Counting fish using a hydroacoustic camera

Counting fish using a hydroacoustic camera

What is the potential for migratory fish to colonise the Selune?

Diagram of how the acoustic camera works - by Guillard and Lebourges-Dhaussy (2014)

An acoustic camera has been installed in the Sélune at Ducey, downstream of the two dams, since 2013. Hydroacoustics, which uses the properties of sound in water, enables a continuous recording in the water regardless of the brightness or clarity of the water. Part of the waves emitted by the sonar are reflected by all the objects passing through its detection beam. It is therefore a non-intrusive observation tool that continuously records the activity of local aquatic fauna at the monitoring site, day and night.


The acoustic camera at Ducey downstream of the (former) dams. The camera beam shows the passage of fish, in green in the photo (Photos: F.Martignac) © François Martignac

Analysis of the recordings allows us to:

  • Count the passage of fish, particularly migratory fish;
  • Identify species on the basis of their behaviour, morphology or interactions;
  • To estimate migration fluxes and fish stocks in the river;
  • And to improve our knowledge of how the river functions before and after the restoration of ecological continuity in the Selune.


Example of an image recorded by the DIDSON acoustic camera on the Sélune showing the passage of a sea lamprey up the Sélune (Photo DIDSON: F.Martignac)

See also

The acoustic camera at Ducey was installed as part of a research project on the analysis of migratory flows. This project aimed at optimising the analysis of recorded images in order to count the passage of fish during the assessment phase (before dismantling).

Modification date : 17 August 2023 | Publication date : 31 July 2023 | Redactor : Selune Team