Spatial ecology and population dynamics of brown trout Salmo trutta L. in reservoirs and headwater tributaries.

This investigation compared the spatial ecology and population dynamics of brown trout Salmo trutta L. between reservoirs with (impact; Langsett Reservoir) and without (control; Grimwith Reservoir) barriers to fish movements into headwater tributaries, and the effectiveness of a fish pass intended to remediate connectivity. Passive integrated transponder (PIT) telemetry revealed that fish that emigrated from Langsett and Grimwith tributaries were 1-3 and 0-2 years old, respectively, and predominantly did so in spring and autumn-early winter in both systems. Weirs at Langsett Reservoir appeared to thwart emigration rate (26%) relative to Grimwith Reservoir (85%). Acoustic telemetry (two-dimensional positions) in the impacted reservoir revealed that the largest home range was in October-December (95% monthly activity space S.D. up to 26.9 ± 6.69 ha in November), activity was influenced by both month and time of day, and fish occupied shallow water depths (relative to reservoir depth), especially at night. Brown trout tagged in Grimwith and Langsett Reservoirs (42.9% and 64.1%, respectively) and fish tagged in the tributaries that emigrated (37.2% and 27.7%, respectively) were detected immigrating into tributaries throughout the year. At both reservoirs, peak immigration for ≥3-year-old trout occurred primarily in autumn-early winter. Overall passage efficiency went from 3% prior to remediation to 14% after and there was no significant increase in fish densities following the construction of the fish pass. Fish were attracted towards and entered the fish pass under a wide range of river levels, but only succeeded in passing upstream during low levels, which are uncommon druing the main migration period. Overall, this investigation significantly furthers our understanding of brown trout spatial ecology and population dynamics in reservoirs and headwater tributaries.

An improved method of local coloring in vertical-slot fishways to enhance the fish migration effect of grass carp.

Vertical-slot fishway (VSF) has been used in many water conservancy projects to restore the river connectivity. A high-quality fishway project should facilitate fish to discovering the exit and passing through, avoiding to long stay in the fishway and delay the migration. Current research on fishway engineering has not yielded an expected passing ratio of fish migration, and it is therefore of great significance to further study the assisting effect of VSF in fish migration. To begin with, we preliminarily determined the attractive and repelling colors of grass carps based on their swimming behavior in a static water pool configured with local colors. Combined with the migration route of the grass carp in a VSF pool without local coloring, four local coloring cases were designed. Based on the camera results of the four experimental local coloring cases, a comparative analysis was conducted with the blank control group frame by frame. This was followed by the statistics of the number of successfully migrated grass carps and their total completion time. On that basis, the assisting effect of VSF in fish migration under the four cases was evaluated in terms of the reduction rate of migration route length, the reduction rate of completion time, and the improvement rate of passing ratio. The research outcomes indicated that green and blue act as attractive colors while yellow and red serve as repelling colors for grass carp. Adding colors to the training wall and dividing wall in the VSF pool, the migration route of grass carp was appropriately adjusted, alongside a shortened completion time and an improved passing ratio. Of the four local coloring cases, the recommended case showed a significant effect on migration route, with more concentrated moving trajectories and shortened route length. Typically, the migration route length decreased by 26%, and the frequency of fish long staying at the junction between the training wall and dividing wall was markedly reduced, as well as the frequency of fish swimming along the water flow from upstream to downstream. The completion time was shortened by 26%, and the passing ratio was enhanced by 44%. The approach of combining local coloring with fish behavior and fishway hydraulics in the pool surpassed the method that optimizes the fishway design only from the fishway hydraulics. The improved method greatly shortened the migration route length, reduced the completion time, and significantly improved the passing ratio of fish passage objects in the VSF. The present research mainly focuses on using model experiments to evaluate the local coloring cases. In the future studies, we will configure local colors to the sidewalls of on-site fishways using environmentally friendly paint or colored organic glass panels. With the monitoring results of the completion time and passing ratio of fish passage objects, the recommended case can be further verified and optimized, thereby providing a more reasonable and feasible local coloring case for assisting fish migration in the VSF project.

Enhancing migratory potential in fish passes: The role of pier shape in minimizing debris accumulation.

