Richard Collins: Ocean sound pollution is increasing — and it's affecting whales
Humpback whales can 'talk' to each other even when tens of kilometres apart — but noise levels in the oceans have been aggravated by ocean warming. Picture: AP Photo/Michael Dwyer, File)
The Self-Contained Underwater Breathing Apparatus (SCUBA) was invented in 1943 by French engineer Emile Gagnon and a naval lieutenant named Jacques Cousteau. Use of the device would transform our understanding of ocean life while Cousteau, with his ground-breaking television documentaries, became the John the Baptist predecessor of David Attenborough.
, directed by Cousteau and Louis Malle, won the Palme d’Or at the Cannes Film Festival in 1956. Limerick County Library had a copy of the accompanying book. With its close-up photos of a shark head-butting Cousteau’s camera, it made an indelible impression on me.
The film and book, however, were guilty of a glaring error... their title was most misleading. The undersea world is far from silent. Our ears are tuned to airborne vibrations, not underwater ones, which led Cousteau to conclude that sound is virtually absent in the deep. Nor do human vocal chords function effectively — divers’ speech becomes muffled and weak.
Humpback whales, however, can ’talk’ to each other when tens of kilometres apart. Sound propagates faster and farther in water than in air. It has even been claimed that whale ‘songs’ travel up to 15,000km ‘in some levels of the ocean’. Sperm whales produce a pulse so powerful that it demobilises the fish they hunt. Nor are sea mammals the only ocean vocalisers: about 20% of fish species are known to communicate using sound. There may even be an ocean version of the dawn chorus.
Being sensitive to sound, however, has a downside. Noise is nuisance, as people living close to the new runway at Dublin Airport will tell you. Aircraft screaming overhead, they claim, are driving local residents mad.
Predicting the contribution of climate change on North Atlantic underwater sound propagation @thePeerJ https://t.co/ExjzyCG0ks pic.twitter.com/Y9vsEUWCHc
— Behav Ecol Papers (@BehavEcolPapers) October 10, 2023
Aircraft noise doesn’t trouble sea creatures but the throbbing of ships’ engines does. Dredging, drilling, and pile-driving for wind-turbine installation generate noise pollution. So do submarine-detection SONAR systems and the discharges of weapons during naval exercises. Noise levels in the oceans have been rising relentlessly since the Industrial Revolution. They have increased by 12dB in the last 50 years. In a process known as the Lombard Effect, creatures such as whales must shout louder in order to be heard above the cacophony.
Now, according to a paper just published, there’s a further threat. Researchers from Utrecht University say that ocean warming is aggravating the underwater noise problem. Sound transmission through water is amplified with increased temperature and acidity. The sea west of Ireland was 4°-5°C warmer than normal this summer and the oceans are not only warming, they are becoming more acidic.
"During this century, we will see an increase in seawater temperature" and "ocean acidification will decrease sound absorption at low frequencies, increasing sound propagation" according to the Utrecht research. Modelling the soundscape in six different seas, the researchers found variations in temperature rise between regions. The situation in the North Atlantic, as the ice cap continues to melt and freshwater pours into the sea, is complex. Climate change, they say, will lead to stratification in the ocean there. A ‘sound channel’ will open up, enabling noise to travel farther.
Silence please!
