Blog [Interview]

Exchange with Delphine Mathias

Underwater acoustics study manager

To monitor sound levels during tests and then during drilling and installation work, Ailes Marines contracted, on the recommendations of the CDPMEM22, the Société d'Observation Multi-Modale de l'Environnement (SOMME), an office of independent studies specializing in the observation of marine ecosystems. 

Delphine Mathias, underwater acoustics study manager at SOMME, analyzes the sound data provided by the RUBHY acoustic buoy designed and developed by RTSYS and GISMAN and deployed during drilling operations. 

What studies are you carrying out on the park?

We carry out acoustic monitoring measurements to characterize the underwater noise emitted during drilling and park installation work in order to assess its impact on the marine environment. We intervened in 2018 during the second geotechnical campaign and in 2021 when the work began. We studied continuous, real-time underwater noise measurements from the buoy deployed 400 m from the drillship.  

In what context do these studies take place? 

These measurements carried out on site are part of the continuity of scientific studies carried out over 24 months between 2018 and 2020 with Dr. Laurent Chauvaud, research director at the CNRS and Pr. Frédéric Olivier from the National Museum of Natural History . These studies carried out in the laboratory focused on the effects of noise during work on species fished in the bay of Saint-Brieuc: scallops, clams, sea almonds.

What are the results ?

We were able to monitor the sound level of the drilling in real time by recording data collected by the buoy every 10 minutes. Analysis of the noise emitted by the drilling of the Aeolus ship confirms an emission of between 180 and 190 decibels at the source of the drilling. These emissions fall between 137 and 151 just 100m from the drilling point. At 1 km from drilling and trenching operations, the sound levels received correspond to an ambient noise level representative of an area frequented by several types of vessels (fishing vessels, tugboats).

Have you also carried out biomonitoring using valvometry on scallops? 

Yes indeed, we have equipped scallops with valvometers. We placed them in cages and submerged them near a drilling point. The objective being to study their state of health and their reaction by analyzing the frequency of opening and closing of the valves (number of jumps) during drilling operations. In this experiment, we did not observe a difference in the number of jumps made at different distances from the Aeolus vessel during drilling activities. We also did not record any mortality linked to the noise emitted during drilling on shells equipped with valvometers.

What are your conclusions ?

The results of these studies carried out on site corroborate the results obtained in the laboratory, namely that the noise levels emitted during the work do not cause excess mortality in the species studied. The noise level of the work corresponds to that reported on other sites for drilling work and emitted by vessels over 100m long.

What will become of these studies? 

We submitted the results of these studies to the Ailes Marines company, the prefectural authorities and the fisheries committee, CDPMEM22. The results are presented to the park management and monitoring committee.  

These studies will improve knowledge on the behavior of fish species and more specifically on the effects of sound on scallops. This study, carried out on no other offshore wind farm in the world, represents a world first for marine scientific research. This work and research will be the subject of scientific publications.