How to Listen Like a Fish with Marine Biologist Sophie Nedelec

Intro: SpectreVision Radio.

Sophie: When we think about our ears, we think about these big, kind of gramophone style organs that we have on either side of our face that are amplifying that sound. Fishes don't need that because their body is mostly made of water and they exist in a medium that's mostly water, any sound wave that's propagating up to their body can pass directly through their body, so their whole body is vibrating as the sound wave is passing through them.

Intro: This is phantom power.

Mack: Welcome to another episode of Phantom Power, a podcast about sound. I'm Mack Hagood.

Do fish have ears? what is the nature of underwater hearing and how does it differ from hearing in the air? If humans are the evolutionary descendants of ocean creatures, do we retain any fishy traces in the way we hear the world? And what about all the noise we make in our oceans because we work and travel on the water while rarely putting our ears in the water? What are the consequences of that for aquatic life? save the planet. Do we need to learn to listen like the fishes once again? Those are some questions I would like to explore today with my guest, Marine biologist and bioacoustics expert Sophie Nedelec.

And speaking of oceans, today marks a bit of a sea change here at Phantom Power. We've always been a podcast about sound in the arts and humanities, but now that we are doing two episodes a month, that's giving us the space to branch out a bit and to engage with some of my other sonic interests. And so we're going to occasionally do what I'm calling SOS episodes shows on the Science of Sound.

And to help out with this effort, I've recruited one of my favorite scientists, my friend, and Cincinnati neighbor, Dr. Nate Morehouse. Nate's an associate professor in the Department of Biological Sciences at the University of Cincinnati, and Director of the Institute for Research in Sensing, or IRIS. And Nate's my wing man today.

Nate, welcome.

Nathan Morehouse: Good to be here, Mack, thanks.

Mack: Nate, do you want to tell us a little bit about who you are and what you do beyond what I just said?

Nathan Morehouse: Yeah, sure. I'm a sensory biologist. I run a research team here at the University of Cincinnati focused on animal vision predominantly. we studied this in insects and spiders. How do they see color? How do they see depth and motion? And we apply these insights to understanding how they communicate with each other and navigate their sensory worlds to make choices about who to mate with and what to eat, where to go. And my role as director at the Institute for Research and sensing, that deep seated interest for me about sensing and perception in the world really goes broad and we recruit in voices from the humanities, the social sciences, and the fine and performing arts into questions that at least here have oftentimes been held, mostly in the sciences and engineering fields. so I'm oftentimes in these kinds of conversations between sensory studies and sensory biology or sensory ecology, a place that I love to think and play and explore.

Mack: Yeah man, I really love what you're doing, the way you engage across disciplines. And I'll just have to say it like, I think biologists are my favorite scientists. Like if anyone has done any union organizing in the engineering building or the computer science building, as I have, man, that is like some serious, sometimes Ayn Randian space there. But the biologists are always down to clown, so I dig the biologists

Okay, so now that I've needlessly stereotyped the, different academic disciplines, let's welcome our guest today. She has a PhD in Bioacoustics and Behavioral Ecology from the University of Bristol. She is a Dorothy Hodgkin Fellow of the Royal Society.

She's a senior research fellow at the University of Exeter. Sophie Nedelec, welcome.

Sophie: Hi Mack, thanks for the introduction. It's great to be here with you today.

Mack: So I've rattled off some impressive titles that you hold, but like, can you tell us a little bit about yourself and what you do?

Sophie: Yeah, sure. So I'm a scientist who's really curious about sound and the way that animals perceive and use sound in the environment and the way that they're threatened by some of the sounds that humans make. So, I run a research team at the University of Exter where we are focusing on sound in the way that fishes and invertebrates detect it under the water.

So we try to use instruments that can sense sound in the same way that some of their ears are working, and we're exploring the ecology of that underwater, acoustic world. Um, a lot of the research I've done up until now has been really focusing on the threat of underwater noise pollution.

and that's mainly been from vessel traffic, which is the most common source of underwater noise, and traffic noise can affect animals underwater in a similar way to the way that we can feel affected by traffic noise. So anyone that remembers the road quieting that happened in lockdown and the peace and quiet that you maybe experienced and the fact that you could hear birds in your garden that you'd never noticed were there before, can kind of imagine the situation underwater.

But the. fact is that sound underwater travels further and faster than it does in air. Wavelengths are actually five times as long. And added to that light doesn't really travel very well under the water. So a lot of the animals that live underwater are really reliant on the way that sound propagates to know what's happening and where things are underwater.

