Sign up for


and other email updates

Transcript: Blinded By The Noise—Whales and Dolphins in a Noisy Ocean

Welcome to "On the Line", a NOAA Fisheries podcast.

[Music playing]

Host: Whales and dolphins see the world very differently than we do. We’re visual creatures and we use our sense of sight to navigate through the world, but marine mammals use sound to make sense of their world. That’s because sound waves travel really well under water—they can go hundreds of miles, much farther than they do in air. Light, on the other hand, can only penetrate a few hundred feet.

Over millions of years marine mammals have evolved to become exquisitely tuned instruments for both emitting and receiving sound. But unfortunately for them, the ocean is becoming an increasingly noisy place. We fill the water with the blare of military sonar, with blasts from air guns as we search for undersea oil, and with the never-ending thrum of shipping traffic. This increasing cacophony has gotten to the point where it has the potential to impact the health of many marine mammal populations.

Today we have two NOAA scientists "On the Line" who research the effects of ocean noise on marine mammals. They’ll talk to us a bit about the problem, and also tell us about a project they’re working on that they hope will help. It’s an ocean mapping project called CETSOUND, spelled "C"-"E"-"T"-SOUND. That’s short for "cetacean" and "sound" mapping. The word cetacean just means whales and dolphins.

Sofie Van Parijs is a marine mammal biologist at NOAA’s Northeast Fishery Science Center, and she’s one of the scientists working on CETSOUND. I asked Dr. Parijs why is sound so important to marine mammals.

Sofie Van Parijs: I think the big thing to understand for marine mammals is that sound is their primary modality for any kind of communication and interaction. So they use it for socializing. They use it for finding food. They use it for even navigating, and that’s because sound travels much better through water than it does in air.

Host: Now me, when I first heard about the problem of ocean noise, I was like, whatever, it’s a bit of noise. Get over it dolphin. But then I found out just how sensitive whales and dolphins, and many other types of marine mammals, are to sound. Their heads and jaws contain what scientists call "acoustic fat". That specialized fatty tissue forms complex arrays of the acoustic chambers and lenses that collect and focus sound. When they’re hit with intense pulses of man-made sound it can damage those structures. And many species rely on their acute sense of hearing to accomplish the most basic tasks like finding prey and avoiding predators, maintaining pod structure, and finding mates.

Sofie Van Parijs: For them sound is just a heightened sense, so they’re going to be able to use the sounds of everything around them, their entire environment. You know the sea floor, the other animals that are around, the waves crashing against the side of the ocean bed, as well as any shores. So they are using sound to really orientate themselves and understand what’s going on in their environment.

Host: So in places where the ocean is filled with man-made noise, whales and dolphins become—the only way I can think of saying it—is they become partially blinded. Leila Hatch is another marine mammal biologist at NOAA and also an expert on the effects of sound on marine mammals. I asked Dr. Hatch if ocean noise is a new problem, or if it’s been around for a while and we’re just beginning to recognize it.

Leila Hatch: Well, we are beginning to recognize it, but it is a growing problem. So those two things actually go together, and that’s because our uses of the ocean environment are continuing to mount, and most of those uses include an acoustic signature. They add a noise contribution to the environment, either purposefully, because we’re trying to use sound and waves much like what animals are doing underwater, or incidentally. We’re just doing something, and as a byproduct we’re producing noise.

Host: An example of where we use sound purposefully is in oil and gas exploration. Boats run transects in ocean while towing an array of seismic air guns behind the ship. Those guns create explosive noises every 10 or 15 seconds. The noise you’re hearing now...that’s a recording made during seismic exploration.

When the sound waves reflect off the bottom, geologists decode the signal to find pockets of oil or gas under the sea floor. The noise can fill up entire ocean basins and we’re doing that more, and in more places every year.

Scientists have been studying the effects of these loud but discreet noise event on marine mammals for a long time. But there’s another type of ocean noise that scientists are just beginning to get a handle on, and that’s something they called chronic noise. Again, Leila Hatch.

Leila Hatch: The largest contributor to ocean noise at low frequencies comes from commercial shipping. We transport over ninety percent of the world’s goods by ship, and that’s only continuing to grow.

Host: If you’ve ever been in the engine room of a ship you know that they make a tremendous amount of noise, but loud as that is, the bigger problem is something called cavitation. Mike Bahtiarian is a noise control engineer who specializes in quieting ships. Here, Bahtiarian explains what happens when air bubbles in water pop, or to use the fancy term, when they cavitate. He says imagine a propeller in the water.

Mike Bahtiarian: As it starts to spin faster and faster, the blades cut through the water so quickly that it produces tiny, tiny bubbles—tiny air bubbles. But it’s creating thousands, millions, millions of tiny little air bubbles. And then when they pop they make noise, and that noise can be quite high depending on the size and the speed of the propeller.

