Localizing sounds from ships and cetaceans with a glider equipped with a 8 hydrophones’ network : First results from a 20 day - 600 km exploration of the Western French Mediterranean Sea in 2019

In response to concerns about the impact of manmade noise on marine ecosystems, research and regulatory communities are currently collecting in situ measurements of oceanic noise levels and identifying their anthropogenic contributions. Gliders equipped with passive acoustics payload are ideal candidates to collect noise level data across oceanic basins and over long time periods. They are also ideal to detect individual sound sources such as boats, whales or dolphins. They offer the synoptic view of the eco-acoustic situation: the map of the anthropogenic noise, the presence of animals and the quantification of the noise they are faced with.

Here, we report on the use of a new acoustic payload, a network of eight hydrophones mounted on a glider SEAEXPLORER to allow for a better acoustic characterization through localization of sources thanks to the array of hydrophones.

We present an innovative algorithm to estimate the bearing of cetacean calls and ship noise from the glider’ array of hydrophones. This algorithm is applied to a 20 days – 600 km exploration ran in 2019 in the Western French Mediterranean Sea. The trajectory of the glider was chosen to sample 1) the highest and lowest shipping densities and 2) the deepest and the shallowest water in the Gulf of Lion.

The results are simultaneous time series of:

• cetaceans detections (click of odontocetes), the number of individuals and their bearings,
• ships detections and their bearings,
• ambient noise level.

They are analyzed to report on the level of effects of the anthropogenic noise on odontocetes in the Western French Mediterranean Sea.