A natural ocean soundscape is fundamental to healthy marine life, but it is drowned out by an increasingly loud cacophony of noises from human activities, according to the question’s first comprehensive assessment.
The damage caused by noise is as bad as overfishing, pollution and the climate crisis, scientists said, but is dangerously overlooked. The good news, they said, is that noise can be stopped instantly and doesn’t have any lingering effects like other problems do.
Marine animals can hear at much greater distances than they can see or smell, making sound crucial for many aspects of life. From whales to crustaceans, 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, kills directly.
Carbon dioxide emissions from burning fossil fuels also make the oceans more acidic, meaning the water carries sound further, leading to an even noisier ocean, the researchers said. But the movement of marine mammals and sharks into 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 smallest plankton to sharks perceives their acoustic environment, ”said Professor Steve Simpson of the University of Exeter in England, and member of the review team. “As a result, animals must produce sound to communicate, but also to receive sound.” He said the noise pollution was like “acoustic fog” in the ocean.
“Marine animals can only see tens of meters at most and can smell hundreds of meters, but they can hear across entire ocean basins,” said Professor Carlos Duarte of the University of Sciences and King Abdullah technologies in Saudi Arabia, who led the study. review. Duarte said major ocean health assessments ignore noise: “Yet the scientific literature, when read carefully, provides compelling evidence that human-made noise is a major source of disturbance to the ocean. the marine ecosystem. “
The article, published in the journal Science, analyzed more than 500 studies evaluating the effects of noise on marine life. About 90% of studies found significant damage to marine mammals, such as whales, seals and dolphins, and 80% found impacts to fish and invertebrates. “Sound is a fundamental component of ecosystems, [and noise] the impacts are pervasive, affecting animals at all levels, ”the analysis concluded.
The most obvious impact is the link between military sonar detonations and seismic surveys and deafness, mass stranding and death of marine mammals. But many uses of sound can be damaged, such as the buzzing that male toadfish use to attract females and the horns that cod use to coordinate spawning.
Baleen whales call out to help cohesion and breeding groups that can traverse ocean basins, and humpback whales sing intricate mating songs that have regional dialects. Sperm whales and various dolphins and porpoises use sonar to echolocate their prey. Other animals use sound for food: some shrimp make a “clicking” sound to stun their prey.
However, over the past 50 years, the increase in shipping has resulted in a 32-fold increase in low-frequency noise on major routes, according to the study. Fishing boats use sonar to find schools of fish, and bottom trawlers create a rumble. The construction and operation of oil platforms and offshore wind farms are also the source of noise pollution, as are world war ii bomb explosion in the North Sea.
“Fish, clams, crabs and corals all hear sound and use it to find healthy places to settle,” Simpson said. “So the noise of shipping or construction takes away that sense of rallying. It also means that whales that could have lived as a family and hunted hundreds of miles must live within 10 miles of each other in order to communicate.
“We find that animals are also directly stressed by noise, and therefore make bad decisions which often lead to death,” he said, noting that the noise of motor boats on the Great Barrier of coral in Australia leads to double mortality from predators.
There are solutions, the review found, with a modernization of five large container ships by shipping giant Maersk in 2015, showing that new propeller designs reduce noise and also increase fuel efficiency. Quieter propellers are the top priority, said Duarte; half of navigation noise comes from only 15% of ships.
Electric motors are another possible solution, as are small speed reductions. For example, reducing the speed of noisy vessels 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. , rather than sending sound waves throughout the water column.
“Cutting the noise is perhaps the easiest fruit to make a difference and we can change that today,” said Simpson. “I really have hope that we will hear a healthier ocean in our lifetime.”