Dr. Lori Schweikert: The Science of Fish Vision and What It Means for Anglers

Full transcript of the Tom Rowland Podcast, Episode 122 with Dr. Lori Schweikert.

Introduction

Dr. Lori Schweikert: Most recently, I'm studying the hogfish, as you mentioned. These animals down in the Florida Keys and coastal Florida are just incredible. Going out there spearfishing for them, just as a recreational angler having fun, taking them, spearing them in the Keys when season was open, throwing them on the deck of my boat. And one day, I got up out of the boat after spearing, picked them up, went to go put them in the cooler, and I saw the side of the animal that was facing the boat hull had turned the color white and had taken on this pattern on the skin that was the texture of that boat hull.

Dr. Lori Schweikert: So if you've interacted with a hogfish, you might know that they have this incredible ability to change color. When I saw that day that perhaps the animal, after it was dead, after it was spearfished, that its skin was still changing color and changing color in response to its environment, I was totally blown away. Since then, the last couple of years I've been doing research on the side about how that color change happens and how they might be able to sense the environment with their skin. So it's a pretty amazing thing, both trying to use what I've studied out on the water, but also being inspired by those experiences back in the lab. I'm Dr. Lori Schweikert.

Tom Rowland: And this is the Tom Rowland Podcast. That was Dr. Lori Schweikert. She is a very interesting person to talk to. I really enjoyed having her on the show today. She is a researcher with degrees in marine biology from Florida, and she's done a tremendous amount of research. What separates her in my mind and makes this a really interesting conversation for this particular podcast is that she's not just a fish researcher, but she's also an active fisherman herself and gets a lot of inspiration, as you just heard, from her experiences on the water, bringing that back to the lab.

Tom Rowland: When she has questions about something, she goes back and studies it. She has also been able to apply her work to her own fishing on the water. I found it to be a great conversation, not only about the hogfish. Stand by, because most of the conversation actually is about the tarpon and how incredible their eyesight is. Tarpon are the superheroes of fish, as Russell Kleppinger called them, and as Dr. Lori Schweikert tells us, that is exactly right. They have incredible vision, and she's going to tell us exactly why. I had so many questions about fish vision and what they can see, what they can't see. And in my own mind, I'm thinking, how can I apply that to catching more fish? So stand by for an awesome conversation with Dr. Lori Schweikert.

Marrying Science and Angling

Tom Rowland: All right. I have with me a very special guest today, Dr. Lori Schweikert. She's a marine biologist. She has a degree that she got in Florida, and she is also an angler. What she just told me right before I hit record is that her passion is really marrying together the science and being an angler. Is that true, Lori?

Dr. Lori Schweikert: Absolutely. I think that the love of the natural world is what drives both scientists, marine biologists, and anglers. And through that, I'm able to really connect those parts of my life.

Tom Rowland: That's cool. So did this start for you as a young person, that you were interested in fishing? Or how did you decide to go down this path in your education?

Dr. Lori Schweikert: I hear this a lot from some of my marine biology friends, that they just had these formative experiences growing up, and it really set the tone for them moving through their education, that that's what they wanted to do. So I was raised on Long Island, New York, and did quite a bit of fishing up there with my father. He'd take me out through the Hamptons, Shinnecock. We would just fish, and a lot of time fishing, maybe not so much catching, not to throw my dad under the bus. But I just fell in love with the ocean, with the beach, with these animals at a pretty young age.

Dr. Lori Schweikert: And then I had the privilege of vacationing in Florida, not only seeing what Orlando had to offer, but what coastal Florida and natural Florida had to offer. From a young age I wanted to go into marine biology, and that's why I got my degrees in Florida and have continued my life here.

Tom Rowland: That's cool. So when you first think about pursuing that — I have two sons right now and another daughter that's in tenth grade, but my boys are both in college. And so we go through this college process of picking a school, and they're expected to kind of know what they want to do. I think very few kids that age actually do. When you were going from high school to college, did you have an idea that marine biology was what you were going to do from the beginning, or did that happen after you had taken some classes in college?

