Iberian Barbel Research Articles

Assessment of Retrofitted Ramped Weirs to Improve Passage of Potamodromous Fish

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.

Passage Performance of Technical Pool-Type Fishways for Potamodromous Cyprinids: Novel Experiences in Semiarid Environments

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.

E-flows to reduce the hydropeaking impacts on the Iberian barbel (Luciobarbus bocagei) habitat. An effectiveness assessment based on the COSH Tool application

Hydropower plant (HPP) operations, in response to variations in market energy demand and electricity production, can generate rapid and frequent fluctuations of discharge in rivers downstream. This phenomenon, termed hydropeaking, may negatively impact fish populations. The present study aims to investigate the effects of hydropeaking on the Iberian barbel (Luciobarbus bocagei) habitat conditions. A two-dimensional (2D) model was used to obtain the habitat suitability downstream of a HPP. The influence of the ecological flow (E-flow) regime on the habitat conditions and flow fluctuations owing to hydropeaking was assessed. COSH-Tool was applied to the sub-daily flow series to quantify and characterize the rapid fluctuations (with and without an E-flow regime) with the purpose of assessing the impacts on fish habitat. The monthly distribution of peaking events showed a marked seasonal pattern associated with the Mediterranean climate, with most of the rapid fluctuations concentrated during the wet season. A peaking event occurred within three days of the low flow period. Approximately 80% of the 10-year time series returned a zero value of discharge (no power production). The median of the rates of stage (water level change during an increase or decrease of flow divided by the time of that change) resulted in 30.7 and 28.3 cm/h when the E-flow regime was not considered, and the rate of change was 26.3 and 22.4 cm/h when the E-flow regime was considered respectively for rapid increases and decreases. The flow ratio (peak flow divided by base flow) obtained for the E-flow regime was 334.3. Results showed that the hydrologic parameters associated with hydropeaking are attenuated with the E-flow regime. In certain cases, the E-flow regime should be regarded as an alternative mitigation measure for rivers subjected to hydropeaking.

Performance of a Pool and Weir Fishway for Iberian Cyprinids Migration: A Case Study

One of the movement barriers that fish populations must overcome for migration success in the upper basin of Tormes river (Salamanca, Spain) is a 20 m high dam. The design of its pool and weir fishway for potamodromous fishes (mostly Iberian barbel—Luciobarbus bocagei—and Northern straight-mouth nase—Pseudochondrostoma duriense) to overcome the obstacle was improved in 2013. The aim of this study was to assess the efficiency of the fishway using FDX passive integrated transponder (PIT)-Tags inserted into the fish and PIT-Tag detection antennas at the fishway. During several sampling events, 7113 barbel and nase individuals were tagged and released at the point of capture along the basin (2538 and 4575 of which were tagged downstream and upstream, respectively). PIT-Tag Detection Antennas close to the top and bottom of the fishway monitored tagged fish continuously for 10 months (from March to December 2017), to analyze the performance of the fishway. Upstream passage efficiency was greater for barbel (60% and 25% for barbel and nase, respectively). Differences in passage efficiency between species may be due to differences in their size. Mean length for barbels attempting to pass was 336 mm (±47 mm) while for nases was 143 mm (±26 mm). Moreover, both the number of attempts to pass and ascend time for nases were higher than for barbels. Entrance efficiency was low (3.5% and 10.8% for barbel and nase, respectively), although 2017 was a very dry year, thus these results are most likely influenced by flow rates. Therefore, the fishway has proved to be functional but is actually poor for efficiency purposes, especially for small fish.

Uncommon hepatic macrophagic foamy-cell nodules in Iberian barbel (Luciobarbus bocagei Steindachner, 1864) from the Vizela River (Portugal).

