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See detailA complete check-up of European eel after eight years of restocking in an upland river: Trends in growth, lipid content, sex ratio and health status
Nzau Matondo, Billy ULiege; Delrez, Natacha ULiege; Bardonnet, Agnès et al

in Science of the Total Environment (2022), 807

By combining field research and careful laboratory analysis of samples over the course of an eight-year study, we met the challenge of assessing the life history traits and health status of eels restocked ... [more ▼]

By combining field research and careful laboratory analysis of samples over the course of an eight-year study, we met the challenge of assessing the life history traits and health status of eels restocked in freshwater ecosystems. We found that restocked eels exhibited good growth performance; moreover, the stocks were femaledominated, showed a good Fulton's condition factor (K) and lipid stores and had high survival probability estimated using the best model of Jolly-Seber stock assessment method for open populations. A necropsy revealed the absence of internal lesions. A swimbladder examination revealed the absence of the parasite Anguillicola crassus. Polymerase chain reaction (PCR) analyses revealed an increase of Anguillid herpesvirus-1 (AngHV-1) prevalence throughout the study. Most positive subjects expressed viral loads compatible with a latent infection and correlated positively with K. All restocked eels were contaminated by at least one of the organic pollutant congeners studied, but the pollution loads corresponded to the lowest range of pollutant concentrations reported in the available literature for European eels and did not exceed the maximum residue and contaminant limits in food and feed of several national and international regulations. Pollutant loads were negatively correlated with K, lipid content and eel density for polychlorinated biphenyls PCB 138, 153 and 180 and K for pesticides p.p’- DDE, p.p’-DDD, p.p’-DDT and PBDE47. This study highlights the potential role played by upland aquaticecosystems in enhancing riverine silver eel production from the perspective of species conservation. To be successful, restocking must be accompanied by improved ecosystem quality and migration routes for eels in inland freshwaters. We also provide some recommendations for future research to improve the management of restocking programmes. [less ▲]

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See detailMigration behaviour of Atlantic salmon smolts (Salmo salar L.) in a short and highly fragmented gravel-bed river stretch
Renardy, Séverine ULiege; Colson, Dylan; Benitez, Jean-Philippe ULiege et al

in Ecology of Freshwater Fish (2021)

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 ... [more ▼]

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. [less ▲]

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See detailEvaluation de la qualité biologique des rivières wallonnes sur base des indices biologiques poissons. Rapport final 2021
Dierckx, Arnaud ULiege; Benitez, Jean-Philippe ULiege; Renardy, Séverine ULiege et al

Report (2021)

Ce document reprend les informations recueillies dans le cadre d’un travail effectué par l’Université de Liège pour le compte du Service public de Wallonie-DEMNA et financé dans le cadre d’un marché ... [more ▼]

Ce document reprend les informations recueillies dans le cadre d’un travail effectué par l’Université de Liège pour le compte du Service public de Wallonie-DEMNA et financé dans le cadre d’un marché public de services qui a pour objectif l’évaluation de la qualité biologique des eaux de surface basée sur les indices biologiques « poissons » dans huit cours d’eau de Wallonie. [less ▲]

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See detailTrying to choose the less bad route: Individual migratory behaviour of Atlantic salmon smolts (Salmo salar L.) approaching a bifurcation between a hydropower station and a navigation canal
Renardy, Séverine ULiege; Takriet, Abderrahmane ULiege; Benitez, Jean-Philippe ULiege et al

in Ecological Engineering (2021), 169

Contrary to small- and medium-sized rivers, little attention has been paid to the downstream migration of Atlantic salmon smolts in large-sized rivers and the size-related impact of hydropower stations ... [more ▼]

