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Objective: Restoration of many populations of anadromous American Shad Alosa sapidissima and river herring (Alewife A. pseudoharengus and Blueback Herring A. aestivalis) has been hampered by the presence of barriers to their spawning migrations and insufficient monitoring of run size. Here, we describe results of a 10‐year (2012–2021) study of American Shad and river herring passage at the Island Farm Weir (IFW), the downstream‐most migration barrier on the Raritan River, New Jersey, United States. Methods: We used passive integrated transponder tags applied to fish that were captured and released downstream of the IFW to estimate passage rates and migration delays associated with upstream movements through an antenna array on a vertical slot fishway within the weir. By combining estimated passage rates with video monitoring of the total numbers of American Shad and river herring transiting the fishway, we estimated the annual run size below the weir. Result: Results suggest that the fishway on the IFW is moderately effective for American Shad (passage rate = 41%; 95% credible interval [CI] = 21–61%) but ineffective for the smaller‐bodied river herring (passage rate = 0.5%, 95% CI = 0–2%; fallback‐adjusted passage rate = 1.1%, 95% CI = 0.0–4.5%). The IFW may have also delayed the spawning migrations of those fish that did pass, with total passage times ranging from 0.4 to 20.9 days (mean ± standard deviation = 8.2 ± 5.3 days) for American Shad and 15.0 days for the one river herring that passed within the same year that it was tagged. Run size estimates during the study period ranged from 103 to 2624 individuals for American Shad and from 1486 to 53,334 for river herring. Conclusion: Restoration of these species in the Raritan River will likely require removal of the IFW or replacement of its current fish passage device with one that increases the passage rates of alosines. Impact statementUsing a combination of electronic tags and video monitoring, we found that a fish passage structure on the Raritan River, New Jersey, works moderately well for the large‐bodied American Shad but passes only a small fraction of the smaller‐bodied river herring. [ABSTRACT FROM AUTHOR]

The paper presents a 2D computer structure modelling and discharge simulation for an improved aquatic fauna passage consisting on a three compartments stepped concrete channel and considered as a side appurtenant for a small head dam on a river upper course. The foreseen structure aims to reduce the barraging environmental impact by offering optimum flow conditions under given water discharging circumstances, meaning even for ensuring the minimum required sanitary/ecological river discharge as split by the main path through the gate dam and the side passage path. The hydraulic simulation looks to establish the side passage discharge development and in the same time to estimate the extreme values of water velocity, especially at narrowing sections. In case there is necessary, the numerical results would point to further geometrical optimisation by adjusting the existing structural details or by considering additional constructive elements in order to fulfil specific requirements (usually with respect to the maximum water velocities) as indicated by in-force regulations. [ABSTRACT FROM AUTHOR]

Structural solutions in terms of fish ladders and the use of natural materials to construct them often raise concerns regarding the possibility of using the standard calculation methods. The fish ladder being designed on the Wisłok river consists of three pools, separated from each other by baffles made of rock boulders. The purpose of this study was to analyze water surface profiles for fish ladder at specific values of flow rates. The paper presents the results of hydraulic calculations under the conditions of constant flow rate based on the concept of a minimum specific energy. According to this method, water flow through boulders is critical. Thus, it does not take into account head losses, which are hard to estimate and which are the integral part of typical calculation methods, e.g. the use of equations to determine the flow rate of a weir. An additional advantage of this method is that there is no need to assume the flow pattern of one specific weir. Verification calculations of the water depths were conducted using the HEC–RAS software, under an assumption of an one-dimensional steady water flow. Water depths in the fish ladder, calculated using both methods, were similar, despite the adopted different calculation concepts, and can be used in ichthyologic analyses.

AbstractThe abundance, distribution, and diversity of fishes in Ribb Reservoir were studied based on a total of 1629 fish samples collected from February to October 2021. Fish samples were collected using gillnets of different stretched mesh sizes. Except for temperature and pH, most physico-chemical variables revealed significant spatial variation (ANOVA, p

The purpose of this study was to allow fish to move upstream past barriers or difficult sections of passage, even on steep stream-type fishways. Therefore, the authors devised a roughness arrangement to raise the water depth in the fishway and reduce its flow velocity. Roughness was used as a group in the arrangement so as to expect afflux effects. Water depth was raised and the flow velocity was reduced around the roughness groups, which allowed fish to hold position and move upstream. Although rapid flow was locally formed in some spots in the fishway, its area was small, enabling the fish to move upstream sufficiently. The experimental results obtained in this study will be applied as a removable stream-type fishway to small channels, head constructions, and so on where fishways cannot be installed due to management. [ABSTRACT FROM AUTHOR]