[Ship noise]

Host: This is what a ship sounds like underwater.

[Ship noise]

Host: So, that’s the problem. The question is, what do we do about it? On land, we have whole industries dedicated to noise control. There are mufflers on our vehicles, sound barriers along the highway, and engineers have spent decades making jet engines quieter.

The noise control engineer, Mike Bahtiarian said that new propeller designs can reduce cavitation while at the same time improving the fuel efficiency of a ship. So, maybe the next generation of ships will be quieter than the ones we have today. But ships last a long time. The ships that we’re building today, many of them will still be in use fifty years from now.

And our uses of the ocean are only going to increase, so we’re not going to be able to eliminate man-made noise from the ocean. But we can organize our activities in the water so that we reduce the amount of noise that happens at times and in places that are particularly important to marine mammals.

And that brings me to the mapping project I mentioned a few minutes ago. It’s called the CETSOUND project. That’s short for cetaceans and sound.

Sofie Van Parijs: So, CETSOUND is two different components. There is a component where we map cetacean—so that’s whales and dolphin—distribution, and provide the best available information we have on mapping where they are and how they use an area across a year. And then the other component is the sound mapping component representing the sound levels that each of those areas are exposed to.

Host: Mapping sound levels in a place as big as the U.S. exclusive economics zone in the ocean is no small task, but new developments in acoustic technology are beginning to make this possible. For one, the recording devices themselves have advanced dramatically in recent years.

Sofie Van Parijs: Ten years ago or so these were clunky and cumbersome and extremely expensive and you could only put them out for short periods of time. But now there has been this huge technological revolution in terms of the acoustic recorders, and their capacity for recording sounds over years now and way out on the shelf break. And they’re also considerably more affordable than they were. So it means our capacity to collect data has increased hugely.

Host: And it’s not just that the recording devices have changed. Scientists at NOAA and elsewhere have been busy developing the next generation of sensor platforms for use in the ocean. These include autonomous gliders, remotely operated vehicles that roam the ocean carrying acoustic recorders and other types of sensors.

Sofie Van Parijs: It has become a much more mobile thing. You can slap it on a glider. You can put it on the side of a buoy. You can sink it to the bottom of the ocean. It’s just much more versatile.

Host: It’s the combination of new sensors and new platforms for carrying them that enables us to keep an ear on what’s happening in the ocean, and to map both the occurrence of marine mammals themselves and the noise that they are exposed to. And with those maps we can do a better job of managing noise in the ocean.

For instance, we can make sure that pile driving to put in a new bridge doesn’t happen during the calving season, or that shipping lanes avoid the most common migration routes.

Sofie Van Parijs: If you have an area where it’s bright red, which means there is a lot of sound in the ocean and you overlay that with an area where you have bright red in terms of that’s where, let’s say right whales go in the spring time. If those two overlap, well then you’re going to have an issue in terms of sound.

Leila Hatch: So we’re trying to set something in motion that will change what has been an insidious growth in background noise in the other direction. First stabilize that trend and then generate a reduction, and we’re doing so in the face of significant scientific uncertainty about what it means to these animals. But, with the precautionary principle in mind also that everything points to the fact that this is really something that, in combination with the other stressors these animals face, is an important component of protecting their ecosystem.

[Music playing]

Host: Us humans, we’re visual creatures. We can’t really address a problem until we can visualize it. And that’s exactly what these maps accomplish. They allow us to visualize something that until recently we were mostly blind to. Now that we can see the sound, we can start to do something about it.

As usual in scientific research the CETSOUND project is a big collaboration. Leila Hatch and Sofie Van Parijs are only two of the scientists involved. There are many others from NOAA, from government agencies, and from universities. The military and industry are also involved. The Navy and the Bureau of Ocean and Energy Management are both major funders of the CETSOUND project. And, in terms of shipping noise, NOAA is working with the International Maritime Organization on voluntary ship quieting guidelines.

As always, you can get more information on our podcasts page—that’s There you’ll find a link to the CETSOUND project website where you can check out the maps. We also put up links to a really cool NOAA website where you can download sounds made by all kinds of whales and dolphins and other marine animals.

Thanks for listening. Join us again next time for more stories about ocean life and ocean science. I’m Rich Press and you’re listening to "On the Line."

[Music playing]

You have been listening to the NOAA Fisheries podcast, "On the Line." Join us next time for a firsthand look at the people and the science behind managing our nation's fisheries. For more information, visit NOAA Fisheries at

"On the Line" is a production of the NOAA Fisheries Office of Communications.

<< Return to Story Page