Up to Their Ears in Undersea Noise
Air Date: Week of May 17, 1996
How do different animals hear? How does infrasonic versus ultrasonic sound detection affect a marine animal's behavior? What if any impact do ships propellers or military underwater tests have on ocean life? Dan Grossman looks at some of these questions in this sound-rich report exploring some of the scientific research being conducted into undersea noise.
CURWOOD: Usually we think of pollution as a thing: sewage, industrial chemicals, trash, which we can identify by sight, smell, or chemical testing. But what if pollution were not a substance but a wave, a sound wave? Throughout the depths of the world's oceans we've been causing such pollution for more than 100 years, and we know little about its effects on the billions of ocean dwelling creatures. A recent controversy over a plan to measure changes in ocean temperature by sending blasts of sound across the Pacific got producer Dan Grossman wondering what we do know about how marine animals use sound, and how sound pollution might be affecting them.
(Cetacean cries underwater)
GROSSMAN: I'm Daniel Grossman. Among all the ocean songs few are more intriguing than the music of the humpback whale.
(Whale songs continue)
PAINE: The first time I ever heard the sounds of humpback whales, I heard them in the boiler room of a ship with a lot of other noise going on, and a very dear friend of mine had been recording them. And he said here, let me play you some whale sounds, and I had never heard anything like it. It just completely blew my doors off. I was just stunned.
GROSSMAN: Biologist Roger Paine went on to publish the first study of humpback songs. He says the extraordinary melodies illustrate the importance to sea life, not just to whales but to many marine species, of hearing. In the turbid seas, vision is almost useless. Distant objects appear perpetually wrapped in fog. Sound, in contrast, travels well. Researchers say humpbacks may attract mates with calls heard tens or even hundreds of miles away. Dolphins echolocate or navigate with high-pitched whistles. Other ocean dwellers also sense their surroundings and communicate with sound. But ever since the industrial revolution, manmade sounds have filled the seas. Chief among these is the drone of the propeller.
(The sound of a propeller)
PAINE: And a propeller is a very noisy thing. And the result has been that we are polluting the seas with loud sounds, so the point where 24 hours a day the deep ocean is basically throbbing, roaring with the sounds of ships.
(Propeller sounds continue, followed by soundings)
GROSSMAN: The explosive clap of soundings to probe the ocean floor, and the piercing screech of military sonar add to the clamor.
GROSSMAN: Human activities now overwhelm the natural compositions of cracking ice, breaking waves, and animal cries like this narwhal.
(A narwhal cries)
GROSSMAN: Roger Paine was among the first scientists to warn that noise pollution might threaten the marine environment. Surprisingly, after searching high and low for proof, he's concluded, at least for whales, there is no threat.
PAINE: I've spent no small part of my life, many years actually, attempting to show effects of loud industrial noises on whale populations. But the evidence is that they continue to mate, they he being continues to find she or vice versa. And so my suspicion is that they probably are doing all right. That's a very dangerous suspicion because I haven't a particle of evidence except that the populations continue to reproduce, that it is correct.
GROSSMAN: But not all researchers are convinced the whales are doing all right.
(Sounds of scraping, paper shuffling)
TAYACK: Here we go.
GROSSMAN: Peter Tayack is an expert on marine mammal behavior at the Woods Hole Oceanographic Institution on Cape Cod.
TAYACK: Once one understands the importance of sound to these animals, and one has spent any time recording underwater, it's clear that there may be a potential impact of manmade noise.
GROSSMAN: Professor Tayack sat on a National Academy of Sciences Committeewhich issued a study of ocean noise in 1994. The committee concluded that the hubbub of human activities at sea could disrupt important behaviors of the ocean's inhabitants, like feeding and reproduction.
TAYACK: If whales are producing sounds as loud as they can in order to communicate over long ranges, say a male to find a mate, or a mother to keep in contact with its infant, then if the noise level rises, the range over which they can communicate may be lower. And this may seriously limit, say, the distance which an infant can move from the mother. Or it might limit the number of females that could respond to an advertising male, particularly if you already have reduced populations.
