suggested that upstream passage for Neotropical migrant fishes is not useful if there is no large free‐flowing stretch upstream of a dam that contains spawning habitat and has a large natural floodplain (nursery habitat). In this paper, we discuss that, in addition to providing passage for pre‐spawning migrants, upstream fishways also provide passage for other fish migrations (e.g. foraging), and that all up‐ and downstream migrations during life history need to be addressed at dams to conserve fish resources. We also argue that an upstream fishway is important even if the upstream reach does not have spawning or nursery habitats. In addition, we discuss the need for protection of downstream migrant fish, and the importance of fish behaviourists and engineers working together on fishway design and operation to solve fish passage issues. Copyright © 2008 John Wiley & Sons, Ltd.     

Not just a migration problem: Metapopulations,habitat shifts,and gene flow are also important for fishway science and management

Worldwide, fishways are increasingly criticized for failing to meet conservation goals. We argue that this is largely due to the dominance of diadromous species of the Northern Hemisphere (e.g., Salmonidae) in the research that underpins the concepts and methods of fishway science and management. With highly diverse life histories, swimming abilities and spatial ecologies, most freshwater fish species do not conform to the stereotype imposed by this framework. This is leading to a global proliferation of fishways that are often unsuitable for native species. The vast majority of fish populations do not undertake extensive migrations between clearly separated critical habitats, yet the movement of individuals and the genetic information they carry is critically important for population viability. We briefly review some of the latest advances in spatial ecological modelling for dendritic networks to better define what it means to achieve effective fish passage at a barrier. Through a combination of critical habitat assessment and the modelling of metapopulations, climate change‐driven habitat shifts, and adaptive gene flow, we recommend a conceptual and methodological framework for fishway target‐setting and monitoring suitable for a wide range of species. In the process, we raise a number of issues that should contribute to the ongoing debate about fish passage research and the design and monitoring of fishways.     

Fish Associations among Un‐notched,Notched and L‐head Dikes in the Middle Mississippi River

Wing dikes and other anthropogenic modifications have heavily altered riverine ecosystems. Recent efforts to reach a compromise between the needs of the river transportation industry and natural resource conservation include dike modification. Dike notching permits water flow through the landward portion of the dike and has been purported to provide suitable habitat for fish and other river biota while maintaining the navigation channel. L‐head dikes are flow‐control structures that create calm backwater‐like habitats downstream. However, few researchers have examined the actual effects of dike notching on water quality or fish communities. We compared standardized catch per unit effort and overall community structure for 50 fish species among un‐notched dikes, notched dikes and L‐head dikes in the Middle Mississippi River, sampled as part of the US Geological Survey's Long‐Term Resource Monitoring Program. There were no differences in standardized catch per unit effort for 64% of the fishes examined. Five species known to be associated with lotic habitats were most abundant near L‐head dikes. Seven species were more abundant at un‐notched dikes than notched dikes, while six species were more abundant at notched dikes than un‐notched dikes. Non‐metric multidimensional scaling suggested differences in overall fish community structure between un‐notched and other dike types. Detailed physical habitat studies should be conducted to better understand the effects of dike modification. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Connectivity is a two‐way street—the need for a holistic approach to fish passage problems in regulated rivers

We evaluated the effects of a rehabilitation project, whose goal was to re‐establish longitudinal connectivity for anadromous trout in the regulated river Emån. We used a holistic approach, by tagging and following both upstream‐migrating spawners (N = 348) and downstream‐migrating smolts (N = 80) and kelts as they passed two hydroelectric plants (HEP 2‐3) with nature‐like fishways. When migrating upstream, 84–88% of the spawners stopped, primarily at spawning grounds, before reaching HEP2. The proportion of stoppers was lower (56%) for fish that had been to the fishways in previous years, indicating that the recolonization rate is likely to increase over time. Of the spawners that approached the fishway at HEP2, 77% rapidly located the fishway situated next to the tail‐race, resulting in an attraction efficiency of 81% and a passage efficiency of 95%. The time required to locate the fishway inside the former channel at HEP3 was substantial, but the attraction efficiency (89%) and passage efficiency (97%) were nevertheless high. The kelts swam downstream mainly in spring, using spill gates and the fishways, to swim past HEP2 and 3 and continue downstream to the Baltic Sea. Iteroparity was confirmed by the fact that 20% of the spawners were tagged in previous years. Smolt loss was about 30% for both HEPs, with a higher turbine‐induced loss 30% for fish passing through Francis runners than a Kaplan runner. Fifteen per cent of the tagged smolt reached the sea and none of these fish had swum through the Francis runners. It will probably take many years before longitudinal connectivity is fully re‐established in the river Emån, due to substantial losses of both upstream‐migrating spawners (35% loss) and downstream‐migrating smolts (50%) and kelts. In addition, smolt production in areas upstream of HEP3 is far below carrying capacity. Thus, additional measures that not only facilitate movement of upstream spawners, but also reduce mortality and injuries of downstream migrants are urgently needed to create a self‐sustaining fish population. Copyright © 2009 John Wiley & Sons, Ltd.     