The meander‐type fish pass is a slotted fishway characterised by the exclusive use of rounded and smooth components. Due to the specific geometry and arrangement of the basins, which differ considerably from the conventional vertical slot pass, there are significantly different hydraulic conditions. The water flow is guided along the basin walls by means of a dominant main current while the water body is much calmer towards the centre of the basin, where very low flow velocities are found. A detailed assessment of the functionality is currently impossible due to the small number of surveys of fish passage hitherto carried out. However, considerable potential is indicated by the high passage rates at some sites and the lack of selectivity with regard to species and small fish, together with the design advantages and the adaptation possibilities after construction work is completed. In this study, we offer some recommendations for dimensioning to enable this potential to be exploited. These are oriented around recommendations for conventional vertical slot passes regarding basin size, flow depth and slot width. Due to the great potential of the meander‐type fish pass, it is desirable to construct still more individual pilot passes to implement comprehensive surveys of fish passage on a sound methodological basis. [ABSTRACT FROM AUTHOR]

The purpose of this study was to allow fish to move upstream past barriers or difficult sections of passage, even on steep stream-type fishways. Therefore, the authors devised a roughness arrangement to raise the water depth in the fishway and reduce its flow velocity. Roughness was used as a group in the arrangement so as to expect afflux effects. Water depth was raised and the flow velocity was reduced around the roughness groups, which allowed fish to hold position and move upstream. Although rapid flow was locally formed in some spots in the fishway, its area was small, enabling the fish to move upstream sufficiently. The experimental results obtained in this study will be applied as a removable stream-type fishway to small channels, head constructions, and so on where fishways cannot be installed due to management.

The Chinese mitten crab is one of the top invasive species in Europe. In Flanders (Belgium), they are associated with river ecosystem degradation, especially the loss of aquatic vegetation and associated ecosystem services. Management measures have therefore been put in place to reduce the number of crabs migrating between the sea and freshwater areas and ultimately control the population. Although we are still long way from the goal, a low‐cost method has been applied to successfully catch migrating crabs. In this article, we outline the design and functioning of the trap. We monitored the population in a lowland river, measured migration speeds and calculated crab densities. With over 1 million crabs caught in 2 years, the trap proved to be very effective. Median anadromous (spring) and catadromous (autumn) migration speeds were 0.69 and 0.96 km day−1, respectively. Anadromous migrating crab density was calculated to be up to 3.20 ind. m−2 river bed. Resident crab density was calculated to be up to 2.05 ind. m−2 river bed. We conclude that this trap is a very useful tool for water managers to catch Chinese mitten crabs in rivers and discuss the pathways towards reducing the population and protect the entire freshwater catchment. [ABSTRACT FROM AUTHOR]

Hydrodynamic modelling is based on the similitude theory and the dimensional analysis. The complexity of flows in different geometric environments and fluids, requires the use of the similarity criteria in both the construction of a physical model and a numerical simulation model. That is why expressing a criterion of similarity is important. In modelling of open channel flows, the Froude similarity criterion is used. By definition, as a ratio between the force of the inertia and the weight mass, the Froude number is dependent on the square of the velocity. And yet, there are situations in which the Froude number expression is preferred as linear speed dependence. The paper shows that the way of expressing the Froude number is especially important when we scale and design a fish ladder or fish passage.

The seasonal pattern and the composition of downstream drift of fish eggs and larvae through the fish ladder of the Porto Primavera dam, located in the Upper Paraná River, Brazil, were studied. Additionally, the condition of individual larvae with regard to injuries was examined. Samples were collected monthly over three reproductive seasons at upper and lower pools at the twilight (nightfall and dawn). Ichthyoplankton densities were low, especially for eggs, and the downstream passage of fish eggs and larvae through the fish ladder was negatively correlated to water residence time of the reservoir. Highest larvae densities occurred between December and March, with highest densities in February. The ichthyoplankton abundance was similar between sites and times of day, with the predominance of partially damaged larvae (60%). Seventeen taxa were identified, especially non-migratory species. Long-distance migratory species represented less than 1% of the total. Since many migratory species have found favorable habitats for spawning and development in the tributaries of Porto Primavera Reservoir, the dispersion of larvae from these free-flowing tributaries located far from dam through reservoir may not be beneficial for their survival. At the same time, despite the low density and diversity of migratory species larvae drifting downstream from the dam, this fish ladder may have dispersive potential as long as the reservoir displays a shorter water residence time. [ABSTRACT FROM AUTHOR]

This review serves as a guide to improve multispecies fish passage. Human development along waterways in California during the last 160 years has adversely affected fish populations in many watersheds. Conflicts in water usage will only intensify with modern developments and population growth. Since most past fishpassage improvement efforts in California have focused on salmonids, I summarize the published studies and considerations that affect multispecies fish passage. To be effective, conditions in fishways need to meet the specific hydraulic requirements, as well as abilities, behavior, and size consideration for all fish species being considered. Turbulence, water depth, velocity, passage location, and design of a passage facility are essential elements to successful fish passage. Because of a lack of research on most of the native species, species-specific passage criteria are not fully defined, and it may be helpful to use data for physically similar, surrogate species found in similar habitats. [ABSTRACT FROM AUTHOR]