Contrary to small- and medium-sized rivers, little attention has been paid to the downstream migration of Atlantic salmon smolts in large-sized rivers and the size-related impact of hydropower stations. From 2014 to 2016, we investigated the downstream migration of n=72 acoustic-tagged smolts in the Meuse river at a bifurcation zone between a hydropower station equipped with three Kaplan turbines and a navigation canal. A hydrodynamic model that solves the depth-integrated shallow water equations on a Cartesian grid using a finite volume technique was used to infer the influence of water discharge and flow velocity on the smolts’ behaviour upstream of the hydroelectric complex. Of the migrating smolts, 41.5 % performed back and forth movements before approaching the complex for the first time, sometimes over long distances and at a slow pace, leading to significant delays (3‒298 h). Beyond about 250 m3 s-1, the water flow direction changes towards the hydropower station with a gradual acceleration. A median water discharge of 161 m3 s-1 and associated median flow velocity of 0.14 m s-1 tended to favour a more direct and downstream movement towards the hydropower station. On the other hand, the navigation canal was mainly approached at low water discharge (median 132 m3 s-1), due to a higher flow velocity (median 0.11 m s-1) at the entrance. Of the released smolts, only 38.6 % passed through the complex, of which 36.4 % migrated by the navigation canal and 63.6 % by the hydropower station, with a median research time of 04:44. Among all the released individuals, the escapement rate at the end of the study site was 2.9 % by the canal and 8.3 % by the Meuse river. This site, which offers two non-optimal, unattractive and unsafe migration routes, turns out to be problematic for successful downstream smolt migration. [less ▲]

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See detailWhat are the best upland river characteristics for glass eel restocking practice?
Nzau Matondo, Billy ULiege; Benitez, Jean-Philippe ULiege; Dierckx, Arnaud ULiege et al

in Science of the Total Environment (2021)

The fitness of restocked European eel (Anguilla anguilla), an endangered fish species, was studied in relation to the environmental variables of habitats in six upland rivers that are typologically ... [more ▼]

The fitness of restocked European eel (Anguilla anguilla), an endangered fish species, was studied in relation to the environmental variables of habitats in six upland rivers that are typologically different in terms of their hydromorphological and physicochemical characteristics, food resources and fish communities. These rivers received a total of 76,370 imported glass eels in 2017. During a three-year period, we monitored eels with respect to total length, annual growth rate, condition factor and density using capture-mark-recapture experiments to understand the effects of the characteristics of receiving rivers on restocking success levels. Our results showed the survival of the restocked eels in the six rivers and revealed significant differences between them in terms of total length, condition factor and density. Better performance in eel yield variableswas observed in a eutrophic alkaline river with greater roughness of riverbed substrates, dominant pool- and riffle-type flowfacies and lower brown trout density. The variables conductivity and total hardness had higher explanatory power and were strongly associated with increased eel density. This study suggests that a well-selected habitat/river in a restocking programme can be beneficial for the species and recommends restocking practice as a management tool to achieve eel conservation goals. [less ▲]

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See detailImproving bypass performance and passage success of Atlantic salmon smolts at an old fish-hostile hydroelectric power station: a challenging task
Ovidio, Michaël ULiege; Renardy, Séverine ULiege; Dierckx, Arnaud ULiege et al

in Ecological Engineering (2021), 160

Old hydroelectric power stations often provide unsafe migration routes to fish, apart from passing through mobile gates during high flow. The installation of retrofitted bypass is considered to be a ... [more ▼]

Old hydroelectric power stations often provide unsafe migration routes to fish, apart from passing through mobile gates during high flow. The installation of retrofitted bypass is considered to be a potential solution to improve fish passage at such old structures, but their performances are often insufficient. In the Ambl`eve River (Belgium), a mobile 3.3 m high dam feeds two principal Francis turbines (12 + 14 m3 s-1) and is equipped with three mobile gates, a modern vertical slot upstream fish pass and a retrofitted downstream bypass functioning at a very low flow (1% of maximum turbined flow). A bypassed river section (length 8.4 km) downstream of the dam was set at 3 m3 s-1 and supplies a Francis microturbine. From 2015 to 2016, we used 1150 hatchery Atlantic salmon smolts (Salmo salar), and we placed antennae with automatic radio-frequency identification (RFID) stations to analyse the migration routes used (n = 5). We tested the attraction efficiency and the performance of the bypass with and without the placement of a guidance system at the entrance and examined the proportion of smolt passage at the different migration routes under three functioning configurations. The placement of the guidance system markedly improved the attraction efficiency and the overall passage efficiency. The median time spent at the entrance of the bypass was from 7 to 12 min, and the time spent near the entrance of the bypass was less than 1 h for 67.1% (release 1), 88.2% (release 2) and 63.7% (release 3) of the smolts. During the threerelease events, the smolts arrived near the entrance of the bypass mostly during the dusk and dark periods (87.5%, 96.0% and 95.5%, for releases 1, 2 and 3, respectively). In a configuration without opening a mobile gate, the bypass was the most used migration route, followed by the microturbine and the main turbine. Stopping the microturbine and opening a mobile gate has consequences of making it the first choice of passage followed by the main turbine and the bypass. The re-establishment of safe and quick downstream migration has to be considered with a holistic view of the functioning of the hydroelectric powerstation. [less ▲]

