Search Results (9)

Most freshwater fish need to move freely through rivers to complete their life cycles. Thus, river barriers that hinder or block their longitudinal movement (e.g., dams, culverts, gauging stations), directly affect their reproductive, feeding, and habitat routes. A holistic solution to these barriers would need to allow directed, undistracted, and bidirectional fish migration between different habitats; that is to say, it would need to allow two-way migration. The most extended solution that would allow upstream fish migration is a fishway. However, for downstream migration fish have alternate routes such as spillways, turbines, or bypasses. Studies and discussions about two-way migration and bidirectional movement through a fishway have been focused on large dams and reservoirs; thus, there is a lack of available data on other environments, less popular species, or smaller dams and weirs. In this sense, it is possible to hypothesize that a fishway, especially in a smaller facility, could enhance two-way migration by allowing bidirectional movement. Therefore, as a first step to analyzing the possibility, we studied longitudinal connectivity (two-way migration and bidirectional movements) through a small run-of-river hydropower plant (HPP) with a step-pool type fishway, a common and representative configuration of several small HPPs around the world. A potamodromous cyprinid—the Iberian barbel (Luciobarbus bocagei)—was selected as the target species. In this study, radio and PIT tracking data were collected for four different years and combined to characterize movement in the full system: fishway, turbines/spillways, and the river reach downstream (up to 3 km) and upstream (up to 4 km) from the HPP. The results demonstrated the existence of several types of movement with inter-annual and intra-annual variability. Several fish even returned over the years. This suggests that, in this type of HPP facility, a fishway can provide bidirectional connectivity and two-way migration, thus ensuring that a great proportion of fish complete their life cycles. Full article

A river is an ecosystem where fish fauna represents an important structural element. To re-establish connectivity, it is imperative to allow movement between functional habitats. Due to the hydromorphological complexity of large anthropized rivers and the lack of study techniques that can be used in such environments, relevant data with regard to fish ecology are scarce. On the River Meuse, Belgium, at a point 323 km upstream from the North Sea, the Lixhe hydroelectric dam is equipped with two fishways. Both were continuously monitored using capture traps for 20 consecutive years (from 1999 to 2018), representing 4151 monitoring events. The objectives of the present study were to describe the overall abundance and movement indicators of mainly holobiotic potamodromous fish species and to analyse their temporal evolution. We captured 388,631 individuals (n = 35 fish species) during the 20 years of fishway monitoring; 22.7% were adults (>75% of which were cyprinids), and 83.3% juveniles (>90% cyprinids). From 1999 to 2018, the results showed a drastic reduction in yearly captures for some native species as well as the apparent emergence of non-native (e.g., Silurus glanis) and reintroduced species (e.g., Salmo salar). The annual capture periodicities associated with environmental factors were clearly defined and were mostly related to the spring spawning migration of the adult stage. This long-term monitoring demonstrated how the fishways are used by the whole fish community and allowed a better understanding of their movement ecology in a large lowland anthropized river. The appearance of non-native species and the drastic decline in abundance of some common and widespread European fish should prompt river managers to adopt conservation measures. Full article

With the aim of building more compact fishways and adapting them to field conditions to improve their location by fish, it is common to use turning pools, reducing the longitudinal development of the construction. However, depending on their design, turning pools may affect the hydraulic performance of the fishway and consequently the fish passage. To study these phenomena, turning pools in a vertical slot and in different configurations of submerged notches with bottom orifice fishway types were assessed. Both types of fishways were studied using numerical 3D models via OpenFOAM, a computational fluid dynamics software, in combination with fish responses, assessed with PIT (Passive Integrated Transponder) tag telemetry for three different species of potamodromous cyprinids in several fishways. Results show differences between the hydrodynamics of straight and turning pools, with lower values in the hydrodynamic variables in turning pools. Regarding fish behavior, the ascent was slower in turning pools but with no effect on passage success and without being a problem for fish migration. This information validates the use of turning pools as a key design component for fishways for studied species. Full article

Requalification of low-head ramped weirs through the addition of substrates (retrofitting) has attracted attention in recent years. However, few studies are available on how this measure affects the negotiation of ramped weirs by fish. This study aimed to assess the performance of an experimental ramped weir (3.00 m long with 10% slope; 0.30 m head-drop) to enhance the passage of a potamodromous cyprinid species, the Iberian barbel (Luciobarbus bocagei). Attention was given to testing the effects of the addition of a substrate, in this case cobbles, to the ramp (Nature) vs. a smooth bottom (Control), and discharge (Q; 55 L·s⁻¹ and 110 L·s⁻¹ (or specific discharge per unit width, q = 92 L·s⁻¹·m⁻¹ and 183 L·s⁻¹·m⁻¹)) on fish passage performance. Fish physiological responses to stress and fatigue, measured by glucose and lactate concentrations in blood samples, were also analysed. Results showed that the Nature design generally increased fish movements and successful upstream passages, and enhanced fish passage performance by enabling faster negotiations. Fish movements were also affected by increasing discharge, registering reductions with 110 L·s⁻¹. Results of the physiological parameters indicate that both glucose and lactate concentrations were also influenced by discharge. The outcomes from this study present important information about fish passage performance across low-head ramped weirs and could provide data needed to help biologists and engineers to develop more effective structures to alleviate small instream obstacles. Full article

