This project aims to develop and apply a non-invasive method for monitoring migratory fish flows in the Sélune River. The development of this method is based on the analysis of images and videos taken by a hydroacoustic camera positioned in the watercourse.

This project compares the implementation, acceptance, and progress of dam removal projects in France, using the example of the Sélune, and in the United States, where several similar removal projects have taken place.

In a nutshell: The food web project takes a broad look at the aquatic communities found in the Sélune River, ranging from microorganisms to fish, in both its tributaries and the river itself, from its source to where it flows into the estuary. The approach aims to study the interactions between these biological components, with the primary objective of understanding the overall functioning of the ecosystem. The goal is to understand the balances within aquatic ecosystems, from the headwaters of the watershed to the lower reaches of the river, both before (current state) and after (river restoration) the restoration of continuity through the removal of dams. Objective: to answer the following questions: · What role do dams and their reservoirs play in shaping aquatic communities within the river and in the functioning of this ecosystem? · How does the river ecosystem recover at the exact location of a dam reservoir after it has been drained? · What roles do certain key species (particularly amphihaline fish and invasive species) play in ecological balances? · What consequences can be expected from dam removal operations, from the headwaters to the estuary entrance, on these communities and the functioning of the river ecosystem reconnected to the ocean? Methods: inventories; physicochemical characterization; functional ecosystem analysis; stable isotope analysis; food web analysis Data: Measurements of water’s physicochemical quality Community inventories Estimation of (1) the degradation of coarse organic matter (tree leaf litter) via the detritus pathway, and (2) the photosynthetic activity of microorganisms and biofilms in the algal pathway. Data from isotopic analyses of communities; identification of energy sources (food, carbon cycle) in food webs Role of keystone species (invasive crayfish and fish predators) Analysis of food web structure

In a nutshell: Restoring the connectivity of inland water bodies is one of the key measures of the Water Framework Directive, and must be achieved either by modifying existing barriers or by removing them entirely. This second solution was chosen for the Sélune River as part of an operation that is subject to scientific monitoring. The goal of this monitoring, within the context of studying biocoenoses, is to help us understand the consequences of this removal on migratory and invasive species. The removal of dams and the restoration of river connectivity can have both positive and negative consequences. Objectives This project aims to provide answers to the following interconnected questions: Which species are taking advantage of the removal of dams to (re)colonize the Sélune and its tributaries? What are the consequences of restoring river continuity on species distribution and their demographic and genetic structure at the watershed scale? What are the consequences of (re)colonization dynamics on the traits of the species concerned? Methods: scientific fishing; hydroacoustic camera monitoring; DNA analysis; demographic analysis Data - Trout fishing (IAT) - Eel fishing (IAA) - Lamprey fishing (IAL) - All-species fishing (PTE) - Crayfish fishing (IAE) - Identification of upstream-migrating Atlantic salmon - Otolith sampling from smolts - Counts of lamprey and salmon spawning grounds - Inventories of aquatic plant communities - Crayfish detection

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)

The aim of this project is to understand the exchanges between the groundwater and the water in the Sélune river. This knowledge will help prevent the physical, chemical, and biological changes that restoring continuity will cause to the water quality of the Sélune. Data: - water level records - temperature measurement records at various locations in the river sediments and in the piezometers - data from differential pressure sensors at certain points along the river, - data on the concentration of chemical elements (N, P, dissolved gases, etc.) in the sediments - fiber-optic data - Lidar campaign data Sites: At the start of the project, there are two main sites, each covering a few hundred meters, located nearby: - the Signy Bridge - the Biards Bridge Additional sites may be added later, if logistical constraints (such as the portability of certain measurement protocols) permit.

This project assesses the impact of restoring connectivity between fish populations following the removal of dams on the Sélune River. It is based on the calculation of a genetic fragmentation index for five fish species. Data: - Genetic analysis and F-index

The goal of this project is to establish methods for monitoring the return of iconic migratory fish, such as salmon and eels, to the Sélune Valley following the restoration of its connectivity.