Search Results (24)

Throughout the world, emerging barriers in river systems block longitudinal connectivity for migrating fish, causing significant impacts by precluding them from carrying out vital life cycle activities. Fishways are still the main mitigation solution implemented, where barrier removal is not feasible. Within the multiple technical fish passage devices, the vertical slot fishway (VSF) is considered the most reliable. Early design guidelines, established for cyprinids, indicate that the volumetric dissipation power (P_v) in the pools should be P_v < 150 Wm⁻³, while most frequent slope values range from 10 to 12%. In this study, an experimental approach was conducted to question and debate the validity of these recommendations. For this, the Iberian barbel (Luciobarbus bocagei, Steindachner, 1864) passage performance was assessed in a full-scale fishway that exceeded P_v design guidelines, under different configurations. These varied in discharge (Q) and mean pool water depth (h_m): VSF1 (Q = 81 Ls⁻¹; h_m = 0.55 m); VSF2 (Q = 110 Ls⁻¹; h_m = 0.80 m); and the same design was equipped with a deep notch: DN1 (Q = 71 Ls⁻¹; h_m = 0.55 m); DN2 (Q = 99 Ls⁻¹; h_m = 0.80 m). The slope was set to 15.2% while the head drop per pool was Δh = 0.28 m, which generated a P_v that ranged from 222 in VSF1 to 187 Wm⁻³ in DN2. Passage behaviour was assessed using PIT telemetry and time-to-event analysis to evaluate the barbel upstream passage using standardized metrics: (i) motivation (ii) ascend success, and (iii) transit time. The hydrodynamic scenarios experienced by fish were characterized through a numerical model using computational fluid dynamics (CFD). The results, contrary to what was expected, showed a higher performance in VSF1 confirmed by the ascent analysis and transit time. Although no differences were found in fish motivation, the results indicate that larger fish displayed lower times to perform the first passage attempt. The CFD results show that, although maximum velocities and turbulence (turbulent kinetic energy (TKE) and Reynolds shear stress (RSS)) do not change significantly between configurations, their distribution in the pools is quite different. Regarding TKE, larger volumes with magnitudes higher than 0.05 m²s⁻² were notorious in both DN1 and DN2 configurations compared to VSF1, influencing passage efficiency which is in line with the ascent and transit time metrics results. Overall, the present research undeniably debates the literature design guidelines and reinforces the need to jointly assess species-specific fish passage criteria and fishway hydrodynamics, whereas precaution should be taken when using very general recommendations. Full article

River ecosystems are exposed to a multitude of stressors, including increasing pesticide run-off driven by precipitation and irrigation. Pyrethroids are the fourth major group of insecticides in use worldwide and have extremely negative effects on aquatic fauna. In this study, we aimed to assess the effects of an acute 2 h sub-lethal exposure to different levels of the pyrethroid esfenvalerate on the swimming behaviour of two Cypriniformes species: the native Iberian barbel (Luciobarbus bocagei) and the non-native invasive bleak (Alburnus alburnus). The experimental set-up consisted of previous exposure to three esfenvalerate concentrations (control, 1.2 (low), and 2.0 (high) μg/L) before being stocked in a three-artificial-flume-channel mesocosm for behavioural trials through direct observation. Monitored behaviours included (i) routine activity, (ii) shoal cohesion, and iii) boldness. Significant differences in fish behaviour were detected for the native species (barbel), as individuals spent significantly more time holding position (i.e., resting) in the control (44.9%) than in the high esfenvalerate concentration (25.2%). Concordantly, control barbels were also found to perform more directional changes than the ones exposed to high esfenvalerate concentrations. Behavioural changes were also found for boldness, measured by the proportion of fish attempts to negotiate the upstream ramp, which were significantly higher in the control (37.4%) and in the high concentration (41.5%) compared to the low one (21.1%). Finally, regarding shoal cohesion of the barbel, it was tighter in the control (81.3%) than in the low- (70.5%) and high- (71.1%) esfenvalerate treatments. For the invasive bleak, there were no significant differences in any of the behavioural traits upon previous exposure to an increasing esfenvalerate concentration. This experimental study demonstrated that even short-term exposure to the pyrethroid esfenvalerate was sufficient to alter the behaviour of a native Cypriniformes fish species while not affecting the non-native species. This may confer greater competitive advantages to non-native fish species in the context of global changes. Full article

