In situ demonstrator of a method to track in three dimensions cetaceans with passive acoustics in the context of close interactions impacts with marine renewable energy devices

Abstract

Collision risk and close interactions of cetacean with marine renewable energy (MRE) devices are among the main concerns and the least documented of the list of potential impacts of MRE. In this study, we developed a method to track in three dimensions click trains emitted by cetaceans in a close vicinity to MRE devices. We deployed two synchronized directional recording arrays 150 m apart from each other near Cherbourg (France). With an acoustic tag VEMCO© placed at several depths we performed transects with several trajectories simulating the potential behaviors (diving, surfacing, avoidance, and attraction) and click production of delphinidae. Thanks to the directional recording arrays and by crossing the direction of arrival of the same sounds calculated on each array, we build 3D maps of the synthetic clicks. We manage to reconstruct the trajectories (absolute positions x, y, and z in meters) of the emitter. In the areas located 100 m upstream and downstream of the two recording arrays, the location accuracy is maximum. This method could also be used to prove the departure and the non-return of cetacean from an exclusion zone. Moreover, this approach has been designed to be operational for the monitoring of cetaceans in environmental impact assessment studies.