Assessment of the St. Lawrence Estuary Soundscape

The St. Lawrence Estuary is renowned for the abundance and diversity of marine mammals that come to feed in summer or live all year round in its waters. It is also a major seaway linking the Great Lakes to the Atlantic Ocean. Due to the high maritime traffic in this seaway, negative impacts on marine mammals are an issue to be studied. In the current context of sustainable development and protection of marine species at risk in Canada, such as the beluga whale (Delphineptarus leucas) and blue whale (Balaenoptera musculus), it is essential to determine the noise levels to which these species are exposed. In this chapter, the underwater soundscape recorded from August to October 2021 by the Marine Acoustic Research Station (MARS) – consisting of four vertical arrays of three hydrophones deployed in the middle of the Laurentian Channel – is analyzed. In addition to recording the ship’s signatures, they continuously acquire ambient noise created by all traffic and cetacean emissions to provide a complete picture of the acoustic context of the St. Lawrence Estuary. An analysis of the relative contribution of wind and traffic noises to ambient noise at three different 1/3-octave bands has been achieved. At low frequencies (50 Hz), used by blue whales’ long-range communication signals, traffic noise dominates the soundscape. At mid-frequencies (300 Hz), used by humpback whales’ short-range signals, a mixed regime is observed. At high frequencies (6300 Hz), used by belugas’ whistles, wind noise dominates the soundscape.