How Sound Rules Life Underwater

IRA FLATOW: This is Science Friday. I’m Ira Flatow. I’ve always thought about the ocean as a quiet and serene place. You take a dip underwater and the sounds above you melt away, right? But actually, the ocean is quite a noisy place. Think whale songs or echolocation, which whales and dolphins use to communicate. Cephalopods can make and hear sounds too, even without ears. Yes.

And then there’s human-made noise, like the giant shipping containers that criss-cross the globe. All kinds of sounds happening in the oceans, and that’s what we’re going to be talking about, the loud underwater world beneath the waves.

And joining me is Amorina Kingdon, science journalist and author of the book Sing Like Fish, How Sound Rules Life Underwater. She’s in Victoria, British Columbia. Welcome to Science Friday.

AMORINA KINGDON: Thank you so much.

IRA FLATOW: I’m so eager to talk about this because as somebody who considers himself close enough to a fish, I love the water. I’m a scuba diver. And I want to know what inspired you to write this book.

AMORINA KINGDON: [LAUGHS] Well, I, like most humans, kind of thought that the ocean and the underwater was a silent world. And when I was a kid, I remember swimming and putting my head underwater and kind of thinking that sound didn’t really work there.

And then I was working on a story for Hakai Magazine here in Victoria, and it was about the relationship between cleaner wrasse and their client fish. And so cleaner wrasse are these little tiny fish that live on various reefs, and they set up these stations where they clean larger fish and they bite parasites off of them. And in exchange, the larger fish doesn’t eat them. It’s kind of a symbiotic relationship.

And this study found that when there was motorboat noise around that that whole relationship dynamic kind of changed. Like, the cleaner wrasse would try to take more bites or they’d cheat more often, and the rate at which the bigger fish caught them would change.

And I just kind of had this moment where I realized that, you know, sound and noise, it doesn’t just affect obvious things like hurting your ears or something like that. It can change the minutia of the behavior of animals. And then I started to think, OK. Now I start to see how sound can impact all these different facets of life underwater, so then I started really digging in.

IRA FLATOW: So where did this idea of the ocean being a quiet place come from? Is it just that humans are not good at hearing sounds underwater? I mean, if you put your head underwater in the ocean, you really don’t hear much.

AMORINA KINGDON: Yeah, I mean, I think that’s a part of it. Even if you stick your head underwater in the bathtub to rinse shampoo when you’re a kid, most people have some moment where they just think, oh, there’s nothing here. There’s nothing to sense.

And actually, for decades of scientific exploration until fairly recently, people even specifically studying sound underwater would just put their head underwater. And if they didn’t hear much, then they would just assume that there wasn’t much to hear.

But actually, a lot of the scientists I spoke to recently have said that the trope of the silent world kind of came about when Jacques Cousteau in the 1950s did his very famous film about all the animals in the ocean and the coral, and it was called The Silent World. And so I think that that image just kind of stuck.

IRA FLATOW: Yeah Yeah. So how does sound move differently underwater versus on land? I know there’s different density, water and air, right?

AMORINA KINGDON: To make a long story short, sound is a pressure wave, and it can move through anything that compresses even a little bit. And like you said, water is a lot denser than air. And sound actually moves pretty easily through water, almost more easily than air. And it moves four and a half times faster. So in air, it’s about 330 meters per second. In water, it’s about 1,500 meters per second.

IRA FLATOW: Wow.

AMORINA KINGDON: And the other thing that happens underwater is that sound loses energy less quickly. So it travels a lot farther a lot faster. And when it gets there, it’s, for lack of a better word, kind of decayed or distorted, maybe a little bit less than it would in air.

IRA FLATOW: Mm-hmm. You write about the plainfin midshipman, a very strange-looking fish with a strange way of producing a very loud sound. So let’s play for our audience what that fish sounds like.

[LOW TONE]

I thought that was a ship horn or a foghorn.

AMORINA KINGDON: I’ve heard– I’ve heard a ship horn. Yes, it’s almost mechanical-sounding, isn’t it?

IRA FLATOW: Yeah, it is, but it’s not.

AMORINA KINGDON: No. It’s extremely, extremely fast muscles. And that’s the male, and he’s got these really, really bulked up, massive muscles right alongside his swim bladder, which is sort of an air-filled bladder in his body that normally a fish uses to control his buoyancy.

And he’s vibrating that muscle really, really, really hard against that swim bladder and just making that hum. And he’s actually doing that almost onshore. So plainfin midshipman will– in the spring, they’ll come up. The males will come up and they’ll make a nest right at the tide line. Sometimes when the tide’s low, they’ll actually be out of the water.

And they’ll go under a rock and they’ll sit in a little pool, and they will make this hum. They will make this really, really loud, very droning, [LAUGHS] perhaps not immediately interesting sounding to us, hum.

And what it does is it travels out into the water, and it reaches female midshipman who are kind of out in the more open water. And they hear that sound. And in the spring, their ears actually become more sensitive to the frequencies in that hum. And so they hear this sound and they go and they find the male with the loudest hum, the biggest muscles, presumably the best ability to guard the eggs, and they go and try to find him.