Dr. Lori Schweikert: That's a great question. I've been told that I'm a bit of an exception or a rarity to have so firmly known what I wanted to do from a young age, but I don't think that's necessarily the common thing or even the right thing. But no, I knew in high school I wanted to do marine biology. I had a real interest in behavior — what motivates animals and drives them to behave and survive the way they do. And I actually pursued a degree in psychology.

Dr. Lori Schweikert: I say that because no matter what your degree is early on or what your interests are, it's okay to change or divert from that path. So I did get a psychology degree. It laid a lot of the foundation for what I study now, but I ultimately did make a little course correction, really going into biology, marine biology, and really embracing that. So part of it there was a plan, and part of it was the journey.

Tom Rowland: That's really interesting, that you were kind of drawn to marine biology because of the behavior of animals, and that led you to psychology. When you study both of these at a high level, how much overlap is there between the behavior of animals like you and I and the behavior of animals like fish? Do you see any kind of overlap there?

Dr. Lori Schweikert: Oh, absolutely. I think humans are set apart. I think that we are quite special in our own ways. But at the end of the day, we're given the bodies that we have and the worlds in which we live, and trying to understand how an animal perceives that world and reacts within that world and is motivated within that world can very simply be drawn as a parallel, whether you're a guppy in a pond or a person walking down the street. And that, I think, really ties me to why study sensory systems? Why study vision? Maybe, you know, the adage — you put yourself in someone else's shoes, you can really deeply understand them. So yeah, I'm doing it from that perspective.

The Tarpon and Its Extraordinary Vision

Tom Rowland: That's really interesting. And so that leads me to one of the big questions I had. Your research — and I really don't know that much, I quickly did as much research on you as I could because my friend Jeff Arias attended a fishing club meeting where you spoke, and he must have sent me two or three text messages during your presentation saying, you've got to get her on the podcast. So I'm really excited about that. But what was interesting to him and became really interesting to me too was your research on fish vision. I'm sure you've done a tremendous amount of research outside of fish vision, but I wanted to talk to you today about fish vision. And in the quick little bit of research that I did, I saw that you had referenced rainbow trout, tarpon, and whales. You've done a lot of different research on many different fish. Right? Hogfish?

Dr. Lori Schweikert: Absolutely. Tarpon, all of it.

Tom Rowland: So the tarpon, that's one that is — for the audience that listens to this, that's one of the main fish that a lot of people go after, or one of their bucket-list fish. Last week I put a video on my Instagram, and it was of a guy in Mexico, and he had a sardine in his hand. Just like at Robbie's in the Florida Keys, there were some small residential tarpon there. He held his hand out, and then the video went into slow motion. As he pulled his hand back and went to throw it, you could see this one fish peel out before the rest of them. It took off, and the camera follows this sardine out, and you can see the wakes of the fish. You can clearly follow this one fish that knew just what was going on and led the pack out there.

Tom Rowland: And the moment of impact — it was no accident. It followed the fish all the way in the air and ate it the second it hits the water. He didn't overrun it. He didn't underrun it. He didn't go into an area where he thought it would be. There's no question that he followed that, seeing it from in the water while the fish is out of the water, and he follows it for 20 feet or whatever, and then eats it. And then after that video, I check my DMs, and I get two more videos that same day: oh, look, this is what happened at our dock. One of them was Jack Crevalle doing almost exactly the same thing, and another was tarpon at Robbie's doing the same thing.

Tom Rowland: When you throw a fish in the air, not only can these fish clearly see it, but they've also been clearly conditioned very quickly to this behavior. When the arm goes back, that means you go out and catch this fish before another one does. The jack crevalles are a little bit more aggressive. When I see them with tarpon, they usually get it first. There was so much interest in those three posts that I did right away, and that makes the timing of you coming on this podcast perfect. So what's going on there? A tarpon clearly has outstanding vision, but it's a fish that is nocturnal at times, can feed in the daytime, can feed in the brightest conditions, but can also feed in the darkest conditions. They can obviously see really well. What has your research shown about the tarpon and its vision?

Dr. Lori Schweikert: I really appreciate you bringing that story up. I've been down to Robbie's and I've seen it for myself, and you never quite get used to those animals. You're humbled by their presence, and certainly humbled when they jump up to eat a fish from your hand. I will say, I just love it because it's funny. It's the first thing I said at that fishing seminar that I gave recently: anglers and people out on the water typically know more about these animals before scientists do. You see them behaving in the real world and what they're capable of doing, and then seemingly, at least in my own experience, sometimes biologists come up years later with maybe the fundamental understanding of why things operate the way they do. So I just love hearing the stories and connecting that experience to the study.

