The opening of the dams should impact the functioning of Atlantic salmon populations migrating up the Sélune River and its tributaries. Restoring the river's ecological continuity will alter population flows by allowing amphihaline sea trout to migrate further upstream and native trout to move downstream and upstream of the dams. The trout population is monitored at a network of stations covering the entire Sélune basin using an abundance index, which is carried out every two years before 2021 and every year since then. Field campaigns comply with the fishing protocol developed by INRAE and OFB. The aim of this method is to estimate the abundance of juvenile Atlantic salmon (Salmo salar) at a station (or sector). This protocol targets juveniles of the year (aged 0+) whose abundance reflects the renewal of generations within the population (or recruitment) and survival after the embryonic development phases under gravel and the first months of life in the open environment. Field campaigns are carried out by INRAE and the Manche d'Ille-et-Vilaine Federation for Fishing and the Protection of the Aquatic Environment (FDAPPMA50 and FDAAPPMA35). This dataset provides individual biometric data on Atlantic salmon caught during PAS fishing sessions in the Sélune watershed, by station and by fishing session.

The spawning grounds of the sea lamprey (Petromyzon marinus) are located within the perimeter of the Sélune Observatory. As this species is migratory, its colonisation of the Sélune river and its tributaries will probably be influenced by the removal of the Sélune dams. The spawning grounds are characterised by a depression accompanied by a sediment ejection dome immediately downstream. The stones returned to the dome are lighter, making the nests easily visible and identifiable for up to several weeks after spawning. This data is available for the years 2015, 2019, 2020, 2021, 2022, 2023, 2024 and 2025. The Sélune Observatory's activity reports (see attached links) give details of the prospecting conditions.

The study of riparian vegetation in exposed areas is based on the observation of natural plant communities colonising newly exposed mudflats, across different temporal scales (intra- and inter-annual variations) and nested spatial scales. The botanical survey is carried out using the Braun-Blanquet method. The sampling protocol is stratified in order to maximize the recorded diversity. For each study area, a transect perpendicular to the riverbed is established, on which quadrats of 25m2 (5x5m) are positioned. These quadrats are used for the identification of substrates and the determination of species present (on the ground and in vertical strata). All species in the quadrats were surveyed and their abundance was estimated. The main vegetation units have also been described. This layer provides the locations of these study areas as well as the various information characterizing them (watercourse, reference point, position on the catchment area, transect, associated drainage basin) for the campaign sessions from 2021 to 2026.

The opening of the dams should impact the functioning of Atlantic salmon populations migrating up the Sélune River and its tributaries. Restoring the river's ecological continuity will alter population flows by allowing amphihaline sea trout to migrate further upstream and native trout to move downstream and upstream of the dams. The trout population is monitored at a network of stations covering the entire Sélune basin using an abundance index, which is carried out every two years before 2021 and every year since then. Field campaigns comply with the fishing protocol developed by INRAE and OFB. The aim of this method is to estimate the abundance of juvenile Atlantic salmon (Salmo salar) at a station (or sector). This protocol targets juveniles of the year (aged 0+) whose abundance reflects the renewal of generations within the population (or recruitment) and survival after the embryonic development phases under gravel and the first months of life in the open environment. Field campaigns are carried out by INRAE and the Manche and Ille-et-Vilaine Federations for Fishing and the Protection of the Aquatic Environment (FDAAPPMA50 and FDAAPPMA35). This dataset provides abundance data for Atlantic salmon (0+, 1+, 2+ and cumulative) as well as the salmon abundance index (PAS) by station and fishing session.

