Predation of migratory species by juvenile catfish (silurus)

The project “Predation of migratory species by juvenile catfish (silurus)” assesses the predation pressure of migratory fish species by juvenile catfish on the Selune River and other fluvial systems in France.

The project in short…

Theme	Biocenosis, functioning and evolution
Full title	Predation of migratory species in their young stages by juvenile catfish (Silurus glanis)
Objectives	1. Evaluate the predation pressure by catfish on migratory fish species in the Selune River. 2. Compare this pressure with other systems in France where the same problem arises
Study subject(s)	Wels catfish (Silurus glanis) ; migratory fish
Methods used	Scientific fisheries; metabarcoding; analysis of stomac contents; biometrics; participatory science
Project length	2021-2023
Coordinator(s)	Frédéric Santoul and François Martignac
Laboratories involved	UMR Laboratoire Evolution et Diversité Biologique (EDB), Toulouse UMR Ecologie et Santé des Ecosystèmes (ESE) INRAE/Agrocampus Ouest, Rennes Pôle MIAME pour les migrateurs OFB-INRAE-Agrocampus Ouest-UPPA, Rennes
Funding source	OFB

Scientific context

The predation pressure by catfish

Earlier works on the interaction between catfish and migratory species showed that 50% of the prey consumed by adult catfish were migratory fish. Recently, new studies have quantified the predation of adult Wels catfish on adults of three diadromous species. These three species are the Atlantic salmon, the sea lamprey and the big shad. However, very little information currently exists on the potential predation of juvenile catfish on the juveniles of these migratory species. Nevertheless, preliminary results are worrying.

In Portugal, on the Tagus, lamprey larvae were found in the stomach contents of young catfish.
In France, on the Selune River, preliminary analyses of the stomach contents of catfish revealed predation of migratory species.

Catfish in the Selune River

Little information is available on the distribution and current abundance of catfish in the Selune river, where the conservation of migratory species is a priority. Nevertheless, the indices collected in recent years all lead to the same observation. Catfish, which represented more than 50% of the biomass of the reservoir emptied in 2018 (i.e. 6.5 tonnes), are being increasingly witnessed in the lower parts of the Selune River:

Reported as early as 2014 in the acoustic chronicles recorded at Ducey, site visits seem to have increased since 2019, with individuals of a size never before observed on the site, ranging up to 150 cm.
In 2019, around ten adult catfish between 80 and 120 cm were caught by salmon fishermen on the lower part of the Selune.
Nearly thirty young catfish, the majority of which are juveniles of the year (or 0+), were caught during scientific fisheries using different fishing gears.

The goal of Selune River restoration is to re-establish the free movement of many migratory fish species. The expansion of catfish on the Selune River with certainly a strong increase to come of juvenile stages, as well as the relatively small size of this environment make it a privileged site for the study of the predation of juvenile catfish on migratory species in their young stage.

Study subject(s)

The project focuses on juvenile catfish and their predation pressure on migratory fish species in the Selune River and other French fluvial systems.

Objectives and methodology

Given the adaptive capacities, and the very opportunistic nature of the catfish, this research project aims first of all at examining whether juvenile catfish significantly integrate migratory species into their diet.

Through this question, the project is interested in assessing the threat posed by the establishment of an expanding catfish population in a highly migratory hydrosystem such as the Selune.
This approach will allow, secondly, comparing this predation pressure with that of other systems in France where the same problem arises (e.g. Garonne, Adour …).

A fishing decree prohibits the release and live transport of catfish caught since 2019 in the Selune valley. Scientific fishing actions upstream and downstream of the dams, as well as in the areas of confluence with the major tributaries of the Selune, also make it possible to capture and freeze catfish from their juvenile to adult stages. Morphological readings, as well as the collection of fins, muscles, faeces samples and stomach contents are thus carried out on these individuals. Analysis of stomach contents and faeces samples using metabarcoding methods will identify the species included in their diet.

Communication actions are also carried out with local amateur fishermen, in partnership with the departmental teams of the OFB and the Manche Fishing Federation (50). The objectives of these actions are:

To encourage fishermen not to put catfish individuals back into the river.
To inform them about the procedure to follow to hand over the captured individuals to the search teams.

Results and conclusions

This project is ongoing. Results and conclusions will be elaborated later.

Publications and reports

This research project is ongoing. Here you will find the list of reports and publications.

The project “Predation of migratory species by juvenile catfish (silurus)” is part of the second phase of the Selune scientific program. Find all the research projects here.