The main intent of this work (after the by chance finding, in archived histological slides) is to characterize one previously non-described liver lesion of the Iberian barbel from the Vizela River (Portugal). This ran through a textile and dyeing industrial region. The lesion type was made of groups of foamy cells (presumptive macrophages), which appear either as a "smaller non-nodular form," without a connective tissue capsule and displaying an irregular profile, or as a "bigger nodular form," presenting a thin capsule and a circular profile. The nodular forms could appear multi-layered, resembling "cross-sectioned onions". The lesions number, dimension, and structural complexity were greater in bigger fish, appearing only after a history of poor water quality. In extreme cases, the lesions slightly protruded the liver surface. Special histological staining proved the connective tissue nature of the capsule (and its eventual septa), the presence of proteins, glycoproteins, lipofuscin, melanin, iron (putative hemosiderin), and copper, in a variable number of foamy cells within the lesions. At times, degenerating hepatocytes appeared at the border of the lesions. It is proposed that this lesion type incorporates both macrophages and degenerating hepatocytes, looking as one (unpublished) form of a macrophage aggregate. The term "foamy-cell nodules" was advanced for this abnormality. The lesion could have been induced by pollution, because: no parasites were ever associated with the lesion; there was co-existence of the lesion with a water quality status scored as "bad"; such lesion neither existed in fish sampled after mitigation and remediation measures nor in reference fish.

Oxygen Depletion Affects Kinematics and Shoaling Cohesion of Cyprinid Fish

Numerous anthropogenic stressors impact rivers worldwide. Hypoxia, resulting from organic waste releases and eutrophication, occurs very commonly in Mediterranean rivers. Nonetheless, little is known about the effects of deoxygenation on the behavior of Mediterranean freshwater fish. To fill this knowledge gap, we assessed the impact of three different dissolved oxygen levels (normoxia, 48.4%, 16.5% saturation) on kinematics indicators (swimming velocity, acceleration, distance traveled) and shoaling cohesion of adult Iberian barbel, Luciobarbus bocagei, a widespread cyprinid species inhabiting a broad range of lotic and lentic habitats. We conducted flume experiments and video-tracked individual swimming movements of shoals of five fish. Our results reveal significant differences between the treatments regarding kinematics. Swimming velocity, acceleration, and total distance traveled decreased stepwise from the control to each of the two oxygen depletion treatments, whereby the difference between the control and both depletion levels was significant, respectively, but not between the depletion levels themselves. Shoaling cohesion showed dissimilarities between the treatments regarding the maximum distance between fish, as the high depletion treatment differed from each of the other two, indicating that under severe oxygen depletion some individuals move away from the shoal. Overall, our results show how oxygen depletion changes fish behavior, which may entail ecological responses, highlighting the need to maintain an unfragmented river network to ensure movement dispersal among habitats, thus providing conditions for species escapement from hypoxia.

Passage Performance of Potamodromous Cyprinids over an Experimental Low-Head Ramped Weir: The Effect of Ramp Length and Slope

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.

Repulsive Effect of Stroboscopic Light Barriers on Native Salmonid (Salmo trutta) and Cyprinid (Pseudochondrostoma duriense and Luciobarbus bocagei) Species of Iberia

A repulsive effect, that some induced primary stimuli, like sound and light, is known to be provoked in fish behavior. In the present study, two strobe light frequencies, 350 flashes/minute and 600 flashes/minute, were tested in laboratorial conditions, using three native freshwater fish species of northern Portugal: Brown trout (Salmo trutta), Northern straight-mouth nase (Pseudochondrostoma duriense) and Iberian barbel (Luciobarbus bocagei). The results showed a differential repulsive behavior of the fish species to light stimulus, and particularly to a frequency of 600 flashes/minute. S. trutta presented the most repulsive behavior, whereas the L. bocagei showed less repulsion to the light stimulus. No relevant differences were found between pre-test and post-assessments, confirming a rapid recovery of natural fish behavior after the deterrent effect. The results highlighted the potential of behavioral barriers, particularly in salmonid streams, based on strobe light stimulus.