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See detailÉvaluation de l’efficacité des passes à poissons du barrage de Nismes et de la Foulerie sur l’Eau Noire
Sonny, Damien; Colson, Dylan; Watthez, Quentin et al

Report (2020)

Cette étude a pour objectif de déterminer l’attractivité et l’efficacité des passes à poissons qui équipent le barrage de Nismes et de la Foulerie, sur l’Eau Noire. Ce suivi permet à la DCENN de valider ... [more ▼]

Cette étude a pour objectif de déterminer l’attractivité et l’efficacité des passes à poissons qui équipent le barrage de Nismes et de la Foulerie, sur l’Eau Noire. Ce suivi permet à la DCENN de valider le bon fonctionnement des passes, de disposer éventuellement d’indices de dysfonctionnement et d’améliorer si nécessaire le fonctionnement des passes ciblées, et enfin de disposer de retours d’expériences sur des choix techniques afin d’optimiser les designs futurs de passes à poissons sur d’autres cours d’eau de Wallonie. [less ▲]

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See detailEvaluation de la qualite biologique des rivieres Wallonnes sur base des indices biologiques poissons. Support technique aux inventaires 2020
Dierckx, Arnaud ULiege; Benitez, Jean-Philippe ULiege; Renardy, Séverine ULiege et al

Report (2020)

Ce document reprend les informations recueillies dans le cadre d’un travail effectué par l’Université de Liège pour le compte du Service public de Wallonie-DEMNA et financé dans le cadre d’un marché ... [more ▼]

Ce document reprend les informations recueillies dans le cadre d’un travail effectué par l’Université de Liège pour le compte du Service public de Wallonie-DEMNA et financé dans le cadre d’un marché public de services qui a pour objectif l’évaluation de la qualité biologique des eaux de surface basée sur les indices biologiques « poissons » dans huit cours d’eau de Wallonie. Cette mission s’inscrit dans le contexte de la mise en oeuvre de la Directive cadre 2000/60/CE établissant un cadre pour une politique communautaire dans le domaine de l’eau. Ce rapport présente les résultats des inventaires piscicoles effectués en mai, juin et juillet 2020 [less ▲]

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See detailSuivi de la dévalaison dans la Vesdre et mesure du fonctionnement des ouvrages pour la faune piscicole
Benitez, Jean-Philippe ULiege; Renardy, Séverine ULiege; Dierckx, Arnaud ULiege et al

Report (2020)

Ce rapport présente les résultats des recherches menées dans le cadre du marché public de Service N°O3.06.04-19D014 : « Suivi de la dévalaison dans la Vesdre et mesure du fonctionnement des ouvrages pour ... [more ▼]

Ce rapport présente les résultats des recherches menées dans le cadre du marché public de Service N°O3.06.04-19D014 : « Suivi de la dévalaison dans la Vesdre et mesure du fonctionnement des ouvrages pour la faune piscicole », publié par le Service Public de Wallonie –Direction Générale Agriculture, Ressources naturelles et Environnement – DDRCB - Direction des Cours d’Eau Non Navigables (Ir Olivier Detrait). Ce projet a été obtenu par le bureau d’étude PROFISH en sous-traitance avec l’Université de Liège – Laboratoire de Démographie des poissons et d’Hydroécologie. Cette étude a pour objectif de déterminer les capacités de dévalaison des poissons sur un cours d’eau de première catégorie et confrontés à différents barrages et centrales hydroélectriques. Le modèle biologique étudié pour cette étude est le smolt de saumon atlantique, Salmo salar, (migration de dévalaison printanière) et le cours d’eau choisi est la Vesdre, rivière fragmentée par de nombreux barrages, dont le barrage de Bacquelaine, équipé d’une Vis d’Archimède. Plus précisément, cette étude vise à déterminer des taux de franchissement et des voies de passages au droit d’ouvrages hydroélectriques ainsi que des timings de migration afin d’évaluer l’incidence des ouvrages cumulés sur la bonne progression de la dévalaison des smolts. [less ▲]

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See detailDevelopment of an accurate model to predict the phenology of Atlantic salmon smolt spring migration
Nils, Teichert; Benitez, Jean-Philippe ULiege; Dierckx, Arnaud ULiege et al

in Aquatic Conservation (2020), 30

1. Changes in migration timing, resulting from the alteration in river continuity or the effect of climate change, can have major consequences on the population dynamics of diadromous fish. Forecasting ... [more ▼]