Stavby a objekty na vodních tocích mají důležitý krajinotvorný, vodohospodářský a ekologický význam. Ovlivňují krajinný ráz a vytváří podmínky pro vznik nových biotopů. Ve venkovské krajině se v minulosti i současnosti budují malé vodní nádrže, mlýny, pily, malé vodní elektrárny, jezy a další vodohospodářské objekty a stavby, které více či méně ovlivňují daný tok i okolní krajinu. Při navrhování a výstavbě těchto objektů je nutné respektovat environmentální vztahy a postupovat v souladu s trvale udržitelným využíváním daného území. V minulosti bylo vybudováno mnoho objektů, které negativně ovlivnily daný tok i krajinu a zároveň ani neumožňovaly migraci ryb a obojživelníků, řada objektů je v současné době nefunkčních a mají negativní vliv na daný tok i okolní krajinu. V takových případech se přistupuje k revitalizaci toků, případně i odstranění nefunkčních objektů, často jsou budovány rybí přechody. Součástí práce je zhodnocení možností využití pozemků přilehlých k pevnému jezu na řece Svratce v obci Ujčov, a to z hlediska nenarušení biodiverzity, estetického a ekonomického potenciálu daného území. Byla vypracována studie s několika možnostmi využití daného území.

Abstract: Many fish passes have been built across the world in recent years. This study analyses the performance of a modified type of pool and weir fishway with two access branches, using passive integrated transponder telemetry. A circum‐Mediterranean barbel, Luciobarbus bocagei (Steindachner, 1864), was chosen as the target species. Both hydraulic values (flow and volumetric energy dissipation) and biological parameters (attraction, entrance and passage success) were measured in the fishway, these being related to the environmental variables affecting upstream fish movement. Flow discharge, water temperature and atmospheric pressure were important for fish entering the fishway. There was no preference between path routes, even though the main discharge was concentrated in the turbine channel. This type of fishway design could be an alternative for the conservation of fish populations where multiple fish approach options are possible. [ABSTRACT FROM AUTHOR]

Com o objetivo de avaliar preliminarmente a eficiência e a seletividade do mecanismo de transposição de peixes de uma Pequena Central Hidrelétrica (PCH) localizada no rio Ijuí, foram realizadas quatro expedições de coleta. Foram coletados 3017 indivíduos, representando 18 espécies e pertencentes a nove gêneros, seis famílias e três ordens. As espécies mais abundantes foram Pimelodus absconditus (Azpelicueta, 1995) e Schizodon nasutus (Kner, 1858), resultando num percentual de 49 e 27 respectivamente. Por esse motivo, foi feita a análise do sexo e do estágio de maturação dos indivíduos dessas espécies. Da espécie P. absconditus, foram coletadas 66 fêmeas no estágio B (36,67%) e 99 machos nos estágios A (1, 11%) e B (53,89%) e 15 indivíduos imaturos (8,33%). Já em S. nasutus, foram encontradas 93 fêmeas nos estágios A (7,59%), B (18,99%) e C (7,59%) e 52 machos nos estágios B (56,96%), C (3,80%) e D (5,06%). Concluiu-se, portanto, que a escada é seletiva, podendo ascender por ela apenas espécies de menor porte, pois a maioria dos indivíduos avaliados estava em estágio de maturação.In order to evaluate the efficiency and selectivity of the mechanism transposition of fish from a PCH, 4 collecting expeditions were performed. The collection was made in a period of 24 hours until the end of a Piracema, January 31, 2008. It was collected a total of 3017 specimens, representing 18 species, which 6 belongs to families and 3 to orders. The most abundant species were Pimelodus absconditus (Azpelicueta, 1995) and Schizodon nasutus (Kner, 1858), resulting in a percentage of 48.36 and 26.95 respectively. Hence, the analysis was made regarding sex and stage of maturation of individuals of these species. From the P. absconditus specie, 66 females were collected in stages B (36.67%), and 99 males in stages A (1.11%), B (53.89%) and 15 were immature individuals (8.33%). Already in S. nasutus, 27 females were found in stages A (7.59%), B (18.99%), C (7.59%) and 52 males in stages B (56.96%), C (3.80%) and D (5.06%). It was concluded that the ladder is selective, which shows that only species of small size can rise it, because most of the individuals were at maturation stage.

Fishways can restore functional connectivity within rivers for migratory fish where barriers compromise connectivity. Providing fish passage is particularly important for semelparous, anadromous species that require access to upriver habitats to successfully reproduce. From 2017 to 2020, we used a combination of acoustic and radio telemetry to investigate the passage success of Chinook salmon (Oncorhynchus tshawytscha) in the upper Yukon River through the wooden Whitehorse Rapids Fishway and compared this to the migration of salmon in the nearby free-flowing Takhini River. The upper Yukon River population of Chinook salmon studied here is highly unique, completing a 2800 km inland migration to Whitehorse, YT, before attempting to pass the Whitehorse Hydro Plant (WHP) to reach spawning sites upstream. We found that upstream passage success was variable across four years of study (0%–66%), was low overall at 31%, and was considerably lower for female salmon. In contrast, salmon migrating up the free-flowing Takhini River had high migration success to spawning grounds and had many times faster migration rates. Attraction (86%), entrance (77%), and passage efficiency (36%) were less than that reported for Chinook salmon at other fishways. Within the fishway, a disproportionately high number of salmon returned downstream upon reaching a daytime-operated viewing chamber (fish trap) located ∼115 m up the fishway. Upon passing the fishway, salmon had high migration success to spawning grounds, though 12% of salmon returned downstream of the WHP, typically after multiple days and after traveling dozens of kilometres upstream of the facility. Findings from this study reveal opportunities to improve fishway performance and thus connectivity for one of the world's most impressive animal migrations. [ABSTRACT FROM AUTHOR]

