Human-Made Noise in the Oceans is a Growing Problem

(Inside Science) -- The depths of the oceans are often thought of as a silent world, where almost no sounds are ever heard -- but that was never the case, and they’ve only become noisier as human technologies have advanced. There’s a growing underwater din from shipping, coastal industries, and off-shore oil rigs and wind farms, for example, and it has badly impacted animals like whales, dolphins and fishes that may struggle to hear their own sounds in the cacophony.

“It’s not silent,” says Doug Nowacek, a professor of marine conservation technology at Duke University in North Carolina. “People have this idea that it is just so quiet down there, so who cares if you make a bunch of noise, because the animals don’t care. But it’s a world full of sound.”

Just how noisy it’s become beneath the waves, and what people can do about it, is the subject of a new review appearing in the journal Science, written by an international team of scientists who looked at more than 40 years of studies. Led by marine ecologist Carlos Duarte of King Abdullah University of Science and Technology in Saudi Arabia, the review details the rapidly growing problem of noise in the oceans caused by human activities, and how it affects the animals that live there.

The team determined that underwater noise from fishing, shipping, and development has sharply increased over the last 100 years, making the modern oceans far noisier than ever before. But they argue the harmful effects of underwater noise pollution could rapidly decline if efforts are made to reduce it.

Sound carries especially well underwater, and animals rely on it for everything from finding their way around and feeding, to breeding and choosing the places they will live. Whales and dolphins that sing to each other and use echolocation to navigate and hunt are the best-known, but countless species of fish and marine invertebrates also depend on sound to live their lives.

Human-made noise in the ocean comes from a wide variety of sources. Duarte told Inside Science in an email that the main ones are shipping, drilling for oil and gas, trawling and other industrial activities; coastal works, such as construction, industries, dredging, and aircraft at coastal airports; underwater seismic surveys and military sonars, which can be fatal to deep-diving whales; and explosions, such as those from accidental blasts or dynamite fishing, which is occasionally used in parts of Southeast Asia.

And while humans have added noise to the oceans, their activities have also made it harder to hear the many natural sounds that contribute to the undersea soundscape, such as the sounds of meadows of seagrass, forests of kelp, mangrove swamps, and the environments around coral reefs. “Fish and invertebrate larvae drifting in the ocean depend on these auditive clues to swim to the habitats where they need to settle, to live their juvenile and adult lives,” Duarte said.

Although underwater noise has directly caused mortality only in extreme cases, it has driven marine animals from parts of their normal ranges, limiting their food resources. It has also stressed marine animals that have to move away from the noise or learn to cope with it, Duarte said. Social interactions among animals that depend on sound, such as the mating calls of some fish, have also been impaired. “The cumulative impacts … must have important population-level consequences, likely comparable to those of other global ocean stresses, such as overfishing, habitat destruction, chemical pollution, or climate change,” he said.

But solutions to the growing problem of underwater noise are at hand, if there are sufficient efforts to put them in place, such as revising policy frameworks and producing regulations to cut underwater noise, Duarte said. “It will be easy,” he said. “The technology solutions for the most part are already available and will deliver near-immediate benefits.” The review notes that reducing underwater noise will become a sustainability issue as the world’s economic reliance on the oceans increases.

Duke University’s Nowacek, who has studied human-made underwater noise throughout his career but who was not involved in the new review, echoed both its concerns and the solutions it proposed. “There are operational things, and there are technological things,” he said. For example, ships can travel more slowly, which greatly decreases the noise they make, while noisy technologies like underwater surveys and other human activities can be made more animal-friendly.

And it won’t take long for ocean ecosystems to recover: “One of the beauties of noise is that when you stop making it, it goes away,” he said. “Unlike chemicals in the groundwater, or [pollutants] in the air, the minute you turn off the source … within a few minutes, it’s gotten quieter.”