Mapping underwater noise with a SeaExplorer glider at a basin level: Feedback from the first 1000km-long acoustics exploration of the Western French Mediterranean Sea

Abstract

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 developing models that map the levels of underwater noise at large scales, forecasting the impact of shipping noise on marine fauna. The objectives of in situ measurements are twofold. First, they provide necessary inputs, i.e. the acoustic signatures of individual ships to feed the models. Second, they are used to calibrate the model and adjust its parameters. The usefulness of the data collected depends on the duration of acquisition and measurement diversity (e.g., shipping density, water depth). Gliders are ideal candidates 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 acoustics payload travelling for 30 days along a 1000km-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,–the anthropogenic contribution of shipping to the global noise budget and the acoustic footprint of main shipping lanes,–comparisons of the lowest Mediterranean ambient noise levels to the ones of a pristine area with regard to shipping noise,–comparisons between long term coastal fixed mooring measurements ( 3 continuous points) and glider measurements and assessment of the pro and cons of each method (fixed mooring and glider).