1. Changes in migration timing, resulting from the alteration in river continuity or the effect of climate change, can have major consequences on the population dynamics of diadromous fish. Forecasting the phenology of fish migration is thus critically important to implement management actions aimed at protecting fish during their migration. 2. In this study, an 11-year monitoring survey of Atlantic salmon smolts (Salmo salar) from the Ourthe River, Belgium, was analysed within a European Special Area of Conservation to improve the understanding of environment-induced spring migration. A logistic model was fitted to forecast smolt migration and to calculate phenological indicators for management, i.e. the onset, end, and duration of migration, while accounting for the influence of photoperiod, water temperature, and hydrological conditions. 3. The results indicated that the photo-thermal units accumulated by smolts above a 7 C temperature threshold was a relevant proxy to reflect the synergistic effect between temperature and photoperiod on smolt migration. After integrating the effect of river flow pulses, the model accurately explained the inter-annual changes in migration timing (R2 = 0.95). The model predictions provide decisive management information to identify sensitive periods during which mitigation measures (e.g. hydropower turbine shutdown, river discharge management) should be conducted to promote smolt survival. 4. The model was used to predict phenological characteristics under future scenarios of climate change. The results suggest a joint effect of hydrological alterations and water warming. Temperature increases of 1–4 C were associated with earlier initiation of migration, 6–51 days earlier, and spring flood events greatly influenced the duration of the migration period. Accordingly, the combined effects of human-induced modifications of the hydrological regimes and increasing temperatures could result in a mismatch between the smolt and favourable survival conditions in the marine environment. [less ▲]

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See detailEvaluation of the performance of successive multispecies improved fishways to reconnect a rehabilitated river
Ovidio, Michaël ULiege; Sonny, Damien; Watthez, Quentin et al

in Wetlands Ecology and Management (2020), 28

The equipping of barriers with fishways has useful applications for testing hypotheses of fish migration and connectivity in river networks, but multiple passage performance for potamodromous fish is ... [more ▼]

The equipping of barriers with fishways has useful applications for testing hypotheses of fish migration and connectivity in river networks, but multiple passage performance for potamodromous fish is poorly known to date. The aim of this study was to analyse the performance of new fishways installed in the river Vesdre (Belgium). Thirty-eight barbel (Barbus barbus; mean: 508 mm, 2133 g) and seven chub (Squalius cephalus; mean: 372 mm, 935 g) were captured by electric fishing and fish pass monitoring and were equipped by RFID-tags and/or radio-transmitters. They were translocated downstream of three different fishways (nature-like pool-type, block ramp, and technical pool-type) in the lower course of the Vesdre. Detection antennas connected to automatic receivers were placed downstream and upstream of each fishway to evaluate the approaching rate, the overall and adjusted passage efficiencies, the passage delays, temperature, dates and time period. The best passage performance and passage delays were observed for the block ramp fishway (88%; 9 h median time to pass) in comparison with pool structures (47 and 73%; 94 and 144 h median time to pass, respectively). The overall passage efficiency was 18.2 and 29.4% for two successive fishways, and 18.2% for three fishways. Passages occurred mainly during dark periods at median temperatures of 14 C (barbel) and 12.3 C (chub), and during highly variable flow conditions. This study provided evidence of the success rate of the reestablishment of the ecological continuity in the river Vesdre as a result of the construction of improved fish-passage structures. [less ▲]

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See detailAn Evaluation of Restocking Practice and Demographic Stock Assessment Methods for Cryptic Juvenile European Eel in Upland Rivers
Nzau Matondo, Billy ULiege; Benitez, Jean-Philippe ULiege; Dierckx, Arnaud ULiege et al

in Sustainability (2020), 12(1124),

Restocking of the critically endangered European eel Anguilla anguilla is widespread, but it is rarely scientifically evaluated. Methods used to assess its associated performance by estimating the ... [more ▼]