GROSSMAN: The Academy's panel warned that profound uncertainties remain, and recommended more research. Research like Peter Tayack's.
TAYACK: Let me show you some of the deflection of migration of whales. Let's see. (Pulls out a file cabinet) Here are tracks of migrating gray whales, gray whales migrating past the Big Sur coast, that were observed from a shore station.
GROSSMAN: Migration routes observed from the California coast show that undisturbed, the whales travel in long, straight lines. But another chart shows that when researchers play the sound of an oil rig from underwater loudspeakers, the whales alter their routes.
TAYACK: You can see that up here, kilometers away from the sound's source, the whales started deflecting either in-shore or off-shore of the source, and some of the whales got a more erratic, zig-zaggy kind of track.
GROSSMAN: In this experiment, the whales deviated only slightly off course, with no known long-term impact. But Peter Tayack worries that they might squander precious energy reserves if they made many such detours, or that mechanical noise could scare timid animals from critical calving or mating grounds.
(Low underwater growling sounds)
TAYACK: It was definitely a nail biter when we first released seals carrying these devices. Nobody had ever seen data of this sort.
GROSSMAN: This is the sound of an elephant seal swimming miles off the California coast. Peter Tayack's team built a lightweight instrument to record seals. The device, glued to seals' coats, permits researchers for the first time to swim alongside these nomads.
TAYACK: The device is so sensitive that we can actually hear every breath that a seal takes, and we can often hear its heartbeats. When they swim, we often can hear the swim stroke, can often hear a shhh shhh shhh, which can give you important information about how they're swimming. So this allows us to both record, what are the sounds a seal hears as it swims hundreds of meters below the sea surface hundreds of miles out to sea, and also how might this affect its dive pattern? How might it affect its heart rate or breathing pattern?
GROSSMAN: Elephant seals are especially interesting to researchers because they swim to great depths in the region of a natural conduit for ocean sound called the Deep Sound Channel. Discovered by Navy researchers in World War II, the Channel conveys sound unimpeded for thousands of miles. This unusual property has recently attracted the attention of climate researchers at the Scripps Institution of Oceanography in San Diego. They plan to monitor changes in ocean temperature by sending loud signals through this channel halfway around the world. In the process they hope to clock the pace of global warming. But some scientists fear the signal could harm deep-water animals like the elephant seal. Peter Tayack's research could settle the question.
GROSSMAN: This is the sound of a grouper. Although ocean noise pollution research has focused on mammals like whales and seals, there are plenty of other fish in the sea.
MERBERG: Not only are marine mammals affected by high noise levels in the sea. We also have every bit of supporting preliminary evidence that it also affects fishes.
GROSSMAN: Arthur Merberg is a professor of marine science at the University of Miami. He published one of the first papers suggesting manmade sound could be a threat to fish.
MERBERG: Coastal fishes, coral reef fishes, freshwater fishes.
GROSSMAN: And aquarium fish, like this domino damselfish.
MERBERG: Now the question is, how does it affect it?
GROSSMAN: Professor Merberg is seeking the answer. He begins by putting juvenile red drum fish in a chamber he calls a hearing tube.
MERBERG: And we determine their hearing ability from the low frequency of about 200 Hertz up to about 1,000 Hertz.
GROSSMAN: Frequencies like this.
(A low beep)
GROSSMAN: And this.
(A switch clicks; higher beeps sound)
MERBERG: And after a conditioning, a training period, they tell us by specific movements: do they hear the sound or don't they hear the sound?
GROSSMAN: Professor Merberg moves them to a tank where he blasts them with pulses of sound 50 times louder than the faintest sound they can hear.
GROSSMAN: Then he returns them to the hearing tube.
MERBERG: And we again examine their hearing ability. When we do this, we find that they have decreased hearing.
GROSSMAN: That's bad news for fish in the wild.