So the noise that we are introducing as humans by driving vessels around, by pile driving during construction, by emitting seismic air gun blasts to explore for oil and gas and that kind of thing, it's creating a cacophony in the ocean that spreads far and wide and has wide reaching impacts.

Mack: Yeah, so well, maybe let's start with the fish. I've got some goldfish in my house. I have noticed that they don't appear to have ears on the sides of their head. I mean, that would not be very streamlined if they did. I suppose it'd be kind of hard to swim, but do fish have ears that I can't see? Let's just start with the basics here.

Sophie: Yeah, that was really the way that I felt when I first started getting into this field as well, I was shocked to realize that fish have ears at all, and I think many people who aren't familiar with this field feel exactly the same way. And I mean, it's for a good reason that we can't necessarily relate immediately because when we think about our ears, we think about these big, kind of gramophone style organs that we have on either side of our face that are amplifying that sound and helping that cross from the air water boundary into our head, which allows us to sense it.

fishes don't need that because their body is mostly made of water and they exist in a medium that's mostly water, any sound wave that's propagating up to their body can pass directly through their body, so their whole body is vibrating as the sound wave is passing through them. the reason that doesn't happen for us is that sound will bounce off the interface of two different media.

So between air and water, there's a big difference in the density and that means that most of the energy in a sound wave that reaches that surface will be reflected off of that boundary. So that's why we need these, big organs on the side of our face to amplify the sound enough so that enough of that can get inside our body, that we can actually detect what's going on.

Mack: We've got fleshy pinna on the sides of our head that are like sound collectors because the fish is in water and the fish is also made of water there's not this medium change between, well obviously it's not air, but like there's not a medium change between the body of the creature and the medium it's immersed in.

Sophie: Yeah, exactly. There'll obviously be a slight difference because the fish is not a hundred percent water, but its body is mostly water and that means that most of the sound energy is gonna propagate directly through its body. But they do make use of the fact that the sound wave won't pass through materials of a different density as the mechanism for that hearing.

So inside their head in the kind of inner ear structure, fishes have a dense otolith, which is like a bone. and you can kind of think of this a bit like a marble inside of a matchbox, that if a sound wave passes through the body of the fish, the body's of the fish is the matchbox, and the otolith is the bone inside.

The fish's body will kind of rattle, as the sound wave comes through it, and the marble will also move, but it moves with a lag because it's denser and because of that lag, it's kind of bumping into the edges of the box. So the otolith that the fish have inside of their head, they're kind of moving with this lag in relation to the body of the fish.

And the fish has a sensory epithelium, it's like a skin covering that otolith with sensory hair cells poking out of it, that are just brushing against that otolith and those hair cells are able to feel that relative motion or that rattling between the body of the fish and the otolith.

Mack: So the otolith, is it made of like mineral or something? is the fish body converting? like what is this stone?

Sophie: Yeah, it's a calcarea structure. so like bone, it's really like bone, and interestingly, they grow with the body of the fish. So, in the same way that trees lay down rings in their trunks as they're growing, fish otoliths do the same thing. So whenever the fish's body grows, it will lay down extra otolith.

And that's been used by many scientists to look at fish growth over time. you can look back at different years and kind of create chronologies of how the fish was growing at different points in time.

Mack: So, the fish has sound waves going through its entire body. Or at least we should say sound, 'cause we might wanna come back to the distinction between sound waves and perhaps sound particles and water. But for the time being, we can just say the fish has sound going through its whole body. What extra information exactly are the otoliths providing here?

Sophie: So the otoliths are kind of the method for transducing the sound wave into an electrical signal that can travel to the fish's brain. So the hair cells that are overlaying that otolith, they're called mechano sensory hair cells. And that's the basis of hearing in all animals, it's hair cells that bend because there's some kind of vibration or some kind of movement.

And when they bend enough and the right direction, then that triggers an impulse to be sent to the brain, which says 'I'm detecting a sound.' So the fish has got three pairs of otoliths inside their inner ear, and the information from those is gonna be integrated, into the fish's brain, but it's not actually only the inner ear that the fish is using to detect sound, but they can also detect sound using their mechano sensory lateral line, which runs the whole length of their body as well.

That's able to detect the kind of low frequencies, and the information from that will integrate with the information from the otoliths.

