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The periphyton‐based system is a low‐cost and sustainable strategy for small‐scale producers who have limited technology and budgets. This study aimed to evaluate the effects of different feed restriction levels (50% and 67%), using periphyton as a natural food source, on the growth performance of Nile tilapia reared under real culture conditions in cages placed in a farm dam. Three treatments were tested: F100—fish fed daily only on feed; F50—fish fed every other day, plus periphyton; and F33—fish fed every two days, plus periphyton. Considering the results of fish growth in F50 and F33 compared with F100 and the low amount of periphyton dry matter, it is reasonable to state that the fish under feed restriction did not take advantage of the periphyton due to its low availability. This low availability of the periphyton is possibly associated with the water N:P ratio and its variation over the experimental period. Therefore, periphyton‐based systems are not indicated for conditions with a low N:P ratio or subject to great variations in this ratio. [ABSTRACT FROM AUTHOR]

The Federal Energy Regulatory Commission (FERC) regulates most hydropower dams in the United States and grants operational licenses that include conditions for the conservation of sea‐run fish. FERC is the primary authority in relicensing, but the process invites input from other federal and state resource agencies. As a result, relicensing decisions often reflect trade‐offs among competing authorities, values and objectives. FERC relicensing decisions in the Kennebec and Penobscot Rivers in Maine were assessed to characterise agency engagement and identify factors that influence fish passage decisions. Qualitative and quantitative analysis of FERC project documents from 1984 to 2019 showed that conservation measures are focused almost exclusively on Atlantic salmon, Salmo salar L., and American eel, Anguilla rostrate Leseur. Incorporation of fish passage mitigation requirements has increased coincident with increased agency engagement and the use of regulatory authority. Strong fish passage prescriptions are found at coastal projects (where sea‐run fish exist) likely resulting from both state and federal agency input. Despite wide interest in basin‐scale and interagency fish passage planning, implementation of collaborative processes has been slow, with most dams being considered and licensed individually. As a result, there are opportunities to spatially integrate the FERC process in the future and support effective stakeholder engagement. [ABSTRACT FROM AUTHOR]

Mortality of fish entering the turbine draft tube (DT) from the tailrace is common during turbine startup or dewatering in Brazilian hydropower dams. Mortality can be reduced if such operations occur when few fish are present in the DT, but estimating abundance therein using traditional gears (e.g., cast net, gillnet, hook-and-line) is constrained by flow and access. We deployed a Dual frequency IDentification SONar (DIDSON) to record and count fish in the DT for the first time using an innovative approach. Methods used elsewhere for manual counting fish in DIDSON images generated dissimilar results. Therefore, we compared three methods of counting fish manually in the frames of DIDSON software from two Brazilian dams: numerical counting (number of fish in the frame), qualitative counting (percent of the frame occupied by fish), and intersection counting (number of intersections of the grid frame with fish). We assumed that the numerical counting provided the best estimates of the true value but could not be used in 32.2% of the frames from one of the dams due to the presence of uncountable aggregation of fish, bubble curtain, or poor contrast between fish and the DT floor. Qualitative counting was the most congruent, whereas intersection counting was the least, based on comparisons with numerical counting. [ABSTRACT FROM AUTHOR]

The recent large-scale hydropower development in the Amazon basin has raised concerns about the impacts on the movements of migratory fishes such as goliath catfish (Brachyplatystoma spp.). In the Madeira River, the efficiency of a 1400-m long fishway in the Santo Antônio hydropower plant (SAE HPP) was evaluated between 2012 and 2016 using telemetry techniques. Tagged fish (N = 388) were released 2000 m downstream of the dam and near the entrance or inside the fishway (N = 149). Fixed radio stations monitored fish movements and residence near 14 different structures of the SAE HPP; four acoustic receivers in the reservoir and one downstream the dam monitored whether fish moved away or past the dam. The findings revealed that 15% of the fish released downstream were detected near the dam but none were detected in the reservoir upstream. For the group of fish released in the fishway, no B. rousseauxii (N = 64) was detected moving upstream and into the reservoir and 5 individuals of B. vaillantii (N = 41) exited the fishway to the reservoir. This was the first long-term telemetry monitoring of fish movements near a dam in the Amazon and the results provided evidence of inefficiency of the fishway for the target species, which led the hydropower company to reconstruct the fishway. [ABSTRACT FROM AUTHOR]

This study identifies hydrodynamic alterations in flow downstream of a dam that are related to hydropower plant (HPP) operation and that might attract Neotropical potamodromous fish to unsafe places in the tailrace during their reproductive migration. Our hypotheses are (1) the hydrodynamic flow in the tailrace presents conditions that are strong attractive for fish than those found in the downstream reach and (2) there are no velocity barriers preventing the upstream migrant from reaching the tailrace over a wide range of turbine discharge. Two calibrated numerical models were created for the Três Marias HPP (Brazil), using different turbine discharges: (1) a three-dimensional (3D) model of flow in the tailrace and (2) a two-dimensional (2D) model for flow in the 3-km reach downstream of the dam. Resulting flow fields of the Três Marias HPP tailrace have elevated hydraulic strain and velocity homogeneity by as compared to the flow field of the downstream reach. The tailrace velocities are slow for mature individuals of all study species, which may swim from downstream reach to unsafe areas in their sustainable and prolonged mode by available corridors for different turbined discharges. [ABSTRACT FROM AUTHOR]

The large catfish Pseudoplatystoma punctifer plays an important role as a top predator in the Amazonian Basin ecosystem. The Madeira River is the largest tributary of the Amazon River marked by a series of rapids and waterfalls. Between 2011 and 2012 some of the rapids were submerged by two hydroelectric dams. Upstream and downstream of the rapids are two sub-basins Mamoré/Guaporé and lower Madeira, respectively. Using mitochondrial and microsatellite markers, we estimated genetic diversity, genetic differentiation, and gene flow between sub-basins and tested if the rapids functioned as barriers limiting the gene flow for this species of catfish. We identified three population clusters, one representing the individuals from the Mamoré/Guaporé sub-basin (upstream) and the other two representing the individuals from the lower Madeira sub-basin (downstream). The rapids restricted but did not block gene flow, which corroborates a clinal pattern of genetic differentiation. [ABSTRACT FROM AUTHOR]

Hydropower is one environmentally friendly option for meeting these energy demands. Because such technologies do not require a weir or a dam, they may be used with minimal environmental effect. The drag-based Savonius turbine is characterized by working at low-flow speeds which fits well the natural water streams. In spite of its simple and robust design, the Savonius turbine suffers from low efficiency and high static torque fluctuations. In view of this, CFD-based optimization is applied to a Savonius-type hydrokinetic turbine inspired by a couple of swimming Koi fish. The two main design parameters; overlap ratio and gap ratio are used in this paper to define the gap between the blades. The maximum power coefficient can be obtained by employing an evolution strategy optimization technique over the constructed metamodel. The results revealed that the optimal design for the bio-inspired Savonius hydrokinetic turbine corresponds to overlap and gap ratios of 0.2085 and 0.0057, respectively. The optimal configuration generates a maximum power coefficient of 0.2521, which is 17.6% higher than that for a conventional shape at the same tip speed ratio. The new bio-inspired design performs better than the conventional Savonius hydrokinetic turbine for the considered operating range. [Display omitted] [ABSTRACT FROM AUTHOR]