Short-term effects of wildfire ash exposure on behaviour and hepatosomatic condition of a potamodromous cyprinid fish, the Iberian barbel Luciobarbus bocagei (Steindachner, 1864)

Wildfires are a common phenomenon in Mediterranean regions that is becoming increasingly frequent and severe, causing several environmental concerns, of which ash runoff represents an important source of disturbance for aquatic organisms, in particular for fishes. Studies on the behavioural response of fishes to wildfire ash runoff are scarce and seldom include cyprinid species. The goal of this study was to investigate in a 3-artificial flume channel mesocosm, the behavioural and hepatosomatic condition responses of a native widespread potamodromous fish, the Iberian barbel (Luciobarbus bocagei), previously exposed for 24 h to different concentrations of wildfire ashes: 0.0 g/L (the control, no ash), 1.0 g/L (low concentration) and 2.0 g/L (high concentration). Behavioural parameters included i) routine activity, ii) boldness and iii) shoaling cohesion. The hepatosomatic index (HSI) was further determined to assess the health condition of fish. Significant differences on fish behaviour parameters were detected between the control and the high concentration of ash. Accordingly, i) an increasing proportion of fish were found on resting activity (56.2% vs 30.6% in the control), whereas the proportion of fish on searching behaviour (58.4% in the control) decreased (41.5%); ii) the proportion of bolder individuals was found to decrease (42.5% in the control vs. 29.4%) and iii) the same trend was detected for shoaling cohesion (61.3% in the control to 33.8%, of all fish within a body length of each other). Such differences were paralleled by an increase in the HSI from 1.62% (control) to 2.40% (high concentration). The present study shows that even short duration exposure to ash-loaded runoff can alter fish behaviour and hepatosomatic condition and highlights the need to maintain an unfragmented river network, or, when this is not possible, to prioritize the removal or retrofitting of barriers to increase movement dispersal and provide conditions for species recovery from fire-disturbances.

Fish under pressure: Examining behavioural responses of Iberian barbel under simulated hydropeaking with instream structures.

Hydropeaking is the rapid change in the water flow downstream of a hydropower plant, driven by changes in daily electricity demand. These fluctuations may produce negative effects in freshwater fish. To minimize these impacts, previous studies have proposed habitat enhancement structures as potential mitigation measures for salmonids. However, the recommendation of these mitigation measures for cyprinids remains scarce and their effects unknown. In this study, the effects of potential habitat mitigation structures under simulated hydropeaking and base-flow conditions are examined for Iberian barbel (Luciobarbus bocagei) in an indoor flume. Solid triangular pyramids and v-shaped structures were evaluated as potential flow-refuging areas and compared with a configuration without structures. A novel, interdisciplinary approach is applied to investigate individual and group responses to rapidly changing flows, by assessing physiological (glucose and lactate), movement behaviour (structure use, sprints and drifts) and the pressure distribution using a fish-inspired artificial lateral line flow sensor. The major findings of this study are four-fold: 1) Under hydropeaking conditions, the v-shaped structures triggered a lactate response and stimulated individual structure use, whereas solid structures did not elicit physiological adjustments and favoured individual and group structure use. Overall, both solid structures and their absence stimulated sprints and drifts. 2) The hydrodynamic conditions created in hydropeaking did not always reflect increased physiological responses or swimming activity. 3) Each event-structure combination resulted in unique hydrodynamic conditions which were reflected in the different fish responses. 4) The most relevant flow variable measured was the pressure asymmetry, which is caused by the vortex size and shedding frequency of the structures. Considering the non-uniform nature of hydropeaking events, and the observation that the fish responded differently to specific flow event-structure combinations, a diverse set of instream structures should be considered for habitat-based hydropeaking mitigation measures for Iberian barbel.

Cyprinid passage performance in an experimental multislot fishway across distinct seasons