Mack: Okay, so we have these otoliths that are sensing sound. before we go onto the lateral line, I just want to get it straight in my head a little bit more like how loose in the fish's body are these things? Are they really like just moving around like a marble in a box or is that more metaphorical?

Sophie: You know, at a very, very small scale.

Mack: Okay.

Sophie: Yeah. They're kind of, floating. And then there's a sensory copular, so there's kind of like a gel that they're in, and then they've got the sensory epithelium that's overlaying them, and they're inside of a semi-circular canal. These canals that face different orientations and the epithelium that's lying over the top of the otolith.

the hair cells on that epithelium are orientated to face in different directions, so that sound waves that are coming from different directions will stimulate different hair cells.

Mack: Okay. Okay.

Nathan Morehouse: And this sense of directionality is, contained within each set. Yeah. So the left hand and right hand side of a fish's hearing has within it native directional sensing of, sound. Is that true?

Sophie: Yeah, and the otoliths are kind of orientated in different directions as well.

Nathan Morehouse: So similar to like an accelerometer set that might tell you if something's being moved up, down, forward, backward. They have this kind of directionality built into each side of their hearing.

Sophie: Yeah, so we literally talk about them as functioning as accelerometers, and that's the type of instruments that I use in my research to try and understand underwater acoustic ecology, thinking that we can try to understand it from the same perspective as the fish. So the instruments that I use will have triaxial accelerometers inside.

And what that really means is there are three accelerometers facing three orthogonal angles. So each accelerometer can only move backwards and forwards along one axis. And if we have three of these pointing in the x, y, and Z axis, then we can kind of integrate that information to get a three dimensional,

Mack: So the fish is hearing in 3D?

Sophie: The fish is hearing in 3D, exactly. They do that much better than we do, because, we just have these two ears. And our method for telling which direction a sound is coming from is based on the difference in the time arrival between the two ears, which means because our ears are on this axis, we're quite good at telling what angle a sound is coming from on the horizontal plane, but we're pretty rubbish at whether the sound is coming from above or below us.

But because the fish have got these hair cells on each otolith pointing in different directions, and each lyth is also facing different directions, their potential for three dimensional sensing is so way beyond what we have.

Mack: we needed the ear on top of our head and on the bottom of our jaw or something like that, then we could compete with them. Oh, well that's, really fascinating. So, tell me this, like, from a self-serving human perspective, do I have any remnants of these in my body, did we inherit any of this kind of hearing or we moved to air, we just switched to a completely different method.

Sophie: Yeah, so both are kind of true. We do actually still have those otoliths and those semicircular canals in our inner ear, but we are no longer using that to detect sound. So we are using that system as a vestibular system, which basically means we're using it to balance, and that's what tells us whether we're going fast or slow. If we're swinging on a swing, if we've rolled out of bed or what makes us feel travel sick maybe, it's that system that's still acting. so that's acting as an accelerometer still, but it's using those kind of really big scale movements rather than the nanometer scale particle motion that the fish are sensitive to.

and we've ended up having to evolve this completely different way of detecting sound using the sound pressure, and we're doing that by the sensory hair cells in our cochlear, which is arranged in a spiral shape, is detecting the whooshing backwards and forwards of the liquid within our, inner ear.

That happens because of the pushing and pulling of the eardrum that happens inside our ear.

Mack: It's kind of interesting to think about in the human inner ear.

We had to get liquid involved, you know, like somewhere in that chain that we had to create like a little ocean for us to listen. I don't know if that's pushing it too far, but it is interesting to me that we wound up bringing some liquid back into human hearing in that way.

Sophie: Yeah. Or, or you could see it as the liquid never left our bodies, you know, like, we began by containing a small amount of sea water

as the very kind of basis going back in evolution as to the fluids in our bodies. And when we left the water, we kept that and we had to come up with new systems for transducing between the information in the air and that liquid in our bodies.

Mack: Okay, so let's now move on to the lateral line. You said that there is this tube that runs the entire length of a fish's body, pretty much, and that that is involved in hearing as well.

Sophie: Yes it is, and most people might have heard of the lateral line and think of it as being involved in schooling. That's the thing that people have most commonly heard of, and it is true that that's the sensory system that fishes are using to tell if there's something moving in the water near to them.

And also for telling how the water near to them is moving. So we call that flow. And so that's movement of the water in relation to the body of the fish. And they have this tube that's running down the side of their bodies, and there are kind of entrance ways to that tube dotted along their body.