The Iberian barbel (Luciobarbus bocagei Steindachner, 1864) and the Iberian nase (Pseudochondrostoma polylepis Steindachner, 1864) are two potamodromous species that migrate upstream in freshwater environments to reproduce. Thus, river fragmentation is a major threat to these species, and fish passes are one of the most-used mitigation measures to restore the longitudinal connectivity of impounded rivers, enabling these species to reach upstream spawning sites. Since 2013, the fish pass installed in the Coimbra dam (Mondego River) has been equipped with a video-recording system to continuously monitor fish passage. Based on visual count data between 2013 to 2015, a total of 61,965 movements of Iberian barbel (up- and downstream) and a total of 138,207 movements of Iberian nase (up- and downstream) were registered, with the migratory upstream movements of nase occurring over a wider period (i.e., January to December) relative to what is described in the literature. The analysis conducted to evaluate the temporal variability in the size of fish using the fish pass showed significant differences between the studied months for both species in both migratory directions; upstream-moving barbel showed a bigger body length in May, and nase showed bigger body lengths in the months of May, June and November. Boosted Regression Trees were used to identify the environmental variables that triggered these movements, with water temperature and flow being, overall, two of the most important variables for both species in both migratory directions. This study updates the relatively scarce available information concerning these species migrations, including movement activity and the associated peaks, size-structure characterization during the migratory periods, and the identification of environmental variables that seem to trigger Iberian barbel and nase movements. Full article

To fight against global warming, we have to change our ways of consuming energy. Due to its low carbon impact and strong dispatchability, hydroelectric production will be one of the bases of this transition. However, peak electricity demand produces rapid and artificial flow fluctuations in tailwaters, i.e., hydropeaking, which has negative effects on fish biota. Thus, developing effective mitigation measures against hydropeaking is an urgent matter. The present study aims to limit the impact of this flow fluctuation on an Iberian cyprinid fish: the Iberian barbel (Luciobarbus bocagei). We experimentally tested different angles of flow refuge entrances (45° and 70°) in an indoor flume (6.5 m × 0.7 m × 0.8 m) to determine if this would affect the behavior of the fish. For each angle configuration, two refuges were installed and distanced 2.30 m from each other on the same side of the flume. Three possible resting locations were defined: downstream, inside, or upstream of each structure. Both angles were tested at 7 L/s (base flow), simulating the normal conditions of the river, and 60 L/s (peak flow), simulating a hydropeaking event. Each replicate comprised a group of five fish. For each, the frequency and residence time were quantified. The preliminary results indicated that the fish movement patterns changed when peak flow occurred. The downstream refuge was more frequently used in both configurations during peak flow. Additionally, the inside parts of the refuges were more frequently used, instead of the parts immediately downstream or upstream, and the time spent inside the refuge at peak flow was higher when compared to base flow. Additionally, hydraulic experiments were carried out at each configuration to determine the velocity field using ADV (Vectrino) technology. For the base flow, mean water depth and average velocity were 8 cm and 12 cm/s, respectively, increasing to 24 cm and 39 cm/s during peak flow. Measurements showed that velocity was equal to 74 cm/s in the narrowed area due to the refuge location, and velocity was null inside and directly downstream of the refuge. The results from this study will allow the development of guidelines for designing flow refuges for cyprinid fish, and hence mitigate the impact of hydropeaking. Full article

Iberian rivers often face annual periods of flow intermittence during the dry season, when habitat availability for freshwater organisms is drastically reduced. Climate change and the presence of small barriers such as weirs may further exacerbate this lack of suitable habitat, particularly for freshwater and migratory fish that perform seasonal movements to complete their life cycle, by narrowing the submersed area and their possibilities of overcoming these barriers. Using the River2D model, we investigated how the current released flows from a nearby large hydropower plant in the Tagus River affect the passability of native fish species at a downstream rock weir (Pego), equipped with a nature-like fish ramp. Using mean daily flow data from gauging stations, we compared the passability of six fish species under low flow conditions (Q90), considering a historical period (1991–2005), and two flow datasets based on climate change projections until the end of the century (2071–2100) for the Tagus River Basin (“moderate” RCP 4.5 and “extreme” RCP 8.5). Target species included three migratory guilds: (i) anadromous—Allis shad (Alosa alosa), twaite shad (Alosa fallax) and sea lamprey (Petromyzon marinus); (ii) catadromous—European eel (Anguilla anguilla) and thlinlip grey mullet (Chelon ramada); and (iii) potamodromous species—Iberian barbel (Luciobarbus bocagei). Overall, our results show that the passability of all fish species may only be ensured with a minimum flow of 3 m s⁻¹ and by using a fish ramp. Furthermore, the passability for all species was found to be significantly lower in the RCP scenarios when compared to the historical period. Our study suggests that climate change is expected to reduce the passability of native fish species in weirs in Iberian rivers, highlighting the importance of considering future flow conditions for a proper management of fish populations in the presence of weirs and other barriers. Full article