Biodiversity preservation is a primary challenge of the 21st century, focusing on restoring unobstructed river flows and mitigating the effects of barriers, supported by European biodiversity strategies up to 2030. Maintaining ecological continuity, such as unblocking fishways clogged by floating debris disrupting natural fish migration paths, remains a challenge despite conventional protective methods. This study, taking a vertical slot fish pass in Wroclaw on the Odra River as a case study and based on research on bridge piers, suggests modifying pier shapes from rectangular to rounded in order to reduce debris accumulation. Field studies, utilizing an OTT MF Pro flow meter, were conducted to validate the numerical model. The measured flow rate in the field was 3.15 [m³·s-1], while the numerical modeling yielded a flow of 3.19 [m³·s-1]. Focusing on optimizing the shape of cross-wall piers to enhance fish migration conditions, the study examined six different pier configurations, analyzing flow speed in the main slot, crucial for migration. Using 2D hydraulic modeling with Iber, it assessed the migratory potential of different pier designs by analyzing hydraulic conditions and comparing them with the swimming capabilities of fish species native to the Odra River. Results indicate that rounding the pier edges positively affects flow speeds in the main slot, enhancing fish migration possibilities, contributing to fish pass functionality improvement and supporting broader biodiversity and ecosystem health goals.

Genetic consequences of improved river connectivity in brown trout (Salmo trutta L.).

Fragmentation of watercourses poses a significant threat to biodiversity, particularly for migratory fish species. Mitigation measures such as fishways, have been increasingly implemented to restore river connectivity and support fish migration. The effects of such restoration efforts are typically tested using telemetry and fisheries methods, which do not fully capture the broader population movements that may have important consequences for population viability. We performed a before-and-after control-impact (BACI) study using genetic tools (SNPs) to investigate the effect of a newly implemented fishway, aiming to enhance upstream spawning migration of brown trout (Salmo trutta Linnaeus) in a reservoir with two headwater tributaries fragmented by man-made weirs. Another reservoir with two barrier-free tributaries was also analysed as a control. Our results showed that the isolated brown trout population was spawning in the reservoir before the installation of the fishway, and we found genetic structuring and differentiation between fragmented headwater tributaries before the fishway construction, but not in the control reservoir. Unexpectedly, after the fishway construction we observed signals consistent with increased genetic differentiation between populations of newly recruited juvenile fish in the reservoir tributary and fish in the reservoir. We propose this was caused by newly enabled philopatric behaviour of brown trout to their natal spawning tributary. In contrast, we did not find any genetic changes in the tributary without a fishway or in the barrier-free reservoir system. Given the scarcity of similar studies, we advocate for an increased use of genetic analyses in BACI studies to monitor and evaluate the effect of efforts to restore habitat connectivity and inform future management strategies.

A design of a nature-like fishway to solve the fractured river connectivity caused by small hydropower based on hydrodynamics and fish behaviors.

Achieving a harmonious alignment between the biological characteristics of fish and hydrodynamics patterns is crucial for ensuring the efficacy of fish passage facilities. In this study, based on the hydrodynamic characteristics of the river and the biological characteristics of fish, we evaluated the internal flow field in the nature-like fishway of Congen II hydropower station located along the Chabao river and explored methods to improve the operation efficiency. Based on comprehensive considerations of the flow field, turbulent kinetic energy, and the migration pathways of fish, it is found that the implementation of a continuous oblique bottom slope represents a more cost-effective and operationally convenient solution. The influence of different permutation of bulkheads in the nature-like fishway on operational efficiency was further examined. Our investigation revealed that the nature-like fishway with the continuous slope of 2% and the arrangement of three bulkheads in each row (model 3) exhibited a relatively simple velocity distribution and linear flow line, which poses challenges for fish in locating resting areas. In addition, the distribution of low turbulence kinetic energy area in the mainstream made it less favorable for fish to transition from the mainstream to the rest area within the fishway. The nature-like fishway with the continuous slope of 2% and the arrangement of two or three bulkheads in staggered rows (model 4) demonstrated better performance. Several potential fish migration routes for both model 3 and model 4 were proposed based on the numerical simulation results. In model 3, fish exhibited a continuous sprint through the concentrated high-speed area, which was less favorable for fish to rest and forage. In contrast, model 4 exhibited a diversified flow velocity distribution, enabling fish to make timely changes in their direction during migration. This feather proved to be advantageous in enhancing fish migration within the passage. The design of nature-like fishway in this study provides an important reference and technical support for the construction and optimization of the nature-like fishway for low dams, and is of great significance for restoring river connectivity destroyed by small hydropower construction and improving fish migration.

