Fish Passage Solutions Research Articles

Coastal river connectivity and the distribution of ascending juvenile European eel (Anguilla anguilla L.): Implications for conservation strategies regarding fish‐passage solutions

Abstract Many diadromous fish populations are declining and at risk of collapse. Lack of river connectivity is a major contributor to these declines, as free migration routes between marine and freshwater habitats are crucial for life‐history completion. For the conservation and ultimately recovery of such species, it is imperative that remedial measures aimed at increasing connectivity are effective. This study investigated the distribution patterns of ascending juvenile European eel (Anguilla anguilla L.) in rivers in south‐western Sweden, with a focus on the effects of barriers and measures that aim to reduce the impact of barriers, i.e. fish‐passage solutions (FPSs). Eel occurrence data were spatially and temporally integrated with the national databases of dams and FPSs in a Geographic Information System (GIS) environment to evaluate their effect on ascending eel distribution. The types of barriers assessed were: (i) dams with nature‐like fishways; (ii) dams with eel ramps; (iii) dams with technical fishways; and (iv) dams without FPSs. Dams fitted with eel ramps or technical fishways, as well as dams without FPSs, produced a significant negative effect on the probability of eel occurrence upstream. This negative effect was not found for dams fitted with nature‐like fishways, indicating that these solutions may function better than the other FPS types in this study. The probability of eel occurrence decreased with distance from the sea and increased with area sampled, number of electrofishing runs, water temperature, and with the size of the bottom substrate. We suggest that future conservation strategies for improving the natural immigration of juvenile eels should include optimizing FPS function (e.g. placement and design), the continued maintenance of FPSs, the construction of nature‐like fishways, and preferably the removal of dams, which will also benefit the downstream migration of maturing eels as well as restoring other ecosystem services.

Living in an amphidromous world: Perspectives on the management of fish passage from an island nation

Abstract Amphidromy is a form of migratory life history typified by the reproduction of fish in freshwater environments, the early downstream dispersal of post‐hatch larvae to marine environments, and the return of small‐bodied young juveniles to freshwater environments for growth to adulthood. Island freshwater fish communities are frequently dominated by fish species with amphidromous life histories. Amphidromous life cycles leave fish communities highly susceptible to habitat modification and disruptions to connectivity across marine and freshwater environments. This means that managing waterway connectivity is fundamental to their conservation; however, the unique and often geographically restricted amphidromous communities that characterize many small island nations have received little consideration in the development of strategies for the management of fish passage. The ecology and locomotory capabilities of amphidromous species are often poorly studied, partly because their small size at migratory life stages renders current state‐of‐the‐art in situ biotelemetry methods unsuitable. The small size of fish also means that seemingly small obstructions can severely impede migrations. The steps necessary to advance the management of fish passage for island fish communities are: curating and maintaining barrier inventories; evaluating barrier permeability; developing effective barrier mitigation options; and prioritizing restoration and conservation efforts. New methods for understanding the ecology and locomotory capabilities and behaviour of amphidromous fishes are required to advance the management of fish passage for island fish communities. Fish passage solutions that imitate natural streams, such as those promoted in new guidelines in New Zealand, may be the most effective way of improving waterway connectivity; however, integrated approaches to freshwater fish conservation that account for meta‐population dynamics, in combination with the management of fish passage, are necessary to optimize conservation outcomes for amphidromous species.

Comparison of coarse‐resolution rapid methods for assessing fish passage at riverine barriers: ICE and SNIFFER protocols

AbstractMan‐made barriers have led to river fragmentation, restricting fish migrations to critical habitat. Fragmentation is relevant to the Water Framework and Habitats (Annex II fish) Directives of the European Union. SNIFFER (Water Framework Directive 111) is a United Kingdom‐developed fish passability assessment method with passability scores based on published data describing the physiological abilities of different fish species/life stages. SNIFFER is an objective protocol, but final scores require assessor opinion on specific nonquantified elements. The French ICE fish passability assessment protocol covers a larger number of fish species/life stages and removes the requirement for velocity readings (except in a few situations) and expert opinion with assessors following a decision tree process. In most situations, fewer direct measurements are required for the ICE protocol, and the evaluation process is quicker and simpler. Both protocols utilize a similar passability scoring system (0 = total barrier, 0.3 = high impact, 0.6 = low impact, 1 = no risk). Comparison of outcomes for species categories for both protocols was made in paired comparisons for 112 transversal sections (fish passage routes) recorded at 52 barriers (in‐river structures) of varying complexity in Irish rivers. Overall scores were found to be in high agreement for species groups at impassable (Score 0) and no risk (Score 1) barriers. Protocol agreement dropped significantly for high‐impact (Score 0.3) and low‐impact (Score 0.6) barriers. Results are discussed in the context of barrier passability at the 52 structures examined, primarily in the context of Atlantic salmon (Salmo salar L.) and of sea lamprey (Petromyzon marinus L.). In total, 22 of the structures had one or more fishways or fish passage solutions built into them as part of the original design. Both protocols identified substantial problems for sea lamprey and adult salmon at the majority of the fish passage solutions surveyed. The merits and shortcomings of both protocols, for managers assessing fish passability at complex riverine structures, are discussed.