Dams and other man‐made barriers impair upstream fish migration and thus threaten fish populations that need access to upper river reaches to complete their life cycle. For many years, fishways have been used to mitigate this impact. Fishways around the globe are typically built based on recommendations made for northern hemisphere species, particularly salmonids. These recommendations do not consider the locomotor characteristics and skills of other species, especially those living in the tropics. Among tropical species, freshwater eels and gobies of the Sicydiinae subfamily are important cultural and economic species that are particularly sensitive to the impact of man‐made barriers. Our experimental study aimed to test different substrates and slopes for ramp‐like fishways adapted to tropical eels and sicydiines. Among the five substrates tested for 368 eels Anguilla marmorata, elastomer pins appeared to be the most efficient. Elastomer pins also appeared to be more efficient than the fine concrete which is currently used in fishways for sicydiines (Sicyopterus lagocephalus, N = 1797, and Cotylopus acutipinnis, N = 1303). The slope had a lesser effect on the climbing success of sicydiines compared to substrate type, except for gradients greater than 50° that induced a slight decrease in success. Our results indicated that ramp‐like fishways fitted with 1.0 cm diameter elastomer pins, positioned in staggered rows with a diagonal spacing of 1.3 cm, wetted with low‐flow and angled less than 50°, are well adapted to accommodate the different locomotor characteristics and skills of tropical eels and sicydiines. [ABSTRACT FROM AUTHOR]

The presence of microcystins (MCs) in waters exclusively intended for drinking water production is a major problem for both ecosystems and public health. The current study aimed to identify the environmental factors that explain the spatial and temporal variations in the abundance of cyanobacteria and the concentration of microcystins in the Guenitra Dam, a Mediterranean water body used for drinking water production, irrigation supplies and fisheries. The Guenitra Dam waters are mesotrophic to eutrophic; they shelter nine genera of cyanobacteria in which Microcystis flosaquae is dominant in the frequency of occurrence and densities. Cyanobacterial densities in the Guenitra Dam exceed the level of vigilance in January; the alert level 1 was shown during the rest of the year and the alert level 2 was in November, with a peak registration of more than 189 million cells / mL. The highest cell densities were found in surface waters and decreased with depth. In autumn, more than 99% of the overall cyanobacteria density was detected. The MC-LR contents did not exceed 0.5 μg.L-1 except in November (1.02 μg.L-1 in St5) and December (1.5 μg.L-1 in St4). From January to September, the levels did not surpass 0.22 μg.L-1. Statistical analysis revealed the existence of very highly significant (p <0.0001) positive correlation of M. flosaquae with microcystins (MC-LR) and highly significant (p <0.001) of M. flosaquae with NH4 +. During the bloom found in November, the presence of MC-LR in the drinking water was recorded, with a concentration of 0.57 μg.L-1, which is clearly higher than that allowed (0.1 μg.L-1) by the WHO. The presence of MC-LR in the drinking water is indicative of a failure in the water treatment process. The presence of cyanobacteria and cyanotoxins in raw and drinking waters of the Guenitra reservoir involves regular monitoring of the cyanobacterial communities and cyanotoxins in raw water. [ABSTRACT FROM AUTHOR]

In Ghana, the Pwalugu Dam in the Upper East is in the final planning stage. Whereas promoters of Ghana's first dams emphasized the need for generating electricity to modernize and industrialize the new nation, the planners of Pwalugu have focused on water issues. Due to climate change, droughts have had a devastating impact on local agriculture. The dam's primary purpose is an irrigation scheme and flood control. This essay historicizes these concerns by revisiting the Akosombo Dam, Ghana's largest hydroelectric dam, completed in 1965. The discussion juxtaposes personal recollections of dam-affected communities with reports by administrators, biologists, and social scientists. The essay draws on government records, scientific studies about Volta Lake, and oral histories. Ultimately, it argues, builders and administrators of the Akosombo Dam failed to address most water issues, despite ample knowledge about their existence. One hopes that these shortcomings will not be repeated in the Pwalugu project. [ABSTRACT FROM AUTHOR]

On December 6, 1974, two pressure-driven steel gates of the Cahora Bassa Dam, each weighing 220 tons, stopped the mighty Zambezi River in its course. After five years of toil by more than five thousand workers, the construction of Mozambique's Cahora Bassa was complete. At the time, it was the fifth-largest dam in the world. The hydroelectric dam was the last megaproject constructed in Africa during the turbulent era of decolonization. Through the voices of peasants and fishermen, displaced by the dam and the workers who built it, this essay analyzes the far-reaching social, political, and ecological consequences of Cahora Bassa. It also explores the devastating impact on riparian life downriver from the dam, which dramatically reduced the annual inundation of the floodplain that supported hundreds of thousands of farmers as well as fish, birds, and mammals. [ABSTRACT FROM AUTHOR]

The construction of dams creates a series of reservoirs, causing severe environmental changes and a biodiversity crisis. We aimed to investigate the relative roles of the construction of upstream cascade dams and the longitudinal gradient in environmental conditions in the spatial and temporal variations in fish assemblages in a downstream reservoir. Fish assemblage and abiotic data from four longitudinally distributed reaches in the Three Gorges Reservoir (TGR), China—one of the largest reservoirs worldwide—were collected over 8 years (2011–2018) and analysed. The results showed that the blockage to fish passage, as well as the flow modification, caused by the upstream dams and reservoirs can significantly affect the variations in fish assemblages downstream of the TGR; fish assemblages in the upper area of the TGR were more vulnerable to upstream dam construction than those in the lower area. The longitudinal environmental gradient was more important in determining the spatial and temporal distributions of fish assemblages in the reservoir than the combined effects caused by the upstream dams and reservoirs. The spatial distribution pattern of fish assemblage structure in the TGR was mainly determined by the gradient difference in the flow regime among stations, whereas the construction of two upstream dams mainly affected the temporal variations in fish assemblages of the TGR by altering the downstream flow and thermal regimes and blocking fish movement down to the TGR. [ABSTRACT FROM AUTHOR]