Effects of substrate roughening on the swimming performance of Schizothorax wangchiachii (Fang, 1936) in the Heishui River: Implications for vertical slot fishway design.

Re-establishing the natural connectivity of rivers using fishways may mitigate the unfavourable effects of dam construction on riverine biodiversity and freshwater fish populations. Knowledge of the swimming performance of target species in specific regions is critical for designing fishways with a high passage efficiency. Substrate roughening with river stones of fishways is considered to improve fish swimming capacity by benefiting from reduced-velocity zones with lower energetic costs. However, the effectiveness of rough substrates in energy metabolism is rarely tested. We investigated the effect of substrate roughening on the swimming capacity, oxygen consumption and behaviour of Schizothorax wangchiachii from the Heishui River in a flume-type swimming respirometer. The results showed that substrate roughening improved critical and burst swimming speed by ~12.9% and ~15.0%, respectively, compared to the smooth substrate. Our results demonstrate that increased reduced-velocity zones, lowered metabolic rate and tail-beat frequency support our hypothesis that lower energetic costs improve fish swimming performance in rough substrate compared to smooth treatment. The traversable flow velocity model predicted that maximum traversable flow velocity and maximum ascent distance were higher over rough compared to smooth substrate fishways. Fishway substrate roughening may be a practical approach to improve fish swimming upstream for demersal riverine fish.

How Useful? Fish-Friendly Irrigation Guidelines for the Lower Mekong Lack Definition in Five Key Areas.

A proliferation of irrigation infrastructure throughout the Mekong River has impacted the ability of certain fish species to migrate to fulfil their lifecycle. In response, fishways, a type of fish-friendly irrigation structure, have been developed to provide passage for these fish. In recent years, several guidelines documents providing guidance on fish-friendly irrigation structures and their construction have been published. The development process from guideline inception to publication is unclear, while their purpose, audience, and contribution to fishway practice are vague. This study is the first to review the development of three fish-friendly guideline documents, using structural criteria analysis, combined with qualitative data from 27 key informant interviews. It aimed to understand document elements such as purpose, audience, scope, and framing. The results showed reviewed guideline utility and impact could be improved by attention to five key aspects, namely: definition of target audience; engagement of target audience in guideline design; definition of guideline scope; specificity of recommendations; and evaluation. Attention to these 5 aspects may result in guidelines that are perceived as more useful by their target audience and have greater impact on water management practice.

Spawning migration behaviour of sea trout (Salmo trutta L.) in a boreal river system: effects of flow conditions and obstacles on migratory activity.

In this study, radio telemetry was used to examine the upstream spawning migration behaviour of anadromous brown trout (sea trout), Salmo trutta L., in a boreal river system, the River Isojoki, western Finland. The aim was to study the movement activity and migration characteristics of trout during the upstream spawning migration, as well as to locate the important spawning habitats and study the spawning characteristics. Furthermore, the authors analysed how flow conditions and a hydropower dam, with adjacent fishways, affected the upstream spawning migration. Tagged trout spawned in both the main stem and four tributaries, with spawning taking place from early October to November. The movement activity of radio-tagged trout was influenced by a hydropower dam (Perus dam), with spring migrators spending prolonged periods at the dam area, postponing the migration upstream. Flow conditions affected the total time spent at the dam area, as well as the movement activity in the free-flowing sections above the dam, with increasing flow stimulating activity. In addition, time of river ascent and location of spawning area had a significant effect on the movement activity of tagged trout. These results are further evidence that synergistic effects of flow and migratory obstacles can negatively influence migrations of anadromous fish, regardless of constructed fishways. The management of flow regimes and the efficiency of fishways are vital, as climate change will likely influence the flow and increase the water temperature of boreal river systems, further aggravating issues caused by obstacles.

Effect of Parameters of Pool Geometry on Flow Structure in Nature-like Fishway.