This study demonstrated the use of environmental DNA (eDNA) to determine habitat connectivity for migration of fishes between the sea and river. Environmental DNA is DNA fragments released by fishes in water, which can be used as a species-specific marker of the presence/absence of the target species. A year-round water sampling regime at 15 sites on the Yodo River, Japan, was conducted to determine whether three major man-made barriers on the river inhibited the migration of fishes using species-specific detection of DNA fragments from three target migrant species, temperate seabass, Lateolabrax japonicus , flathead grey mullet, Mugil cephalus , and ayu, Plecoglossus altivelis altivelis . The presence/absence of eDNA from target species was consistent with known patterns of species’ seasonal migration. The detection of the DNA of temperate seabass and flathead grey mullet at sites upstream of the dam closest to the river mouth indicated successful upstream migration of these species via a fish ladder bypassing the dam. On the other hand, DNA of these two species was not detected from the upstream side of the two remaining dams, which are not equipped with fish ladders. Ayu is the only species among the three target species with a land-locked population in Lake Biwa located at the headwater of Yodo River. Ayu DNA was detected at most of the sites in the freshwater area during the warm months; however, in the coldest month of February, eDNA was only detected in the uppermost site of Yodo River at the southern tip of Lake Biwa. The eDNA we detected at this site suggests that it was derived from juvenile ayu spending their winter months in the lake. These results suggest that the eDNA analysis presented here can accurately track the seasonal migration of fishes in a river, demonstrating its application as an indicator of habitat connectivity for fishes in association with man-made barriers in a river. The sampling of eDNA involves merely scooping a tank full of water; therefore, it is a simple, rapid, and cost-effective method for long-term monitoring of habitat connectivity associated with the construction of barriers in a river. [ABSTRACT FROM AUTHOR]

A fish ladder designed to facilitate fish passage at the outlet end of perched culverts is investigated with a 3D computational fluid dynamics model. The fish ladder consists of a series of alternating arch baffles with geometries providing options for fish passage over varying flow and debris conditions within the ladder. At high flows, the baffle's protruding center arch increases pool depth, reducing the volumetric bulk turbulence of the pools and improving fish habitat. The arch baffle is compared to a standard baffle design currently in use and demonstrates potential advantages for fish passage. A recirculation zone of low velocity occupies a large volume of the pool believed to provide appropriate hydraulic habitat for resting and staging jump attempts upstream. This numerical study provides an acceptable design for future physical prototype testing in the laboratory or field to verify hydraulics and evaluate fish passage effectiveness. [ABSTRACT FROM AUTHOR]

The specific selection of a weir and orifice type experimental fish ladder in the dam of the Itaipu Reservoir (Paraná River) was evaluated by samplings in the river downstream and at two points along the ladder (at heights of 10 m and 27 m) during 28 months. Among the 65 species recorded in the river (immediate downstream of the dam), 27 were captured on the ladder. The species that showed highest density on the ladder, the majority migratory, were moderately, or only slightly, abundant downstream. Among the most abundant species downstream, only one, non-migratory, was recorded in the ladder. The structure presented a negative selection in relation to large migratory pimelodids that might be overcome by enlarging the scale of its design. The sampling demonstrated a moderate selection of species along the ladder and its hydraulic model proved satisfactory regarding the attraction and efficient ascent of the fishes.A seleção específica de uma escada de peixes do tipo seqüência de tanques, com passagem de fundo (tipo weir and orifice), na barragem da hidrelétrica de Itaipu (rio Paraná), foi avaliada através de amostragens no rio a jusante (amostragem trimestral em 1997) e em dois pontos ao longo da escada (10 e 27m de altura; nov/94 a jan/97 e nov/94 a fev/97, respectivamente). Das 65 espécies registradas no rio imediatamente a jusante da barragem, 27 foram capturadas na escada. As espécies com maior densidade na escada, em sua maioria migradoras, tiveram abundância moderada ou baixa a jusante. Entre as mais abundantes a jusante, apenas uma, não migradora, foi registrada na escada. A escada apresentou seleção negativa aos grandes pimelodídeos migradores que pode ser superada com a ampliação na escala do projeto. As amostragens evidenciaram baixa seletividade específica ao longo da escada, sendo seu modelo hidráulico satisfatório na atração e eficiente na ascensão de peixes.