Fishways have been widely used for upstream passage around human-built structures, but 'success' has varied dramatically. Evaluation of fishway success has typically been conducted at local scales using metrics such as fish passage efficiency and passage time, but evaluations are increasingly used in broader assessments of whether passage facilities meet population-specific conservation and management objectives. Over 15 years, we monitored passage effectiveness at eight dams on the Columbia and Snake rivers for 26,886 radio-tagged spring-summer and fall Chinook Salmon O. tshwaytscha, Sockeye Salmon O. nerka, and summer steelhead O. mykiss during their migrations to spawning sites. Almost all fish that entered dam tailraces eventually approached and entered fishways. Tailrace-to-forebay passage efficiency estimates at individual dams were consistently high, averaging 0.966 (SD = 0.035) across 245 run×year×dam combinations. These estimates are among the highest recorded for any migratory species, which we attribute to the scale of evaluation, salmonid life history traits (e.g., philopatry), and a sustained adaptive management approach to fishway design, maintenance, and improvement. Full-dam fish passage times were considerably more variable, with run×year×dam medians ranging from 5–65 h. Evaluation at larger scales provided evidence that fishways were biologically effective, e.g., we observed rapid migration rates (medians = 28–40 km/d) through river reaches with multiple dams and estimated fisheries-adjusted upstream migration survival of 67–69%. However, there were substantive uncertainties regarding effectiveness. Uncertainty about natal origins confounded estimation of population-specific survival and interpretation of apparent dam passage 'failure', while lack of post-migration reproductive data precluded analyses of delayed or cumulative effects of passing the impounded system on fish fitness. Although the technical fishways are effective for salmonids in the Columbia-Snake River system, other co-migrating species have lower passage rates, highlighting the need for species-specific design and evaluation wherever passage facilities impact fish management and conservation goals. [ABSTRACT FROM AUTHOR]

American eel (Anguilla rostrata) often pass hydropower dams during adult spawning migrations. We conducted a 4-year acoustic telemetry study that characterized passage risks through two dams (West Enfield and Milford) in the Penobscot River, Maine, USA. We released tagged fish (n = 355) at two sites, estimated survival and delay under variable river conditions, and compared performance among dammed and free-flowing river sections. Survival rates (standardized per river kilometre, rkm) were lower at West Enfield (Φrkm = 0.984 ± 0.006 SE) and Milford (Φrkm = 0.966 ± 0.007 SE) compared with undammed River sections (Φrkm = 0.998 ± 0.0003 SE). Cumulative mortality was 8.7% (4.4 km) and 14.2% (5.5 km) through dammed sections and 8.7% throughout the rest of the river (58.1 km). Fish that already passed an upstream dam incurred higher downstream mortality compared with individuals without passage experience. Additionally, fish endured long delays at dams, and >10% of fish were delayed >24 h. Low flows exacerbated the risk of mortality and delay. These results offer evidence for direct, latent, and sublethal consequences of dam passage for migrating eels. [ABSTRACT FROM AUTHOR]

A South African inland fisheries policy will depend on a reliable long-term supply of social-ecological data covering freshwater fisheries at a broad geographic scale. Approaches to systematic planning of research and monitoring are demonstrated herein, based on a fishery-independent gillnet dataset covering 44 dams, and geographic information system maps of monthly and annual climate variables, human land use, and road access in a 5 km zone around 442 dams. Generalised linear mixed models were used to determine the covariates of gillnet catch per unit effort. Such covariates are required for a model-based process to select a subset of state-owned dams for a long-term fishery survey programme. The models indicated a monthly climate influence on catch per unit effort and climatic drivers of fish species distributions. However, unexplained variation is overwhelming and precludes a model-based survey design process. Non-hierarchical clustering of 442 dams was then done based on annual climate and human land use variables around dams. The resulting clusters of dams with shared climate and land use characteristics indicates the types of dams that should be selected for monitoring to represent the full range of climate and land use characteristics. Surrounding land use could indicate the socioeconomic characteristics of fisheries, for example, dams that may support subsistence-based communities that require increased research effort. Finally, although primary catchments could be useful for organising national-scale management, land use cover in the 5 km zone around dams varied widely within the respective primary catchments. Beyond these proposed approaches to plan research, this study also reveals various data deficiencies and recommends additional future studies on other possible methods for systematic research planning. [ABSTRACT FROM AUTHOR]

1/18 Neotropical Ichthyology Original Article Neotropical Ichthyology, 19(3): e200133, 2021 https://doi.org/10.1590/1982-0224-2020-0133 Special Issue Human impacts on fish diversity A cascade of dams affects fish spatial distributions and functional groups of local assemblages in a subtropical river Jaqueline de Bem1, Josiane Ribolli1, Cristhiana Röpke2, Kirk O. Winemiller3 and Evoy Zaniboni-Filho1 Dams reduce the longitudinal connectivity of rivers and thereby disrupt fish migration and the spatial distribution of species, impacts that remain poorly studied for some Neotropical rivers from mega-diverse basins. We investigated the spatial distribution of fish species with different trophic and movement/ reproductive/size characteristics to assess how functional groups have responded to a cascade of dams on the Uruguai River in southern Brazil. Fish abundance, biomass, and species composition were evaluated at eight locations along the longitudinal gradient. The fish assemblage in the upper stretch was mainly characterized by small and medium-sized species at higher trophic levels, whereas the sites located furthest downstream displayed more medium and largesized species, including many carnivorous species. Species with high fecundity, seasonal migrants, and catfishes with internal fertilization were common in the river´s middle and lower reaches. Detritivorous species dominated areas distant from the dams. Overall, functional diversity of local fish assemblages was greater in lower reaches. The cascade of dams has impacted the distribution of functional groups of local fish assemblages of Uruguai River. The alteration of functional groups in upper reaches of the river has potential consequences for ecosystem processes and services, such as nutrient cycling and fisheries. [ABSTRACT FROM AUTHOR]

We tested for effects of two dams on fish assemblages in the St. Joseph River, Indiana. Fishes were collected by boat electrofisher twice annually, at 23 sites from 1998 to 2018. Fish collection data were aggregated into CPUE counts of species per 500 m, and CPUE were pooled across sites above and below the dams. We used multivariate analyses to test for spatial and temporal variation for assemblages above and below dams. Assemblages above and downstream of the dams differed significantly when examined by collection year. The effects (abundances of fish species) of the dams on fish assemblages were different at the South Bend dam from those at the Elkhart dam. Trajectories of temporal change in fish assemblages above and below dams were all gradual and directional. Temporal variation in fish abundance categorised into trophic traits (guilds) differed by location. We suggest that moderate to high stress from anthropogenic impacts on the St. Joseph River appears to result in high assemblage variation above and below dams. The St. Joseph River fish community appears to be unstable, likely from multiple anthropogenic impacts to water quality, habitat degradation and hydrologic alteration. We found that 25 of 33 hydrologic variables in four of five Indicators of Hydrological Alteration groups were significantly altered from 1931 to 2019. However, hydrology variation as potential disturbance events did not visually match observed temporal assemblage variation. [ABSTRACT FROM AUTHOR]

Downstream passage for juvenile Chinook salmon Oncorhynchus tshawytscha (Walbaum) and steelhead Oncorhynchus mykiss (Walbaum) through the fish weir at Foster Dam, Oregon, was evaluated to assess the weir's efficacy as a long‐term passage solution. Radio telemetry was used to estimate survival, passage and effectiveness for the fish weir, spillway and turbines. Survival of Chinook salmon through the fish weir varied by season and reservoir elevation (66%–87%), and passage proportions were low (8%–20%). Fish weir effectiveness was low to moderate (0.39–2.09). Steelhead survival was lower (57%–77%) but passed the fish weir in higher proportions (77%), and weir effectiveness was consistently high (2.96–5.49). The results indicate the existing fish weir will not be a suitable long‐term passage solution for all species. However, because of the high passage proportions and effectiveness observed for steelhead, further development of the surface‐flow concept appears to be promising for safely passing downstream‐migrating fishes. [ABSTRACT FROM AUTHOR]