IRA FLATOW: And you went along with some researchers studying them, right? What was that like?

AMORINA KINGDON: Well, I found that the plainfin midshipman, when you meet it face to face, is a very funny-looking fish. Actually, it’s very slimy. It doesn’t have scales. Its skin is very smooth. And it has this really big, triangular head. And they do not– they do not look particularly impressive, especially not during the daytime or in the morning.

And I actually went to quite a few different places around Southern Vancouver Island, trying to listen to them, trying to find them. I had a little dip hydrophone that I bought when I started working on this project. And everywhere I went, whenever I was on the coast, I’d just put it in the water and see what I could hear.

IRA FLATOW: Cool.

AMORINA KINGDON: I was trying to find this fish for years, and I couldn’t quite find it where they were– they were going. And then it was actually just last year. It was a spring night. I had actually got a broom handle to help fish the cord of the hydrophone off the dock, and I managed to get it into the water.

And as soon as it plunked into the water, I could hear this hum. It was really loud in my headphones. And as soon as I pulled the hydrophone back out of the water, it vanished. I couldn’t hear it above the water at all.

And I was looking around, and there were sailboats moored, and there was a little town over there and some condos. And I was just thinking, wow, there’s this whole thing going on underwater. These fish are mating and they’re finding each other and they’re humming. And I would never know– you would never know if we hadn’t gone out with a broom handle and dipped this hydrophone in the water.

IRA FLATOW: Let’s talk a bit about something really fascinating too, and that’s how invertebrates perceive sound underwater, yet they don’t have ears.

AMORINA KINGDON: Yes. And this was one of the most mind-blowing things that I learned. And there’s a structure that evolved really, really early in the history of animals. It actually evolved underwater back before animals even had bones. And it’s a hair cell.

And essentially, that is, at its simplest description, a cell that has a little protrusion on it called a hair. And when that hair bends or is bent by something, it fires a signal into an attached neuron.

And so that is the basis. It’s kind of like a transducer. It transduces a mechanical force into an electric signal. If you remember, sound is a pressure wave, and so it’s actually moving the molecules. So whenever you have a hair cell, you have at least the potential for detecting a sound.

And so in animals like squid or a lot of other invertebrates that evolved pretty early, they don’t have ears, an ear being a structure that’s specifically designed to hear sound. But what they do have are balance organs, for example, which are called, in some animals, a statocyst.

And to take, for an example, a statocyst, it’s basically a chamber lined with hair cells, and there’s a little stone or a thing of sand in the middle. And as the animal kind of moves through the water, pitches, yaws, turns right, left, up, down, the mass and the inertia of the mass will move against the hair cells and it’ll tell the animal what direction it’s oriented.

And that structure seems to be able to also perceive low, loud sounds. And it seems to be the case, at least with squid or other shellfish. And these hair cells are not just in statocysts. They can be in organs, in shellfish called abdominal sense organs. They can be in crustacean antennae. Tons of different structures that aren’t purpose built for hearing sound or detecting sound, but they can still tap into that stimulus wherever it’s in the water.

IRA FLATOW: Wow. You start off the book shadowing researchers who are studying kelp forests. I’m particularly fond of kelp forests because we’re growing kelp right here in Long Island Sound, where I live. What a fascinating way to start the book. How does kelp affect how sound travels underwater?

AMORINA KINGDON: Well, that’s actually exactly what they were trying to research. And the thing that I thought was fascinating about that study– obviously we have a lot of kelp here too on the West Coast, all up and down– is that those scientists by their own admission, they’re not sound scientists. They’re not acousticians. They’re not physicists. They’re community ecologists and biologists who are studying the kelp ecosystem as a whole.

And they’re looking at how it may change in the future, because kelp doesn’t really like warm water. So if there’s warming from climate change, it’s going to diminish. You know, there’s tons of baby animals that live in kelp. Kelp’s a nursery. It’s a refuge. It’s food. It’s a really critical ecosystem in the ocean.

And so what I thought was fascinating was that people who don’t study sound are now including sound as just a basic parameter of marine ecosystems that should be studied because we’re starting to realize more so than ever before just how central sound is underwater.

IRA FLATOW: Right.

AMORINA KINGDON: Like, when I dove into that kelp forest, we saw urchins, and we saw fish, and we saw invertebrates, and we saw nudibranchs. And all of these animals could detect the sound of my swimming, even though none of them had necessarily what we would recognize as like an ear, a human ear.

IRA FLATOW: Aside from the sea life that lives there, the ocean makes its own sounds, right?

AMORINA KINGDON: Oh, yes. Yes. The ocean is not a quiet place at all. It’s– [LAUGHS] even before animals, the wind and waves make sounds. There’s bubbles that form at wave crests, and they pop. They oscillate and make a sound.

And then ice makes a sound. So in the Arctic regions, you have cracking and booming and melting and ice quakes. And then icebergs can drag along the sea floor and they make sounds as they melt. And there’s also mudslides. There’s earthquakes. Like, an earthquake can often be picked up hundreds and hundreds of kilometers away.