Dr. Lori Schweikert: Tarpon are a phenomenal example of what fish visual systems can do. And fish vision generally is a topic of interest of which I could build an entire career — or anyone could — because of the pressures that these animals face in their visual environment underwater, and we can certainly get into that. But to answer your question about what's happening there, a lot of vision has to do with the cells of the retina as well as the size of the eye. We know tarpon have their large eye — their scientific name is actually Megalops atlanticus, or large-eye of the Atlantic. With that large eye and their densely packed retinal cells, they're good at seeing not only motion and contrast, but they have phenomenal color vision. Using those in tandem to localize that prey and see that prey item, and then using its other senses to know where it struck the water, is going to make it a really efficient predator in its environment.

Recognition, Resolution, and Seeing Above the Water

Tom Rowland: Well, they certainly are, and you don't have to fish for them very long to see that firsthand. They're just an amazing fish. Some of the things — I had Russell Kleppinger on the podcast, and he had fished with some tarpon scientists, and they had done some different studies. I might butcher the story, but apparently there was one person that would feed these tarpon in the tank. When that person would come in, they would all go to this one part of the tank where they got fed. And when other people would come in, they wouldn't bother with that behavior, because those people never fed them. I don't know if that's possible or not, but it made for an awesome story — that these fish were able to recognize either some sort of facial recognition, or somebody's posture, or just how quickly someone walked in the room. They were able to discern that it's time to be fed.

Tom Rowland: But the vision of the tarpon — it's hard for me to imagine that there could be a fish that could see much better and under so many different conditions: muddy water, clear water, dark light, super bright light, no clouds. They're obviously seeing out of the water. They're seeing birds. If you're fishing for laid-up tarpon and a small seagull flies over a tarpon, it freaks them out — they totally see that. And they're seeing the bird and not the shadow, often. It's one thing when a shadow comes over, and of course that scares them. But when they're seeing the bird, or they see the fly line in the air, how is that happening? Because if we get in a pool and look up, you're seeing kind of a blurry figure. If somebody's standing on the edge of a pool and you're underneath with a mask on, you look up and you can kind of see a blurry figure, but I don't know that I'd be able to tell that his hand just went back and he's about to throw something, or discern how many people are up there. If you were really close to the surface, you could, but if you're four feet down, that's really difficult. So our eyes obviously don't work like a tarpon.

Dr. Lori Schweikert: In my own research, I'm not too familiar with in-air vision of tarpon explicitly. Animals that see underwater and in air, like amphibious animals such as a frog, have special adaptations that allow their eyes to be adjusted to both how light behaves in air and how light behaves underwater. But with the tarpon, my understanding is that it is having vision that is fully appropriate for that vision underwater. Now, tarpon, relative to other fish, have — to my understanding — truly outstanding resolution of their vision.

Dr. Lori Schweikert: Humans have pretty sharp resolution of their vision, able to make out objects and targets in front of them at about half of what birds of prey can do, but we still have, relative to other animals, pretty good sharpness to our vision. And I think that tarpon, with their cell density in their retina and the size of their eye, their resolution is close to what humans are capable of doing. So that probably helps them between the water and air interface and being able to see things pretty sharply, at least relative to other fishes, and to do those things you're saying — perhaps see someone chucking a fish, or especially a bird coming overhead.

Plasticity: How Fish Retinas Adapt and Heal

Dr. Lori Schweikert: You talked about tarpon living in this array of environments. From muddy backwaters, you can find them in more rivery environments, or you can find them in the open ocean. There are kind of two things going on there. The first thing is that with all fish having to deal with these different clarities and colors of environments, they have the ability, over the course of life — we know across fishes — both to heal their retinas after damage and to change the function of their retinas, their vision, over life to adjust to the environments in which they live. That's very different from humans. We kind of have what we have, and our retinas are pretty static over time. But fish have a little plasticity and can deal with these things.

