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Cyprinid fish play a major role in riverine ecosystems because of their high abundance, variety of life-history patterns, and habitat requirements. The nase (Chondrostoma nasus) is an algivorous, rheophilic, lithophilic, and oxyphilic species and is very pollution-sensitive. Thus, it represents a good indicator for habitat quality in the lower rhithral and upper potamal zones of the European river system. Due to its high level of ecological requirements, the species is very sensitive to human disturbance, leading to habitat loss and river fragmentation, climatic disruption causing a modification of hydrological and thermal regimes, organic and inorganic chemical water pollution, as well as sediment deposition. Its populations are declining in most of its distribution areas. This paper aims to synthesise the scientific knowledge on the different aspects of the nase ecology thanks to consultation of the scientific literature by addressing the following themes: European repartition, morphology and identification, reproduction and life cycle, diet, movement dynamics of adults and juveniles, and the characteristics of spawning grounds and habitats of juveniles and adults. We also provide an overview of the impact of human activities and climate shifts on natural ecology and conservation and present restoration measures based on the results of some studies that have successfully improved their habitats and/or preserved their populations. A series of key research questions are identified that should stimulate new research on this species as well as conservation measures for sustainable conservation. This paper may be particularly of interest to researchers in aquatic and fisheries sciences, river managers, and environmental conservationists. [ABSTRACT FROM AUTHOR]

The temporal dynamic use of newly installed fishways after a reopening event is not well known as most studies are not performed just after the opening and are generally limited to a single season or year. We carried out monitoring of three fishways for several consecutive years on three rivers in Belgium from the date of their opening. To identify the colonisation dynamics of fish species, we analysed temporal patterns in specific diversity, abundance, biomass, and associated environmental conditions. We detected different capture peaks and the appearance of new species several years after opening the migratory axis (up to 8 years post-opening). The dynamic of colonization showed that the same species may migrate earlier or later depending on the river. The analysis of the periodicity of capture indicated that some species made movements throughout the year while others at more precise periods. Moreover, the periodicity of movements was either stable or fluctuating over the year of monitoring, depending on the species. Our results highlight the importance of long-term monitoring to detect temporal dynamics in fish colonisation, allowing to improve our understanding of the opening effect of a migratory axis.

Mitigation measures for downstream-migrating Atlantic salmon smolts (Salmo salar L.) are commonly insufficiently attractive to enable safe entrance and passage with no delay. Combining 2D telemetry with hydrodynamic modelling has been shown to be a good tool to better understand the influence of hydrodynamic factors on the migration route choice of fishes. In this study, we investigated the smolt downstream migration at a hydropower plant in Belgium that offers five migration routes, including two Archimedes screws and one nature-like fishway. At the hydropower plant, the Archimedes screws were the most used migration routes, due to higher discharges and more important water depths at their entrance. The weir and the canal intake were less used by the smolts. The nature-like fishway turned out to be less used, with 23% of the smolts. Its associated crossing time was significantly longer, probably due to shallow water depths and high flow velocities. The nature-like fishway had the potential to become a good migration route for salmon smolts after improvements to increase attractiveness and passage efficiency. Moreover, the Archimedes screws were not detrimental to the smolts and did not cause any significant delays to the crossing time. [ABSTRACT FROM AUTHOR]

Dam construction and streamflow regulation are increasing throughout the world, with impacts in impounded aquatic ecosystems. Hydropower dams, some of them causing a phenomenon called "hydropeaking" during their operation, are known for having a variety of impacts on downstream aquatic biota, particularly fish, and respective habitat. This can result in significant changes, from the community (e.g., fish assemblage structure) to the individual level (e.g., physiological and behavioural adjustments). Researchers and managers involved in the assessment of hydropeaking impacts must be resourceful and use methods that allow their precise evaluation, from large to fine‐scale habitat and biological responses. In the last decades, technological advances allowed for the development of techniques and instrumentations that are increasingly being used in hydropeaking impact and mitigation assessments. This paper aims to provide a review, to researchers and managers interested in this field, of some of the most innovative methods and techniques, involving technology, that are available to study hydropeaking effects on downstream ecosystem, particularly from a fish perspective. We discuss the fundamentals behind such techniques, their advantages, and disadvantages, while also providing practical examples of their application and of the type of results that can be obtained. We finish by discussing some of the shortcomings of these methods and how related technology can evolve to solve current limitations. [ABSTRACT FROM AUTHOR]

