The Covid-19 lockdown has produced the quietest year for the world’s oceans in recent memory, according to a group of scientists working on a global map of underwater soundscapes. Noise pollution from ship engines, trawling activities, oil platforms, subsea mining and other human sources declined significantly last spring, say the researchers, who are part of a collaborative network of 231 non-military hydrophones. They believe the relative hush can provide valuable comparative data for an unplanned experiment in how sound affects whales, coral and other marine species. Like light pollution on the land , human noise is a growing concern in the oceans because it has been proven to disrupt species that depend on sound for communication and navigation. Low-frequency signals can travel thousands of kilometres. Studies in the north-east Pacific showed an increase of 3 decibels each decade in human-generated sounds below 100 hertz between the 1960s and early 2000s. By one reckoning, the volume of this audio pollution is now around the same level as the natural background noise of the ocean. This faded substantially last year at the height of lockdown in March, April and May, starting – like Covid – around China and then spreading worldwide. […]

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