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Influence of dam removal on the life history traits of thalassotoic amphihaline species: the case of eels and flounder in the Selune River

Coordinator(s)

Nils Teichert and Eric Feunteun

Scientific context

Restoring the continuity of the Selune by removing these dams will enable many species, particularly migratory fish, to recolonise the upper reaches of the catchment. This will have the potential effect of modifying the life traits of migratory fish, which will then be able to swim up or down the river to live or reproduce. This is the case for eels and flounder, two migratory species that live in rivers and reproduce at sea. On the Selune, the restoration of continuity will potentially have two effects on these populations:

• The recolonisation of upstream habitats should lead to a reduction in competition, a change in life traits (growth, size, fecundity and age at reproduction) and in the health status, particularly of eels.
• Sediment and nutrient fluxes will be modified, with probable consequences for the quality of downstream habitats, particularly in the estuary, and an impact on the nursery function for flounder.

Subject(s) of study

The project focuses on the study of two migratory species known as thalassotoic, which live in rivers and reproduce at sea: eels and flounder.

Objectives

The aim of this project is to monitor the process of restoring continuity to the Selune by studying changes in the life traits of migratory fish. The main objective of this research project is to characterise the life traits of eels and flounder before the continuity of the Selune is restored, in order to quantify its effects afterwards. The project also aims to study the life history (dynamics) of these fish, as reflected in their use of the river's various habitats. In this way, it will be possible to quantify the influence of the removal on the stocks of individuals, such as eels, and to draw lessons to support future actions to manage or restore ecological continuity.

Methods

The simultaneous study of flounder and eel provides a relatively exhaustive view of the effects of restoring continuity by removing dams. Flounder are the main integrators of changes downstream of dams at the river-sea interface (estuarine nursery). Eels, on the other hand, integrate changes in the accessibility and quality of habitats throughout the catchment area. As part of this project, the research teams are analysing the link between:

• Life traits (age, size, weight, fat content, condition, growth rate, etc.),
• Life history (growth habitat, dependence on the estuary),
• Trophic position (d13C and d15N isotope analyses)
• The health status of silver eels (condition indices, study of gut microbiome and parasite communities).

Laboratoire(s) impliqué(s)

• MNHN - National Museum of Natural History, marine station of Dinard
• BOREA - UMR Biology of Aquatic Organisms and Ecosystems, Dinard
• ECOBIO - UMR Ecosystems, Biodiversity, Evolution, Rennes