The opening of the dams should impact the functioning of Atlantic salmon populations migrating up the Sélune and its tributaries. Restoring the river's ecological continuity will alter population flows by allowing Atlantic salmon to migrate further upstream and downstream of the dams. The Atlantic salmon population is monitored at a network of stations covering the entire Sélune basin using an abundance index, which was carried out every two years before 2021 and annually since then. Field campaigns comply with the fishing protocol developed by INRAE and OFB. The aim of this method is to estimate the abundance of juvenile Atlantic salmon (Salmo salar) at a station (or sector). This protocol targets juveniles of the year (aged 0+) whose abundance reflects the renewal of generations within the population (or recruitment) and survival after the embryonic development phases under gravel and the first months of life in the open environment. Field campaigns are carried out by INRAE and the Manche d'Ille-et-Vilaine Federation for Fishing and the Protection of the Aquatic Environment (FDAPPMA50 and FDAPPMA35). This dataset provides the locations of these study sectors for IAS fishing sessions in the Sélune watershed by fishing session.

In few words : The primary objective of the biomonitoring project “Impact of Dredging on the Animal and Plant Communities of the Sélune” is to establish a baseline assessment of the biological quality of the Sélune upstream and downstream of the two dams, as well as within the reservoirs. It also aims to identify risks (acute exposure) during the work to stabilize contaminated sediment from the Yvrande. It thus seeks to answer the following questions: How does the lotic ecosystem recover after the disappearance of a reservoir, and what new ecological equilibria result? What will be the effects of the dredging work on the quality of the environments and their consequences on the biocoenoses that develop there? This project assesses the impact of dams on aquatic animal and plant communities in relation to water quality (zooplankton, macroinvertebrates, phytoplankton, periphyton, macrophytes). Methods : IBMR ; IBGN ; IBD ; suivi des biofilms ; caractérisation physico-chimique Data : - Monitoring of physicochemical conditions (water temperature, conductivity, pH, etc.) - Concentrations of nitrates, silicates, nitrogen, and total phosphorus - Monitoring of invertebrate communities - Monitoring of phytoplankton and zooplankton communities, and measurement of phytoplankton biomass - Monitoring of biofilm (2015–2017) - Monitoring of aquatic plants (1996) - Floristic surveys of aquatic plants (2015, 2017) - Toxicological characterization of fish in the Vezins Reservoir - Analysis of fish stomach contents (GCA)

The study of riparian vegetation in exposed areas is based on the observation of natural plant communities colonising newly exposed mudflats, across different temporal scales (intra- and inter-annual variations) and nested spatial scales. The botanical survey is carried out using the Braun-Blanquet method. The sampling protocol is stratified in order to maximise the diversity recorded. For each study area, a transect perpendicular to the riverbed is established, with strips parallel to the watercourse marked out in the field according to the degree of exposure. This layer shows the location of these study areas, the route of the transects, and information on the vegetation units recorded between 2021 and 2026.

The study of riparian vegetation in exposed areas is based on the observation of natural plant communities colonising newly exposed mudflats, across different temporal scales (intra- and inter-annual variations) and nested spatial scales. The botanical survey is carried out using the Braun-Blanquet method. The sampling protocol is stratified in order to maximize the recorded diversity. For each study area, a transect perpendicular to the riverbed is established, on which quadrats of 25m2 (5x5m) are positioned. These quadrats are used for the identification of substrates and the determination of species present (on the ground and in vertical strata). This layer indicates the location of these study areas, the layout of transects and information regarding the quadrats recorded between 2021 and 2026

This project examines the life history traits of eels and flounders—two migratory species that live in rivers and spawn in the sea—prior to the restoration of the Sélune River’s connectivity, in order to anticipate the subsequent effects of this restoration. Data: - Catches of eels and flounder (recorded at least within the framework of the Observatory, for eels) - Fat content (measured using a fat meter and chloroform extraction); - Energy content (calorimetric bomb test on muscle tissue) - Position and trophic niche - Age and growth rate - Migration and basin use profile - Prevalence and abundance of parasitic metazoans (overall and for each parasite species), diversity of parasite communities - Diversity and status of the intestinal microbiome determined Sites: 6 sites in total: Sélune (Pêcherie + Roche qui Boit), Oir, Beuvron, Sée, Couesnon, Marais de Dol - Eels: 5 sites (Sélune Pêcherie + Roche qui Boit, Oir, Beuvron, Sée) - Flounders: 4 sites (Sélune, Sée, Couesnon, and Marais de Dol)