New engineering solutions are required to minimise the effects of an increasing number of anthropogenic barriers on watercourses. Longitudinal connectivity must be provided through fishways to allow free passage for the whole fish community. Recently, a multislot fishway (MSF) was developed, with two consecutive vertical slots that divide the overall head drop by two, thus reducing the flow velocity, the magnitude of turbulence and operational discharge compared with a standard vertical slot fishway (VSF) with similar pool and slot dimensions. The present study assessed the effectiveness of a MSF design for two cyprinid species with different ecological traits, under laboratory conditions, namely the Iberian barbel (Luciobarbus bocagei), a large-bodied potamodromous benthic fish, and the southern Iberian chub (Squalius pyrenaicus), a small-bodied water column fish. Experiments were conducted in a full-scale experimental fishway, in spring and autumn. Results showed differences in passage performance between seasons and species. During spring, chub had a higher entry efficiency and shorter transit time to fully negotiate the fishway, whereas no seasonal differences were found for the barbel. Overall, the MSF could be considered a cost-effective design for cyprinids with different ecological traits because it offers lower operational costs than a standard VSF. However, concerns about the entrance and attraction conditions should be addressed. In addition, because of the lower operational discharge, the propensity for obstruction with woody debris and sediments should not be disregarded.

Spatial preferences of Iberian barbel in a vertical slot fishway under variable hydrodynamic scenarios

Fish require access to multiple habitats to persist. Therefore, obstacles blocking a fish’s volitional ability to move between habitats can lead to its decline. A common way of addressing this problem is the construction of fishways. The design criteria of fishways are based on steady, uniform flows with the assumption that the water levels remain the same across the fishway. However once constructed, fishways are fundamentally dynamic systems exhibiting different hydrodynamic scenarios. These scenarios are classified as uniform and non-uniform water level profiles and are driven by changes in the up- and downstream water levels caused by operational and hydrological variability.In this paper, we demonstrate the need to consider a wider range of fishway hydrodynamic scenarios for an integral assessment of fishways. To do this, the spatial distribution of Iberian barbel (Luciobarbus bocagei) in a full-scale model of a vertical slot fishway under three different hydrodynamic scenarios is investigated. Video tracking was used to analyze the fish’s spatial distribution, and an acoustic Doppler velocimeter and lateral line probe were applied to characterize the local hydrodynamic conditions of each scenario. Spatial differences were tested using Syrjala's test and the relation with hydrodynamic variables analyzed by means of zero-inflated Poisson models. This study revealed three significant findings: 1) Fish made broader use of the fishway pool in scenarios with lower water drops, which are highly correlated with regions of overall lower turbulence and velocity magnitude. 2) The relative importance of physical variables varied between scenarios. Specifically, the protection offered by walls was found to be a determining factor in the spatial usage. 3) It is shown that a vertical slot fishway designed with the standard dimensions for fish passage under the assumption of uniform flow conditions may result in an adverse hydrodynamic environment for fish swimming under non-uniform conditions.

The potential of lateral refuges for Iberian barbel under simulated hydropeaking conditions

Fish responses to hydropeaking may range from sub-organismal adjustments to key life-event changes. It is currently difficult to quantify these responses and to assess the potential of artificial refuges accordingly. To address this problem, two experimental trials were conducted in an indoor flume. In the first, two hydropeaking events were tested in the presence of deflectors as flow refuges. In the second, the presence and absence of deflectors was tested for the same hydropeaking event. A multidisciplinary approach combined physiological and movement behaviour responses of Iberian barbel (Luciobarbus bocagei) with hydrodynamic models. These were used as a complementary tool to explain the fish responses. In the first experiment, no evident physiological adjustments occurred. However, individual refuge use and swimming activity were higher in the single-step event where velocities above 0.6 m.s−1 were observed. In the second experiment, the levels of glucose were the highest in the repeated single-step event with deflectors, whereas in their absence no visible changes were observed. The sequence of discharges affected the frequency of individual sprints and group drifts, particularly evident with deflectors. Additionally, the deflector use increased in the first peak in opposition to the second. Overall, the fish responses were indicative that the low velocity areas (<0.1 m.s−1) existing behind the deflectors were favourable under hydropeaking conditions. However, the flow complexity resulting from the presence of deflectors impaired their ability to successfully find them. The integrated approach used in this study provided novel insight considering the responses of cyprinids to hydropeaking in the presence and absence of deflectors as a mitigation measure. This study emphasized the importance of characterizing the hydrodynamic conditions due to hydropeaking, particularly after including the artificial refuges.

