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On the morning of March 24, 1989, the tanker Exxon Valdez ran aground on a reef off southern Alaska, spilling 42 million liters of oil into the ocean. The environmental legacy of this and subsequent tanker spills heightened public concern about oil pollution. Public outrage is also growing over the scourge of plastics in the oceans, and this is translating into legislative efforts to curb the problem. Scientists have also begun to notice another pervasive form of pollution that could be having profound effects in the ocean: noise.
Since the 1950s, it’s estimated that the ambient noise level in the ocean has risen by around three decibels per decade—a fourfold increase. While much of this excess noise can be attributed to commercial shipping, many other human activities are contributing to the problem, including underwater construction, seismic surveys, and the use of sonar.
Scientists have only recently begun exploring the ecological impacts of noise pollution, and as a result, it’s been difficult to firmly state the scale of the problem. But now, a new systematic review has added weight to the theory that human-made noise is detrimental to marine life.
The majority of marine noise research has focused on larger mammals that have long been known to use sound to communicate, such as dolphins and whales. But around 800 fish species are now thought to produce sound, too. Kieran Cox, a doctoral candidate at the University of Victoria and a Hakai Institute scholar,* recently published a meta-analysis of the effects of marine noise on fish, compiling existing research to paint a decisive picture of the consequences. As a form of research, meta-analyses lend statistical muscle to an area of study by combining data from multiple independent experiments.
In the new study, Cox and his colleagues combined the results of 42 research papers by scientists from 11 countries, revealing that anthropogenic noise has had a significant negative effect on fish behavior and physiology.
“There’s a huge amount of information embedded in the aquatic soundscape,” says Cox. Introducing a lot of unnatural noises disrupts sound-dependent behaviors and physiological processes.
The summary shows that in the presence of increased marine noise pollution in both volume and frequency, fish move faster, dive deeper, and change direction more frequently—exertions that waste valuable energy. Species with complex nest systems—like sticklebacks, midshipman, or damselfish—spend more time maintaining their nests, which is also energetically costly and has been shown to overtire some species.
Fish exposed to increased noise are also less able to respond to predatory attacks. “If fish are bombarded with anthropogenic noise, they’re more likely to startle,” says Cox. But after persistent amounts of noise, the fish find it harder to distinguish which sounds indicate a threat, which makes them more susceptible to predators, he explains.
Foraging ability also takes a hit. Fish consumed less food and were also shown to forage less efficiently, unsuccessfully striking at food and struggling to discriminate between food and non-food items, for example. Physiologically, overexposure to noise increases the fishes’ minimum hearing threshold, essentially deafening it. Stress levels rise as well.
Arthur Popper, a biologist at the University of Maryland, has some criticism of the meta-analysis. “The authors have not looked at the papers critically to evaluate the methods and quality of the work,” he says. Research studies conducted in laboratories—36 of which were included in the meta-analysis—are not necessarily reflective of how animals behave in the wild, he adds.
Cox concedes that meta-analyses are by definition dependent on the quality of previous research. “As a summary of the studies done to date, it’s the best we can do,” he says. But the results “seem to fit with what we know about [noise] pollutants in general.”
For a new field of study like marine noise, this kind of summary assessment is important, says Steve Simpson, a marine biologist at the University of Exeter in England. “It was nice to see all of the research efforts from a few groups around the world being brought together.” He says even as recently as a decade ago, anthropogenic noise was not the focus in the field of underwater acoustics.
“The more that we’ve considered fish and invertebrates, we’ve realized that there really aren’t many animals in the ocean that aren’t affected by their acoustic environment, and therefore [by] human noise,” says Simpson. Indeed, recent studies have found that even plankton are sensitive to noise, meaning that noise pollution may have the power to disrupt whole food chains, he adds.
Fortunately, marine noise can be controlled. “There are a lot of ways—spatially, temporally, and technology-driven—that we can reduce noise in the ocean,” says Simpson.
To Cox, the takeaway is clear: it’s crucial that sound be included in future discussions about ocean conservation. “If you want to preserve species, sound has to be part of the conversation.”
*The Hakai Institute and Hakai Magazine are both part of the Tula Foundation. The magazine is editorially independent of the institute and foundation.