The opening of the dams will have a significant impact on trout populations in the Sélune. 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. The field campaigns comply with the Vigitruite® fishing protocol, developed by INRA and intended for use throughout France. This abundance index, relative to the area of favorable habitats in the watercourse, makes it possible to assess the quantity of young trout present in the river, resulting from natural reproduction in previous years. This table provides individual data on trout caught according to the year of study.

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.

Microbial communities play a major role in the functioning of ecosystems: they are at the base of the food chain (primary production) and participate in the degradation of organic matter. These communities are also known to respond rapidly to environmental changes. Like macro-invertebrates, they can be used as ecological indicators. Benthic diatoms are the main photosynthetic organisms in this biological community. The relative abundance of the various species is used to calculate an environmental quality index (EQI). Major differences in communities between the upstream and downstream zones were observed when the dams were in place. These differences will change once the dams are removed. 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, aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. Since September 2014, the stations are ideally sampled every month from April to October (7 annual surveys) using artificial substrates (glass slides placed in the water). In addition to the diatom survey (floristic list, IBD calculation), the chlorophyll-a concentration is measured. This layer shows the location of the study sectors used to monitor photosynthetic biofilms and the campaigns carried out.

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.

Benthic macro-invertebrates (insects, crustaceans, molluscs, worms) form an important link in the food chain. 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 taxonomic composition of the communities at 5 stations in the main river, located upstream, downstream and in the new lotic habitats. The sampling frequency involves two annual sampling campaigns (spring and autumn). The protocols implemented are the installation of 4 artificial substrates (SUBART) per station and a survey after 1 month of immersion as well as 12 Surber samples per station, in accordance with standard NF T 90-333 (2016), allowing the calculation of the I2M2 in accordance with standard NF T 90-388 (2020) and Mondy et al. 2012, 2012. This layer shows the location of the study sectors used to monitor benthic macroinvertebrates and the campaigns carried out. This monitoring was finalised with the latest field acquisitions in 2025.

Microbial communities play a major role in the functioning of ecosystems: they are at the base of the food chain (primary production) and participate in the degradation of organic matter. These communities are also known to respond rapidly to environmental changes. Like macro-invertebrates, they can be used as ecological indicators. Benthic diatoms are the main photosynthetic organisms in this biological community. The relative abundance of the different species is used to calculate an environmental quality index (EQI). Major differences in communities between the upstream and downstream zones were observed when the dams were in place. These differences will change once the dams are removed. 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, aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. Since September 2014, the stations are ideally sampled every month from April to October (7 annual surveys) using artificial substrates (glass slides placed in the water). In addition to the diatom survey (floristic list, IBD calculation), the chlorophyll-a concentration is measured. During each campaign, an INRAe experimental sampling protocol is implemented. This protocol involves the immersion (1 month) of glass slides, in situ measurement of chlorophyll-a concentration via BentoTorch and then collection of the biofilm on these glass slides. The biofilm is conditioned in (1) 99.9% ethanol for determination of IBDs and floristic lists (outsourced service, based on standard NF T90-354) and (2) mineral water for measurement of chlorophyll-a concentration using a spectrometer. Taxon identification is based on version v17 of the TAXREF reference. The dataset is currently under embargo.

Microbial communities play a major role in the functioning of ecosystems: they are at the base of the food chain (primary production) and participate in the degradation of organic matter. These communities are also known to respond rapidly to environmental changes. Like macro-invertebrates, they can be used as ecological indicators. Benthic diatoms are the main photosynthetic organisms in this biological community. The relative abundance of the different species is used to calculate an environmental quality index (EQI). Major differences in communities between the upstream and downstream zones were observed when the dams were in place. These differences will change once the dams are removed. 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, aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. Since September 2014, the stations are ideally sampled every month from April to October (7 annual surveys) using artificial substrates (glass slides placed in the water). In addition to the diatom survey (floristic list, IBD calculation), the chlorophyll-a concentration is measured. During each campaign, an INRAe experimental sampling protocol is implemented. This protocol involves the immersion (1 month) of glass slides, an in situ measurement of the chlorophyll-a concentration via BentoTorch and then the collection of the biofilm on these glass slides. The biofilm is conditioned in (1) 99.9% ethanol to determine IBDs and floristic lists (outsourced service, based on standard NF T90-354) and (2) mineral water to measure chlorophyll-a concentration using a spectrometer. NB: the year 2023 is not covered in terms of measuring chlorophyll-a concentration via spectrometry due to a problem with the low-temperature storage of samples. This dataset provides measurements of the average daily concentration of chlorophyll-a and pheopigment in µg/cm2/day.

Microbial communities play a major role in the functioning of ecosystems: they are at the base of the food chain (primary production) and participate in the degradation of organic matter. These communities are also known to respond rapidly to environmental changes. Like macro-invertebrates, they can be used as ecological indicators. Benthic diatoms are the main photosynthetic organisms in this biological community. The relative abundance of the various species is used to calculate an environmental quality index (EQI). Major differences in communities between the upstream and downstream zones were observed when the dams were in place. These differences will change once the dams are removed. As part of the Sélune Observatory, the stations are sampled every month from April to October (7 annual surveys) using artificial substrates (glass slides placed in the water). In addition to the diatom survey (floristic list, IBD calculation), the chlorophyll a concentration is measured. This layer gives the IBD and EQR (normalised) index value for a station during a campaign.

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. The relative abundance of different species is used to calculate an environmental quality index (IBMR). 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 reference stations, are outside the area of influence of the former dams (one downstream, the other upstream). At these stations, aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. The parameters monitored are specific composition and cover, at 8 stations in the main course, located upstream, downstream and in neolotic areas of 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. Taxa are sampled for laboratory identification. This layer gives the value of the IBMR and EQR (normalized) index at a station for a campaign, as well as information concerning the robustness of this index, the quantities of taxa used to calculate these indices and also information in terms of the proportion of major floristic groups (heterotrophs, algae, bryophytes, pteridophytes, helophytes, phanerogrames, floating vegetation and submerged vegetation).

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. The relative abundance of different species is used to calculate an environmental quality index (IBMR). 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 reference stations, are outside the area of influence of the former dams (one downstream, the other upstream). At these stations, aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. The parameters monitored are specific composition and cover, at 8 stations in the main course, located upstream, downstream and in neolotic areas of 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. Taxa are sampled for laboratory identification. This layer gives Taxon identification is based on version v17 of the TAXREF reference. The dataset is currently under embargo.