A natural ocean-sounding landscape is fundamental to a healthy marine life, but is drowned out by an increasingly cacophony of noise from human activities, according to the first comprehensive assessment of the case.
The damage caused by noise is just as harmful as overfishing, pollution and the climate crisis, the scientists said, but it is dangerously overlooked. The good news, they said, is that noise can be stopped immediately and not like the other problems.
Marine animals can hear over much greater distances than they can see or smell, and this makes sound crucial for many aspects of life. From whales to shellfish, marine life uses sound to catch prey, navigate, defend territory and attract mates, as well as find homes and warn of attacks. Noise pollution increases the risk of death and in extreme cases, such as explosions, can kill directly.
The emission of carbon dioxide by burning fossil fuels also makes the oceans more acidic, meaning the water carries further noise, leading to an even noisier ocean, the researchers said. But the movement of marine mammals and sharks to previously noisy areas when the Covid-19 pandemic rocked ocean traffic showed that marine life could recover quickly from noise pollution, they said.
“Everything from the smallest plankton to sharks feel to their acoustic environment,” said Prof Steve Simpson at the University of Exeter in England, and part of the judging team. “As a result, the animals have to produce sound to communicate, but also to receive sound.” He said noise pollution was like an “acoustic fog” in the sea.
“Marine animals can see no more than ten meters and smell hundreds of meters, but they can be heard all over the ocean basins,” Prof Carlos Duarte told King Abdullah University of Science and Technology in Saudi Arabia, citing the review. Duarte said large-scale assessments of ocean health ignore noise: “However, the scientific literature, if read carefully, provides compelling evidence that human-caused noise is a major source of disruption to the marine ecosystem.”
The review, published in the journal Science, analyzed more than 500 studies that assessed the effects of noise on marine life. About 90% of the studies caused significant damage to marine mammals, such as whales, seals and dolphins, and 80% had effects on fish and invertebrates. “Sound is a fundamental component of ecosystems, [and noise] the impact is crucial and affects animals at all levels, ”the analysis concluded.
The most obvious impact is the link between military sonar and explosions of seismic surveys and deafness, massive strandings and deaths of marine mammals. But many uses of sound can be impaired, such as the hum that male toadfish use to attract females and the horns that cod use to coordinate spawning.
Baleen whales make calls to help cohesion and reproduction that can move across basins, and humpback whales sing intricate mating songs with local dialects. Sperm whales and various dolphins and pigs use sonar to echo prey. Other animals use sound to feed: some shrimp make a ‘snap’ sound to stun prey.
However, over the past 50 years, increased shipping has increased lower frequency noise on major routes 32 times, the review said. Fishing vessels use sonar to find the fish of the fish, and make trawlers rumble beneath them. The construction and operation of oil rigs and foreign wind farms also caused noise pollution, as well as the explosion of World War II bombs in the North Sea.
“Fish, mussels, crabs and corals all hear sound and use it to find healthy places where they can go home,” Simpson said. ‘So, the ship or construction noise takes away the feeling of home. It also means that whales that may have lived in a family and hunted more than hundreds of miles must live within ten miles of each other in order to communicate.
“We find that animals are also directly affected by noise, which is why they make poor decisions that often lead to death,” he said, noting that the noise of motorboats on the Great Barrier Reef in Australia leads to the double death rate of predators .
“Underwater noise is a serious concern, and it is increasing,” said Prof Daniel Pauly of the University of British Columbia in Canada, who was not part of the review team. “The noise that mammals are exposed to is devastating … Sound waves underwater are much louder than sound waves in the air.”
There are solutions, according to the review, with the construction of five large cargo ships by Maersk in 2015, which show that new propeller designs reduce noise and also increase fuel efficiency. Calmer screws are the top priority, Duarte said; half the sound of the shipment comes from only 15% of the ships.
Electric motors are another possible solution, as well as small reduction in speed. For example, by reducing the speed of noisy vessels in the Mediterranean from 15.6 to 13.8 knots, the noise is reduced between 50 and 50% between 2007 and 2013. Seismic surveys can also be performed using vibrators on the bottom, rather than sending sound waves through the entire water column.
“Cutting noise is possibly the fruit that hangs the lowest to make a difference, and we can change that today,” Simpson said. “I really hope we hear a healthier ocean in our lives.”