Tom Rowland: So when you say they can heal their retina from damage — that would obviously be useful because they're sustaining damage regularly, I guess. What kind of damage are they having to their retina that they would adapt that way?

Dr. Lori Schweikert: I think that may be more of a byproduct of the fact that when they're swimming over depth from surface waters to deep waters, or between habitats like muddy backwaters to open ocean, the need to be able to make the cells and the neurons of the retina plastic to meet those visual needs is what creates that regenerative, or again plastic, ability of the retina. And perhaps a byproduct of that is their ability to heal the retina. Also, these animals spend quite a bit of time in clear water and coral reef waters, and there's a lot of ultraviolet light scattering there, and that's hard on the eyes. So it wouldn't be a surprise to me that maybe part of their plasticity is then to deal with those detrimental effects of that UV light sensitivity in shallow waters.

Dr. Lori Schweikert: And so that's part of why I study fish generally, because of this plasticity — but also over the course of the day. You talked about their ability to see in all these environments. Tarpon have incredible night vision. Many of the cells of the retina, the rods that let us see at night, are densely packed in their retinas. They also have eye shine. Like you'd see a deer on the side of the road, these tarpon have a reflective mirror in the back of their eye. Using these things together, they're really effective nighttime hunters. So they have a bunch of tricks up their sleeve that allow them to see at different times of the day, but also at different times of their life.

The Diversity of Fish Color Vision

Tom Rowland: So when you're learning all of these things about tarpon vision and other fish vision — what other fish have you done significant research on besides the tarpon?

Dr. Lori Schweikert: I've done some research, a little bit early on, on snook and redfish vision. And then also most recently I did a massive review of the published literature about what is known about fish vision generally — where we're at in the field and kind of where we need to go.

Tom Rowland: Can you give us a little layman's condensed version of that?

Dr. Lori Schweikert: Let me just give you a little background first. The bottom line is, when it comes to your own vision or fish vision, half of the equation is the light that's available on the water — that's present in that light environment. If you're swimming in Lake Okeechobee or you're swimming off the Keys, it's going to be a completely different light environment. So that's half of the equation. The other half of the equation is what your game fish of interest is able to see. And the animals that live in these different environments, you can bet, have visual systems that are adapted well to see under the conditions in which they live.

Dr. Lori Schweikert: So, fish have the most diverse color vision ability of all known animals. You have fish that see in black and white forever, very highly sensitive vision, and you have fish like the tarpon that have color vision that far surpasses our own ability — being able to see colors that we can't even imagine, such as those in the UV, or light associated in the ultraviolet. In doing my research, sweeping across all known fishes for what they're able to see, on average many have a color vision ability similar to ours. What we have is called trichromatic vision, where we have three types of cone cells in the retina that allow us to see all the colors of our visual world. The majority of fish have this trichromatic vision, a lot of sensitivity over the blue wavelengths. That makes sense with our blue oceans and blue water. And then you have outliers. Some of the outliers, like the tarpon, have five cone cells — extraordinary color vision ability, and again bleeding down into those ultraviolet wavelengths. So it depends on where the animal lives and what it would require that vision to do, which really tells us what their abilities are.

Tom Rowland: So when you say it depends on where the animal lives, is that like where the species could possibly live? Take a tarpon, for example. We can find tarpon up in the Ten Thousand Islands — it's very muddy. You have muddy rivers in Costa Rica that have tarpon, or you could see them in Key West on a white sand flat where the water is crystal clear. So the species is going to live in a lot of these different areas. That particular fish might not, but he still maintains all these qualities in his eyes. Is that what you're saying?

Dr. Lori Schweikert: Exactly. Some specific examples: where a fish lives across depth. If you're fishing for tarpon that can be found in shallow waters above coral reefs, on flats, they're exposed to all the colors that are available within sunlight — as opposed to fish that are at great depth where sunlight is powerfully filtered and there's only essentially blue light to support their vision. So across different depths is where it's going to determine the fish's visual ability. And just like you said, across habitat — we studied tarpon color vision over their life cycle, over their different stages. The juveniles, the young of the year that live in these really muddy, red backwater environments, we see them have very good color vision over that red end of the spectrum, less over the blue. And as they migrate into these coastal waters and eventually offshore to spawn, they have this giant shift of their sensitivity over to the blue-violet, more of the green end of the spectrum. So where they live in depth and habitat really matters.