River fragmentation by large hydropower plants (LHP) has been recognized as a major threat for potamodromous fish. Fishways have thus been built to partially restore connectivity, with fish lifts representing the most cost-effective type at high head obstacles. This study assessed the effectiveness with which a fish lift in a LHP on the River Lima (Touvedo, Portugal), allows potamodromous fish—Iberian barbel (Luciobarbus bocagei), Northern straight-mouth nase (Pseudochondrostoma duriense) and brown trout (Salmo trutta fario)- to migrate upstream. Most fish (79.5%) used the lift between summer and early-fall. Water temperature was the most significant predictor of both cyprinids’ movements, whereas mean daily flow was more important for trout. Movements differed according to peak-flow magnitude: nase (67.8%) made broader use of the lift in the absence of turbined flow, whereas a relevant proportion of barbel (44.8%) and trout (44.2%) passed when the powerhouse was operating at half (50 m³s⁻¹) and full-load (100 m³s⁻¹), respectively. Size-selectivity found for barbel and trout could reflect electrofishing bias towards smaller sizes. The comparison of daily abundance patterns in the river with fish lift records allowed the assessment of the lift’s efficacy, although biological requirements of target species must be considered. Results are discussed in the context of management strategies, with recommendations for future studies. Full article

The addition of substrates to small instream obstacles, like low-head ramped weirs, has been considered a useful management solution to retrofit those structures and enhance fish passage. Substrate dimensions and spatial arrangement, together with discharge, and consequently water depths, appear as important factors for the creation of hydrodynamic conditions that may facilitate the successful passage of fish, though related studies are scarce to support decision-making. This study assessed the influence of discharge (Q) and different retrofitting designs (RD) on the upstream passage performance of a potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei). Different substrates (small boulders, large boulders, cobbles) and spatial arrangements (aligned, offset) were tested. Numerical modelling was performed to characterize the hydrodynamics. Results indicate that Q and RD influenced the upstream negotiation of ramped weirs. Cobbles randomly distributed along the ramp (Nature design) was the most successful configuration, recording the highest number of upstream passages. Low velocities along the ramp, and low turbulence downstream, were registered in this configuration, indicating that the use of natural substrate may help to increase the permeability of ramped weirs to fish movements. The outcomes from this work can help engineers and biologists to design more appropriate passage structures for low-head instream obstacles. Full article

Endemic freshwater fish from semiarid environments are among the most threated species in the world due to water overexploitation and habitat fragmentation problems. Stepped or pool-type fishways are used worldwide to reestablish longitudinal connectivity and mitigate fish migration problems. Many of them are being installed or planned in rivers of semiarid environments, however, very few studies about fish passage performance through pool-type fishways has been carried out to date on these regions. The present work focuses on the passage performance of two potamodromous cyprinids endemic of these regions, with different ecological and swimming behavior: southern Iberian barbel (Luciobarbus sclateri) and Iberian straight-mouth nase (Pseudochondrostoma polylepis). These are assessed in two of the most common types of stepped fishways: vertical slot and submerged notch with bottom orifice fishways. Experiments were carried out during the spawning season in the Segura River (southeastern Spain), using a passive integrated transponder (PIT) tag and antenna system. Ascent success was greater than 80%, with a median transit time lower than 17 minutes per meter of height in all trials, and for both species and fishway types. Results show that both types of fishways, if correctly designed and constructed, provide interesting alternatives for the restoration of fish migration pathways in these regions. Full article

Low-head ramped weirs are a common instream obstacle to fish movements. Fish passability of these structures, where water passes over but does not generate a waterfall, is primarily related to ramp length and slope, but their relative contribution has seldom been considered. This study aims to assess the passage performance of a potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei), negotiating an experimental ramped weir with varying ramp length (L) and slope (S). Four configurations were tested, with a constant discharge of 110 L∙s⁻¹. Results suggest that both factors influenced passage performance of fish. Attraction efficiency (AE) increased with increasing L and S, whereas the number of successes (N) and passage efficiency (PE) decreased upon increasing L. For S, it was found that both N and PE peaked at the intermediate level (20%). These results suggest that configurations with the lowest slopes may not necessarily be the best option because they may be less attractive for the fish and their demand for space is higher. Higher slopes (but not excessive) could be more attractive to fish, less space-demanding, and therefore, more cost-effective. Future studies should investigate how discharge and boulder placement influence fish passage across ramped weirs, to improve habitat connectivity. Full article

Most fishway studies are conducted during the reproductive period, yet uncertainty remains on whether results may be biased if the same studies were performed outside of the migration season. The present study assessed fish passage performance of a potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei), in an experimental full-scale vertical slot fishway during spring (reproductive season) and early-autumn (non-reproductive season). Results revealed that no significant differences were detected on passage performance metrics, except for entry efficiency. However, differences between seasons were noted in the plasma lactate concentration (higher in early-autumn), used as a proxy for muscular fatigue after the fishway navigation. This suggests that, for potamodromous cyprinids, the evaluation of passage performance in fishways does not need to be restricted to the reproductive season and can be extended to early-autumn, when movements associated with shifts in home range may occur. The increased effort during the non-reproductive period suggests that adapting the operational regime of fishways, at biologically meaningful seasons in a year, should be assessed by considering the physiological state of the target species. Full article