And there are sensory hair cells inside of the tube. So where you have pressure differentials between two of those entrances, you'll get a small amount of water flowing from one entrance to another and that is sensitive, like I said, to the flow of the water particles relative to their body. But it's actually also sensitive to the acoustic particle motion, which is not just the movement of water from one place to another, but the vibration of particles in the water as a sound wave is passing through the water.

And that's the motion that will also pass into the body of the fish.

Mack: So now we're getting into the thing that, I think this is how I first discovered your work. Actually, I think I ran into your work from two different angles. Maybe we'll talk about another one later. But one of the ways I first heard about you is I was trying to research this idea of particle motion as being part of the hearing process, because that is quite different from how I've ever thought about hearing before, and Nate, feel free to jump in and save me when I get out over my skis on this, but like, my understanding of human hearing is that we hear sound waves. The sound waves are what we might think of as patterns in particles of air hitting one another. If I hear a sound from my neighbor's house, it's not like a particle of air traveled from my neighbor's house to my ear. It's more like the particles of air over at my neighbor's house started vibrating. And then there was this sort of domino effect, so to speak. Things quivering back and forth, knocking each other along until the particles of air in my ear started to vibrate. so And so that's a wave motion, that's hearing a sound wave. But the fish, apparently underwater maybe can hear that way, perhaps with the otoliths, but they also hear using the lateral line, the motion of particles of the water itself is, am communicating this right?

Sophie: So, you are absolutely right that it's all about waves and sound is literally defined as propagating as a wave. It's a longitudinal wave, and it's happening because of particle motion. Because one particle moves a bit closer to its neighbor, you get an area of higher pressure, and then because of that area of higher pressure, the neighboring particle will move closer to its neighbor.

But then because of the increased pressure between those particles, the first particle also moves back towards its neighbor on the other side. So you get neighboring particles are oscillating backwards and forwards or vibrating and bumping into each other. And I think the domino effect is a really good analogy, and if you could just imagine that there's a set of dominoes that knock each other over, but then they also knock each other back again. So they kind of dominoes that are kind of flip flopping. That's what's happening. And the space between the dominoes is where the changes in pressure are happening and the movement of the actual dominoes is the particle motion.

Both are needed in order for it to be an acoustic wave that's propagating from one side to another.

Mack: But in the fish experience of sound, the fish not only perceives the sound wave as we do, but it directly experiences the particles themselves. am I getting that distinction right?

Sophie: Yeah. And so the particles of the sound wave in the water move the particles of the body of the fish, which end up moving the particles of the body of the fish next to where the otolith is. So it's like that sensory epithelium overlaying the otolith, all of the particles making that up are causing that to move backwards and forwards over the otolith.

And so it's that relative motion that those hair cells are picking up. and then the lateral line is slightly different in that it's these little pressure differentials between the different channels that cause water to flow through different bits of the channels of the lateral line, but that's still caused by the same acoustic wave.

Nathan Morehouse: Something I wanna just jump in here is that many animals want to detect flow or particle motion. Some of it is for a sense of self movement through an environment, some of it is to detect things that are changing flow around them, like other members of their species or a predator, et cetera. So being aware of particle flow around you is really important, especially for smaller animals.

I know a lot about this kind of thing for terrestrial animals like crickets, for example, that have mechano-sensory hairs on organs on their backend called cerci. That's really essential for their awareness of the surrounding area. But I think one thing that we're discovering as scientists is that many of these systems. Maybe originally functioning as flow sensors can hear. We know this about, for example, spiders. That spiders can hear far field sound with a system of mechano-sensory hairs that, are likely to have originated to detect fluid flow and particle movement. And I think this is probably also true in the underwater environment.

Things like the lateral line that began as flow sensing can be repurposed fairly easily into a hearing function through small modifications that allow them to essentially listen in to these particle movements.

Mack: It's interesting, and Sophie, just to build on that, like you were the lead author on an article called Particle Motion, the Missing Link in Underwater Acoustic Ecology. So what was the purpose of that paper? Like, in what way is this particle motion the missing link?

Sophie: so the reason we called it the missing link was that, we were focusing on the experiences of fishes and invertebrates, which have the majority of the ears in the ocean, and in the underwater world, and in the substrate for that matter. And probably because we are mammals and we sense pressure, we have invented equipment for sensing pressure and understanding pressure.