Tom Rowland: So that's what you're talking about — the repairing of the retina, the plasticity they're able to use to go from this red-type environment into this blue-type environment and change their eyes?

Dr. Lori Schweikert: Absolutely.

Tom Rowland: That's incredible. Because you just wonder — it's so obviously different, and that's a very good explanation. When you have that tannic acid coming out of the mangroves, the water is red. It is red, and they can see every bit as clearly as they can see in perfectly clear water. And apparently on a dark night in Key West Harbor, they're blasting crabs and shrimp. They can see that perfectly, because it sounds like a war. I've just always been amazed at the tarpon's vision.

Largemouth Bass, Lure Colors, and What Fish Really See

Tom Rowland: Now what about largemouth bass? Have you done any research on the largemouth bass?

Dr. Lori Schweikert: I have not specifically, but I have some colleagues that are looking into that now. And just as you would expect, these animals living in these more inshore environments have more sensitivity to these redder types of wavelengths. It's important to understand why color is so important, why I keep bringing it up. The bottom line is, vision in air, we all understand. We're all familiar with it — there's a lot of light up here, a lot of different colors for our eyes to see. The light we experience on a day-to-day basis is fairly predictable. But underwater, water acts as this powerful filter of intensity and color. White light, sunlight, is made up of all the colors. And as white light is passing through that water column — whether you're in the environment of a largemouth bass or the environment of a tarpon — it works the same. You have all the colors available at the surface, but then red light is lower energy light that's filtered out very quickly, and you have just blue penetrating to depth.

Dr. Lori Schweikert: But that's not the only thing. Like you mentioned tannins, you mentioned runoff. The other half of what determines the visibility of water and the coloration of water are ecological variables like algal blooms, or turbidity — mixing up of the sediment of the bottom. So it's these factors together that drive that background light environment in which the fish can see. So yes, they need to be very good at seeing the colors and seeing at the brightness that's available in their environment, because vision is life or death for them. It's either to get that prey and survive, get away from that predator, or to find their own mates and move on that way. And where our eyes would fail in these environments, theirs have overcome.

Tom Rowland: That's really interesting. The reason I ask about largemouth bass is because there's no fish on the planet that has more lures of every conceivable color, design, and shape than the largemouth bass. If you go into Bass Pro Shops, there are literally colors I've never even seen before. So when you look at that, you're like, okay, is this really necessary — all of these different colors? Sometimes I'm looking at that and I'm like, well, that's obviously there to catch a fisherman more so than it is to catch a bass or a tarpon or a grouper. You have the lures that are kind of designed to catch a fisherman. They look cool, they have a nice design, they're shiny. But now when I'm listening to you talk about how important the vision is, when you go into Bass Pro Shops and see this vast array of colors, do you think this is completely unnecessary, or do you think, wow, these guys really seem to know a little bit about what they're doing? What about the millions of different color lures?

Dr. Lori Schweikert: I love that. I've got to bring up the example that one thing you've seen kind of hit the market is UV reflectivity of lures. And there are tons of fish that can see UV reflectivity. But UV light, despite that it's so powerful, by its nature doesn't penetrate to depth very well. It scatters very quickly in the water column. So basically, if you're out there and you've spent money on a UV reflective lure and you're casting it down to great depths — beyond just a couple of meters — you're not utilizing any UV reflectivity down there. It's simply not down there to reflect off that lure. So bottom line, I think there's science behind lure visibility. There's a lot of experience behind it, and I don't want to downplay any of that. But at the end of the day, I think we have to be careful about what's simply just marketing and maybe what's not so important.

Dr. Lori Schweikert: In terms of the bass, in my experience, what I've seen — they're in these not-so-clear environments, very red-shifted environments. And so, using this vast array of color, is it really playing to their color vision ability? Or is it just simply that you need to have a dark, silhouetted lure in the water column that they're able to visualize against that background light? Maybe at that point it's less about color, but more about contrast, more about that movement or sound of that lure through the water that's really driving them to hit.