Dams can impede access to habitats that are required for the completion of life history phases of many migratory fish species, including anadromous sturgeons. Various forms of fish passage have been developed to permit migratory fishes to move above dams, but many dams still lack such structures. Translocation of ripe, mature fish above dams has been used as a first step to determine the efficacy of potential fish passage systems. The anadromous Gulf sturgeon, Acipenser oxyrinchus desotoi, inhabits the Gulf of Mexico and coastal rivers from Florida to Louisiana, and requires upriver spawning habitats to complete its life cycle. Historic overfishing and other anthropogenic threats, including dam construction, led to species declines and subsequent listing as threatened under the Endangered Species Act. In the Apalachicola River, FL, the 1957 completion of Jim Woodruff Lock and Dam (JWLD) created Lake Seminole and blocked Gulf Sturgeon from accessing 78% of historic riverine habitat—including potential spawning habitat—in the Apalachicola‐Chattahoochee‐Flint River Basin. The objective of this pilot study was to determine the efficacy of passage around JWLD through the trap‐and‐transport of 10 male Gulf sturgeon from the Apalachicola River to the reservoir above the dam. Through the use of acoustic telemetry, we were able to assess the ability of these fish to navigate Lake Seminole, access potentially suitable spawning habitat in the Flint and River, and complete their seasonal outmigration to the Gulf of Mexico. In this study, 2 translocated sturgeon moved 69 km upstream into potential spawning habitat in the Flint River, but 6 fish fell back through the lock/spill gates at JWLD within days of translocation. Four sturgeon appeared to remain trapped in the reservoir, and their long‐term survival was deemed unlikely. Given our low sample size, and examination of male fish only, we cannot conclude that a trap‐and‐transport program would ultimately fail to restore spawning above JWLD, but our findings suggest that the risk of adult mortality is nontrivial. Alternatively, we suggest future studies examine the population level trade‐offs associated with translocation of adults or consider alternatives such as a head‐start program to rear and release juvenile sturgeon above JWLD to study viability of their passage in addition to effects on overall recruitment in the population. [ABSTRACT FROM AUTHOR]

This paper provides a compendium of the utilisation potential of aquatic invasive plants found in the Owabi Dam in the Ashanti Region of Ghana. In total, seven aquatic invasive plants were identified in the Owabi Dam, which included Ceratophyllum demersum, Nymphaea odorata, Polygonum lanigerum, Arthropteris orientalis, Typha domingensis, Pistia stratiotes, and Cyprus papyrus. Some of the identified invasive plants were found to be highly nutritious and suitable for human consumption or use as feed for livestock, fish, and poultry. Other plants had high medicinal potential and aesthetic value. Several of the invasive plants were suitable for bio-industrial usages as feedstock to produce biofuels, insecticides, and biofertilizer, among other products. Therefore, if an effective utilization method of these currently unutilized aquatic invasive plants is established, it can provide a source of livelihood and income generation for individuals and households and contribute to controlling the impact of invasive plants on the Owabi Dam. [ABSTRACT FROM AUTHOR]

We evaluated the association between the El Niño Southern Oscillation (ENSO), an important climatic phenomenon on Earth, with water level variation and fish assemblage attributes (i.e., abundance, species richness and structure of the assemblage) of the Paraná (dammed) and Ivinhema (undammed) rivers, located in the upper Paraná River floodplain, Brazil. Cross-Correlation Function analyses were performed using the Oceanic Niño Index (ONI; which indexed ENSO events) as the influential time series on water level and fish assemblage attributes time series. ONI were positively associated with water level and with most of the fish assemblage attributes tested, but these patterns differed between the two rivers. This indicates that El Niño events affect the structure of the fish assemblages, mainly in the Ivinhema River, which presented more assemblage attributes associated with ONI. In addition, dams may play a regulatory effect over the water level of the Paraná River, which probably explains the different patterns of assemblage attributes in both rivers. Thus, ENSO events are associated with the composition and structure of the fish assemblages in the studied area, and their effects are apparently minimized in the Paraná River due to the presence of upstream dams. [ABSTRACT FROM AUTHOR]

Located in Batam City, Duriangkang Dam plays an essential role in providing clean water in the area, also being the first and largest estuary dam in Indonesia. However, with a total effective water volume of 107,000,000 m3, Duriangkang Dam is now heavily polluted because of enormous wastewater loads from both domestic and industrial sources that are directly discharged into the dam. The practice of fish farming has also contributed to its demise. Based on water samples collected during 2016 to 2018, the water condition for Duriangkang Dam is no longer classified as the 2nd class of raw water, based on Indonesian water standards. The present study utilizes the WASP model to evaluate and simulate possible solutions for controlling the Duriangkang Dam water pollution rate. The water quality indicators of dissolved oxygen (DO), total phosphorus (TP) and biochemical oxygen demand (BOD) concentrations are modelled. The calibration and verification results indicate the model exhibited an excellent fitting for DO, BOD and TP concentrations. Under several scenarios, it was determined that the best way to control the pollution rate within the dam is by implementing scenario 8, which include total control of the fish farms and domestic wastewater loads. [ABSTRACT FROM AUTHOR]

There is scarce information on the distribution of African clawless otter across many of its range habitats and how humans who mostly use similar resources perceive otters. This information gap precludes efforts to improve conservation of the otters especially in areas increasingly threatened by anthropogenic activities and habitat loss. We used local expert opinion assessment and field surveys as well as questionnaire to document the distribution of the African clawless otter and uncovered threats in the Mtera dam in central Tanzania. Our surveys detected otter presence in only 50% of the sites known by the local fishers in the area. More than 56% of the surveyed community were aware of the otter presence and reported four major threats faced by this carnivorous species including use of illegal fishing gears, overfishing, increased human population density that puts pressure on the land, water and fish resources and increased human habitation of the dam sides. These threats have the potential to drastically change the otter habitats and the ecosystem services offered by the dam with dire consequences to the human economy and food security. Improving conservation of the Mtera dam ecosystem is an increasing priority. [ABSTRACT FROM AUTHOR]

Passage of hydropower plants by upstream-migrating salmonid spawners is associated with reduced migration success, and the need for knowledge of fish behavior downstream of dams is widely recognized. In this study, we examined fishway passage of landlocked Atlantic salmon (Salmo salar) in River Klarälven, Sweden, and brown trout (Salmo trutta) in River Gudbrandslågen, Norway, and the influence of prior experience on passage success in 2012 and 2013. Fishway trap efficiency varied from 18% to 88% and was influenced by river discharge. Most salmon (81%) entered the fishway trap on days without spill, and salmon moved from the turbine area to the spill zone when there was spill, with small individuals showing a stronger reaction than large fish. Analysis of fish with and without prior trap experience showed that a higher percentage of the "naïve" fish (70% of salmon and 43% of the trout) entered the fishway traps than the "experienced" ones (25% of the salmon and 15% of the trout). Delays for fish that entered the trap ranged from 3 to 70 days for salmon and 2 to 47 days for trout. [ABSTRACT FROM AUTHOR]