MERBERG: The decreased hearing ability, you now start to affect what the function of sounds are to fishes, such as identifying individuals of a colony, individuals recognizing members of one's own species, detecting prey. So therefore, you're affecting the survival and reproduction of species.
(An elongated beep continues, ends.)
KATTEN: We have ears from humans, ears from seals, ears from manatees...
GROSSMAN: Biologist Darlene Katten is up to her ears in auditory organs. A researcher at Harvard University and Boston's acclaimed Massachusetts Eye and Ear Infirmary, Professor Katten uses high tech medical diagnostic tools to make detailed images of these animal parts. By looking carefully at the ear's anatomy, she infers what frequency an animal can hear and how well.
KATTEN: What I do is to get the ears from these animals, or the heads, after they've stranded and died, for instance, and then analyze them for the structure and look at the structures to figure out what they're hearing. (A door shuts.) At the moment, in the freezer, we have heads. We have some heads from stranded marine mammals, and we have a baby hippo head to look at as well.
GROSSMAN: Professor Katten's ability to interpret X-ray images has earned her the respect of surgeons who consult her before operating on people with hearing problems. Her research focuses primarily on marine mammals. But she also gleans important information from other aquatic species, like sea turtles and the baby hippopotamus, whose head she's examining today.
KATTEN: So let's go take a look at the hippo.
GROSSMAN: The researcher removes the frozen head from a plastic tub.
(Head bangs against tub)
GROSSMAN: It has long, stiff whiskers and shiny gray skin. She puts it on a narrow table of a CAT scanner, where just moments earlier a young man with hearing trouble was examined.
(Buttons are pushed, beeps sound)
GROSSMAN: Darlene Katten watches intently at a screen displaying images recorded by the scanner. With this device, she can literally look inside the head of a whale or seal and learn what it can hear. She and other researchers have discovered that the ratio of hearing nerve cells to sight cells is 20 times higher in some whales than it is in humans.
KATTEN: There's your ear. And he's got lots of fluid up in there. I'm looking at the world through the eyes or the ears of these animals that have capacities I don't have. So I get to hear, in a sense, what the ocean sounds like to a dolphin, or what it sounds like to a blue whale.
GROSSMAN: Blue whales hear infrasonic frequencies, much lower than the human ear does. In contrast the bottlenose dolphin, also classified as a whale, is most sensitive to ultrasonic frequencies, much higher than humans can detect. So the same supertanker rumble that might be deafening to the whale would be almost inaudible to the dolphin. This dramatic variation between animals complicates the task of assessing the impact of noise pollution.
KATTEN: Impact is a very complex combination of an animal's sensitivity to the sound, the health of its ear, and the absolute intensity. So it isn't one number. You can't say that oh, a 200 dB sound, is going to impact every ear exactly the same way.
GROSSMAN: Professor Katten agrees that so far the case against manmade industrial noise is inconclusive. But unlike biologist Roger Paine, Darlene Katten is concerned.
KATTEN: Clearly humans are dumping a lot of sound into the ocean. We're using it for our commercial purposes, we're using it for exploration. We're using it all the time for recreation. And I expect we are having an impact. It would be somewhat naive to think that we weren't. What we have to decide as humans is whether we're willing to take the risk of changing that environment, impacting the animals in exchange for what we see as our benefits.
GROSSMAN: Countless marine animals share the world's seas with some 28,000 cargo, military, and research vessels. They're often in close contact, as in this recording of humpback whales diving near a boat in Alaska's Glacier Bay.
GROSSMAN: Glacier Bay has some of the country's strictest rules to reduce the impact of noise and other disturbances on marine life.
(Whale sounds continue)
GROSSMAN: Biologists here want to study the acoustics of ships entering the bay in order to give preference to those with the least impact. They say if the tide is ever going to turn against noise pollution and toward quieter ships, it may start here. If funded, the study could begin this summer. For Living on Earth, I'm Daniel Grossman in Boston.
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