Mapping underwater noise, detection of ships and cetaceans using a SeaExplorer glider at a basin level: Feedback from the first 1000 km-long acoustic exploration of the Western French Mediterranean Sea

Abstract

In response to concerns about the impact of man-made noise on marine ecosystems, researchers and environmental managers are currently collecting in situ measurements of oceanic noise levels. The objectives of in situ measurements are to provide the acoustic signatures of individual ships, with the use of AIS databases, to feed the models; to calibrate the model for mapping of shipping noise, and to assess marine biodiversity through the sounds emitted by marine animals (invertebrates, fishes, and cetaceans). The usefulness of the data collected depends on the duration of acquisition and the diversity of the measurements (e.g., shipping density and water depth). Gliders are ideal vehicles to collect noise level data across oceanic basins and over long time periods. Here, we show results from a SeaExplorer glider equipped with a high quality acoustic payload travelling for 30 days (09/15/2017-10/15/2017) along a 1000 km-long transect of the Western French Mediterranean Sea. The trajectory of the glider was chosen to sample the highest and lowest shipping densities. We here report on the statistical distribution of oceanic noise levels in the bandwidths assessed by the European Marine Framework Strategy Directive as well as on the detection of cetacean and ship sounds along the transect.