Vertical slot versus submerged notch with bottom orifice: Looking for the best technical fishway type for Mediterranean barbels

When engineers and ecologists face a fishway design, many issues need to be considered, the type of fishway being the first and foremost. It is an especially complex issue in areas with species whose migratory and swimming behavior are as yet poorly known as Mediterranean barbels. The present study focuses on the fish passage of two of the most common types of technical fishways: Vertical Slot (VS), and Submerged Notch with Bottom Orifice (SNBO). Both types were studied and compared in terms of ascent ability (as the success rate and transit time) and motivation (as the proportion of attempts and attempt rate), with Iberian barbel (Luciobarbus bocagei) as the target species.Ascent ability in VS and SNBO were similar. More than 90% of fish ascended the fishways successfully and the median transit time to ascend a total water height of 2.25 m was less than 23 min. Fish length had an effect on ascent time, with the biggest ones being faster. Motivation was greater for VS, although not seeming to have a relevant influence in the passage.These results support the use of VS and SNBO in areas with Iberian barbel and provide new data of fishways performance helping ecologists and engineers with their decision making, mainly in Mediterranean areas with similar habitats and species.

Do artificial velocity refuges mitigate the physiological and behavioural consequences of hydropeaking on a freshwater Iberian cyprinid?

AbstractThe rapid flow fluctuations experienced downstream of hydropeaking facilities can alter the river hydromorphology. Given the dependence of riverine fish on physical habitat, those alterations have the potential to change the physiology and behaviour of fish. We assessed whether artificial velocity refuges mitigated the physiological and behavioural consequences of hydropeaking for the Iberian barbel (Luciobarbus bocagei). Hydropeaking trials were conducted in an indoor flume equipped with deflectors that created low flow velocity areas to serve as refuges. The FLOW‐3D was used to obtain detailed characterizations of the different velocity fields, which facilitated the interpretation of fish responses. Changes in flow magnitude and duration triggered stress responses, demonstrated by the increased blood glucose levels in the single up‐ramping event for 60 L s−1and in the step up‐ramping event. Fish tended to seek out velocity refuges to avoid higher flow velocities and harsh hydraulic conditions at peak flows, and during the longer events. The movement behaviour frequency increased when fish were subjected to the highest peak flow (60 L s−1), particularly the individual sprints and the drifts. For the base flow (7 L s−1) and the lowest peak flow (20 L s−1) conditions, fish swam freely in the flume, whereas in the harshest hydraulic conditions they showed more difficulty in finding velocity refuges. This research presents a novel approach by combining physiology and behavioural observations with hydraulic modelling to assess the extent to which artificial flow refuges mitigate the consequences of hydropeaking. Our work serves as a model approach for future mitigation studies for fish in hydropeaking rivers.

Fulfilling spawning flow requirements for potamodromous cyprinids in a restored river segment

The Baixo Sabor hydroelectric scheme was recently constructed (began operating in 2015), blocking fish migration immediately at the river mouth. As a compensation measure for spawning habitat loss the Vilariça River which confluences with Sabor River, immediately downstream from the Baixo Sabor scheme, was chosen for rehabilitation site as an attempt to replace the spawning grounds lost in Sabor River for the potamodromous cyprinid Iberian barbel (Luciobarbus bocagei). Restoration activities included: placement of submerged weirs with fish ramps to increase the lotic/lentic sequence, bank reinforcement, boulder placement and river water profile increase. Water from the nearest reservoir was channeled underground to the lower Vilariça River in order to increase the water flow. The most appropriate volume of water was determined by means of a 1D model coupled with the CASiMiR to determine the weighted usable area for barbel spawners. Nine spawning grounds were identified. Fish migrations began in mid-April when water temperature increased (c. 16°C) and water flow decreased. Barbel tend to spawn in coarse substrate with shallow water and moderate current. Ontogenetic differences in habitat use were reported, with barbel juveniles preferring weaker currents and deeper zones when compared to spawners. Females also display different preferences, which are more apparent after spawning. Both life-stages exhibit the maximum habitat suitability at c. 1.5m3/s. The habitat model used in this study was able to accurately predict the occurrence of spawning grounds, representing, therefore, a valuable decision-making support tool for river managers.