IRA FLATOW: How about rain?

AMORINA KINGDON: Rain makes a sound. Yeah. And you can actually tell– if you listen very carefully with the right instruments, you can tell the drop size from the sound underwater. You can track storms. Even snow makes a sound.

IRA FLATOW: Snow?

AMORINA KINGDON: I thought this was beautiful.

IRA FLATOW: Snow makes a sound?

AMORINA KINGDON: Snow makes a sound. A snowflake falling on water creates kind of a double sound. It’s like a plink when it falls. And then as it melts underwater, it creates this kind of high shrieking hiss noise. And it’s very, very subtle. But yeah.

And this was actually discovered completely randomly about 100 kilometers north of me on a lake in 1985. One of the researchers was listening to rain, and it turned into snow, and he just kept recording and he discovered this sound that snow makes. So the ocean is absolutely full of noise.

IRA FLATOW: And we make some of that noise, we humans, don’t we?

AMORINA KINGDON: Yes, we do.

IRA FLATOW: Loud noises.

AMORINA KINGDON: Yes, we do. Some loud, some soft. But yes, a lot of it.

IRA FLATOW: And are the animals aware of this?

AMORINA KINGDON: Oh, yes. Yes. Now, it does depend on the animal’s hearing range, the frequencies that they hear at. But humans make noise, all different kinds of noise. Broadly speaking, you could classify it into two camps. They’re sort of very loud, very impulsive noises that tend to come from things like pile driving or close up to air guns, or things like that.

And then you get this more chronic, droning noise that comes from ships and shipping lanes. And that second one has pervaded pretty much the entire ocean. You can hear ships at the bottom of the Mariana Trench. You can hear ships basically everywhere in the ocean.

The amount of shipping in the world has really risen recently. I believe that the energy from shipping noise in the ocean actually doubled each decade from about the 1960s to about the 2010s, and that’s doubling each decade.

IRA FLATOW: How can scientists then study how these loud, human-made noises are affecting marine life?

AMORINA KINGDON: Well, we’ve done a lot of– the first initial studies were on marine mammals because a lot of that was a little bit more obvious to study. So they have some tags that you can put on a whale that stick on with a suction cup, and they can follow a whale and study how it reacts to sound, how it responds. Does it run away? Does it make sounds? Does it make sounds differently?

And so a lot of that has helped start the process of figuring out how we affect these animals. But there’s also a lot of animals that we just haven’t even thought to study, like the fish and the invertebrates that we thought didn’t really care about sound until recently. It’s really difficult to study how they respond to sound because we can’t directly interview them. And sometimes the effects are not quite very obvious.

So one of the unfortunate things about our studies of impacts of things on animals is that we tend to say, oh, is the animal still alive? Is it visibly hurt? No? Well, then it’s probably fine.

But if you think about all the different ways that sound can work with these animals lives– finding mates, finding food, navigating, staying in touch with each other– if sound impacts those things, you can– it’s like with the cleaner wrasse or the larger fish. It’s not an obvious impact, but it can really ripple down through how it lives its life and whether or not it has offspring, whether or not it survives. So we’re just starting to understand how invertebrates perceive sound and what matters to them, let alone how human noise affects them.

IRA FLATOW: So we need to know more about how they perceive sound before we start talking about how we reduce our own sound in the ocean. I mean, should we be making boats quieter? Things like that.

AMORINA KINGDON: We definitely need to know more about how these animals perceive sound. And we’re even discovering that on the sea floor, there may be animals that can tap into vibrations the same way that they tap into sound. I mean, we’re just starting to really look at this kind of thing.

There are actually some regulations that are starting to be discussed right now. The IMO is discussing underwater sound. The International Organization for Standardization, ISO, is actually starting to put research into how exactly you should measure a ship sound.

And that’s actually a weird question. You would think, oh, you just put a hydrophone in the water and measure how loud a ship is. But it turns out it’s actually really complicated.

So something that big, most of the sound comes from its propeller. And the sound moves and spreads through the water totally differently whether the ship is high in the water or low in the water, if it’s in deep water, if it’s in shallow water. So even just measuring a ship noise, let alone how it affects anything else, turns out to be this really complex mathematical problem. And so we’re just studying that now to try to figure out how we can fix that.

But there’s also efforts to engineer quieter ships. Naval architects are figuring out how they can make different propellers, different bow shapes that might reduce wash on the hull, all that kind of stuff.

IRA FLATOW: We could go on forever because I’m a water person like you are.

[LAUGHTER]

But we’ve run out of time. This is such a great book, Amorina. Thank you for taking time to be with us today.

AMORINA KINGDON: Thank you so much.

IRA FLATOW: Amorina Kingdon, science journalist and author of the book Sing Like Fish, How Sound Rules Life Underwater. She’s based in Victoria, British Columbia. Of course, that’s in Canada. If you want to read an excerpt of the book, go to sciencefriday.com/likefish. That’s sciencefriday.com/likefish.

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