Rivers are experiencing increasing salinization due to anthropogenic disturbances, and salinity has been shown to negatively affect freshwater fish behavioral expression, potentially disrupting ecological processes. In this study, the aim was to determine the sublethal effects of secondary salinization (anthropic in origin) on freshwater fish behavior, using a widespread native cyprinid species, the Iberian barbel (Luciobarbus bocagei), as the model species. Behavioral trials were performed in a mesocosm setting, focusing on fish cerebral lateralization, routine activity, boldness, and schooling behavior. The impact of salinity stress was assessed by exposing the barbels to three levels of a salinity gradient—Control (no salt added to the water, 0.8–0.9 mS/cm), Low (9 mS/cm), and High concentration (18–19 mS/cm). Behavioral parameters were recorded every three minutes by visual observation. Our results show that, with increased salinity in the flume channels, fish were less active, and formed less cohesive shoals. Moreover, individuals became bolder, since a higher number of attempts to escape their environment was recorded in greater salinity levels. Laterality of the population appeared to become more evident, as fish revealed a tendency in their decision making to turn left more frequently. Behavioral changes in fish caused by salinization stress should be further researched regarding other freshwater species with different tolerances, in addition to their interaction with other environmental stressors. This broader approach would allow us to recognize salinity thresholds, and also understand the true scope of the consequences of salinization for fish species. Full article

River ecosystems are exposed to a multitude of stressors, of which pesticide run-off is increasingly becoming a global environmental concern due to adverse effects on aquatic organisms. Of those, pyrethroids are now the fourth major group of insecticides in use worldwide; however, their sublethal effects on freshwater fish are still largely unknown. The present study aimed to assess the effects of an acute 2 h sublethal exposure to different levels of the pyrethroid pesticide esfenvalerate on the behaviour of two Cypriniformes species: the native Iberian barbel (Luciobarbus bocagei) and the non-native invasive bleak (Alburnus alburnus). Fish were previously exposed to three esfenvalerate concentrations (control, 1.2 μg/L (mild), and 2.0 μg/L (severe)), before being placed into a three-artificial-flume channel mesocosm for behavioural trials on (i) routine activity, (ii) shoal cohesion, and (iii) boldness. Significant differences in fish behaviour were detected for the barbel, as individuals were found to spend a higher proportion of time holding their position (i.e., resting) from the control to the severe esfenvalerate concentration. Behavioral changes were also detected for boldness, measured by the proportion of fish attempts to negotiate the upstream ramp, which were significantly higher in the control and in the severe concentration compared to the mild one. For the invasive bleak, there were no significant differences in any of the behavioural parameters upon previous exposure to an increasing esfenvalerate concentration. The present study demonstrated that even a short-term exposure to the pyrethroid esfenvalerate was sufficient to alter the behaviour of a native fish species, while no affecting the non-native, which may confer them greater competitive advantages in the context of global changes. Full article

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

When the flow velocity over a river structure exceeds the swimming capacity of fish, it behaves as a velocity barrier. Depending on the hydrodynamic circumstances of the structure as well as the fish’s swimming ability and motivation, the barrier can be permanent, partial, or intermittent. This is the case of flat-V gauging weirs, a common type of velocity barrier in Spanish rivers and in other European rivers. Flat-V weirs are broadly used as they provide precise information about river discharge for water resource management under different hydraulic scenarios, especially during low flow conditions. However, depending on their size, local river morphology, and the river flow scenario, they can produce excessive velocities and thus, reduce or hinder fish upstream movements. Due to their variable geometry, velocity barriers exhibit a non-uniform flow velocity field, which means that flow velocity varies along the barrier. Therefore, any predictive swimming model to assess the barrier effect on fish must consider the spatial variation to achieve a valuable forecast. This work aims to estimate fish passage over Flat-V weirs by linking their 3D hydraulic performance with the swimming capacity of fish. For this, a predictive model is developed using as target species the Iberian barbel (Luciobarbus bocagei), combining research on their swimming ability with 3D models of the structure. Results of the model show the river conditions and weir dimensions that permit the ascent of this species through the sloped wall of the weir. This information has direct implications for the design and assessment of velocity barriers as well as for the retrofitting of velocity barriers, making them compatible with the fish migration. Full article

Understanding fishway attraction is one of the main open challenges in fishways research, and unraveling the mechanisms and relationships that trigger it is crucial to improve the performance of fishways. Furthermore, attraction is usually understood in terms of upstream migration; however, taking into account the possible bidirectional use of fishways, it is equally important to study this phenomenon during downstream migration, although this is usually considered negligible. Therefore, this study aims to advance our understanding of fishway attraction efficiency by considering both upstream and downstream movements in a key small hydropower plant scheme in the Iberian Peninsula. To achieve this, one of the most common Iberian fish species, the Iberian barbel (Luciobarbus bocagei, Steindachner), was monitored via telemetry in a stepped fishway. The studied fishway, considering the specialized literature, would be classified as poor in attraction, i.e., difficult to find due to its low competing discharge and the long distance between the main river flow and both fishway entrances. Fish were PIT tagged and released in different upstream and downstream locations and on different dates. The results showed that a significant proportion of the tagged barbels was able to successfully locate the fishway from both sides, in spite of the mentioned localization drawbacks, with inter-annual variability and with repeated events throughout the years. This suggests that even a fishway with a theoretical poor attraction can still be localized by fish, allowing their use as a two-way migration route, at least with species and HPP schemes such as those already studied. Full article