Upstream movement of river lamprey through a culvert retrofitted with spoiler baffles under experimental conditions

ABSTARCTCulverts used to convey river water under roads and embankments are one of the most common small-scale barriers to longitudinal fish movements worldwide. Using an open channel flume, this study assessed the ability of upstream migrating adult river lamprey (Lampetra fluviatilis) to ascend a pipe culvert when unmodified (control [C]) and retrofitted with spoiler baffles (treatment [T]) under three flow regimes (low discharge [L], high discharge [H] and high discharge with a raised downstream water level [HD]). Few lamprey attempted to ascend the culvert under low (11%) and high (21%) discharge in both the control and the treatments. Despite a greater percentage attempting to pass (75%) under HD, they frequently failed. Contrary to our predictions, upstream progress was impeded by the spoiler baffles and may reflect low motivation or avoidance of the physical and/or hydraulic conditions encountered. This study emphasizes the need to better understand the factors influencing the behaviour and motivation of fish as they ascend fish passage structures, and of the importance of reporting negative results as fish passage solutions that are promising for some species may be ineffective for others.

An angled rack with a bypass and a nature-like fishway pass Atlantic salmon smolts downstream at a hydropower dam

Hydropower dams disrupt longitudinal connectivity and cause fragmentation of river systems, which has led to declines in migratory fish species. Atlantic salmon smolts rely on intact longitudinal connectivity to move downstream from rearing habitats in freshwater to feeding grounds at sea. Smolts often suffer increased mortality and delays when they encounter hydropower plants during their downstream migration. Currently, there are few examples of downstream passage solutions that allow safe and timely passage. We assessed the performance of two passage solutions at a hydropower dam, namely, an angled 15-mm rack with a bypass and a large nature-like fishway. The performance of these new fish passage solutions was evaluated by tracking radio-tagged Atlantic salmon smolts as they encountered the facilities. The radio-tagged smolts passed the dam 9.5h after release (median) and exhibited a dam-passage efficiency of 84%, with passage rates increasing with body length. Fish passage occurred through both the rack bypass and the nature-like fishway. The passage efficiencies were 70–95% for the rack bypass and 47% for the nature-like fisway. The new fish passage facilities resulted in improved passage conditions at the site, confirming that angled racks with bypasses as best-practise solutions for downstream passage, but also that large nature-like fishways may act as downstream passage routes for salmon.

Improving Upstream and Downstream Fish Passage at Retis Dam on Hârtibaciu River - Sibiu County (Transylvania)

Abstract Retis (dam Retis), hydro-technical development like many other transverse hydraulic structures cancel the longitudinal connectivity of Hârtibaciu water course, blocking the migration of different (migrating) species of fish in the river. Also, the lateral connectivity was heavily affected on this water course at a rate of 60%. Therefore, proposing engineering solutions to recover both (lateral and longitudinal) types of connectivity is vital to restore the local ecobiom. The purpose of this article is to establish longitudinal connectivity through an engineering solution that facilitates the fish migration upstream - downstream of Retis dam. This paper proposes an engineered fish passage solution for Retiș Dam on the Hârtibaciu River, using the criteria described in the Water Framework Directive 2000/60/EC document. Anthropogenic barriers located in the Hârtibaciu River disrupt and delay movement of local fish fauna including: Alburnoides bipunctatus (Bloch, 1782), Squalius cephalus (Linnaeus, 1758), Alburnus alburnus (Linnaeus, 1758), Rhodeus amarus (Bloch, 1782), Gobio gobio (Linnaeus, 1758), Romanogobio kessleri (Dybowski, 1862), Barbatula barbatula (Linnaeus, 1758), Barbus meridionalis Risso, 1827 Misgurnus fossilis (Linnaeus, 1758), Cobitis taenia Linnaeus, 1758, Cobitis romanica (Băcescu, 1943), and Cobitis aurata (De Filippi, 1863).