Habitat loss as the main cause of the slow recovery of fish faunas of regulated large rivers in Europe: the transversal floodplain gradient

In large European rivers the chemical water quality has improved markedly in recent decades, yet the recovery of the fish fauna is not proceeding accordingly. Important causes are the loss of habitats in the main river channels and their floodplains, and the diminished hydrological connectivity between them. In this study we investigate how river regulation has affected fish community structure in floodplain waterbodies of the rivers Rhône (France), Danube (Austria), Rhine and Meuse (The Netherlands). A typology of natural and man‐made aquatic habitats was constructed based on geomorphology, inundation frequency and ecological connectivity, along the transversal river–floodplain gradient, i.e. perpendicular to the main stream of the river. Fish species were classified in ecological guilds based on their flow preference, reproduction ecology and diet, and their status on national red lists was used to analyse the present state of the guilds and habitats. Ecological fish guilds appear to be good indicators of ecological integrity and functioning of river–floodplain systems. A transversal successional gradient in fish community structure that bears some resemblance to the gradient found in natural rivers can still be discerned in heavily regulated rivers. It resembles the longitudinal river gradient; even some predictions of the River Continuum Concept are applicable. Overall, richness and diversity of species and ecological guilds decrease with decreasing hydrological connectivity of floodplain waterbodies. Anthropogenic disturbances have affected fish species unevenly: guilds of specialized species that are highly adapted to specifically riverine conditions have declined far more than generalist species. Fish habitats in the main and secondary channels have suffered most from regulation and contain the highest percentage of threatened species. Rheophilic fishes have become rare because their lotic reproductive habitats are severely degraded, fragmented, absent or unreachable. Limnophilic fishes have become rare too, mainly as a result of eutrophication. Eurytopic fishes have become dominant everywhere. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

Selective use and spatial distribution of native and non‐native fish in wetland habitats

Wetland habitats are crucial for many fish species as spawning, feeding or nursery areas, but the major factors that govern their use by fish are poorly identified. In the present study, we aim to investigate the selective use and the spatial distribution of native and non‐native fish species in different types of wetland habitats (grasslands and reed beds) in a large freshwater marsh (North Western France). The selective use was measured by comparing the community that uses wetland habitats to the total community of the marsh (sampled in the permanent aquatic habitats (canals) during the low water period). The spatial distribution was studied by analyzing the presence probability of fish in wetland habitats as a function of the distance from adjacent canals. All sampled wetland habitats were occupied by fish, and the fish community in wetland habitats was dominated by three native (Abramis brama, Scardinius erythrophthalmus and Anguilla anguilla) and three non‐native (Ameiurus melas, Gambusia holbrooki and Lepomis gibbosus) species. Species richness and total fish abundance differed between canals and wetland habitats as a consequence of a variable propensity to use wetland habitats by native (avoidance and preference) and non‐native (no preference) species. Non‐native species were also more abundant in reed beds than in grassland while no differences were observed for native species. Universally, the presence probability of fish always decreased in wetland habitats as the distance from the canals increased and only a narrow area, close to canals (50–80 m), was well used by fish. However, non‐native fish species used over greater distances in reed beds than in grasslands while no differences were observed for native species. Variable interpretations related to species tolerance, reproductive guilds or diet are proposed to understand the mechanisms that might explain the widespread success of non‐native species in this spatially varying environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Body size,experience, and sex do matter: Multiyear study shows improved passage rates for alewife (Alosa pseudoharengus) through small‐scale Denil and pool‐and‐weir fishways