Histopathology has been used as a very useful tool to provide information on the severity of tissue damage, injuries, and organ functionality. Thus, this work aimed to assess whether seasonal variations (summer and winter) in water quality had consequences on the liver histology of Iberian barbel (Luciobarbus bocagei) and Douro nase (Pseudochondrostoma duriense). The research was carried out in the Vilariça River, a tributary of the Sabor River in Portugal, which is used as spawning grounds by these endemic cyprinids. The liver histopathological changes, assessed through a semi-quantitative system, allowed the identification of 13 histopathological changes located in the hepatic parenchyma, bile duct, and blood vessels. The histopathological changes with a higher prevalence in both species were vacuolization of hepatocytes, endothelial rupture, necrosis, fibrosis, and degenerative vacuolization. The results showed that the severity degree of liver histological alterations ranged between moderate and severe, and the major severity degree was observed in L. bocagei, in the summer season, and at the sampling points located in the downstream and middle stream. The canonical analysis indicated that the exposure of fish to metals may increase the potential risk of liver damage. Thus, in the summer, the high concentrations of Fe, Cu, Zn, As, and Mn justified the prevalence of the biliary duct epithelial detachment, in both species, and the hyperplasia of biliary epithelium, in L. bocagei. In the winter, the high TSS and Cd, Ni, and Cr concentrations justified the prevalence of congestion of blood vessels and degenerative vacuolization in both species. The higher hepatosomatic index of fish caught in the winter was due to the high presence of degenerative vacuolization and hepatocyte vacuolization. The severity of liver histopathological changes reflected differences in the type of contaminants in different seasons and sampling periods, and was thus proven as a valuable indicator of water quality. Full article

The monitoring of river discharge is vital for the correct management of water resources. Flat-V gauging weirs are facilities used worldwide for measuring discharge. These structures consist of a small weir with a triangular cross-section and a flat “V”-shaped notch. Their extensive use is a consequence of their utility in the measurement of both low and high flow conditions. However, depending on their size, local morphology and river discharge can act as full or partial hydraulic barriers to fish migration. To address this concern, the present work studies fish passage performance over flat-V weirs considering their hydraulic performance. For this, radio-tracking and video-monitoring observations were combined with computational fluid dynamics (CFD) models in two flat-V weirs, using Iberian barbel (Luciobarbus bocagei) as the target species. Results showed that fish passage is conditioned by both hydraulic and behavioral processes, providing evidence for scenarios in which flat-V weirs may act as full or partial barriers to upstream movements. For the studied flat-V weirs, a discharge range of 0.27–8 m³/s, with a water drop difference between upstream and downstream water levels lower than 0.7 m and a depth downstream of the weir of higher than 0.3 m can be considered an effective passage situation for barbels. These findings are of interest for quantifying flat-V weir impacts, for engineering applications and for establishing managing or retrofitting actions when required. Full article

Fish need to move upstream and downstream through rivers to complete their life cycles. Despite the fact that fishways are the most commonly applied solution to recover longitudinal connectivity, they are not considered viable for downstream migration. Therefore, alternative facilities are recommended to facilitate downstream migration. However, a few recent studies have disagreed with this general assumption, showing the potential for bidirectional movements. This study advances our understanding of the potential of fishways for downstream migration by studying their efficiency in a run-of-the-river hydropower plant in the Duero River (Spain). To achieve this, downstream movements of the Iberian barbel (n = 299) were monitored in a stepped fishway for two years with passive integrated transponder (PIT)-tag technology, considering the effect of fish origin and release zone. The results showed that 24.9% of barbels descended through the fishway, with the origin and release zone affecting the fishway location. In addition, downstream movements were observed throughout the whole year, except in winter. The study concludes that, under specific scenarios, fishways could act as safe alternative routes for downstream migration. 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

The Iberian barbel (Luciobarbus bocagei) is one of the most common cyprinids in the Iberian Peninsula, whose migratory routes are often hampered by anthropogenic barriers. Fishways might be an effective mitigation measure if they integrate designed operational characteristics that account for the biomechanical requirements of this species. Understanding the flow conditions inside the fishway, and how barbel responds to the hydrodynamics of the flow is imperative to improve free migratory routes with minimum energetic cost associated. Herein, we analyze and synthesize the main findings of research on pool-type fishways for upstream passage of the Iberian barbel and derive recommendations of design criteria for pool-type fishways for this species and others of similar biomechanics capacities. Ultimately, we identify research needs to improve upstream passage of this species. Full article