Many uncertainties such as variable irregular structure and complex flow conditions bring difficulties to the design of a nature-like fishway. This study defines the main factors and parameters affecting flow conditions such as permeability ratio, offset ratio, bottom slope and pool length to simplify and generalize the irregular geometry of the nature-like fishway. According to the engineering requirements of the Mopiling nature-like fishway, the effect of the above parameters of pool geometry on the flow structure is investigated through a 3D turbulent numerical simulation, and the parameter thresholds are summarized according to the optimization of the flow conditions. The results show that under the same conditions, the maximum velocity of the control section increases with the increase in permeability ratio, bottom slope and pool length, and the offset ratio has limited effect on the maximum velocity of the control section. It is recommended that when the bottom slope is 1/250 and the pool length is 10 m, the permeability ratio should not be greater than 0.30 and the offset ratio should be located between 0.15 and 0.60. When the bottom slope is adjusted to 1/200, it is recommended to control the permeability ratio below 0.20, the offset ratio between 0.30 and 0.60, and the pool length can be adjusted to 8 m. Within the above threshold range of the design parameters, the maximum velocity in the fishway can be basically controlled at about 1.0 m/s. The mainstream in the pool is clear and the flow pattern is good, which can basically satisfy the requirements of fish passing. The relevant design parameters and optimization strategies can provide reference for similar projects.

Analysis of Movements and Behavior of Bighead Carps (Hypophthalmichthys nobilis) Considering Fish Passage Energetics in an Experimental Vertical Slot Fishway.

An understanding of fish movement behavior in response to flow field variables is important for exploring the hydrodynamic strategies of fish in fish passages. In this paper, bighead carps were taken as an example. The fish movement behavior response to water flow field information by means of estimating the energetic expenditure using an IBM approach in an experimental fishway was investigated. Fish swimming velocity, drag force, and energy expenditure were analyzed in varied flow conditions related to hydraulic variables, including velocity (V), turbulent kinetic energy (TKE), and strain rate (SR). The result indicated that the fish will require more energy in high TKE zones. This study provides a reference for optimizing the design of fish passages and fisheries management. This method can be applied to assess the efficiency of fish bypass structures and conduct fish survival studies.

Experimental study on the passage behavior of juvenile Schizothorax prenanti by configuring local colors in the vertical slot fishways.

The vertical slot fishway is one of the most widely used fishways in the world. To solve the problems of long passage time and low passage rate of fish passing objects in the conventional vertical slot fishway, this study proposed a method of configuring local colors in the internal sidewall of the fishway pond to improve the vertical slot fishway based on the approach-avoidance effect of fishes on different colors. Taking Schizothorax prenanti as the research object, comparative fish passing experiments were carried out to analyze the effects of configuring local colors on the passage behavior. It has been found that green and yellow are the approach and repellent colors for Schizothorax prenanti, respectively. By configuring local colors of the guide wall and partition wall at the upstream and downstream of the pond, the passage track of Schizothorax prenanti was significantly changed, which in turn affected their passage time and passage rate. The configuration of local green to the guide wall and partition wall on the upstream negative side, and local yellow to the sidewall of the guide wall on the upstream negative side, the guide wall on the downstream positive side, and the partition wall on the downstream positive side can shorten the overall passage time of Schizothorax prenanti by 9 % and increase the passage rate by 23 %. Compared with the scheme that completely depends on the flow conditions to change the structure of the pond, the method of configuring local colors in the pond is an improved method combining fish ethology and hydraulics. The scheme of local color configuration significantly shortens the passage time and passage rate of fish passing objects in the vertical slot fishway, and can be applied to the fishway design and the improvement of operation effect, which has a certain practical application value.

Wetland fishes avoid a carbon dioxide deterrent deployed in the field.

Biological invasions are poorly controlled and contribute to the loss of ecosystem services and function. Altered watershed connectivity contributes to aquatic invasions, but such hydrologic connections have become important for human transport. Carbon dioxide (CO2) deterrents have been proposed to control the range expansion of invasive fishes, particularly through altered hydrologic connections, without impeding human transport. However, the effectiveness of CO2 deterrents needs to be further evaluated in the field, where fishes are situated in their natural environment and logistical challenges are present. We deployed a proof-of-concept CO2 deterrent within a trap-and-sort fishway in Cootes Paradise, Ontario, Canada, to determine the avoidance responses of fishes attempting to disperse into a wetland. We aimed to describe deterrent efficiency for our target species, common carp, and for native fishes dispersing into the wetland. Our inexpensive inline CO2 deterrent was deployed quickly and rapidly produced a CO2 plume of 60 mg/l. Over 2000 fishes, representing 13 species, were captured between 23 May and 8 July 2019. A generalized linear model determined that the catch rates of our target species, common carp (n = 1662), decreased significantly during deterrent activation, with catch rates falling from 2.56 to 0.26 individuals per hour. Aggregated catch rates for low-abundance species (n < 150 individuals per species) also decreased, while catch rates for non-target brown bullhead (n = 294) increased. Species did not express a phylogenetic signal in avoidance responses. These results indicate that CO2 deterrents produce a robust common carp avoidance response in the field. This pilot study deployed an inexpensive and rapidly operating deterrent, but to be a reliable management tool, permanent deterrents would need to produce a more concentrated CO2 plume with greater infrastructural support.