Restocking of the critically endangered European eel Anguilla anguilla is widespread, but it is rarely scientifically evaluated. Methods used to assess its associated performance by estimating the survival rate and implement restocking for maximum recruitment in rivers have not yet been investigated. Based on two glass eel restocking events using a single release site/point and multiple sites per river performed in upland rivers (>340 km from the North Sea), the recruitment success of stocked eels was scientifically evaluated during a 3-year study using multiple capture-mark-recapture methods and mobile telemetry. We compared the observed data with the data estimated from the Telemetry, De Lury and Jolly-Seber stock assessment methods. For recruitment data, Telemetry was very close to Jolly-Seber, an appropriate stock assessment method for open populations. Using the best model of Jolly-Seber, survival probability was higher (>95%) in both restocking practices, but recruitment yields were higher and densities of stocked eels were lower in multiple sites compared to a single site. Our results suggest that Telemetry can help to rapidly assess cryptic juvenile eel stocks with good accuracy under a limited number of capture-mark-recapture sessions. Artificial dispersal of glass eels on several productive habitats/sites per river appears to be the better-suited practice for restocking. [less ▲]

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See detailHow and where to pass? Atlantic salmon smolt’s behaviour at a hydropower station offering multiple migration routes
Renardy, Séverine ULiege; Benitez, Jean-Philippe ULiege; Tauzin, Amandine et al

in Hydrobiologia (2020), 847

We studied downstream migration behaviour of Atlantic salmon smolt at a hydropower station that offers four safe (weir, new incision gate on weir, downstream bypass, Archimedes screw) and one potentially ... [more ▼]

We studied downstream migration behaviour of Atlantic salmon smolt at a hydropower station that offers four safe (weir, new incision gate on weir, downstream bypass, Archimedes screw) and one potentially unsafe (Kaplan turbines) migration routes. We followed hatchery smolts using radio (n = 17) and RFID (n = 200) telemetry. They were released 1.2 km upstream of the hydropower station in spring 2018, in four groups, at different water discharge (18 to 37.2 m3s-1) and temperature (12.2–17.6 °C) conditions. For radio-tagged smolts, the repartition of the migration routes was 41.2% for the bypass, 17.6% for both the Kaplan turbine and the weir, 11.8% for the Archimedes screw, 0% for the new incision and 11.8% of unknown route. For the RFID-tagged smolts, the repartition was 38.0% for the bypass, 56.5% for the weir and/or the Kaplan, 4.5% for the new incision and 1.0% for the Archimedes Screw. The median time to cross the hydropower station was 58 min, and 88.2% of the smolts succeed to continue their downstream migration. The results demonstrate a diversity of choices of migration routes and underline the importance to optimise the position of fish-friendly turbines and fish passes at hydropower stations to increase their attractiveness. [less ▲]

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See detailRapport final annuel 2020 au Service Public de Wallonie (DGARNE/DNF-SP) de la Subvention 2019-2020 relative au suivi scientifique de la réhabilitation du saumon atlantique dans le bassin de la Meuse
Benitez, Jean-Philippe ULiege; Erraud, Alexandre; Dierckx, Arnaud ULiege et al

Report (2020)

Le présent rapport d’activités intègre les travaux des deux équipes universitaires de Namur et de Liège dans la cadre de la convention relative à la réhabilitation du saumon atlantique dans le bassin de ... [more ▼]

Le présent rapport d’activités intègre les travaux des deux équipes universitaires de Namur et de Liège dans la cadre de la convention relative à la réhabilitation du saumon atlantique dans le bassin de la Meuse pour la période février 2019 - janvier 2020. [less ▲]

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See detailÉvaluation de la qualité biologique des rivières wallonnes sur base des indices biologiques poissons. Support technique aux inventaires 2019
Dierckx, Arnaud ULiege; Benitez, Jean-Philippe ULiege; Rimbaud, Gilles ULiege et al

Report (2019)

Ce document reprend les informations recueillies dans le cadre d’un travail effectué par l’Université de Liège pour le compte du Service public de Wallonie-DEMNA et financé dans le cadre d’un marché ... [more ▼]

Ce document reprend les informations recueillies dans le cadre d’un travail effectué par l’Université de Liège pour le compte du Service public de Wallonie-DEMNA et financé dans le cadre d’un marché public de services qui a pour objectif l’évaluation de la qualité biologique des eaux de surface basée sur les indices biologiques « poissons » dans onze cours d’eau de Wallonie. [less ▲]

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See detailÉtude du franchissement de la passe à poissons de Bomal s/ Ourthe, sur l’Aisne
Watthez, Quentin; Lerquet, Marc; Sonny, Damien et al

Report (2019)

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See detailTesting three stock assessment methods to evaluate the reintroduction success of the cryptic european eel anguilla Anguilla L.
Nzau Matondo, Billy ULiege; Benitez, Jean-Philippe ULiege; Dierckx, Arnaud ULiege et al