The upstream migratory behaviour of yellow-phase European eels was investigated in regulated inland rivers (>320 km upstream the sea), where the stock is in drastic decline. From 2010 to 2015, eels entering the Belgian Meuse River (n = 1357; total length, 231–755 mm) were caught in fish passes, tagged with a pit-tag and released. Their upstream movements were tracked during the next six consecutive years, using three detection stations installed in vertical-slot fish passes of the Meuse and its Ourthe tributary. Among the 1357 eels tagged, 27.6% (n = 374 individuals) were detected at one or more of the three upstream detection stations. Only 6.6% (n = 89) of tagged eels were detected at the two subsequent stations. In this last group, most of the detected eels continued to move upstream through the Meuse rather than leaving it for the Ourthe. Water temperature >13 °C, river flow 24–226 m3/s, dark time 00:00–05:00 h and the spring–summer seasons were the most important cues for upstream migration. Temperatures and flows at detection did not differ between size classes of ascending eels, while the detection period was earlier and daily speed was faster in large (>450 mm) eels. However, small (≤300 mm) eels moved further upstream at slow speeds because they alternated between short periods of movement and long stationary periods. This behaviour suggests the existence of a few nomad individuals and probably more home range dwellers in the entering population. Small eels were better suited to colonise upper rivers.

The succession of migration barriers and different turbine types during downstream migration impede Atlantic salmon (Salmo salar L.) smolts from reaching the sea in time but is poorly studied. We investigated the isolated and cumulative impacts of 14 consecutive migration barriers (MBs) on downstream migration of 200 radio‐tagged smolts over an 18.9 km stretch of gravel‐bed river, by equipping five MBs with automated radio listening stations. At the level of isolated barriers, median research times (i.e. time between the first and the last detection upstream of a MB) varied between 0.1 and 0.7 h. The median crossing delays (i.e. time between the first detection upstream and the first detection downstream of a MB) varied between 1 and 2.9 h. Considering successive MBs, median cumulative crossing delays varied between 2.6 and 32.1 h and increased with the number of MBs. We observed a global mortality rate between 33% and 76%, increasing with the distance travelled and the associated number of MBs. Only 48% of the migrating smolts reached the end of the studied river stretch. Results suggest that the dynamics of the smolt downstream migration over this short highly fragmented stretch had a significant effect in terms of delays, mortalities and seaward escapement rate. [ABSTRACT FROM AUTHOR]

Abstract: Throughout their lives, fish accomplish frequent movements between functional habitats that are often triggered by environmental signals. We aimed to determine if rheophilic cyprinids (barbel, Barbus barbus and chub Squalius cephalus), living in different places of the same river basin, may develop similar movement periodicities and react identically to environmental cues to carry out their spawning migration. We used the capture data of three modern fish passes that were monitored continuously during three consecutive years (2010 to 2012) in three rivers of the Meuse basin in Belgium. We captured 418 individuals at adult stage, and the capture number per species was greater (80%) in spring (during the spawning migration period). The spawning migration of the barbel occurred earlier (median = 122nd day of the year) and at lower temperatures (median = 14.5°C) in the lowland rivers compared to the upland river (140th day of the year and 18.4°C). For the barbel, migration initiation differed depending on the river but finished under similar environmental conditions. In contrast, for the chub, no significant difference between rivers was observed regarding spawning migration periodicity and environmental cues. Within the same river basin, rheophilic cyprinids demonstrate flexibility in their responses to environmental variables and may optimise the start date of migration to spawning grounds depending on their local environment and individual experiences. This phenomenon was more pronounced in the barbel, which has more specific ecological requirements. [ABSTRACT FROM AUTHOR]

The decline of the patrimonial rheophilic nase, Chondrostoma nasus (Linnaeus, 1758) populations was mainly caused by construction of dams and hydroelectric power-plants, together with the straightening and artificialization of the river banks and water pollution. In this study, we tested the hypothesis whether the translocation of few adult nase individuals from a river stretch to another upstream may be a credible way to accelerate the recolonization process of the species in the amblève river (Southern Belgium). In February and March 2011, just before their spawning period, eight adult nases (462-509 mm; 1546-2002 g; presumed males and females) were captured in the lower part of the river amblève. Fin clip samples were stored in alcohol for further genetic analysis. They were equipped with a 14 g radio transmitter and translocated upstream in a 18 km river stretch, where the species had disappeared since decades due to river anthropization. They were manually located two to five times/week using mobile receivers until maximum June 2012 (n = 977 locations). River temperature and flow were hourly recorded during the entire tracking period. The tagged nase individuals displayed various mobility patterns, exploited different areas of the river stretch, occupied longitudinal home ranges from 3.4 to 36.1 km (one individual finally left the new river stretch) and travelled total distances from 12.2 to 186.6 km. The tagged individuals were most of the times apart from one to another, but most individuals grouped together in potential spawning areas in late March-early april 2011, suggesting an attempt to reproduce. In September 2011, electric fishing in two potential detected spawning sites allowed to capture 16 juvenile (0+) nases, demonstrating the existence of spawning activity in the newly occupied river stretch. Individual genetic characterization was performed in 2014 in order to reveal a possible direct lineage between juveniles and adults. Allelic distribution of 22 microsatellite markers unambiguously identified the 16 juveniles as full-sib progeny descending from two of the translocated adults. This demonstrated that the adult nases succeeded to find spawning areas and that progeny found raised-up from the translocated individuals. [ABSTRACT FROM AUTHOR]