Reducing turbulence and associated air entrainment is generally considered advantageous in the engineering design of fish passage facilities. The well-known energy dissipation factor, or EDF, correlates with observations of the phenomena. However, inconsistencies in EDF forms exist and the bases for volumetric energy dissipation rate criteria are often misunderstood. A comprehensive survey of EDF criteria is presented. Clarity in the application of the EDF and resolutions to these inconsistencies are provided through formal derivations; it is demonstrated that kinetic energy represents only 1/3 of the total energy input for the special case of a broad-crested weir. Specific errors in published design manuals are identified and resolved. New, fundamentally sound, design equations for culvert outlet pools and standard Denil Fishway resting pools are developed. The findings underscore the utility of EDF equations, demonstrate the transferability of volumetric energy dissipation rates, and provide a foundation for future refinement of component-, species-, and life-stage-specific EDF criteria. [ABSTRACT FROM AUTHOR]

Fish passage facilities for reservoir dams have been used to restore habitat connectivity within riverine networks by allowing upstream passage for native species. These facilities may also support the spread of invasive species, an unintended consequence and potential downside of upstream passage structures. We documented dam passage of the invasive virile crayfish, Orconectes virilis (Hagen, 1870), at fish ladders designed for upstream passage of American eels, Anguilla rostrata (Lesueur, 1817), in the Shenandoah River drainage, USA. Ladder use and upstream passage of 11 virile crayfish occurred from 2007–2014 during periods of low river discharge (<30 m3 s–1) and within a wide range of water temperatures from 9.0–28.6 °C. Virile crayfish that used the eel ladders were large adults with a mean carapace length and width of 48.0 mm and 24.1 mm, respectively. Our data demonstrated the use of species-specific fish ladders by a non-target non-native species, which has conservation and management implications for the spread of aquatic invasive species and upstream passage facilities. Specifically, managers should consider implementing long-term monitoring of fish passage facilities with emphasis on detection of invasive species, as well as methods to reduce or eliminate passage of invasive species. [ABSTRACT FROM AUTHOR]

Increasing water demand in coastal regions has resulted in the construction of weirs and barrages in coastal freshwaters. These form barriers to migrations of estuarine and euryhaline marine fishes and crustaceans. This study assessed the impact of loss of marine-estuarine-freshwater connectivity caused by a weir at the outlet of Lake Mzingazi, a coastal lake on the subtropical east coast of South Africa. Facultative catadromous estuarine and euryhaline marine fishes were most affected by the weir, which blocked their upstream migration. These fishes were absent in the lake and were prevented from accessing potential nursery habitat. Crustaceans were less affected by the outlet weir. Salinity tolerances of most penaeid prawn species occurring in southern African estuaries prevent penetration into freshwater reaches of connected systems. Movements of palaemonid prawns which either spawn in or have larvae dependant on estuarine water, and the marine spawning brachyuran Varuna litterata, were not completely impeded by the weir. These species have larvae and juveniles that can climb over the weir in its present form. Historically, the lake served as an estuarine nursery and its physico-chemistry and habitats still offer viable and valuable habitat to estuarine species. There is therefore great potential value in installing a fish ladder at the lake outlet that can be used by juvenile fishes and crustaceans. Re-establishing marine-estuarine-freshwater connectivity here will reinstate a natural migration route that has been impeded for over 70 years and partially restore the ecosystem to its original state. [ABSTRACT FROM AUTHOR]

Abstract: Fish passage systems may provide a means to mitigate the barrier effect of dams on migrating fish species. Even though design criteria were initially developed for the fish fauna of temperate regions, they are widely used in tropical rivers with relative success. A fish passage concept has been developed for a hydroelectric power project on the Mekong River in the absence of suitable fish passage design criteria. There are several hydropower dams proposed for development on the mainstem of the Mekong River in Cambodia, Laos, Thailand and China and the impact of hydropower on fisheries is fast becoming a big issue. Located in Laos territory, the present project is one of the promising run-of-river hydropower projects identified by the Mekong Secretariat in 1994. The feasibility study began in 2007 and the outline (basic) design is being completed in 2010. The scheme includes a comprehensive fish passage system, which provides facilities for upstream and downstream passage. The proposed fish passage concept is based on twelve principles and gives emphasis on an adaptive project management, which includes planning, implementation and operation of the fish passage system and other structures of the project. It will cater to the large number of species and high biomass and especially to the variable flow regime and the lack of biological knowledge on the behavior of migrating species. [Copyright &y& Elsevier]