Evaluation of Volitional Swimming Behavior of Schizothorax prenanti Using an Open-Channel Flume with Spatially Heterogeneous Turbulent Flow.

Effective fishway design requires knowledge of fish swimming behavior in streams and channels. Appropriate tests with near-natural flow conditions are required to assess the interaction between fish behavior and turbulent flows. In this study, the volitional swimming behavior of S. prenanti was tested and quantified in an open-channel flume with three (low, moderate, and high) flow regimes. The results showed that, when confronted with alternative flow regimes, S. prenanti preferred to select regions with low flow velocities (0.25−0.50 m/s) and turbulent kinetic energy (<0.05 m2/s2) for swimming, while avoiding high-turbulence areas. Moreover, S. prenanti primarily employed steady swimming behavior to search for flow velocities lower than the average current to conserve energy in low- and moderate-flow regimes. It is hypothesized that in regions with higher flow velocities, fish may change their swimming strategy from energy conservation to time conservation. Additionally, the average and maximum burst speeds of S. prenanti were 2.63 ± 0.37 and 3.49 m/s, respectively, which were 2.21- and 2.28-fold higher than the average (1.19 m/s) and maximum (1.53 m/s) burst speeds estimated from the enclosed swim chamber for fish of similar length. This study contributes a novel research approach that provides more reliable information about fish volitional swimming behavior in natural habitats, as well as recommendations for hydraulic criteria for fishways and the identification of barriers to fish migrations.

Fishway in hydropower dams: a scientometric analysis.

Building dams for hydroelectric use causes several negative effects on the aquatic fauna with special attention to fish communities. In fact, among other impacts, dams act as a barrier for migratory fish, causing discontinuities in rivers and not allowing fish to move to the headwaters to breed and back to the lower portions of rivers, to grow. For more than 300 years, fishways have been used to minimize the impact of dams. Here, we assess the worldwide knowledge about fishways, identifying the temporal and spatial pattern and the situation of Brazil in this global pattern. For this, we conducted scientometric research on the Web of Science repository with the following words: weir, fish, facilities, ladder, pass, dam, fish ladder, fish pass, fishway, hydropower, Petromyzon, and salmon between 1985 and 2019. Initially, we obtained 1282 articles. After a selection, 324 articles aimed to describe fishway efficiency and the relationship with the fish fauna remained. Most of the articles on dams, fishways, and fish are from North America and Europe. Among the articles in South America, most are from Brazil. Nonetheless, information on the topic is incipient in Brazil, since the country has one of the biggest hydropower in the world and 42 scientific articles about fishways published in the international scientific database. Ecology is the area of knowledge with most articles, with continuous growth in the last 10 years. Studies in the field of ecology are strategical, as this field can integrate different areas of knowledge to test the efficiency of fishways in fish conservation and may be able to answer the question: "Are fishways an ecological trap?" Research focusing on this question is important to understand the efficiency of fishways to better evaluate solutions to minimize the negative effects of dams on fish and increase the effectiveness of fishways.

Collective navigation can facilitate passage through human-made barriers by homeward migrating Pacific salmon.

