BI O Rhône: a tracking technology for fishes

Presentation

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Context in which the project was created:

CNR and SIG wish to have a more accurate knowledge of the presence, abundance and behavior of fish during and after sediment management operations* led jointly by Switzerland and France.

Indeed, a modification of the fish biomass has been observed since reservoirs are put into service. The need to know both its current characteristics and the ways of rebuilding stocks, started to emerge.

*Active management of sediments on the Upper Rhone is necessary. Indeed, at the confluence with the Rhône in the city of Geneva, the Arve brings 700,000 m3 of sediments per year, of which 360,000 m3 are deposited in the reservoir of Verbois, located a few kilometers downstream. The progressive fattening of the reservoir increases the risk of flooding, and ultimately the risk of flooding in Geneva’s lower neighborhoods.

 

Strategy and objectives

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The Bi O Rhône project has two objectives:

• Methodological development for the monitoring of the fish fauna of the reservoirs: the aim is to qualitatively and quantitatively evaluate techniques for the exploration of fish fauna in order to develop a sampling method adapted to the Rhône reservoirs and potentially transferable to other rivers of the Rhone dimension.
• Monitoring the impacts of sediment management: it will be necessary to test the possible exploitation of this sampling method in order to preserve the fish fauna of the Upper Rhone during the sedimentary management operations of the French and Swiss hydropower reservoirs, the accompaniment of floods of the Arve and dredging.

The Bi O Rhône project is conducted on 4 successive reservoirs: the hydroelectric reservoir of Verbois ; the hydroelectric reservoir of Chancy-Pougny ; the hydroelectric reservoir of Genissiat and the hydroelectric reservoir of Seyssel.

Expected results:

• Propose moderation solutions to preserve the environment,
• Have a better understanding of fish biomass while maintaining transboundary hydroelectric production,
• Validate a new method of fish management linked to sediment transit.

 

The project’s innovative characteristics

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Technical

The evaluation of the fish population of the reservoirs was carried out thanks to two innovative methods. The first method is the environmental DNA. A tool has been made up to inventory biodiversity, by using the DNA traces let by human being in their environment. DNA can be extracted from environmental samples such as water, the floor or the air, without the need to isolate target individuals beforehand. The metabarcoding DNA (or multispecies approach) allows making an inventory of all the species of a target group (for example, bacteria, vertebrates, fish, etc.) without prior knowledge of their presence in the habitat studied. It is a powerful environmental monitoring tool, especially in aquatic environments.

But this technical has quantitative limits (we do not know the exact number of fish) and limits on the size, the developmental stages, and the sex of the organisms. To overcome these limits, the hydroacoustic method has been used. Data obtained from two echosounders will provide an estimation of the biomass, spatial distribution and size classes. With a more quantitative assessment of fish biomass, this method is therefore complementary to the environmental eDNA method.

Economic/Financial

This method provides a holistic view of the biodiversity in the environment at a lower cost, especially because it is quick and easy to implement. The water withdrawal takes 30 minutes, and the analysis time is usually 2 to 3 months.

Environnemental

Both techniques implemented are neither intrusive nor destructive, unlike the usual fishing techniques in reservoir, which avoids any impact on the environment.

 

Results and outlook

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The coupling of echo sounding and eDNA techniques has shown its potentialities in the first year. It provided a better understanding of the fish biomass in the different reservoirs. This allows seasonal monitoring of inter and intra-reservoir fish species.

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How can this project be duplicated on other rivers?

These techniques are potentially duplicable on all rivers, but also adapted to rivers in reservoirs, lakes,…

Used for a sediment management problem in this project, this technique can answer other questions concerning variations in fish biomass. Nevertheless, it is necessary to be aware of three limitations relating to the use of this technique:

• High currents do not provide echo sounding of quality (spurious noise): it’s important to choose the monitoring stations.
• Better echosounding results have been registered during night (dispersal of fish and increase in fish activity).
• The need for a full-scale test to validate the feasibility (courant, suspended matter, large debris).

To know more

Photo credit: Camille Moirenc/ La Gallery