This study is devoted to parasitism caused by the tapeworm Ligula intestinalis (L.) in the roach Rutilus rutilus (L.), an invasive species, in three Algerian dam lakes dependent on three different watersheds. We follow the quantitative parameters of parasitism and the impact of parasitism on the development of fish. From March 2016 to February 2017, we examined 578, 565 and 629 individuals in Sekkak, ghrib and guenitra dams respectively. The rate of infection varies depending on the site (p-value < 5%). The prevalence is 0.86% in Sekkak, 2.22% in Guenitra and 10.26% in Ghrib. Respectively, the mean intensity of infection is equal to 1.2, 5.2 and 1.3. The occurrence of the parasite is higher in all dams during autumn. Major allometric growth was observed in parasitized individuals in the three dams (b = 3.19 for ghrib, b = 3.98 for Sekkak and b = 3.44 for guenitra) and minor allometric growth in non-parasitized individuals (b = 2.98 to ghrib, b = 2.98 to Sekkak and b = 2.92 to guenitra), with a significant difference between parasitized and healthy individuals in the three dams (p < 5%). Overweight fish are influenced by parasitism in ghrib dam (parasitized individuals: Kp = 1.03 ± 0.07 and healthy individuals: Ks = 1.06 ± 0.11 (p < 5%)) contrariwise to Sekkak and guenitra (parasitized individu-als: Kp = 1.09 ± 0.18 in Sekkak, 0.97 ± 0.09 in guenitra; healthy individuals: Ks = 1.04 ± 0.14 in Sekkak, 1.03 ± 0.12 in guenitra) (p > 5%). At ghrib dam, the parasitism varies depending on the groups of both size and age (p < 5%), on the contrary to the condition factor (p > 5%). [ABSTRACT FROM AUTHOR]

While hydroelectric dams play a significant role in meeting the increasing energy demand worldwide, they pose a significant risk to riverine biodiversity and food security for millions of people that mainly depend upon floodplain fisheries. Dam structures could affect fish populations both directly and indirectly through loss of accessible spawning and rearing habitat, degradation of habitat quality (e.g., changes in temperature and discharge), and/or turbine injuries. However, our understandings of the impacts of dam life span and the initial fishery conditions on restoration time and hence the dynamic hydropower (energy)-fish (food) nexus remain limited. In this study, we explored the temporal energy-food tradeoffs associated with a hydroelectric dam located in the Penobscot River basin of the United States. We investigated the influence of dam life span, upstream passage rate, and downstream habitat area on the energy-food tradeoffs using a system dynamics model. Our results show that around 90% of fish biomass loss happen within 5 years of dam construction. Thereafter, fish decline slowly stabilizes and approaches the lowest value at around the 20th year after dam construction. Fish restoration period is highly sensitive even to a short period of blockage. The biomass of alewife spawners need 18 years to recover with only 1-year of blockage to the upstream critical habitats. Hydropower generation and loss of fish biomass present a two-segment linear relationship under changes in dam life span. When the dam life span is less than 5 years, generating 1 GWh energy cause around 0.04 million kg loss of fish biomass; otherwise, the loss of fish biomass is 0.02 million kg. The loss of fish biomass could be significantly decreased with minimal energy loss through increasing upstream passage rate and/or the size of downstream habitat area. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the environmental impacts generated by the hydroelectric complex in the Madeira River, Brazilian Amazon, based on the perceptions of local fishers and fishery database, it focus attention on three main impacts: (i) on local fishery stocks; (ii) in fish fauna and (iii) on the aquatic ecosystems. The local fishers were selected through the "snowball" approach for the application of semi-structured interviews. All the local fishers confirmed having perceived a decline in fishery productivity following the impounding of the Madeira River. Changes in the condition of the fish were also perceived by the local fishers, including exophthalmia (82%), a reduction in the weight or length of the fish (25%), and irregular breeding patterns (14%). In the case of impacts on the river, changes in the hydrological cycle were the process remembered most frequently (75%). The results elucidated a range of environmental impacts caused by the hydroelectric dams of the Madeira River. [ABSTRACT FROM AUTHOR]

Migration rates, delay, timing, and success of acoustic-tagged Atlantic salmon (Salmo salar) presmolts (n = 120) and smolts (n = 57) are reported as they moved through the large Mactaquac Generating Station (MGS) reservoir and subsequently the lower Saint John River (SJR). The potential relationship between fish movements and the MGS operations was examined directly and via a hydrodynamic model. Migration rates were 15.4–29.3 km·day−1 within the river sections and 5.0–13.3 km·day−1 through the reservoir, a significant reduction of 32%–57%. Migratory timing was temporally mismatched with dam operations such that only a few (n = 3) smolts had the option of dam passage via spill. Migration success estimated as apparent survival was high through the reservoir (81%–100%), declined by 8%–32% during passage at the MGS, and additional losses (27%–55%) occurred during the migration to the lower SJR, such that overall survival to the estuary for the groups tagged as autumn presmolts was 61%–65%, and survival for those tagged as spring smolts was 6%–10%. [ABSTRACT FROM AUTHOR]

The Loskop Dam is the most polluted impoundment in the Olifants River, because it receives pollutants from the entire mine-dominated upper catchment. However, histopathology of fish inhabiting this polluted dam is scantly explored. The current study aimed to investigate the histopathology of the gills and liver of Labeo rosae from Loskop Dam. Alkaline pH was observed throughout the study with most metal concentrations exceeding the water quality guideline for aquatic ecosystems. Regressive changes were the most prominent lesions for both organs with gills showing relatively more pathologies than the liver. Epithelial lifting was 100% prevalent during both seasons in the gills whereas a significant expansion of lipofuscin-laden melanomacrophages (MMCs) showed 100% prevalence in the liver. Gills were significantly different in their prevalence of histopathology between the two seasons, which was not the case for liver. The histopathology recorded in this study shows that the health of L. rosae at Loskop Dam was compromised. Given the exacerbating pollution level in the upper Olifants River, these findings serve as a warning to conservation authorities and emphasise the necessity for regular monitoring of fish health at Loskop Dam to assess pollution levels using fish health as a sensitive indicator to altering pollution levels. [ABSTRACT FROM AUTHOR]

