How Ocean Noise Pollution Wreaks Havoc on Marine Life

Marine scientist Christopher Clark has spent his career listening in on what he calls “the song of life” in the world’s oceans. In an interview with Yale Environment 360, he explains how these marine habitats are under assault from extreme—but preventable—noise pollution.

Bowing to public and fishing industry pressure, the Obama administration recently reversed an earlier decision to allow oil drilling off the U.S. East Coast. But the five-year moratorium on drilling does not prohibit exploratory seismic air gun surveys used to locate oil and gas reserves in rock layers under the seabed. The National Oceanic and Atmospheric Administration is expected to authorize those surveys this spring.

Cornell University
Christopher Clark

Cornell University marine bioacoustics expert Christopher Clark says the acoustical testing — which can go on for weeks, with powerful explosions being continually detonated — will only add to the rising din in the oceans. “Imagine that every 10 seconds there is an explosion that is rattling grandma’s china out of the cupboard, and it is falling on the floor,” says Clark, who notes that the testing can fill whole ocean basins with “one big storm of noise.”

In an interview with Yale Environment 360, Clark explains how noise pollution, most of it from ship traffic, severely disrupts marine life, especially among whales, which communicate and orient themselves through sound. He laments what he calls the “acoustical bleaching” of the oceans, a human-made cacophony that can tear apart the social networks of whales, adversely affecting survival and reproductive success. Science is only just beginning to understand this threat. But the good news, says Clark, is that technologies are being developed to drastically reduce the noise from ships and geological surveying. All that’s needed, he says, is the will to make the change.

Yale Environment 360: The knowledge of underwater sound has exploded in recent decades. It’s a whole different way of understanding the ocean, isn’t it?

Chris Clark: Recently we heard sounds — it was more like an amorphous cloud of noise —coming from a particular area, and it turns out that we were listening to millions and millions of sea urchins feeding on rocks, where they create a rasping sound as they scrape off the algae. As our listening technologies continue to develop, I expect we’ll soon be able to hear the breathing of the planet from the aggregate rise and fall of billions of phytoplankton and zooplankton in the ocean as they move up and down in their daily cycle of life.

Song is what the world does. From the tiniest bugs sitting on branches where the males are singing to attract females and establish their territories, to birds and frogs and whales, the planet is singing. And this is doubly true in the oceans.

‘‘‘We are injecting so much noise that we are effectively acoustically bleaching the world’s oceans.’

e360: People are familiar with chemical and plastic pollution in the oceans. They tend to be less aware of underwater noise pollution. Your work suggests that this is just as great a threat to many marine organisms.

Clark: This acoustic pollution has not yet been fully explored by science, still less explained to the public. We look out at the ocean and see this bucolic seascape, and some seagulls flying along the horizon and maybe a sailboat, and we think everything is hunky dory. Well, it isn’t. We are injecting so much noise that we are effectively acoustically bleaching the world’s oceans.

e360: What are the sources of this sound?

Clark: There are two major types. One would go under the heading of chronic, and that is mostly the byproduct of ships driving engines through water — it’s the grinding of propellers, it’s the hull radiating all the noise from the internal mechanics of a large ship. Many ships today are now bigger than aircraft carriers, and they send out enormous amounts of sound energy at low frequencies that propagate very efficiently in water. Noise from ship traffic is doubling every decade.

e360: Then there are other types of noise that are on again, off again. Could you talk about them?

Clark: The more insidious and acute sounds come from ocean exploration for oil and gas, which is accomplished by setting off huge explosions — it used to be dynamite, and now it is seismic air guns. The exploration companies generally deploy 30 or 40 air guns that all go off simultaneously. A typical air gun survey will go off every 9 to 12 seconds. They go back and forth, back and forth, over huge areas of the ocean, like mowing the lawn — and they do this for weeks and months at a time. This produces a pressure that essentially creates bubbles that expand and contract, generating an immense amount of acoustic energy, a lot of which goes downward and reflects off of geological structures. The exploration companies interpret the reflections of the sound off the layers in the earth’s crust, and they use that information to infer where there is the best chance of discovering fossil fuels.

Sound emitted from Heard Island in the southern Indian Ocean in a 1990s experiment was picked up as far away as the northern and southern Atlantic and Pacific oceans.

e360: How loud are these air gun bursts?

Clark: The sound is six or seven orders of magnitude louder than the loudest ship sounds. It is so loud that when someone is surveying off northern Brazil, I can hear that explosion on a small piece of instrumentation that I deploy 60 miles off the coast of Virginia. I can hear the explosions from surveys off Ireland, I can hear them happening in Nova Scotia. So imagine that every 10 seconds there is an explosion that is rattling grandma’s china out of the cupboard and it is falling on the floor. One summer, some years back there were between 20 and 30 surveys going on simultaneously in the North Atlantic.

When the sound from that explosion travels through the ocean, it changes from a big bang into this big fuzzy ball of reverberating noise. The energy from all these explosions fills the oceans with noise. It becomes just one big storm of noise.

e360: You have studied the impact of anthropogenic sound on whales. Why are they a special concern?

Clark: On a good day, whales can barely see their tails 60 feet away in turbid waters. But they can maintain their social network acoustically for many miles. Whales see the ocean through sound. So their mind’s eye is their mind’s ear. You are dealing with animals that are highly acoustically oriented. Their consciousness and sense of self is based on sound, not sight.