How Does Season Affect Passage Performance and Fatigue of Potamodromous Cyprinids? An Experimental Approach in a Vertical Slot Fishway

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.

Effectiveness of a multi-slot vertical slot fishway versus a standard vertical slot fishway for potamodromous cyprinids

Developing and testing new fishway designs is important to improve these facilities. Discharge-efficient passage systems are required in Mediterranean regions and other areas with dry climates. The present study compares the passage performance of the Iberian barbel, Luciobarbus bocagei (Steindachner, 1864), a potamodromous cyprinid, negotiating two different types of vertical slot fishways (VSF): a standard VSF and a multi-slot VSF (MSF). Results show that differences exist between configurations in the number of fish movements through the first slot. The I. barbel performed a significantly higher number of movements in the MSF. However, no differences were found in the entrance time and entry efficiency. The performance was similar between configurations in terms of successes, suggesting that both fishways could be used to restore longitudinal connectivity. Nevertheless, the MSF is a more discharge-efficient configuration, since it requires 31% less water to operate for the same water depth in the pools. Consequently, the velocity and turbulence have lower magnitudes which generally favour the negotiation by smaller individuals. Since it is a more discharge-efficient and cost-efficient configuration, future studies should focus on the passage performance of smaller species to determine if MSF is a useful solution for the whole fish community.

The effect of weir crest width and discharge on passage performance of a potamodromous cyprinid

Contrary to the vast literature on dams, much less is known about the effects of small weirs on fish movements. This study aims to evaluate the upstream and downstream passage of the Iberian barbel (Luciobarbus bocagei), when facing a small broad-crested experimental weir with varying widths of the weir crest (W) and discharges (Q). Nine configurations (W×Q) were tested. Fish were released downstream of the weir and upstream and downstream passages were monitored. Hydrodynamics were characterised with a flow probe and a three-dimensional acoustic Doppler velocimeter (ADV). Fish negotiated all configurations, registering a total of 273 upstream passages and 192 downstream passages. The number of fish that approached, attempted and successfully ascended and descended the weir varied among configurations, emphasising the complex influence of factors on passage performance. Discharge was preponderant on both passages, proving that fish movements may be hampered by increasing discharges. However, the width of the weir crest only significantly influenced downstream passages, showing that strong velocity gradients experienced on narrower widths of the weir crest may discourage downstream movements. Results from the present study are expected to be useful to identify potential migration obstacles and may be applicable to other cyprinid species.

To swim or to jump? Passage behaviour of a potamodromous cyprinid over an experimental broad‐crested weir

AbstractPhysical stressors, such as man‐made obstacles, are considered one of the main causes that negatively affect freshwater fish. Even small weirs may impact fish populations, including potamodromous cyprinids, by partially or totally blocking upstream migratory movements. Some studies have addressed the effect of key hydraulic parameters on upstream movements past small weirs, but little is known on how these parameters interact to induce swimming or jumping behaviour in negotiating such obstacles. This study aims to evaluate the passage behaviour (swimming vs. jumping) of Iberian barbel (Luciobarbus bocagei), a potamodromous species, over an experimental small broad‐crested weir, considering the effect of different plunge pool depths (D), waterfall heights (H), and weir discharges (Q). Results revealed that passage behaviour was highly dependent on combinations of plunge pool depths and waterfall heights. Barbel navigated most configurations by swimming (overall outcomes: 81.5% swimming vs. 18.5% jumping), except the ones with the higher waterfall heights (25 cm) tested. Therefore, higher waterfalls proved to be preponderant in the switching of passage behaviour from swimming to jumping. Regarding the discharge over the 1‐m‐wide weir (overall outcomes: 85% swimming vs. 15% jumping), contrary to what was expected, there was no evidence that passage behaviour was discharge‐related, for the range of discharges tested (25–100 L/s). These results are useful to identify potential migration obstacles and should be taken into consideration in river restoration projects and when designing fishways for potamodromous cyprinids.