The mass migration of animals is one of the great wonders of the natural world. Although there are multiple benefits for individuals migrating in groups, an increasingly recognized benefit is collective navigation, whereby social interactions improve animals' ability to find their way. Despite substantial evidence from theory and laboratory-based experiments, empirical evidence of collective navigation in nature remains sparse. Here we used a unique large-scale radiotelemetry dataset to analyse the movements of adult Pacific salmon (Oncorhynchus sp.) in the Columbia River Basin, USA. These salmon face substantial migratory challenges approaching, entering and transiting fishways at multiple large-scale hydroelectric mainstem dams. We assess the potential role of collective navigation in overcoming these challenges and show that Chinook salmon (O. tshawytscha), but not sockeye salmon (O. nerka) locate fishways faster and pass in fewer attempts at higher densities, consistent with collective navigation. The magnitude of the density effects were comparable to major established drivers such as water temperature, and model simulations predicted that major fluctuations in population density can have substantial impacts on key quantities including mean passage time and fraction of fish with very long passage times. The magnitude of these effects indicates the importance of incorporating conspecific density and social dynamics into models of the migration process. Density effects on both ability to locate fishways and number of passage attempts have the potential to enrich our understanding of migratory energetics and success of migrating anadromous salmonids. More broadly, our work reveals a potential role of collective navigation, in at least one species, to mitigate the effects of anthropogenic barriers to animals on the move.

Are we designing fishways for diversity? Potential selection on alternative phenotypes resulting from differential passage in brown trout.

Fishways are commonly employed to improve river connectivity for fishes, but the extent to which they cater for natural phenotypic diversity has been insufficiently addressed. We measured differential upstream passage success of three wild brown trout (Salmo trutta) phenotypes (anadromous, freshwater-resident adult and parr-marked), encompassing a range of sizes and both sexes, at a Larinier superactive baffle fishway adjacent to a flow-gauging weir, using PIT telemetry (n = 160) and radio telemetry (n = 53, double tagged with PIT tags). Fish were captured and tagged downstream of the weir in the autumn pre-spawning period, 2017, in a tributary of the River Wear, England, where over 95% of tributary spawning habitat was available upstream of the weir. Of 57 trout that approached the weir-fishway complex, freshwater-resident adult and parr-marked phenotypes were less successful in passing than anadromous trout (25%, 36%, and 63% passage efficiency, respectively). Seventy-one percent of anadromous trout that passed upstream traversed the weir directly. Although the fishway facilitated upstream passage, it was poor in attracting fish of all phenotypes (overall attraction efficiency, 22.8%). A higher proportion (68.2%) of parr-marked trout that approached the weir were male and included sexually mature individuals, compared with that of freshwater-resident (37.8%) and anadromous trout (37.0%). The greater passage success of anadromous trout was likely due to their greater size and locomotory performance compared to the other phenotypes. Barriers and fishways can act as selection filters, likely the case in this study, and greater consideration needs to be given to supporting natural diversity in populations when proposing fishway designs to mitigate river connectivity problems.

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To investigate the swimming ability of two Schizothorax species in the Yalung River and provide basic parameters for the studies on fish behavior and the design of fish passage, we exa-mined the induced velocity, critical swimming speed, and burst swimming speed in Schizothorax dolichonema and Schizothorax prenanti with incremental velocity method and the durable swimming speed in S. dolichonema with fixed velocity method. The results showed that the induced velocity of both species increased first and then plateaued with the increases of body length, with the maximum values being lower than 0.2 m·s-1. The critical swimming speed and burst swimming speed of S. dolichonema were (0.81±0.20) and (1.49±0.26) m·s-1, respectively, while the relative critical swimming speed and the relative burst swimming speed were (4.90±1.73) and (9.77±1.72) BL·s-1 (BL: body length), respectively. For S. prenanti, the critical swimming speed and burst swimming speed were (0.73±0.24) and (1.17±0.39) m·s-1, respectively, while the relative critical swimming speed was (6.88±2.82) BL·s-1, and the relative burst swimming speed was (11.75±2.77) BL·s-1. The swimming duration of S. dolichonema was negatively correlated with the flow velocity of 0.7-1.5 m·s-1, and the relationship between fatigue time (T) and flow velocity (V) was fitted into lgT=-2.52V+5.59. The relationship between expected fishway length (d) and the tolerable maximum average flow velocity (Vf max) was accordingly derived to be Vf max=-0.17lnd+1.74. Taken together, the fishway targeting S. dolichonema and S. prenanti was recommended to generate the in-channel velocity larger than 0.2 m·s-1, while the velocity at the entrance and verticle slot should be 0.73-1.67 m·s-1, and the main-flow velocity in rest pools should be 0.2-0.7 m·s-1.

Identifying operation scenarios to optimize attraction flow near fishway entrances for endemic fishes on the Tibetan Plateau of China to match their swimming characteristics: A case study.