Many whale feeding grounds and migratory routes occur along shallow coastlines, which are now some of the noisiest, most heavily impacted habitats. If females can no longer hear the singing males through the smog of sound, they lose breeding opportunities and choices. If whales can’t hear from other whales that have found a really good patch of food, they lose opportunities to feed.

‘‘‘Whales were trying to hide behind rocks to escape in a sound shadow when seismic surveys were being conducted along the California coast.’

e360: Are there actual behavioral changes that you have observed when whales are exposed to high levels of sound?

Clark: At first, their calling rate may go up a bit — as you and I might do when we shout in a loud space in order to be heard. It’s the cellphone story, you know, ‘Can you here me now? Can you hear me now?’ But then, shortly thereafter, when the noise level goes beyond a certain threshold, the counter-calling, the chitchat between right whales, for example, just stops — they just give up. When the noise decreases, they start up again.

We have demonstrated that in Cape Cod Bay in the run-up to Boston harbor that right whales lose 50 to 70 percent of their opportunities to communicate due to routine ship traffic. It means that as shipping traffic increases, the ocean area over which a whale can communicate and listen has shriveled to a small fraction of what it was less than a century ago. There is this constant stopping and starting of their communication. What you are doing is you are tearing that social fabric over and over again.

e360: What about the impact of seismic surveys on whales?

Clark: We don’t have all the details on that yet. But we can show that there are entire sections of the ocean — 100,000-square-mile areas at a time — that are awash in this sound and where whales just leave the area or shut up completely. We noticed them trying to hide behind rocks to escape in a sound shadow when seismic surveys were being conducted along the California coast. Some of the gray whales actually came right into the surf — we could see their bodies in the breaking waves — to try to get away from this. Hey, if I lived in the ocean and every ten seconds there was a brain-rattling explosion, I’d try to get away, too!

Yan Guilbault/New England Aquarium.
A right whale swims near a cargo ship in the Bay of Fundy, Canada.

e360: Doesn’t the [U.S.] Marine Mammal Protection Act prohibit activities that harm whales and dolphins?

Clark: In theory, but not always in practice. So it’s like you and I would go to a Jimi Hendrix concert when we were young and we would sit as close to the stage as we could get, and the next day your ears might ring a little bit. Well, our government sets a regulatory threshold, the point at which we think these animals may be experiencing temporary threshold shifts like this.

But the thing is, it’s not a Jimi Hendrix concert. It is not a one-time event. It is happening day after day, week after week. Every 10 seconds your ears are being assaulted. What I have been trying to do is change the conversation from, `Is it so loud that it is permanently damaging their ears?’ to looking at this as a chronic problem that may be undermining their ability to thrive.

e360: Is there evidence that sound stresses these animals over the long term?

Clark: The New England Aquarium has been monitoring right whales up in the Bay of Fundy for 25 years, so they have a very long record of where whales are and what they are doing. They did research into hormone levels in whale poop. It turns out that they had samples from before, during, and after the 9/11 event, and they were able to show that there was a change in the concentration of a cortical steroid, which is indicative of stress, that precipitously dropped just after the event, at the same time as ship traffic and airplane traffic dropped off dramatically. So you couldn’t have devised a better test of how whales physiologically respond to noise. It is clear that their stress levels go down immediately when the noise stops.

e360: Is this chronic stress having population-wide impacts on whales?

‘‘‘The noise environment is so atrocious in their habitats that they can’t hear each other up to half the time.’

Clark: Consider this: The industrialization levels and the noise levels in the North Atlantic have been going up steadily for the past century. There is far, far less commercial shipping in the Southern Hemisphere. Southern right whale populations are going gangbusters, increasing by 7 to 8 percent a year. But up north, their cousins in the same kinds of habitats are struggling to get by; there are barely 500 individuals left. Their population is increasing by at most 2 or 3 percent a year. Why is that? One of the reasons we know the northern animals are not doing so well is that they are literally being run over by ships. They are also getting entangled in fishing gear, which kills and maims so many. My contribution is that the noise environment is so atrocious in their habitats that they can’t hear each other up to half the time.

e360: It is not just marine mammals that are affected by underwater sound levels. Fish are also sensitive to sound, aren’t they?

Clark: In fact, I would argue that the whales are fairly robust. They can tolerate pretty severe acoustic conditions. But with fish, we just don’t know. The Norwegians have conducted some good research that has shown that the fish are moving out of noisy areas, and that the survival rate of the newly spawned young are greatly decreased when there are high noise levels. And science is only just beginning to pay attention to what the invertebrates are doing — the squid, the shrimp. They are also commercially valuable animals which depend on sound. We don’t know what happens to them when there is an explosion every ten seconds for three months.

e360: Are there technologies that can cut down on all of this anthropogenic sound?

Clark: We can design ships to be much quieter. One way is to mount the engines so that they are not directly in contact with the hull. There are also ways of making the propeller quieter. The navies of the world have done a lot of research on this.

There are research ships that are one thousand times quieter than earlier ships. The International Maritime Organization has actually made building quieter ships part of their charter.

There is also a new technology called called Vibroseis. Instead of air gun explosions, it uses a very well designed sweep of sound that is orders of magnitude quieter, yet equally powerful for oil and gas exploration. They have already built and are starting to test some of these systems. So the tools are there.

e360: What remains to be done?

Clark: I don’t need to go to another scientific conference and convince my colleagues of what the problem is — scientists know we have a noise problem. We need to get this into the press, we need to go to town hall meetings and let people know what is happening out there so that we can get meaningful political action to address this.