Alewife (Alosa pseudoharengus) passage through 3 fishways was assessed during the 2013–2016 spawning runs in 3 rivers of the Isthmus of Chignecto, Canada. From April 24 to June 10, 5,423 alewife with a mean ± SD fork length of 227 ± 18 mm were tagged with passive integrated transponders. During their tagging year, approximately half of individuals (40% to 64%) went undetected whereas those detected used fishways from April 16 to July 8. Detected alewife were significantly longer than those undetected. Attraction rates to fishway entrances in 2015 and 2016 ranged from 85% to 98%. Annual fishway passage rates for pooled fish tagged that year and returnees, varied from 64% to 97% for 2 Denil style fishways. A pool‐and‐weir fishway that was dysfunctional (2013), repaired (2014), and replaced (2015–2016) yielded 0.5%, 25%, 60%, and 73% annual pooled passage rates, respectively. Larger individuals, previously tagged returnees, and males compared to females of a similar size had higher passage success suggesting some fishways may apply population‐level selective pressures. Alewife passage rates related to fishway style, design, and proper function, with greater passage for the 2 Denils than the pool‐and‐weir fishway in our study. Regular structural maintenance and fish passage reviews are essential management considerations to ensure fishway functioning and river connectivity. Replacement of a fishway with poor fish passage may be the best option to improve passage rates. Future research should address the effects of multiple anthropogenic instream obstructions, environmental variables, negative sublethal post‐tagging effects, and the importance of returnees on fish passage rates in fishways.     

INTRA‐ANNUAL VARIATION IN RIVER–RESERVOIR INTERFACE FISH ASSEMBLAGES: IMPLICATIONS FOR FISH CONSERVATION AND MANAGEMENT IN REGULATED RIVERS

While much is known about the fish assemblages, habitats, and ecology of rivers and reservoirs, there has been limited study of the fish assemblages in transitional habitats between these lotic and lentic habitats. Data about these river–reservoir interface (RRI) fish assemblages are needed to guide integrated management efforts of river–reservoir ecosystems. The aim of these efforts is to recommend flows for natural river function, conserve native riverine fish assemblages, and maintain reservoir sport fisheries. We used a multigear approach to assess the fish assemblages of four RRIs in the Colorado River Basin, Texas. In addition to characterizing RRI fish assemblages using species richness and evenness metrics, and habitat‐use guilds, we used a multivariate approach to evaluate intra‐annual shifts in species composition and abundance. All RRIs had high species richness and evenness values and included both macrohabitat generalist and fluvial species. RRIs also contained high proportions of the fish species available within each river–reservoir ecosystem, ranging from 55% to 80%. Observed intra‐annual shifts in RRI fish assemblages resulted from changes in abundance of dominant species rather than changes in species composition, with abundance of most species increasing from early spring to summer. Fish species responsible for intra‐annual shifts included mostly floodplain and migratory species, suggesting that species both used littoral habitats within RRIs and migrated through RRIs to river and reservoir habitats. The diversity of fishes found within RRIs highlights the importance of including these areas in future conservation and management efforts of river–reservoir ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Stream macrophytes increase invertebrate production and fish habitat utilization in a California stream

Stable flow and thermal regimes, coupled with geologically derived nutrients, are drivers of enhanced productivity in volcanic spring‐fed rivers. However, little information exists on biotic mechanisms or species interactions contributing to elevated productivity at higher trophic levels. In a California stream, juvenile steelhead trout were observed to preferentially select macrophyte habitat at a rate three times greater, on average, than five other habitat types. To understand the potential rearing benefits associated with macrophytes, we conducted a manipulative experiment to determine how macrophytes affect invertebrate prey availability and stream water velocity. Macrophytes supported up to nine times greater abundance of invertebrates than adjacent open gravel habitats. They also doubled invertebrate drift rates and reduced water velocity by up to 42‐fold. The results show that aquatic macrophytes are an important stream habitat feature that may be bioenergetically more favourable for rearing salmonids than more traditional lotic habitats. We suggest that macrophytes have the potential to enhance growth rates of juvenile salmonids when compared with other habitat types. Habitats that confer growth and size advantages may ultimately improve fitness and contribute to conservation of imperilled salmonids.