And that's been used, underwater in the format of hydrophones, which respond to pressure. And there's been a lot of research on the sensory ecology of marine mammals and how they use pressure underwater, how they respond to anthropogenic noise and so on. and these hydrophones, by the way, they function by expanding and contracting as a sound pressure wave passes through them.

it's a little piece of ceramic that will expand and contract with that pressure, and that creates a voltage which comes through a wire that we can then record with a digital converter. so yeah, the reason why we considered particle motion to be the missing link was that it's the part of the sound that's being detected by the majority of animals.

Like I was just saying, there are 35,000 species of fishes at least, and many, many more species of invertebrates. Some fishes can detect pressure, but not all. But they all definitely detect particle motion. And then all of the invertebrates that we are aware of that detect sound are doing it by detecting the particle motion with these accelerometer style transducers amongst other types.

so yeah, the reason for that paper was thinking if we want to understand the sensory world of these animals and the threats that they face, we need to start measuring sound in the same way that they are hearing it. And that's by measuring the particle motion. But the re the reason why we can't just measure the pressure and use that as a proxy for particle motion is that in certain places in the water, and that's especially if you're close to a boundary like the surface or the bottom, or if you're very close to the sound source, then that relationship between the pressure and the particle motion is not very easily predictable.

So one of the main points we were making is that these animals could be threatened by sounds that we are kind of underestimating if all we do is measure the pressure.

Mack: that is so interesting because it sort of ties into what you were saying, Nate, which is that you're sort of just discovering this, flow issue or this particle sensing, because we've come from a sort of anthropocentric perspective where the way we thought about sound was dealing with pressure waves.

And when it comes to hydrophones, I mean, pretty much any sound artist who is interested in sound underwater is using hydrophones. So this is like, you know, moved into the arts as well. Whereas I've never heard anyone really talking much from an artistic perspective about this kind of particle motion.

So I think this is a really interesting space to understand. And also it's a sort of interesting act of imagination and empathy that you guys are partaking into sort of imagine this kind of experience that we literally don't have the tools to experience.

Sophie: I'm just interested in trying to reconstruct the world from the perspective of these animals and how they're sensing in 3D. And one of the ways I'd like to try and do that is by using that particle motion to locate where animals are underwater so we can understand that soundscape in a similar way that we might understand a landscape when we look around us.

Nathan Morehouse: you just talked about. 'cause that seems so essential, especially given how three dimensionally, fish and other things are hearing their worlds. but I did wanna double back because, Mack I completely agree with you that oftentimes we impart our own biases, knowingly or unwittingly on our measurement of the natural world.

Some of that just simply reminds us that we're using technologies that were developed for human uses and are trying to apply them like a hydrophone that was developed with the human as the intended listener, bakes into it human biases. But there is this question of translation, and I guess my question for you, Sophie, is are there human experiences that maybe offer some kind of metaphor?

I'm thinking here about when you can use Proprio reception to feel a big bass beat in a loud PA system. that feel like a reasonable metaphor for the way that the world of sound might feel entirely to one of these kinds of animals, fish or invertibrates, or is that a poor place for people to begin imagining?

Sophie: So, I totally get the experience that you're talking about when you're very, very close to a loud sound system and it's actually 'cause you're in the near field, that you can actually feel the air vibrating and sometimes you can feel that on the hair cells of your skin. So potentially we could relate that to that experience of the lateral line.

There's actually another way that that relates to the hearing of fish, which is slightly different and actually relates to the pressure. And that's because, when that low frequency sound wave is passing through us, we can feel it in our chest. And I think one of the reasons for that is that the air bubble that we have in our bodies, or the two air bubbles we have in our bodies, that's our lungs. Those air bubbles are actually expanding and contracting with that sound wave as it's passing through our bodies, because the air is much more compressible than the surrounding fluid of our bodies.

And that's similar to the way that fish hear sound, because fish that have a swim bladder are actually experiencing the same thing. And so their swim bladder will resonate with the sound wave that's passing through it, and it actually reradiates the sound and is then picked up secondarily by their inner ears.

Nathan Morehouse: So we're not deaf in these ways, we're just very hard of hearing. We have the capacity in some situations to have experiences that are maybe similar, or akin to what a fish or a crab might experience. Yeah.

Mack: I think we've done a pretty nice job of exploring this hearing from a marine life perspective. So now that we're better equipped with some terminology, some concepts, what new things are you learning in your research about protecting marine life and the dangers that humans pose to marine life now with this much better understanding of the role that sound plays in the lives of these creatures?