Tom Rowland: Now, I've always kind of thought that maybe we create all these lures like chartreuse — you know, people say, if it ain't chartreuse, it ain't no use. And we're fishing chartreuse on the surface, and we're fishing chartreuse down deep. I've always kind of thought — just like you were talking about — I don't really know how a fish sees. You're obviously going to think differently because you have a much greater understanding of how a fish sees. But you'll see those charts of what red will look like at 50 feet, and it's just black. Or these other colors — you take a color wheel down as a scuba diver, and you see all the different colors at 50 feet or 100 feet, and they just look like various shades of gray and black. Right?

Dr. Lori Schweikert: Absolutely.

Tom Rowland: What I was thinking is, you see these lures that somebody like Kevin VanDam might fish — a very similar lure to everyone else, but it might be a new color. And for whatever reason, they just eat it, and they're not eating the others. But it's so — instead of yellow it's chartreuse, or instead of blue it's black, or some little different color variation. I've always kind of thought, well, how deep is he fishing that? Because maybe it just looks darker or lighter — or, like you were saying, maybe it's just a darker silhouette. These colors that look so interesting on the shelf, how are they going to look at 15 feet down to a tarpon or a redfish or a grouper? And maybe all those colors are necessary because they don't look like that where you're fishing with them.

Dr. Lori Schweikert: Exactly. And I will say, one of the largest misconceptions for understanding underwater light and lure selection and angling is that red at depth — red light or red colors at depth — doesn't mean that they're harder to see or become invisible. It simply means that there's no red light at depth to reflect from that lure, and thus it looks black. So really, something red at depth — because there's no red light — someone might think, oh, maybe it'll be more invisible or camouflaged or harder to see. It might even be more visible, because it looks black, it's darker against that light background.

Tom Rowland: I'm so glad to hear you say that, because there was a red line that was popular for a while, and I just never bought into it. I was like, yeah, but it's not going to be invisible. It's going to be black. I don't want black line. If I wanted black line, I would get black line. I want clear line, or invisible line — actually invisible line. So red doesn't disappear, it just turns black. The red part disappears.

Dr. Lori Schweikert: Exactly. That's exactly it. Think about if you're on the boat, you wear a white T-shirt, you want to be cool, you want to reflect all that light off you — that's all the colors coming back. Black is just the lack of reflection of that color. There's no light coming back to your eyes. So red color at depth, that's what's going on.

Tom Rowland: And you think the fish are seeing that just the same? The construction of our eyes and the fish's eyes are similar enough that we can make the correlation to say, if we see it black at depth, then a fish is seeing it black too?

Dr. Lori Schweikert: Absolutely, because black is the lack of light reflecting back to that eye. So whether it's a fish or a human looking at it, black is essentially going to be black. And it's something to think about — targeting certain colors at certain depths for visibility. What I've come to learn from my own experience out on the water and talking to anglers is: maybe it's not what's most visible to the fish that they're most likely to hit, but what might be more akin to what they're naturally interested in in the wild. If they see something totally bizarre down there, something that doesn't even look like their prey or act like their prey, just because they can see it very well might not be what they're going to hit. So that's something to keep in mind too. Maximizing visibility may not always be the key to being the best angler, but it's something to keep in mind if you want them to see their prey or see that lure at a distance.

Dr. Lori Schweikert: Maximizing visibility is all about increasing color contrast. So if you use a red lure in red waters, it's going to be harder to see than if you're using, let's say, a white lure or something that's going to have a broader spectrum of reflectance than just matching that background. So color contrast, brightness contrast — if you want to see something, it needs to be either darker or lighter than the background. It needs to differ from the background. Maybe a really reflective jig in some of these waters might be more useful than one that's just matte and might appear the same as the background. And also size — again, because fish have lower resolution vision on average. Think about seeing an eye chart at a doctor; fish are not going to do so well relative to us, having about half on average of the resolution of our own vision. So you're going to want things to be big enough for them to see at a distance.

Dr. Lori Schweikert: And then the inverse is true. As much as we care about them seeing our lure or bait, we care about the fish not seeing our own rigs. Not seeing, like you mentioned, these lines in the water, fluorocarbon. These are things that are of equal importance to how successful we'll be out on the water.

