RETABLISSEMENT DE LA LIBRE CIRCULATION DES POISSONS EN MEUSE : 20 ANNEES DE SUIVIS DE PASSES A POISSONS

editorial reviewe

Session C6: Does Yellow Eel Prefer Old Pool and Weir or New Vertical Slot Fish Pass During Their Upstream Migration?

Abstract: The hydroelectric dam of Lixhe in the River Meuse, 323km upstream from the North Sea at the entry of Belgium near the frontier with the Netherlands is equipped with two basin fish-passes: – the old pool-and-weir configuration (OFP) operates at low discharge (0.13m3/s) and – the new vertical-slot configuration (NFP) operating at high discharge (1m3/s) with attraction flow (1.5m3/s). However, the utilization rate of these fish-passes by the incoming yellow eels remains unknown, because the trap of NFP is not adapted to retain anguillids and small species. Yet, such knowledge is crucial to improve the inland colonization of the species and to increase our understanding of fish-pass utilization given its particular swimming mode. In season 2013, eels caught two times a week using a cone-trap pool in the OFP and net traps in the NFP, were tagged and released the same day 0.3km downstream (n = 396eels). The utilization of OFP and NFP was studied using automatic RFID transponder detection antennas placed in upstream basins of the fish-passes, during years 2013 and 2014. Results revealed that the OFP was the preferred migration route of eels (eel numbers, OFP: NFP, 2013= 88:51 and 2014= 41:16, χ²-test, p\u3c0.0001), which was also used earlier in season. Eels displayed fidelity to their catch fish-passes (\u3e70% of the detected eels, annually). Detection rate was high in the year of eel tagging (2013: 35.1%) before decreasing in the following year (2014: 14.4%). Eels used these fish-passes the night from 22:00 to 04:00, at 14-26°C, river flow \u3c200m³/s and whenever waxing and waning phases of moonlight. Our results provide insight into the utilization of fishpasses by migrating eels. The study suggests further reflection before removing the old fish-pass in large rivers and to think about the eel attractiveness and comfort when the construction of a new fish pass is planned

Multi-year analysis of the fish colonisation dynamic in three newly installed fishways in medium sized Belgian rivers

peer reviewedThe 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.14. Life below wate

Evaluation de la qualité biologique des rivières wallonnes sur base des indices biologiques poissons. Support technique aux inventaires 2012.

Ce rapport a pour objectif l’évaluation de la qualité biologique des eaux de surface basée sur les indices biologiques « poissons » dans un certain nombre de cours d’eau de Wallonie. Il résulte d’une convention entre le Service public de Wallonie et l’Université de Liège

Evaluation de la qualité biologique des rivières wallonnes sur base des indices biologiques poissons. Support technique aux inventaires 2014.

Ce rapport final présente les résultats des inventaires piscicoles effectués en juin-juillet et en septembre-octobre 2014 ainsi que le calcul des indices biologiques « poissons » (IBIP et EFI)

An Evaluation of Restocking Practice and Demographic Stock Assessment Methods for Cryptic Juvenile European Eel in Upland Rivers

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

Assessment of Fish Abundance, Biodiversity and Movement Periodicity Changes in a Large River over a 20-Year Period

peer reviewedA river is an ecosystem where fish fauna represents an important structural element. To re-establish connectivity, it is imperative to allow movement between functional habitats. Due to the hydromorphological complexity of large anthropized rivers and the lack of study techniques that can be used in such environments, relevant data with regard to fish ecology are scarce. On the River Meuse, Belgium, at a point 323 km upstream from the North Sea, the Lixhe hydroelectric dam is equipped with two fishways. Both were continuously monitored using capture traps for 20 consecutive years (from 1999 to 2018), representing 4151 monitoring events. The objectives of the present study were to describe the overall abundance and movement indicators of mainly holobiotic potamodromous fish species and to analyse their temporal evolution. We captured 388,631 individuals (n = 35 fish species) during the 20 years of fishway monitoring; 22.7% were adults (>75% of which were cyprinids), and 83.3% juveniles (>90% cyprinids). From 1999 to 2018, the results showed a drastic reduction in yearly captures for some native species as well as the apparent emergence of non-native (e.g., Silurus glanis) and reintroduced species (e.g., Salmo salar). The annual capture periodicities associated with environmental factors were clearly defined and were mostly related to the spring spawning migration of the adult stage. This long-term monitoring demonstrated how the fishways are used by the whole fish community and allowed a better understanding of their movement ecology in a large lowland anthropized river. The appearance of non-native species and the drastic decline in abundance of some common and widespread European fish should prompt river managers to adopt conservation measures.Programme Saumo