Sophie: Yeah, so at this time that we are living in at the moment, I think it would be misplaced to focus all of our energy on just monitoring diversity, biodiversity, and documenting its demise. I think we need to be actively involved in protection and restoration, and that's really the direction that research in this field is now taking.

So on the anthropogenic noise side of things, that means moving from looking at sound levels that cause effects to recommendations for policymakers and industry, as to what sound levels we need to limit our activities to, and that is being applied successfully in, some places.

We can also think about concepts like limiting noise. For example, the International Maritime Organization, that's the international body that governs shipping, they already have recommendations for how ships can create less noise as they're moving through the water, which saves them energy. we can also think about limiting noise by adjusting the behavior of vessel drivers.

So, you know, we have evidence that if motorboats drive a hundred meters from a reef rather than 10 meters from a reef as they're going past, then the animals that live on that reef are gonna be less impacted. They're gonna have higher reproductive success, which is really important for populations.

Mack: Can I jump in on that? I remember looking at one paper of yours that it seemed like you had some rather counterintuitive insights, perhaps based on your, research into particle motion. If I remember correctly, the people who were driving boats or were told to move more slowly, that that would be quieter would interfere with marine life, less around reefs and something.

But I think you found that that actually was not the case. Could you talk about that?

Sophie: Oh, so we have published a paper recently where we were looking at motorboat speed and how that related to the received sound levels. Is that the one that you mean?

Mack: that's the one I mean, yeah.

Sophie: Yeah. So, we assumed like many would that the slower you go, the quieter your boat will be. But it turns out that with motorboats, particularly that style of outboard motorboat that will go up on the plane when it gets faster.

What that means if a boat goes on the plane is that, as it speeds up, it kind of lifts up out of the water, so less of the hull is in contact with the water, and that reduces the drag between the boat and the water, which means that it takes less energy for the boat to go faster. So because of that, going faster doesn't necessarily make it louder.

So we found that the boat has to go really, really slowly in order for it to get much quieter. They really need to go at a speed that's slow enough to not create a wake, as well as that, just leaving more space between where the boat is and where the living things are is also another way that can work.

Nathan Morehouse: This is where actually properly measuring these things is helpful rather than just going off of common sense right? Now, I mean, it sounds like you can rely on what you hear as sound inside the boat, you know, to maybe adjust behavior, but actually studying these things, oftentimes I get questions, 'well, why do you study that?'

You know, isn't that stand to common sense? And it's these kinds of things which is like, well, hey, go extremely slow or get up on the plane, but don't do this middle velocity close to a reef. which many people might assume was just fine.

Mack: But you could see how that would happen if we associate sound as wave motion. but you know, a boat is displacing a lot of water and creating a lot of particle motion that would interfere with fish that we wouldn't even interpret as sound. Right?

Sophie: Yeah, so the displacement of the hull can create very low frequency sound that fish are able to detect as well. Yeah. Back to your point Nate, about why we can learn more by actually studying things. Again, it's about the air water interface, but something I hear a lot when I tell people that I study the noise of kind of watercraft is anyone who lives by the coast is quite likely to complain quite quickly about the noise from jet skis.

So kind of widely unpopular with people who like peace and quiet when they're by the coast. But actually jet boats create less noise underwater 'cause they're making more noise in the air. So you can hear a motorboat with your ears, that's, you know, a short way away.

But if you drop a hydrophone or an accelerometer for that matter into the water, that boat immediately sounds like it's way closer than it sounds to you in the air because of how that sound is propagating through the water. And because a lot of the sound of that boat is going into the water rather than into the air.

But jet skis are kind of different, so most of their noise is actually happening in the air and there's less of it in the water. Okay.

Nathan Morehouse: Well, and some things also cross that air water boundary I played with, hydrophones in the Puget Sound, and of course all of the fairies up there are dominant features in that acoustic environment, but you can hear sometimes a plane going overhead, so some of this air based sound is also penetrating these underwater environments. done much to think about that or does that feel like it's at a volume level that's of less concern to these waterborne sounds?

Sophie: No, It's absolutely true that if there's a very loud sound in the air, then a portion of that energy is gonna propagate through to the water. And airplanes are obviously incredibly loud, they're way louder than jet skis. And I've experienced that as well when I've been researching on the Great Barrier Reef at Lizard Island, there's a plane that comes and goes twice a day to this very small runway. And, if you're under the water, you can hear it passing over, and I've also heard it on the hydrophones. And also another route that noise from the air can get into the water is thinking about road traffic.