Habitat alterations that result from anthropogenic disturbance impact both the abiotic and biotic conditions of ecosystems, causing changes in biodiversity in many parts of the world. Recently, the use of functional diversity has been suggested as an approach to better evaluate the effects of such disturbance on particular communities. Here, we investigated the temporal changes in species and functional diversities of fish communities in the downstream area of the Three Gorges Dam (TGD) before, during, and after impoundment. We found two regime shifts in the fish community in 2004 and 2013 following impoundment. Although taxonomic diversity declined sharply at the first regime shift, it increased at the second shift. On the other hand, functional diversity declined throughout the same period, indicating the loss of functional diversity despite increased species diversity. Our analysis also showed that the fish communities shifted from under‐dispersion to over‐dispersion due to both a decrease in the relative abundance of migratory fish and an increase in the number of fish adapted to the new hydrologic conditions. Our results indicated that the impacts of dams on downstream fish communities may change over time. Interactions between species may become more important when the environment is stable. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) analysis has seen rapid development in the last decade, as a novel biodiversity monitoring method. Previous studies have evaluated optimal strategies, at several experimental steps of eDNA metabarcoding, for the simultaneous detection of fish species. However, optimal sampling strategies, especially the season and the location of water sampling, have not been evaluated thoroughly. To identify optimal sampling seasons and locations, we performed sampling monthly or at two‐monthly intervals throughout the year in three dam reservoirs. Water samples were collected from 15 and nine locations in the Miharu and Okawa dam reservoirs in Fukushima Prefecture, respectively, and five locations in the Sugo dam reservoir in Hyogo Prefecture, Japan. One liter of water was filtered with glass‐fiber filters, and eDNA was extracted. By performing MiFish metabarcoding, we successfully detected a total of 21, 24, and 22 fish species in Miharu, Okawa, and Sugo reservoirs, respectively. From these results, the eDNA metabarcoding method had a similar level of performance compared to conventional long‐term data. Furthermore, it was found to be effective in evaluating entire fish communities. The number of species detected by eDNA survey peaked in May in Miharu and Okawa reservoirs, and in March and June in Sugo reservoir, which corresponds with the breeding seasons of many of fish species inhabiting the reservoirs. In addition, the number of detected species was significantly higher in shore, compared to offshore samples in the Miharu reservoir, and a similar tendency was found in the other two reservoirs. Based on these results, we can conclude that the efficiency of species detection by eDNA metabarcoding could be maximized by collecting water from shore locations during the breeding seasons of the inhabiting fish. These results will contribute in the determination of sampling seasons and locations for fish fauna survey via eDNA metabarcoding, in the future. [ABSTRACT FROM AUTHOR]

The paper reports a study of the responses of fishing communities, Regência and Povoação, located at the mouth of the Doce River, to the collapse of the Fundão dam, owned by Samarco Mineração, in 2015. After the disaster, the fishermen's social and cultural practices have undergone drastic changes. The arrival of tailings in the river has impaired their routines and income. The fishermen and their families indicate a sense of loss of identity and insecurity because of the uncertainty. They do not know if they will be able to resume fishing in these waters. This feeling contrasts with the results of a study conducted before the disaster. [ABSTRACT FROM AUTHOR]

Secondary contact may have important implications for ecological and evolutionary processes; however, few studies have tracked the outcomes of secondary contact from its onset in natural ecosystems. We evaluated an anadromous alewife (Alosa pseudoharengus) reintroduction project in Rogers Lake (Connecticut, USA), which contains a landlocked alewife population that was isolated as a result of colonial‐era damming. After access to the ocean was restored, adult anadromous alewife were stocked into the lake. We assessed anadromous juvenile production, the magnitude and direction of introgression, and the potential for competition between ecotypes. We obtained fin clips from all adult alewife stocked into the lake during the restoration and a sample of juveniles produced in the lake two years after the stocking began. We assessed the ancestry of juveniles using categorical assignment and pedigree reconstruction with newly developed microhaplotype genetic markers. Anadromous alewives successfully spawned in the lake and hybridized with the landlocked population. Parentage assignments revealed that male and female anadromous fish contributed equally to juvenile F1 hybrids. The presence of landlocked backcrosses shows that some hybrids were produced within the first two years of secondary contact, matured in the lake, and reproduced. Therefore, introgression appears directional, from anadromous into landlocked, in the lake environment. Differences in estimated abundance of juveniles of different ecotypes in different habitats were also detected, which may reduce competition between ecotypes as the restoration continues. Our results illustrate the utility of restoration projects to study the outcomes of secondary contact in real ecosystems. [ABSTRACT FROM AUTHOR]

Sakarya River with a length of 824 km is one of the most important lothic ecosystems of Turkey. Sarıyar, Gökçekaya and Yenice Dams were constructed on the Sararya River for the purpose of electric supply and utility water for agricultural and fishery activities. In this study, sediment samples were collected from 14 stations selected on areas seasonally (2015–2016). Also, cyprinidae species (Carassius gibelio (Bloch, 1782), Capoeta baliki Turan, Kottelat, Ekmekçi & Imamoglu 2006) were caught from Dam Lakes and Sakarya River. Cr, Ni, Cu, Zn, Pb levels in sediment samples and in tissues (liver, gill and muscle) of fish were analyzed in samples by Analytic Jena ContrAA 700 (high-resolution continuum source atomic absorption spectrometer). The data observed were evaluated with national and international quality criteria. According to the data in the study results, heavy metal accumulations in the gill and liver of fish were determined higher than muscle. Zn levels in muscle of C. gibelio caught from Yenice Dam Lake were higher than the permissible limit stated by Turkish legislation and FAO. Also, Cr and Ni levels in sediment samples especially during rainy seasons were higher to dry seasons and Cr and Ni levels were detected higher than sediment quality guidelines. [ABSTRACT FROM AUTHOR]

We employed the trophic upsurge hypothesis as an analytical framework to describe the response of Neotropical fish communities to terrestrial inundation associated with river damming. Data were collected for the impact assessment of the Peixe Angical Dam, Tocantins River, Brazil. Monthly surveys were conducted at nine sites (seven upstream, two downstream) from 15 months before to 20 months after dam closure and a follow‐up survey 60–83 months after closure. Fish responses differed in timing and magnitude across sites. In the new reservoir, populations peaked 8–13 months after flooding, demonstrating increases in richness (84 ± 52%), biomass (329 ± 266%) and abundance (681 ± 348%) with the maxima for richness and abundance tending to precede biomass maxima. Populations of all families increased but were greatest for Engraulidae, Hemiodontidae, Serrasalmidae and Characidae, and lower for the benthic catfish: Sciaenidae, Dorididae, Pimelodidae. Downstream populations peaked 5–12 months after closure or showed consistent decline. Five years after dam‐closure richness and abundance were lower compared to predam levels, with populations at all sites demonstrating an ongoing decline. Reservoir creation triggers reproductive recruitment and otherwise pools spatially disparate populations from across the flooded valley. If the rise in richness is largely explained by the increased catchability of species otherwise present prior to flooding, it may be more appropriate to estimate species loss with reference to upsurge data. As peak biomass coincides with declining richness, modelling fisheries production from annually aggregated data may risk overestimating the potential for sustainable harvests. Upsurge–response curves can help identify the timing of critical ecological thresholds for flood‐managed fisheries. [ABSTRACT FROM AUTHOR]