Poster (2019, September)

Glass eel stocking in rivers as conservation measure is usual, but methods to assess the associate performance by estimating precisely the survival rate are not investigated yet. From 2013 to 2019 ... [more ▼]

Glass eel stocking in rivers as conservation measure is usual, but methods to assess the associate performance by estimating precisely the survival rate are not investigated yet. From 2013 to 2019, scientific stocking tests have been implemented in Belgian rivers (>300 km from the estuary). Two release events, cohort 2013 (density 1-1.5 kg released at a single release point) and cohort 2017 (density 2.4 kg/ha dispersed over sites spaced from 250 m) were conducted in eight typologically different rivers. One reference site per release campaign, with the best recruitment level was selected to test different stock assessment methods. We used both multiple capture-mark-recapture sessions (CMR; cohort 2013: n = 4155 glass eels, 5 sessions in 2014-2019; cohort 2017: n = 1586 glass eels, 4 sessions in 2017-2019) in combination with mobile RFID-Telemetry investigations, over 200-m long river stretches. We compared the observed data with the data corrected using: (i) ratio between RFID detection and electrofishing (DCM), (ii) number of eels captured in a capture session using the DeLury model (DLM) and, (iii) multiple CMR occasions for open-population Jolly-Seber model (JSM). Eel density estimation was close between release techniques. JSM data were close to DCM data and estimated time-varying capture probability, survival probability between sessions and super-population abundances. Our results suggest multiple CMR campaigns with applying JSM were better-suited methodology to assess juvenile eel cryptic stocks, but DCM helped to rapidly assessing stock under limited CMR occasions. Glass eel release on several sites seems to be the best stocking technique. [less ▲]

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See detailRehabilitation effort for anadromous salmonids in the river Meuse basin. Achievements and new challenges
Ovidio, Michaël ULiege; Kestemont, Patrick; Dierckx, Arnaud ULiege et al

Conference (2019, May)

Until the end of the 19th century, the Atlantic salmon (Salmo salar) was widespread in the river Meuse basin and salmon fisheries were prosperous in France, Belgium and The Netherlands. The number of ... [more ▼]

Until the end of the 19th century, the Atlantic salmon (Salmo salar) was widespread in the river Meuse basin and salmon fisheries were prosperous in France, Belgium and The Netherlands. The number of salmon and sea trout captures reaches 57000 ind/year in the Dutch Rhine-Meuse delta. Between 1840 and 1950, the building of navigation dams in the river Meuse and its tributaries, as well as the increase of industrial water pollution and the overexploitation of the stock, led to the extinction of all anadromous fish species. In 1983, the capture of a sea trout (Salmo trutta) in the lower Belgian Meuse brought the problem of the migratory of fish to the surface. Based on scientific advices and feasibility studies carried out from 1983 to 1986, the program Salmon Meuse was launch in 1987. It aims at the restoration of the complete life cycle of migratory salmonids in the international River Meuse Basin. Important rehabilitation efforts have been progressively done since the beginning of the project to the present 1) Improvement of the general quality of the water 2) Restocking with strains originating from France, Ireland, Scotland 3) Hydromorphological restoration of gravel bed habitats 4) The construction of modern fishways for upstream migration in the Meuse and tributaries 5) Adoption of measures to facilitate downstream migration at hydroelectric sites 6) Development of a salmon hatchery with facilities to realise artificial reproduction using returning adults 7) The establishment of international collaboration network 8) The election of the best strains based on genetics of returning adults and the process of smoltification finally 9) The opening of the Haringvliet sluices in the Estuary of the Meuse in the Netherland in 2018. In the year 2000, the first adult salmon originating from restocking program was captured in the fishway of Lixhe, and this return of a salmon, more than 50 years of his extinction, was a major ecological event. From 2000 to 2018, the number of returning Atlantic salmon and sea trout progressively increased and reaches n=60 in the best year. This underline partial achievement of the objectives of the project, but the number of returning adult is sill too low to have a natural sustainable population. Supplementary efforts must be undertaken in the future, especially in terms of success of smolts downstream migration and escapement success as well as an optimization of the restocking practices (in terms of quantity and choice of the best development stage). During our talk, we will synthesise the major key-points of this challenging project whose success requires a balance between the development and maintenance of numerous human activities and the associate preservation of the aquatic environment. We will use examples of results originating from recent scientific research. [less ▲]

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