Intake Approach and Dam Passage by Downstream‐migrating Atlantic Salmon Kelts

AbstractsStudying fish behaviour at hydropower dams is needed to facilitate the design and improvement of fish passage solutions, but few studies have focused on Atlantic salmon kelts. Here, we used radio telemetry (n = 40, size range = 50–81 cm) and acoustic sonar to study kelt movements in the forebay as well as their dam passage survival and subsequent migration success past multiple dams. We also compare radio telemetry and acoustic sonar observations of fish behaviour and used acoustic sonar to measure the depth distribution of fish approaching the turbine intake zone. Passage success at the dam was 41%, and mortality was largely associated with turbine passage (62%). The two fish that passed via the spill gates survived and continued their downstream migration. At the dam, all but one radio‐tagged kelt approached the intake zone shortly after arrival to the forebay, and sonar data showed that approaching fish were predominantly surface oriented (72%, 88% and 96% of the observations were less than 1, 2 and 3 m deep, respectively). Turbine passage rate from the intake zone was higher at night than at day, indicating that the lack of visual cues may reduce the barrier effect of the 70‐mm conventional trash rack. Turbine passage rate also increased with increasing hydropower generation. The percentage of observed upstream movements away from the intake zone compared with the total number of observations was considerably greater in the radio telemetry data (41%) than in the sonar data (4%). Only one fish survived passage of all eight hydropower dams to reach the lake. This low‐passage survival underscores the need for remedial measures to increase the survival of migrating kelts, and the fish's surface orientation as well as their rapid approach to the intake rack should be taken into account when designing such measures. Copyright © 2017 John Wiley & Sons, Ltd.

Response of seaward-migrating European eel (Anguilla anguilla) to manipulated flow fields.

Anthropogenic structures (e.g. weirs and dams) fragment river networks and restrict the movement of migratory fish. Poor understanding of behavioural response to hydrodynamic cues at structures currently limits the development of effective barrier mitigation measures. This study aimed to assess the effect of flow constriction and associated flow patterns on eel behaviour during downstream migration. In a field experiment, we tracked the movements of 40 tagged adult European eels (Anguilla anguilla) through the forebay of a redundant hydropower intake under two manipulated hydrodynamic treatments. Interrogation of fish trajectories in relation to measured and modelled water velocities provided new insights into behaviour, fundamental for developing passage technologies for this endangered species. Eels rarely followed direct routes through the site. Initially, fish aligned with streamlines near the channel banks and approached the intake semi-passively. A switch to more energetically costly avoidance behaviours occurred on encountering constricted flow, prior to physical contact with structures. Under high water velocity gradients, fish then tended to escape rapidly back upstream, whereas exploratory ‘search’ behaviour was common when acceleration was low. This study highlights the importance of hydrodynamics in informing eel behaviour. This offers potential to develop behavioural guidance, improve fish passage solutions and enhance traditional physical screening.

Design and assessment of weirs for fish passage under drowned conditions

In aquatic systems, in-stream structures such as dams, weirs and road crossings can act as barriers to fish movement along waterways. There is a growing array of technological fish-pass solutions for the movement of fish across large structures such as weirs and dams. However, most existing weir structures lack dedicated fishways, and fish often have to rely on drowned conditions to move upstream.In order to assess the adequacy of a given or proposed weir for upstream fish passage under drowned conditions, it is necessary to determine, firstly, the hydraulic properties of the drowned weir with respect to the requirements of the fish community and, secondly, the duration and timing of drowning flows with respect to the hydrograph for the site and the likely timing of fish movements. This paper primarily addresses the first issue.A computer program has been developed and incorporated in a simple-to-operate spreadsheet for the determination of the hydraulic characteristics of a drowned weir which are important to fish movement. The program is based on a theoretical analysis of drowned weirs and subsequent extensive verification in laboratory experiments. Inputs to the program include site information comprising channel cross-section data, channel slope, and channel roughness, and weir information comprising weir height and the required minimum drowned depth over the weir for migrating fish passage. The program then calculates the flow rate at which the required level of drowning occurs, the velocity characteristics above the weir (including transverse distributions), and flow depths and velocities upstream and downstream of the weir.The paper discusses (briefly) the theoretical background of the program and its experimental verification. A case study is then presented that illustrates the use of the program in the field to assess fish passage opportunities at an existing weir and to develop a case for retrofitting a fishway. Some discussion is also provided on the contribution of a modelled drownout volume to the assessment of how significant a barrier a weir is to fish passage. It is shown that the program is an important new additional tool in the assessment of the adequacy of weir structures in providing for fish movement and informing associated fish passage solutions.