So there is evidence that roads that are close to water bodies, there's noise that's actually getting through into the water column,

Mack: do we have good ways of measuring the impacts of human made noise on ocean ecologies, like say compared to climate change or what scale of problem is this?

Sophie: In terms of how good are we at determining what's going on and how big an issue it is, one of the most important things that we've tried to address is the impacts of noise on fitness, so that means the ability for organisms to survive and reproduce. Because impacts on fitness can translate into population level impacts and where we wanna think kind of broadly at the scale of protection and restoration.

It's those population level impacts that are really important, and that's why we've made efforts to research things like survival and reproductive success.

Nathan Morehouse: And the hormonal effects of some of these sound exposures too. I noticed that you'd done some work looking at the hormonal responses of anemone fish to different levels of sound disturbance, and it impacts the male androgens, you know, like testosterone, but it also over long periods of time hits corticosterone, which is a stress response hormone. And these are ways in which animal physiology integrates the stress of something like this into broader patterns of investment in reproduction or lifetime, these kinds of stress hormones can oftentimes be indicative of longevity, et cetera. So these animals are clearly feeling this in ways that are measurable, even just in their basic physiology.

Sophie: Yeah, exactly. And in that study we saw correlations between that physiology and behavior as well. So the males that had an increase in the androgens, they were more aggressive and the fish that had higher cortisol were hiding more in their anemone. And those impacts on the behavior can also impact different elements of their life history as well, like their feeding, their ability to mate and socialize.

Mack: One last thing that I wanted to ask you about is, I think the other way that I came across your work is through some sound artists. A group of guys known as machine listening, Sean Dockery, James Parker, and, Joel Stern, who did a sound art project that was based in part on, I guess them being inspired by some research you had been involved with that used the sounds of healthy ocean reefs to improve the vitality of unhealthy ocean reefs.

can you just talk a little bit about what that was?

Sophie: Yeah, absolutely. So this really comes into the restoration side of the story and how we can use underwater sound and the way that animals are responding to that sound ecologically to the advantage of the reef. This is the hope. So, What we did essentially was to make sound recordings of healthy coral reefs and to play that sound through speakers next to artificial reefs.

And then looked at how many larval fish came and settled onto those reefs and found that the sound of the healthy reefs is really attractive to many different species of larval coral reef fish. And the reason that's important for restoration is that these reef fish most species have this kind of two phase life cycle.

The adult phase is very fixed and kind of territorial onto the reef. but when they spawn, they have larvae that will swim off into the open water. The reason they swim away is so that they're less vulnerable to all of the many predators that live on the reefs, 'cause when they're these tiny larvae, they're very vulnerable to being eaten by anything that the mouth that they will fit inside of.

So they head off into the blue until they've kind of developed the strength to be able to avoid predators a bit better. But once they have got to that stage where they're ready to metamorphos swim back to a reef, they have this issue that they can't necessarily see a reef that they wanna head to.

Because like I said, light doesn't really travel very well in the water, but the sound underwater is a really, really reliable directional cue. So independent of ocean currents, it's a good way for larval fish to know where's a good place for me to settle down and set up my home.

And so these larvae will be able to hear different reefs around them and choose which reef they wanna head for, and they're gonna choose the reef that sounds the healthiest. What it means, if it sounds the healthiest is it has the most animals on it making noises essentially. So that's coming from the sounds of snapping shrimp, which are covering the surface and under the surface of the reef.

And then also the cools of many different species of fishes, which are using their sonic muscles on their swim bladders and grinding their teeth together, making all these different sounds for communication. And these larval fish can eavesdrop on those sounds so that they know where's the healthiest community that I wanna head for.

But yeah, some of this research is involved tapping into that, ability, that ecological process where these larvae will swim towards a good sound, to kind of boost the potential for restoration of reefs.

Nathan Morehouse: Do you, do you know if this is possible this is a memory for these larval fish of what they've heard before? Or do you think that they just know what healthy reef sounds like? That it's genetic. They're born with the capacity to find their way to healthier reef.

Sophie: It's a really good question that we dunno the answer to yet, but yeah, it is possible that because even as embryos, these fish have otoliths, so we know that they're able to detect sounds at that stage. We also know that fish embryos are affected by anthropogenic noise, in terms of their physiology and their growth.