River infrastructures such as weirs, hydropower stations or water reservoirs represent obstructions to migration for diadromous fish. Knowledge of accurate behaviour of fish in front of such structures is required to protect migrants from hazardous areas, guide them towards safe passage or adapt structure to improve the escapement. We developed and made available a method to process acoustic telemetry data based on Time Difference Of Arrival analysis to accurately locate tagged fish. Improved accuracy allows the detection of escape routes and description of dam‐crossing tactics. Sixteen tagged eels were tracked with high accuracy (1–2 m) and ~1 location min−1 frequency during their exploration period on reaching the dam. Two migration routes (spillways and bottom compensation flow pipe) were used by 77% and 23% of eels respectively. Spillways were the preferred route, but a median of 16 days were required to pass the dam versus 1.1 days via the compensation pipe. A minimal water crest of 40 cm was required for passage via spillways. Eels passing through the compensation pipe were exclusively nocturnal and mainly explored the bottom of the dam. Eels passing through spillways explored the whole dam area by night and day, and were not attracted to the compensation pipe entrance. With global warming, more frequent drought periods are expected, potentially leading to decreased opportunities for eels to migrate across safer dams by spillways. To conserve this endangered species, dam management strategies that account for expected hydrologic conditions and distinct exploration behaviours are needed. [ABSTRACT FROM AUTHOR]

We collected 14 Acantharchus pomotis (Mud Sunfish) from the first recently discovered population in Beaver Dam Creek, Tombigbee River drainage, Washington County, AL, in 2011. This effort brings the total number of Mud Sunfish collected in Alabama to 17 specimens since 2000. We captured the specimens using trash-can traps, and Mud Sunfish was the most abundant fish species collected; however, catch-per-unit-effort was low (0.02 fish/trap-night). Male and female Mud Sunfish varied in size from 86 to 125 mm and 90 to 124 mm total length, respectively. Squamation indicated the Alabama population is more closely aligned with Florida and Gulf Slope populations. Currently, Beaver Dam Creek is home to the only known population of Mud Sunfish in Alabama. [ABSTRACT FROM AUTHOR]

Dams contribute to water security, energy supply, and flood protection but also fragment habitats of freshwater species. Yet, a global species-level assessment of dam-induced fragmentation is lacking. Here, we assessed the degree of fragmentation of the occurrence ranges of ~10,000 lotic fish species worldwide due to ~40,000 existing large dams and ~3,700 additional future large hydropower dams. Per river basin, we quantified a connectivity index (CI) for each fish species by combining its occurrence range with a high-resolution hydrography and the locations of the dams. Ranges of nondiadromous fish species were more fragmented (less connected) (CI = 73 ± 28%; mean ± SD) than ranges of diadromous species (CI = 86 ± 19%). Current levels of fragmentation were highest in the United States, Europe, South Africa, India, and China. Increases in fragmentation due to future dams were especially high in the tropics, with declines in CI of ~20 to 40 percentage points on average across the species in the Amazon, Niger, Congo, Salween, and Mekong basins. Our assessment can guide river management at multiple scales and in various domains, including strategic hydropower planning, identification of species and basins at risk, and prioritization of restoration measures, such as dam removal and construction of fish bypasses. [ABSTRACT FROM AUTHOR]

Habitat fragmentation is one of the main threats to biodiversity. Barriers to dispersal caused by anthropogenic habitat alteration may affect phylogeographic patterns in freshwater mussels. Knowledge of the phylogenetic and phylogeographic patterns of unionoids is vital to inform protection of their biodiversity.Here, we assessed influences of dams and their environmental effects on the genetic diversity and population connectivity of a broadly distributed freshwater mussel, Nodularia douglasiae, in Poyang Lake Basin.The results showed high genetic diversity in areas without dams and low genetic diversity in areas with dams. High genetic differentiation and low gene flow were found among the 11 populations. Genetic variation was significantly correlated with dissolved oxygen levels.The observation of low genetic diversity in populations separated by dams indicated that those populations were subjected to genetic erosion and demographic decline because they are disconnected from other populations with higher diversity. High genetic differentiation and low gene flow among the 11 populations could be correlated with anthropogenic habitat alteration.These results indicated that anthropogenic habitat alterations have led to the decline in freshwater mussel diversity. Therefore, we recommend maintaining favourable habitat conditions and connectivity of rivers or lakes, and strengthening study of life histories with host‐test experiments to identify potential host fish species to strengthen the knowledge base underpinning freshwater mussel conservation. [ABSTRACT FROM AUTHOR]

Despite the socio-environmental importance of ichthyofauna, global fish biodiversity has decreased, and the damming of rivers is one anthropogenic activity that causes this reduction. This scientometric study evaluates the main determinants, directions, and gaps of scientific research on the biodiversity of fishes that are influenced by dams. Between 1991 and 2016, there was an increase in the number of studies about this topic, in proportion to the total number of studies that were evaluated. The distribution of these studies among countries is not random, since some socioeconomic and environmental factors (e.g., gross domestic product, number of researchers, number of large dams) determine the distribution of research. Moreover, these studies mostly address the negative impacts of dams on fish communities on a local scale; several studies have shown the importance of mitigating these impacts. In this particular study, we emphasize the need to research the effects of fishing, cascading dams and the phylogenetic diversity of ichthyofauna. We find that the relationship between dams and fish has become popular among researchers, in particular those who are willing to understand the causes, consequences, and severity of these changes on the ichthyofauna. [ABSTRACT FROM AUTHOR]

South Africa is under increasing pressure to develop small-scale fisheries in inland waters. To inform appropriate development of this sector in the Free State Province, the catch rate of double-ended fyke nets was evaluated using survey data from 20 impoundments sampled during the 2013/2014 summer season. Fyke nets were set over night and the total sample effort was 114 fyke net nights. Overall catch per unit effort (CPUE) was 16.8 ± 28.3 kg·net-1·night-1 and catch composition was dependent on impoundment, but generally comprised of a mixture of common carp Cyprinus carpio, African sharptooth catfish Clarias gariepinus, smallmouth yellowfish Labeobarbus aeneus, Orange River mudfish Labeo capensis and moggel Labeo umbratus. The influence of temperature and the potential benefits of baiting the nets were subsequently evaluated through monthly sampling in the hyper-eutrophic Krugersdrift Dam and at the oligotrophic Gariep Dam. Baiting did not significantly influence CPUE, which was significantly higher at Krugersdrift Dam (19.97 ± 23.22 kg·net-1·night-1) than at Gariep Dam (5.02 ± 6.05 kg·net-1·night-1). Increasing temperature had a positive effect on CPUE at Krugersdrift Dam but not at Gariep Dam. Species composition also differed between impoundments and, as a result, we conclude that seasonal catch rates and species compositions will need to be evaluated prior to implementation of fyke net fisheries in specific localities. [ABSTRACT FROM AUTHOR]

The Pak Mun dam is among the most controversial hydropower projects in Thailand. However, the dam's impacts on upriver tributaries have been neglected. We engaged fishers living in three villages along the Sebok River – a major tributary of the Mun River, upstream of the Pak Mun dam – to collect fish catch data for 24 months between 2014 and 2016. Using these data and fishers' knowledge, the negative fishery impacts of the Pak Mun dam and the Ban Ot irrigation dam on the Sebok River were assessed. Both dams have negatively impacted Sebok River fisheries for migratory species. [ABSTRACT FROM AUTHOR]

