Dispersal-recolonisation

Dispersion and recolonisation of the course of the Selune and its tributaries: reference state for amphihaline migratory fish and anticipation of the spatial expansion of the California crayfish

Coordinator(s)

Eric Petit

Scientific context

Restoring ecological continuity on the main course of the Selune river will entail :

• The return of migratory species such as salmon (Salmo salar) and eels (Anguilla anguilla),
• A return to contact between migratory and sedentary forms of trout (Salmo trutta) or lamprey (Lampetra fluviatilis and L. planeri),
• And the possible spread of invasive species.

The colonisation capacity of species depends not only on their dispersal capacity but also on their life history strategies. From this point of view, the removal of the dams on the Selune provides a unique context to study the effects of the ecological restoration of a river on the (re)distribution of key species in its catchment area and the concomitant changes in various biological traits, at different levels of organisation (population, gene, etc.).

Subjet(s) of study

This project focuses on diadromous fish, invasive crayfish (in particular Pacifastacus leniusculus) and certain plant species (Ranunculus penicillatus and Callitriche sp.), which represent major local socio-economic and ecological issues.

Objectives

The aim of this project is to define a baseline for diadromous fish, to assess the distribution of exotic crayfish species, and to characterise the phenotypic and demogenetic evolution of these species.

Based on the theme of the (re)colonisation of the Selune basin, this project aims to provide answers to the following interconnected questions:

• Which species are taking advantage of the removal of dams to (re)colonise the Selune and its tributaries?
• What are the consequences of dam removal on the distribution of species and their demo-genetic structure at catchment scale?
• What are the consequences of the (re)colonisation dynamics on the traits of the species concerned?

Methods

Several methods are used.

Baseline status and sampling of diadromous fish populations

• Fishing for all species of fish, eels, trout and lampreys;
• Assessment of the downstream silver eel population by fishing with guideau or tezelle;
• Fishing for salmon juveniles on the 4 rivers in the Bay of Mont Saint-Michel in order to build up a collection of samples and pre-fishing reference data at genetic and demographic level;
• Sampling of adult salmon otoliths from the 4 rivers in the Bay of Mont Saint-Michel (10-15 individuals/river/year) for microchemical analyses that will enable the individuals that will recolonise the Sélune to be assigned to their river of origin;
• Counting sea lamprey spawning grounds in the downstream part of the dams in the Selune basin and its tributaries;
• Analysis of the size/abundance structures of individuals caught during fishing;
• Otolithometric analysis of yellow and silver eels to determine the age of individuals, and sexing by quantitative PCR.

Development of a tool to measure migratory flows

Recording of coupled ARIS camera/echosounder data at Ducey, then data processing and analysis to validate the model for estimating migratory flows.

Monitoring the colonisation of Sélune tributaries by the Pacific crayfish

Trapping every two years (May and September) using creel nets at stations that become lotic again as the water level in the main course of the Selune drops, and at the entrance of tributaries that were previously located on reservoirs and free of crayfish.

Laboratories involved

• ESE – UMR Ecology and Heath of Ecosystems, INRA/Agrocampus Ouest, Rennes
• ECOBIOP – UMR Behavioural Ecology and Biology of Fish Populations, INRA/Université de Pau et des Pays de l’Adour, Saint Pée sur Nivelle
• U3E – Aquatic Ecology and Ecotoxicology Exper, INRA, Rennes
• BOREA –UMR Biology of Aquatic Organisms and Ecosystems, MNHN, Dinard
• ECOBIO – UMR Ecosystems, Biodiversity, Evolution, CNRS/Université Rennes 1, Rennes