The removal of the dams of the Sélune is the subject of a scientific programme initiated in 2012 in which environmental parameters are monitored in order to provide real feedback on this restoration operation. In 2019, a data observatory was set up to ensure the collection and processing of these parameters (biotic and abiotic). The data acquired from 2012 and at least until 2027 will be centralized through an information system (IS), called SISelune. SISelune aims to help scientists involved in the Sélune programme and make data accessible to all. The Sélune scientific programme has a reference system, composed of points. These points can be used by all program actors to more easily identify any location within the study area. The points are created along the rivers, with an approach "Point kilométrique" (every 100m, going from upstream to downstream). Each of these points has a unique code, corresponding to the association of the watercourse (designated by a short code) and the distance to the source or confluence. Since 2025, each of these points has also been characterized by its position in the watershed (downstream, upstream, ...) in relation to the zone determined by the former dams and their reservoirs, as well as their distance from the sea in 2 forms (LTM: Limite Transversale à la mer / Transverse Sea Limit and LSE: Limite Salure des eaux / Water salinity limit).

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.

The re-establishment of the river continuum on the Sélune after the dams have been levelled will enable colonization of the upper reaches of the basin, which were previously inaccessible to eels. Before the dams were levelled, two main tributaries were used by amphihaline fish for reproduction, in addition to the main river: the Beuvron and the Oir. The eel population of the Sélune was monitored in the pre-flushing phase by abundance index campaigns carried out in 2013, 2015, 2019 on a network of stations covering the entire Sélune hydrographic network. Since 2021, this network of stations has evolved to monitor changes in the part of the watershed accessible following the dismantling of the 2 dams. These data enable us to estimate changes in eel abundance along the Sélune and its tributaries, as well as their size structure before and after the removal of the dams. The inventory is carried out in early September, every other year between 2013 and 2019, then every year since, using an electric fishing device and dip nets. Thirty thirty-second fishing stations are set up. A fishing station comprises approximately 100 meters of river. All eels caught are anaesthetized and biometric measurements are taken (weight, length, horizontal and vertical eye diameter, determination of yellow or silver stage). All eels are released directly at the fishing site. Two different protocols were implemented: the Eel Abundance Index (Pottier and Chapon, 2022) at 23 stations and exhaustion fishing at eight other stations (IAA01 to IAA08) on the Oir River and some of its tributaries, according to an internal protocol. This layer provides station abundances by fishing session.

In 2020, scientific plots were set up, marked out on the ground with colored stakes. These plots are intended to facilitate scientific monitoring, particularly of renaturation. These plots represent privileged areas for scientists, where no sediment or vegetation disturbance is planned until the end of the Sélune program.

The removal of the dams on the Sélune River is the subject of a scientific program launched in 2012, in which environmental parameters are monitored in order to provide real feedback on this restoration operation. In 2019, a data observatory was set up to collect and process these parameters (biotic and abiotic). The data acquired from 2012 and at least until 2027 will be centralized through an information system (IS) called SISelune. SISelune aims to assist scientists associated with the Sélune program and make the data accessible to all. This layer shows the study area, based on hydrographic sub-basins for the continental part and the transitional water body for the Bay of Mont St-Michel.

Macrophytes are a group of aquatic plants. They are at the base of the food chain and can provide a habitat for many other species. As part of the Sélune Observatory, pilot stations have been set up along the main course of the Sélune, distributed from upstream to downstream of the hydroelectric dams. Three stations are located in the former reservoirs of the dams, while the other two, known as the reference stations, are outside the area of influence of the former dams (one downstream and the other upstream). At these stations, the aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. The parameters monitored are the specific composition and cover, at 8 stations in the main course located upstream, downstream and in the neolotic zones of the macrophyte communities. The monitoring frequency consists of one annual campaign for stations outside reservoirs (S0, S1 and S5) and two annual campaigns (spring/autumn) for neolotic stations (S2, S3.4, S4.1 and S6). The protocol used is the sampling protocol for macrophytes and bryophytes in accordance with standard NF T90-395 (October 2003), which defines the IBMR. The taxa are sampled for laboratory identification. This layer shows the location of the study sectors used for macrophyte monitoring, as well as the campaigns carried out and the mesology identified during these different campaigns.

The restoration of the Sélune river continuum after the dams were demolished will allow colonization of the upper reaches of the basin, which were previously inaccessible to eels. Before the demolition, two main tributaries were used by amphihaline fish for reproduction, in addition to the main river: the Beuvron and the Oir. The eel population of the Sélune was monitored in the pre-demolition phase by abundance index campaigns carried out in 2013, 2015, 2019, 2021, and 2023 on a network of stations covering the entire Sélune river system. These data make it possible to estimate changes in eel abundance along the Sélune and its tributaries and their size structure before and after the destruction of the dams. The inventory is carried out in early September, every other year, using electric fishing equipment and landing nets. Thirty fishing points are carried out for a minimum of 30 seconds each. A fishing station covers approximately 100 meters of river. All eels caught are anesthetized and undergo biometric measurements (weight, length, horizontal and vertical eye diameter, determination of yellow or silver stage). All eels are released directly at the fishing site. This layer contains individual data on the eels caught.

In partnership with ANR Reppaval, the Syndicat Mixte du bassin de la Sélune has begun implementing a photographic observatory of the landscapes of the Sélune basin. This is a photographic itinerary consisting of viewpoints spread across the entire territory, where photographs will be taken regularly. The aim is to monitor changes in the landscape, particularly in relation to the Sélune restoration project. The layer shows the location of the sites on the photographic itinerary that are directly affected by the Sélune restoration work: lakes and dams.

The re-establishment of the river continuum of the Sélune after the levelling of the dams will enable the colonization of the upstream part of the basin which was previously inaccessible to trout. As a result, monitoring of amphihaline fish populations on the Sélune is carried out on the main river and its tributaries, both upstream and downstream of the former dams. These enable us to understand the dynamics of these common trout populations before, during and after dam removal. Regarding the trouts, the inventory is carried out using the VIGITRUITE® protocol. This is a standardized protocol for estimating the abundance of juvenile trout (Salmo trutta) in rivers. It is based on sampling per unit effort, a unit fixed at 5 minutes of effective fishing, and thus delivers abundances in numbers of juveniles per 5 minutes. Abacuses for converting abundances into densities are available, and a guide to interpreting densities, from low to excellent, is proposed. Compared with traditional inventories, this protocol enables a smaller number of people to be mobilized in the field. The protocol applies to watercourses up to 8 m wide and never more than 60 cm deep. It has been validated on granite and limestone rivers in Brittany and Normandy. VIGITRUITE® specifically targets juveniles of the year (0+) and yearlings (1+). The 0+ abundance provides information on generation replacement (or recruitment), useful for population demographic monitoring. The abundance of 0+ and 1+ is also a reflection of the quality of the trutticole habitat, and of specific attacks on its integrity (pollution, sedimentation, fragmentation in particular). It is a diagnostic tool for trout populations and their river habitats. This protocol is applied in September of the years in question: every 2 years between 2012 and 2020, then every year from 2021 to 2027. The year 2020 is special because of the COVID. For more information on acquisition conditions, please refer to the Sélune biocenosis observatory reports, the links to which are provided in this document. This dataset provides juvenile trout abundance data (0+, 1+ and cumulative), by station and fishing session.

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.