ABSTRACT Beyond assessing passage efficiency of fishway structures, there is a need to examine the sublethal impacts of passage on the physiological condition of fish. Muscle and plasma samples were collected from pink salmon ( Oncorhynchus gorbuscha) at four sites along a fishway and were compared in order to assess the effectiveness of these methods as they apply to fishway studies. Both plasma and muscle tissue revealed changes consistent with anaerobic activity when fish sampled from within the fishway were compared with field baseline estimates taken from fish sampled 50 m downstream of the fishway entrance. Plasma Cl−, osmolality and haematocrit increased significantly (all p < 0.01) during ascent, whereas muscle glycogen and phosphocreatine declined (both p < 0.03). Both plasma and muscle tissue collected from fish sampled at a site just upstream of the fishway showed physiological profiles that were consistent with metabolic recovery relative to physiological conditions during passage: plasma lactate, haematocrit and muscle lactate had decreased (all p < 0.01), and muscle phosphocreatine increased ( p = 0.01). When examining the physiological changes that specifically occurred between the two sites within the fishway structure, we found no differences in plasma samples, but muscle lactate and water content both showed significant changes (both p < 0.05). These results are consistent with the greater sensitivity of muscle tissue than of blood to exercise-related physiological changes and highlight the usefulness of sampling muscle tissue for assessing fishways that ascended in a short time. Fishway studies could benefit from greater inclusion of physiological tools and approaches to identify the costs of passage and areas of difficulty within a fishway. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Millions of fish ascend through fishways in South America every year, but there is no evidence that downstream passage is occurring in large dams. Based on this concern, this study monitored the fish ladder at Lajeado Dam, Tocantins River, a large Amazonian tributary. To investigate the extent of downstream movements through the fishway, ascending and descending movements were quantified between November 2007 and October 2008. Monitoring showed that the ladder is restrictive to many species in both directions, but downstream passage was much more limited: almost all fish captured in the ladder (99.5%) were ascending the facility. Consequently, the numerical ratio between ascending and descending fish (ind./m) showed high positive values throughout the year (1508:1 on average); migratory species showed higher ratios. All results showed that downstream passage through the ladder is very limited, and that the facility allows only one-way movements (i.e., upstream). This is the first empirical evidence showing that a ladder is critically deficient for downstream passage of fishes in South America. [ABSTRACT FROM AUTHOR]

Electromyogram (EMG) radio telemetry was used in conjunction with physiological biopsy to relate prior physiological condition and subsequent swimming energetics and behaviours to passage success of 13 wild adult sockeye salmon Oncorhynchus nerka at a vertical-slot fishway on the Seton River, British Columbia. At the time of capture, plasma lactate, glucose and cortisol levels indicated that fish were not exhibiting unusually high levels of physiological stress. Very few differences existed between successful and unsuccessful fish in body size, initial plasma physiology and energy state and mean swim speed and energy use during passage. Generally, fish did not employ burst swimming during successful or failed attempts at passage, indicating that failure was probably not related to metabolic acidosis. Plasma Na+ concentration was significantly lower in unsuccessful fish ( P < 0·05), which is suggestive of a depressed ionic state or a possible stress component, although values in all fish were within an expected range for migrant adult O. nerka. Nevertheless, six of 13 fish failed to reascend the fishway and remained in the tailrace of the dam for more than a day on average before moving downstream and away from the dam. During this time, fish were observed actively seeking a means of passage, suggesting that there may have been other, undetermined causes of passage failure. [ABSTRACT FROM AUTHOR]

Due to hydropower development, the upstream migration of wild anadromous salmon and brown trout is impaired in many European rivers, causing negative effects on the long-term survival of natural salmonid populations. This study identified problems for Atlantic salmon during upstream migration in a regulated river in northern Sweden, Umeälven (mean flow: 430 m3 s−1). Tagging from 1995 to 2005 involved radio tags ( n = 503), PIT tags ( n = 1574) and Carlin tags ( n = 573) to study the spawning migration of salmon from the coast past the regulated section of the river to a fish ladder at the dam/spillway 32 km upriver. The results demonstrate that migration success from the coast to the fish ladder varied between 0% and 47% among years, indicating an average loss of 70% of potential spawners. Discharge from the turbines attracted the salmon away from the bypass route. Echo-sounding in the turbine outlet showed that salmon were normally found at 1–4 m depths. They responded with upstream and/or downstream movements depending on flow changes; increased spill in the bypass channel attracted salmon to the bypass. Once in the bypass channel, salmon could be delayed and had difficulties passing the first rapid at high spills. Additional hindrances to upstream migration were found at rapids and the area of the fish ladder, located further upstream in the regulated river section. The average migration duration was 44 days from the estuary to the top of the fish ladder, with large variation among individuals within years. Modelling the salmon population dynamics showed a potential population increase of 500% in 10 years if the overall migration success could be improved from the current 30% to levels near 75%. Consequently improved migration facilities at the regulated river section should be implemented to achieve a long-term sustainability of these threatened anadromous salmonids. [ABSTRACT FROM AUTHOR]