Attracting fish at fishway entrances is vital for ensuring fish passage efficiency, which requires consideration of the swimming characteristics of fish. The objective of this case study was to propose optimized flow conditions downstream of a dam on the Tibetan Plateau to attract fish into fishways. Six local endemic species of Cyprinidae: Schizothoracinae were considered as protection targets. However, the swimming abilities of most endemic fishes on the plateau remain unclear, and no previous projects in this area could serve as a reference. Thus, the swimming performances of the target species were first tested based on three indexes, induction velocity, critical swimming speed and bursting swimming speed, and six behavior zones were classified by different flow velocity thresholds based on the test results. A verified 3D hydrodynamic model was then adopted to simulate the flow field downstream of the dam under four typical reservoir operation scenarios. By matching the simulated flow fields to the different behavior zones, all scenarios were assessed for the passability of the target fishes, and the results showed that there would be different potential migration routes under each scenario. For the most common scenario during the fish passage season, symmetrical use of turbines T1 and T6 was recommended so that the flow would be lower velocity and the turbulence would be less intense near the fishway entrances than the current regime. Moreover, the addition of a new entrance was suggested on the migration routes with high potential use to increase the chance that fish would enter. Beyond providing a solution for this specific case, this study enriches knowledge about the swimming features of endemic fishes on the Tibetan Plateau. Furthermore, this research provides a possible technical methodology that combines fish behavioral characteristics and hydraulic indexes when determining attraction flows in similar fish passage projects.

Managing dams for energy and fish tradeoffs: What does a win-win solution take?

Management activities to restore endangered fish species, such as dam removals, fishway installations, and periodic turbine shutdowns, usually decrease hydropower generation capacities at dams. Quantitative analysis of the tradeoffs between energy production and fish population recovery related to dam decision-making is still lacking. In this study, an integrated hydropower generation and age-structured fish population model was developed using a system dynamics modeling method to assess basin-scale energy-fish tradeoffs under eight dam management scenarios. This model ran across 150 years on a daily time step, applied to five hydroelectric dams located in the main stem of the Penobscot River, Maine. We used alewife (Alosa pseudoharengus) to be representative of the local diadromous fish populations to link projected hydropower production with theoretical influences on migratory fish populations on the model river system. Our results show that while the five dams can produce around 427 GWh/year of energy, without fishway installations they would contribute to a 90% reduction in the alewife spawner abundance. The effectiveness of fishway installations is largely influenced by the size of reopened habitat areas and the actual passage rate of the fishways. Homing to natal habitat has an insignificant effect on the growth of the simulated spawner abundance. Operating turbine shutdowns during alewives' peak downstream migration periods, in addition to other dam management strategies, can effectively increase the spawner abundance by 480-550% while also preserving 65% of the hydropower generation capacity. These data demonstrate that in a river system where active hydropower dams operate, a combination of dam management strategies at the basin scale can best balance the tradeoff between energy production and the potential for migratory fish population recovery.

Selective fragmentation and the management of fish movement across anthropogenic barriers.

Disruption of movement patterns due to alterations in habitat connectivity is a pervasive effect of humans on animal populations. In many terrestrial and aquatic systems, there is increasing tension between the need to simultaneously allow passage of some species while blocking the passage of other species. We explore the ecological basis for selective fragmentation of riverine systems where the need to restrict movements of invasive species conflicts with the need to allow passage of species of commercial, recreational, or conservation concern. We develop a trait-based framework for selective fish passage based on understanding the types of movements displayed by fishes and the role of ecological filters in determining the spatial distributions of fishes. We then synthesize information on trait-based mechanisms involved with these filters to create a multidimensional niche space based on attributes such as physical capabilities, body morphology, sensory capabilities, behavior, and movement phenology. Following this, we review how these mechanisms have been applied to achieve selective fish passage across anthropogenic barriers. To date, trap-and-sort or capture-translocation efforts provide the best options for movement filters that are completely species selective, but these methods are hampered by the continual, high cost of manual sorting. Other less effective methods of selective passage risk collateral damage in the form of lower or higher than desired levels of passage. Fruitful areas for future work include using combinations of ecological and behavioral traits to passively segregate species; using taxon-specific chemical or auditory cues to direct unwanted species away from passageways and into physical or ecological traps while attracting desirable species to passageways; and developing automated sorting mechanisms based on fish recognition systems. The trait-based approach proposed for fish could serve as a template for selective fragmentation in other ecological systems.