A natural soundscape of the ocean is fundamental to healthy marine life, but it is being drowned out by an increasingly loud cacophony of noise from human activities, according to the first comprehensive assessment of the problem.
Noise damage is just as damaging as overfishing, pollution and the climate crisis, scientists said, but it is being dangerously overlooked. The good news, they said, is that the noise can be stopped instantly and has no prolonged effects, as with other problems.
Sea animals can hear at much greater distances than they can see or smell, making sound crucial to many aspects of life. From whales to crustaceans, marine life uses sound to capture prey, sail, defend territory and attract companions, as well as find homes and warn of attacks. Noise pollution increases the risk of death and, in extreme cases, such as explosions, kills directly.
Carbon dioxide emissions from burning fossil fuel are also making the oceans more acidic, meaning that water carries sound farther, leading to an even louder ocean, the researchers said. But the movement of marine mammals and sharks to previously noisy areas when the Covid-19 pandemic reduced ocean traffic showed that marine life could recover quickly from noise pollution, they said.
“Everything, from the tiniest plankton to the sharks, detects their acoustic environment,” said Professor Steve Simpson of the University of Exeter in England and part of the review team. “As a result, animals have to produce sound to communicate, but also to receive sound.” He said that noise pollution is like an “acoustic fog” in the ocean.
“Marine animals can only see through tens of meters at most, and can smell through hundreds of meters, but they can hear through entire ocean basins,” said Prof Carlos Duarte of King Abdullah University of Science and Technology in Arabia Saudi, who led Reveja. Duarte said that the main assessments of the health of the oceans are ignoring noise: “However, the scientific literature, when read carefully, provides compelling evidence that man-made noise is an important source of disturbance to the marine ecosystem.”
The review, published in the journal Science, analyzed more than 500 studies that evaluated the effects of noise on marine life. About 90% of the studies found significant damage to marine mammals, such as whales, seals and dolphins, and 80% found impacts on fish and invertebrates. “Sound is a fundamental component of ecosystems, [and noise] the impacts are widespread, affecting animals at all levels, ”concluded the analysis.
The most obvious impact is the link between military sonar and detonations from seismic and deafness surveys, mass strandings and deaths of marine mammals. But many uses of sound can be harmed, such as the humming sounds that male frog fish use to attract females and the horns that cod uses to coordinate spawning.
Fin whales produce sounds to help cohesion and reproduce the group that can travel across ocean basins, and humpback whales sing complex mating songs that have regional dialects. Sperm whales and several dolphins and porpoises use sonar to echo their prey. Other animals use sounds to feed: some shrimp make a “popping” sound to stun the prey.
However, in the past 50 years, increased maritime transport has increased low-frequency noise on major routes by 32 times, the review said. Fishing vessels use sonar to find schools of fish and bottom trawlers create a thunderous noise. The construction and operation of oil platforms and offshore wind farms also cause noise pollution, as does the detonation of World War II bombs in the North Sea.
“Fish, shellfish, crabs and corals hear the sound and use it to find healthy places to live,” said Simpson. “Therefore, the noise of transport or construction takes away this feeling of return. It also means that whales that may have lived in a family and hunted for hundreds of miles must live less than 10 miles from each other in order to communicate.
“We found that animals are also directly stressed by noise, so they make the wrong decisions that usually lead to death,” he said, noting that the noise from motorboats on the Great Barrier Reef in Australia leads to twice as much noise. predator mortality.
“Underwater noise is a serious concern and is growing,” said Professor Daniel Pauly of the University of British Columbia, Canada, who was not part of the review team. “The noise level to which marine mammals are exposed is devastating … Underwater sound waves are much more violent than sound waves in the air.”
There are solutions, the review found, with a retrofit of five large container ships by shipping giant Maersk in 2015, showing that the new propeller designs reduce noise and also increase fuel efficiency. Quieter propellers are the top priority, said Duarte; half of the transport noise comes from only 15% of ships.
Electric motors are another possible solution, as well as small speed reductions. For example, reducing the speed of noisy ships in the Mediterranean from 15.6 to 13.8 knots reduced noise by 50% between 2007 and 2013. Seismic surveys can also be carried out using seabed vibrators, instead of sending waves noise throughout the water column.
“Cutting noise is possibly the shortest-reaching fruit that can make a difference and we can change that today,” said Simpson. “I am hopeful that we will hear a healthier ocean in our lives.”