At present most of the large rivers of South America are impounded. Management plans historically have relied on the construction of fish passages, specifically ladders, to mitigate the impact of these waterway blockages on fisheries and biodiversity. Nevertheless, the design of these facilities is not ecologically sound and they are not monitored continually. Consequently, the real role of South American fish passages in fisheries and biodiversity management is unclear and the results of some studies suggest that ladders are problematic in fish conservation. We examined the characteristics and negative aspects of fish passages within a larger context and considered the notion that these facilities are ecological traps in some Brazilian impoundments. Four conditions are required to characterize a fish passage as an ecological trap: (1) attractive forces leading fish to ascend the passage; (2) unidirectional migratory movements (upstream); (3) the environment above the passage has poor conditions for fish recruitment (e.g., the absence of spawning grounds and nursery areas); and (4) the environment below the passage has a proper structure for recruitment. When these conditions exist individuals move to poor-quality habitats, fitness is reduced, and populations are threatened. To exemplify this situation we analyzed two case studies in the upper Paraná River basin, Brazil, in which the four conditions were met and migratory fish populations were declining. If passages work as ecological traps, regional fisheries will be in danger of collapse and conservation policies toward biodiversity will become more difficult and ineffective. The situation demands the closing of the passage in conjunction with alternative management actions to preserve system functionality, especially the conservation of critical habitats downstream and the restoration of damaged habitats in the region. [ABSTRACT FROM AUTHOR]

Bult, T. P., and Dekker, W. 2007. Experimental field study on the migratory behaviour of glass eels (Anguilla anguilla) at the interface of fresh and salt water. – ICES Journal of Marine Science, 64: 1396–1401. European eels (Anguilla anguilla) in the glass eel phase migrate using ocean currents and selective tidal stream transport. Conventional fish ladders installed at the interface of marine and fresh water, however, require the fish to swim upstream actively. We question the efficiency of these fish ladders for glass eel immigration, and propose a simple siphon over migration barriers, restoring the original selective tidal stream transport. A conventional trap and our siphon were tested concurrently at two sluice complexes in The Netherlands (Tholen, Nieuwe Statenzijl) in spring 2005. In all but one case, the siphon caught more glass eels than the trap, as well as more sticklebacks and other species. Clearly, the natural immigration process can be restored fairly easily and at low cost and with low intrusion levels of salt. Follow-up studies should focus on optimization, and the effect of a passage on the hinterland stock. [ABSTRACT FROM PUBLISHER]

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In autumn, burbot Lota lota migrations through a fish ladder in the regulated Ohrˇe River, Czech Republic, were stimulated by an increase in discharge and a decrease in water temperature but the number of burbot in the ladder was significantly lower when compared with other seasons. The maximum number of burbot in the ladder was recorded in spring when discharge decreased. A sudden decrease in water level caused burbot to leave the refuges in the riverbanks that they had occupied during high winter discharges. The results indicate that the relatively low short-term variability of physical conditions represented by the modified discharge regime can induce a stronger response in fish migrations even in comparison with typical reproductive migrations of these species. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

Fishway research has long focused on post-establishment assessments to optimize fish passage efficiency. Model-based optimization with the use of hydrodynamic-habitat models (HHMs) has rarely been employed to investigate passage suitability based on key hydraulic variables. In this study, a vertical slot fishway was designed, the hydraulic properties of twelve types that varied by slope, slot width and pool size were simulated using a two-dimensional HHM, and the suitability of macroinvertebrates and of seven fish groups, encompassing various guilds and size classes, was assessed for each fishway type at seven discharge scenarios, ranging from 0.1 m3/s to 1.3 m3/s. Suitability was primarily influenced by water depth. At optimal depths, suitability was fine-tuned by flow velocity to different optima per biotic group based on fixed interplays between discharge, slope and slot width: water depths were higher at high discharges, low slopes and narrow slots; flow velocities were higher at high discharges, high slopes and wide slots. Our ecologically optimal, multispecies, vertical slot fishway, had 5% slope and 30-cm wide slots, with discharges shifting between 0.15 m3/s and 0.6 m3/s to balance the needs of all species and life stages studied. Yet, even this optimal fishway could not guarantee 100% suitability for all species. The overall suitability was moderate (approx. 50–60%), higher at the pools and lower at the slots, and critically influenced by the type of substrate. We conclude that technical fishways cannot be simultaneously ideal for all species and life stages of a river reach/basin, due to the often-contrasting habitat preferences that need to be adapted to fixed interplays of hydraulic conditions. Within these limitations, however, model-based ecological pre-optimization is crucial for optimizing and deploying fishways that will guarantee suitable passage routes for a wide range of species and life stages, ultimately restoring the hydromorphological and ecological connectivity of dammed rivers. • We modelled the suitability of 12 vertical slot fishways for various biotic groups • Suitability was primarily influenced by water depth and fine-tuned by flow velocity • Different fishway types and discharges were optimal for different biotic groups • Technical fishways (TFs) cannot be 100% suitable for all biota of a river basin • TFs can be optimized to balance the needs of all biota before real-life deployment [ABSTRACT FROM AUTHOR]