Dams are built to provide energy, to act as water reservoirs for human and animal consumption, and to water cultivated fields; for those reasons, it is of high importance to assess their water quality periodically. This research diagnosed the quality of water of the Quimbo Dam by using the Simplified Index of Water Quality (SIWQ), which contemplates the measure of dissolved oxygen (DO), conductivity, temperature, Chemical demand of oxygen (QDO) and total suspended solids (TSS). Samples were taken in seven different points along the dam, and four points on rivers that tribute their waters to the dam, during field trips from May until October, 2017. In the same way, in each point, samples were taken at different depths (0.1, 5.0, and 10.0 meters). The obtained results from the analysis of physicochemical parameters described above showed that in average the water quality of Quimbo Dam is in a good condition, with potential for fishing and recreational activities; it is not apt for human consumption without conventional treatment; on the other hand, the water from the tributaries showed medium quality, specially Guandinosa stream which presented the lowest value of SIWQ (35.2), classified as useful only for recreation, water for cultivated fields and industrial activities. [ABSTRACT FROM AUTHOR]

Drifting larval fish assemblages were investigated at three sections in the middle reach of the Yangtze River downstream of the Three Gorges Dam to reveal recovery gradients and to identify the major environmental factors influencing their temporal and spatial patterns. Larval fish in the river section closest to the dam showed lower abundance, later occurrence, narrower temporal niche breadth, and more pairs of dominant species with high niche overlap than those further from the dam. Water temperature, transparency, and discharge significantly influenced the larval fish assemblages. They showed longitudinal gradients of increased water temperature, decreased transparency, and increased discharge in a downstream direction. Our results suggested that hypolimnetic and clean water discharge from the dam heavily impacted larval fish assemblage in the river section near the dam. With an increased distance to the dam and the input of some major tributaries, this impact was gradually buffered, thus forming the longitudinal recovery gradients. We suggest that priority for conservation should shift from river sections closer to the dam to those further from the dam. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present and discuss the results of a survey of fishers exploiting dam reservoirs to determine the conditions of conducting fisheries associated primarily with climate change. Overall, questionnaires were obtained from 18 enterprises (of which 16 were chapters of the Polish Anglers Association) regarding a total of 30 reservoirs with a combined surface area of 29,666 ha, which is 49% of the total surface are of this type of basin in Poland, the largest country in East-Central Europe. This sample is highly representative of all the fisheries conducted in this basin category in Poland and in other East-Central European regions. The following questions referring to the impact of climate change were defined and analyzed based on the answers obtained from the questionnaires: survival of hatchlings, fry, and adult fish; the spawning success of selected fish species; selected hydrological and biological reservoir parameters, the possibility of using and the effectiveness of fishing gears; the length of the recreational fishing season; the size of recreational and commercial fisheries catches of different fish species. Information regarding the impact of reservoirs on fish migrations was also obtained. [ABSTRACT FROM AUTHOR]

The construction of dams on large rivers has negative impacts on native species. Environmental flows have been proposed as a tool to mitigate these impacts, but in order for these strategies to be effective they must account for disparate temperature and flow needs of different species.We applied a multi‐objective approach to identify trade‐offs in dam release discharge and temperature for imperiled fishes with contrasting habitat requirements, while simultaneously meeting the needs of human water users.Using the Sacramento River (California, USA) as a case study, our model suggests that current management aimed at providing high discharge for downstream water users and cold water for endangered winter‐run Chinook salmon (Oncorhynchus tshawytscha) has detrimental impacts on threatened green sturgeon (Acipenser medirostris), which require warm water for juvenile growth.We developed an optimal dam release scenario that can be used to meet the needs of salmon, sturgeon and human water users. Our results show that dam releases can be managed to successfully achieve these multiple objectives in all but the most severe drought years.Synthesis and applications. This study shows that managing dam releases to meet the needs of a single species can have detrimental effects on other native species with different flow and temperature requirements. We applied a multi‐objective approach to balance environmental requirements of multiple species with the needs of human water users. Our findings can be used to guide management of Shasta Dam and our approach can be applied to achieve multi‐object management goals in other impounded rivers. [ABSTRACT FROM AUTHOR]

Dams challenge Atlantic salmon (Salmo salar) conservation, while hatcheries are a common but poorly evaluated recovery tool. We developed a spatially explicit smolt survival model for the Penobscot River, Maine, USA, population. By partitioning survival through dams (with flow dependency), free-flowing river reaches, and the estuary (with dam dependency), the model quantified how these factors influenced the number of fish entering the ocean. Given historical impounded conditions, 74%–22% of hatchery smolts released entered the ocean annually from 1970 to 2012. Of 19.7 million smolts stocked, 7.7 million entered the ocean (39%). Survival was most variable at dams (range 95% to 63%), followed by in-river (range 98% to 70%) and estuary (range 88% to 82%). Overall, lower-river stocking sites resulted in significantly higher numbers at ocean entry because of fewer dam encounters and shorter migrations. Higher flows also resulted in reduced losses. By reconstructing these freshwater and estuary dynamics, the model provides a more accurate estimate of ocean recruitment annually and can be used for scenario planning of future stocking locations relative to predicted flows while being adaptable to new survival rates. [ABSTRACT FROM AUTHOR]

This paper explores the effects of two run-of-river dams (Jirau and Santo Antônio) built in cascade in the middle Madeira River (Brazil) on the interruption of long-distance migration routes of the gilded catfish (Brachyplatystoma rousseauxii). A participative monitoring system was set up to compare capture by commercial fishers approximately 1500 km upstream of the dams in Bolivia, before (1998-2007) and after (2015-2017) dam closure. A significant decrease in gilded catfish catches and in catch per unit effort was observed after dam closure, whereas no significant difference in mean weight was found. Back-estimation of age suggests that the few individuals remaining after dam closure in 2009 are a mixture of old homers that returned upstream before dam closure, and residents hatched after dam closure and trapped in the upper Madeira. Unless fishways in the Madeira River dams improve their efficiency, the gilded catfish might become rare and in danger of regional extinction in the upper Madeira basin in the next few years, negatively affecting river fisheries. [ABSTRACT FROM AUTHOR]

Dams are recognised to impact aquatic biodiversity, but the effects and conclusions diverge across studies and locations. By using a meta‐analytical approach, we quantified the effects of impoundment on fish communities distributed across three large biomes. The impacts of dams on richness and diversity differed across biomes, with significant declines in the tropics, lower amplitude but similar directional changes in temperate regions, and no changes in boreal regions. Our analyses showed that non‐native species increased significantly in tropical and temperate regulated rivers, but not in boreal rivers. In contrast, temporal trajectories in fish assemblage metrics were common across regions, with all biomes showing an increase in mean trophic level position and in the proportion of generalist species after impoundment. Such changes in fish assemblages may affect food web stability and merit closer study. Across the literature examined, predominant mechanisms that render fish assemblages susceptible to impacts from dams were: (1) the transformation of the lotic environment into a lentic environment; (2) habitat fragmentation and (3) the introduction of non‐native species. Collectively, our results highlight that an understanding of the regional context and a suite of community metrics are needed to make robust predictions about how fish will respond to river impoundments. [ABSTRACT FROM AUTHOR]