So, you know, they're gonna be able to detect the sounds of the reef that's around them. So there's definitely the potential that they're able to kind of imprint on the sound of a healthy reef and to head back for that when they get to that stage.

Nathan Morehouse: Wow. Fascinating.

Mack: So we're now playing healing sounds for ocean life. What about noise canceling headphones? Can we develop some noise cancellation for undersea environments? Gimme some more good news.

Sophie: So I know that that's something that some technologists are attempting for vessels, to see is there some kind of noise canceling device that can be attached to a vessel, so that it's emitting less noise into the environment.

So if you wanna do an experiment with fish in a tank, It's very hard to get away from the fact that any sound you introduce into that environment is gonna be bouncing off all of the edges of that system and giving the fish information that it's in a tank, which is gonna then affect its behavior and it might not behave in the same way as it would in the wild.

So what we wanted to do was to try to essentially play noise canceling along with our signal, or kind of anti echo sounds as a way of trying to convince the fish they were actually in open water, when they're actually in a tank.

So if they were only detecting the pressure, that would've worked, but because they also detect the particle motion, it can't really work in the same way. So at these very kind of small scales in shallow water, like I said, the particle motion and the pressure might not be acting in a kind of easily predictable way. And so we might be able to tune the pressure so that the fish thinks it's in open water, but if we did that, we'd be doing something else to the particle motion that wouldn't have the same effect.

So yeah, noise canceling might maybe work for those open ocean environments, but not in a small enclosure like a tank.

Mack: Yeah, so, oh man. This is so interesting because the principle of noise cancellation in the air is to create a sound wave, or electronically create a signal that's the equal and opposite signal, like they basically the phase shift of the original sound wave so that the peaks and valleys of the first sound wave are canceled by the new one that you've introduced. But if you're introducing new sound waves in an underwater scenario, then you're also influencing the particle motion, which does not react the same way, right? So if I'm understanding you correctly you're saying you may cancel the sound wave, but that's gonna have all kinds of crazy effects on the particle motion and the fish is still gonna hear that.

Sophie: Yeah, I mean, so the particle motion is still a part of the sound wave. So the sound wave won't happen if you don't have particle motion. It's an essential part of it. But, when you're in these really near field environments, the sound pressure and the particle motion are outta phase with each other.

So yeah, adjusting one. If you fix one of those, it might actually make the other one worse.

Mack: So, no virtual reality for fish and tanks yet.

Sophie: Not yet.

Mack: yeah, we can maybe fool them visually with some nice backgrounds or something, but I guess is all they get.

Nathan Morehouse: Well, and one thing to note here is that this is a place where the whole equation is simplified by the simplicity of our hearing situation, because what we can do with noise canceling is we can do it at the point of entry into the ear, whereas fish and crabs sound is just propagating into their body from any direction, right?

And so even imagining some kind of noise canceling hearing apparatus would be pretty tricky for animals that are really bathed in the sounds that they're experiencing.

Sophie: Yeah, exactly. I think if you really wanted to do it. Yeah. Or you could, you could put them in a tank where every surface is a sound source. So if you were driving all of the walls of the tank and the surface of the water, then you could potentially create something analogous to the sound experience that they might be having in open water.

Mack: Well, and for the book I'm working on right now, I've been investigating some researchers who are doing that for people. So they're creating actual noise cancellation in open space, not in the ear. So that one person can be watching an action movie while the other person reads a book in the same open plan apartment.

that's the demonstration video that they use. You can imagine the genders of the people involved in that demonstration video, but. yeah, so, I don't know, maybe humans will be in virtual spaces and marine life will be too, I well, Sophie this has been super fascinating.

Thank you so much for talking to me, and Nate, thanks for adding some, intelligent, articulate questions to my really dumb ones. This has been a blast.

Sophie: Thanks very much for having me on, it's been really interesting to chat to you.

Mack: Thanks.

Nathan Morehouse: Thanks Sophie. This was really illuminating, in an acoustic way.

Mack: And that's it for this episode of Phantom Power Huge thanks to Sophie Nedelec, and to Nate Morehouse for being on the show. Our show is edited with care in the United Kingdom by Cameron Naylor, video layouts by Patricio Sanz. Our research assistant is Sarah Frosch. And remember, if you'd like to join to get our free newsletter or become a member to get all of our bonus content, you can find all of that at mackhagood.com.

See you next time.