South American rivers have become intensely affected by the construction of hydroelectric dams that block the river's connectivity for migratory fish species. In order to mitigate the problems caused by dams and to reestablish connections between habitats, fishways are implemented. Fishways are structures that aid fish in overcoming obstacles and help preserve migratory, reproductive, and feeding routes. This study performed an inventory of all hydropower plants—present and future—in the Upper Paraná River, with the objective of identifying fishways unknown to scientific literature, as well as the task of mapping them. By doing so, the current situation of structural connectivity via fishways in the Upper Paraná River Basin was described. Overall, 389 dams along 209 rivers were identified; of these, only 9% (35 dams) have fishways. In addition, an alarming explosion of future medium-sized hydropower plants was observed, with an expectation of an almost 500% increase in relation to those existing. This data reveals a trend of reduction of free-flowing river stretches, which are crucial habitats for Neotropical potamodromous species, and point to a deficiency in the structural connectivity of existing hydropower dams. Furthermore, if the implementations of these expected constructions are associated with limited connectivity as a result of the absence of fishways, the management of fisheries and their resources in the Upper Paraná River may become unsustainable. [ABSTRACT FROM AUTHOR]

In this paper, we counted the ascending curimbatás at the fish ladder at the Cachoeira de Emas from October, 1992 to September, 1993 in one whole day (24 h period) per month at different observation points in the dam for 5 min every hour. Most of the fish (80%) were counted not in the fish ladder itself, but in two adjacent spillways at its left, perhaps due to the comparatively increased flow as they are narrower than the ladder. The bulk of the migration occurred in September/October. We inspected the degree of injury of the fish in order to examine the hypothesis that larger fish are less injured, however no conclusion was reached. The degree of injury varied between different points and in different months of the year.

This paper presents results of a fishway evaluation performed at the Engenheiro Sérgio Motta Hydroelectric Power Plant (known as Porto Primavera) - CESP, Paraná River, Brazil. The evaluation was designed to quantify entry and passage proportions of 4 long-distance migratory fish species: Brycon orbignyanus (piracanjuba), Piaractus mesopotamicus (pacu), Prochilodus lineatus (curimba), and Rhinelepis aspera (cascudo-preto). Proportions finding and entering the fishway differed between species, ranged from 7.4 % (Prochilodus lineatus) to 55.4% (Piaractus mesopotamicus). Also, proportion passing was different between species, ranged from 31% (R. aspera) to 100% (Prochilodus lineatus). Fish that were marked and released within the fishway had greater failure rates than those that entered volitionally. Total time to pass ranged from 1.48 hours (Prochilodus lineatus) to 178.9 hours (R. aspera). Failure rates were greatest in the lower end of the fishway. Although some individuals of all species passed successfully, significant challenges remain to restoring connectivity of the upper Paraná River.

We evaluated the seasonality of the ascent of fish in an experimental ladder located close to Itaipu Dam, and its relationships to reproduction, temperature, river level and discharge. Samplings of fish and measurements of abiotic factors were performed from February, 1995 through January, 1997, in two resting pools of the ladder. Pool A was located 10 m above the mean level of the Paraná River; Pool B was located at the upper end of the ladder, at a height of 27 m. Autoregressive models were used to remove the temporal dependence between observations. Residuals of the models were used to relate, using Pearson's correlation coefficient, the densities of fish to the environmental variables. Clear patterns of seasonality were observed for temperature. River level, turbine discharge and spillway discharge, although they showed no clear seasonal dynamics, were time-dependent, because the autocorrelation coefficients for different k values were significant. In the samples of larger-sized fish, 23 species were recorded during the two years of study. Most of the individuals were in a non reproductive state, and about 90% of the individuals belonged to only six species. The temporal variability in total abundance, considering all species, indicated a pattern of seasonal variation; high abundances occurred from October through February (75%) and in Pool A (61% of the 1343 individuals sampled). Low abundances were recorded during winter, with the correlogram of total density confirming this tendency. In the samples of smaller-sized species, six species were recorded, with all six present in both pools, but more frequent in the first pool (64%). Bryconamericus stramineus comprised 99% of the total numbers of smaller fish in the samples. The total abundance of small species showed different temporal patterns of seasonal variation in the two years of study.

Dams constructed along waterways interrupt the dispersion and migration of aquatic organisms, affecting mainly the abundance of migratory fish species. Translocation mechanisms have been constructed at dams aiming to minimize their impact on fish species migration behavior. There is little information available about the effect of the construction of dams on the genetic structure of the Neotropical migratory fish fauna. Therefore, RAPD molecular markers and microsatellites were utilized to evaluate the diversity and genetic structure of the migratory species Leporinus elongatus (piapara) in the Canoas Complex - Paranapanema River - Brazil. Ten groups were sampled in the fish ladders of the hydroelectric dam Canoas I and Canoas II during the reproductive period in three consecutive years. Both markers showed a high level of genetic diversity within these groups. The microsatellite markers demonstrated a loss of heterozygosity and a considerable level of inbreeding in the species. The genetic differentiation found among the groups with both markers utilized is within a range from low to moderate. The data obtained with the parameter of genetic diversity among the groups led to the conclusion that the groups of L. elongatus of the Canoas Complex are structured as a single population composed of sub-populations with low genetic diversity among them. The data on genetic diversity and population structure of L. elongatus are of great importance for the development of the species management and conservation programs in the Canoas Complex, which can also be utilized in aquaculture programs.