First insight of the response of great scallops ( Pecten maximus) to drilling activities during the construction phase of an Offshore Wind farm (Saint Brieuc, France)

There are still major gaps in our knowledge of how invertebrates react to the sounds and vibrations generated by the construction of Offshore Wind Farms (OWFs). With the recent development of such projects in the vicinity of scallop (Pecten maximus) areas in France, particular attention has been paid to this economically important species. In this context, we monitored the activity of 30 scallops during drilling operations associated with the construction of the Saint Brieuc OWF. Equipped with valvometers (Hall effect sensors), the scallopswere deployed at three distances from a drilling point (300, 600, and 3000m) for three weeks, covering the platform vessel installation and the drilling operations. Two acoustic measurement buoys were also deployed (400 and 3000m) to assess the exposure of the scallops to drilling noise. The valve opening data acquired revealed a circadian cycle associated with nocturnal activity (more open at night than during the day) for the majority of individuals (82%). The individuals monitored maintained this cycle throughout the drilling period, regardless of distance from the drilling point. However, an increase in the number of large-amplitude movements was identified for scallops located 300m from the drill ship during its installation. Although the interpretation of this observation is tricky, it shows that scallops were able to perceive the installation of the jack-up vessel up to 3 km, with their response decreasing over thedistance. Further studies involving additional measurements (seismic, particle movement, etc.) are needed to better understand the effect of these activities on this species.