Humans seek peace at sea, but the sea has never been peaceful. The ocean has always been a place of noise: the sounds of disintegrating icebergs, waves, rain, sea creatures. We just didn’t realize that for a long time, until sensitive hydrophones–underwater microphones–became affordable for civilian researchers in the 1970s. (Before then, they had been so expensive that only militaries could generally afford them.)
Suddenly, the ocean became what it is: a place of sound. Marine animals are vocal beings, and when the ocean goes dark, 200 yards or so below the surface, sound is the best way to communicate. They use clicks, songs, and calls in order to gossip, search for mates, avoid fishing gear, and communicate. Sound for them is as important as vision is for us.
We have known for a long time about aquatic mammals and their noises: the humpback, which sings in complicated sequences the length of a concerto; the fin whale, which sends out pulses that divers used to think were the creaks of the ocean floor; the blue whale and its great moans. Due to the ways in which pressure and temperature affect sound waves underwater, there is a narrow band of frequencies at a specific depth, a “channel,” where loud sounds become trapped, bouncing around within the channel without dissipating as they would in air. If a sound, like a whale call, falls into such a channel, it can be heard across an ocean. In 1991, a foghorn-like signal was transmitted from Australia and heard off Oregon three hours later.
Lately, there have been both good and bad surprises about sound. Fish sing! At least eight hundred species of fish use hearing, or some other way of interpreting noise. This is wondrous, but also dangerous, because, in addition to polluting our land, sky, and space, we are also polluting the ocean. Not only with plastic–with noise. We humans have poisoned life on land with our din, and, even though we know that this cacophony damages us psychologically and emotionally, we are now extending the same sound pollution to the seas, with our shipping and sonar and fishing.
Scientists have known this for several decades, since they began looking at long-term data. Ambient noise in the deep ocean from 1950 through 2007 increased by an average of three decibels each decade. That uptick is believed to be ongoing. Every ten years, noise from commercial shipping–an industry that employs a global fleet of between 80,000 to 100,000 vessels–is doubling. The trouble is that assessing what the noise is doing to ocean creatures in situ is fiendishly difficult.
Most research is based on lab studies rather than field experiments, but the results are disturbing enough. When researchers played ship noise to shore crabs (Carcinus maena), the results were disturbing:
[The crabs became] more distracted from food, taking longer to find shelter in response to a simulated predation event, and righting themselves more quickly when turned on their backs. Single exposure to playback of ship noise also led to significantly higher oxygen consumption (indicating a higher metabolic rate and potentially increased stress), with larger individuals affected more strongly. When repeatedly exposed to ship-noise playback, crabs continued to consume oxygen at an elevated level, providing no obvious evidence of habituation or tolerance.
Noise, supposedly a transient pollutant, wreaks long-term damage.
Outside the lab, it’s hard to assess the effect of noise on marine fauna. You can’t switch off shipping–with one notable exception. In 2001, marine biologist Rosalind Rolland of the New England Aquarium was about to set out on the Bay of Fundy, Nova Scotia, when she noticed on the TV that the Twin Towers had been attacked. After grieving, she and her colleagues decided that they still had to work, so they set out into the bay. No planes, no ships. It was quiet. Years later, when I spoke to her for my book on the shipping industry, Ninety Percent of Everything, Rolland remembered her data and found that she had a perfect control: during the week of quiet, underwater noise was lower by six decibels, and the levels of whales’ glucocorticoids (stress-related fecal hormone metabolites) were lower, too.
We can’t wish better science through disaster. Sometimes, though, we can get good science by happy accident. Rob Williams, a marine conservation biologist from Seattle’s Oceans Initiative, knows this well. He was in Bali not long ago, working with Conservation International Indonesia and Denpasar’s Udayana University on developing low-cost surveys to estimate the abundance of whales and dolphins. Such surveys are urgently needed, says Williams, “as countries scramble to respond to a new U.S. seafood trade rule requiring countries to demonstrate that their export fisheries are sustainable with respect to marine mammal bycatch.”
Cetologist Putu Liza Mustika took Williams to a Hindu temple to bless their fieldwork, and told him about Nyepi, a Day of Silence held annually before Balinese New Year. In 2017, it fell across March 27 and 28, and for 24 hours everyone was encouraged to engage in introspection, meditation, and self-reflection. During Nyepi, all Balinese ports–air, shipping, and fishing–are closed, all work is prohibited, lights are dimmed, and wandering tourists, writes Williams, “are guided back to their hotels.” Even though only one of the project’s six acoustic recorders was working, by recording for the whole week it offered a perfect opportunity to listen to the ocean and compare Nyepi to other days.
It was a rich soundscape. Snapping shrimp, at 2″”48 kilohertz, dominated that band for a week, getting three decibels louder at night. Researchers heard four different nightly fish choruses. On non-Nyepi days, one airplane every seven minutes was audible underwater. On Nyepi, although the research area was in shallow water and not near major shipping lanes, the recorder noted a drop of six to ten decibels in bands commonly used by fish and whales for biological signalling.
The Nyepi research has given Williams an idea: “Many world religions and local cultural traditions honor a sabbath, jubilee, or feast day on which work is prohibited. In light of the daunting challenge of accomplishing an international day of silence, we see value in short studies to conduct remote monitoring in a culturally sensitive way during local holy days, in order to estimate how much noise levels drop when people stop working for one day.”
It’s a good idea. As Williams says, “In my experience, if an area is noisy enough for us to worry about its impact on endangered whales, it’s already too noisy to do decent experiments to prove that noise causes harm. We need to look for unusual opportunities to conduct natural experiments to see how animals respond to a quieter ocean.”
There are already ship-quieting projects around the world. The shipping industry talks of changing its propellers, the biggest source of noise, but, having written about shipping for a long time, I know that the biggest driver for change is not whether snapping shrimp can keep snapping. It’s cost, and not the cost to ocean fauna. I don’t know if data and science will persuade the high-pressure, competitive world of commercial freight–which, after all, transports 90 percent of everything–to adjust its propellers, or sonar arrays, or engines. But if they don’t, the stunned, bewildered, hungry, mateless ocean fauna crippled by our noise will be the next casualties of the Anthropocene.
How We Get To Next was a magazine that explored the future of science, technology, and culture from 2014 to 2019. This article is part of our Nature & Climate section, which looks at how human activity is changing the planet–for better or worse. Click the logo to read more.