Applying the Science on the Water

Tom Rowland: As you're going down this path of all this research and learning more and more, you're also spending more and more time on the water, and you enjoy fishing, and you're a good angler. How much are you taking out on the boat with you? Was there a time where you're kind of like, well, I don't know why this lure works, but they should be able to see all this hardware and stuff — if we took all that off, then maybe we'd catch more fish, and then it works because of your research? Have you had a couple of situations like that where you start learning something in the classroom and think differently about it, then go apply it on the water and it really works for you?

Dr. Lori Schweikert: That's an interesting point. Absolutely. I will say, with the tarpon particularly, I've hooked up on tarpon, I've had them spool me. I've never landed one, which is kind of a sad thing to say. But talking about selecting artificials for that mature animal — I knew the extreme sensitivity that they have over the blue and violet range. So selecting a purple mirror lure, a purple artificial out there to try to target them, has been my key. I use as small a diameter leader as possible, as long a leader as possible. I try to put my weights on the line to keep them where they're maybe not going to be so visible to the animal, and really try to use some of what I know out there. At the end of the day, I get far more inspiration for my work from being out there than I even apply my own work.

The Hogfish and Skin Vision

Dr. Lori Schweikert: One example being, most recently, I'm studying the hogfish, as you mentioned. These animals down in the Florida Keys and coastal Florida are just incredible. Going out there spearfishing for them, just as a recreational angler having fun, taking them, spearing them in the Keys when season was open, throwing them on the deck of my boat. And one day, I got up out of the boat after spearing, picked them up, went to go put them in the cooler, and I saw the side of the animal that was facing the boat hull had turned the color white and had taken on this pattern on the skin that was the texture of that boat hull.

Dr. Lori Schweikert: So if you've interacted with a hogfish, you might know that they have this incredible ability to change color. When I saw that day that perhaps the animal, after it was dead, after it was spearfished, that its skin was still changing color and changing color in response to its environment, I was totally blown away. Since then, the last couple of years I've been doing research on the side about how that color change happens and how they might be able to sense the environment with their skin. So it's a pretty amazing thing, both trying to use what I've studied out on the water, but also being inspired by those experiences back in the lab.

Tom Rowland: That's very interesting. You talk about changing colors like that, and that particular fish was able to change just one side of its coloration. I've never kind of correlated that to vision — that that is associated with vision — but I did see that was one of your things. It's this skin vision on the hogfish, very similar to what you were just talking about, that was part of your research. I always kind of thought that they were just able to make themselves more camouflaged. You'll see redfish that will become almost snow white if they're over a white sand bottom. Or like a mutton snapper — you can have two different mutton snappers, one caught on grass, one caught on white sand. One is almost blonde or white, and the other is very dark colored.

Tom Rowland: But you're saying that could also be part of how they're seeing, and how the photoreceptors in their skin are changing with their eyes — almost like they're putting on sunglasses at times, I would imagine. If it's super bright, and you have the same type of fish that's in a darker environment, he's able to see perfectly well and hunt very efficiently. But then that same species can live in a very bright area and do the same. And you're saying that has something to do with their skin as well as just their eyes.

Dr. Lori Schweikert: With these hogfish particularly, but we are finding with other fishes — fishes that change color and pattern to hide in their background environment — that they're using their eyes to understand where they are: I'm on open sand, or I'm on rock rubble, or I'm over gravel, a flounder. And then to know where it is, and that a predator's coming, I need to hide. We're finding more and more that these animals that color change like that have this sensory system in their skin that is sensitive to light, or receptive to light, and it's thought that they're using this so-called skin vision to help them effectively change color under those different conditions.

Tom Rowland: That's fascinating.

Mahi-Mahi, Pelagics, and Color Change in the Open Ocean

Tom Rowland: What do you think is happening with the mahi-mahi? Is anybody researching those? Because I don't think there's another fish that changes color as quickly that is a game fish that people go for so much. Those things will come in and they'll be blue, metallic looking. And then they'll go to the classic green and yellow. And then they can be not that brightly colored. But they can go through the widest color change of any fish that I think I've seen.

Dr. Lori Schweikert: Yeah, they're unbelievable — how they light up right before they strike a prey. They are incredible animals in their ability to change color. And a lot of pelagic fishes, the billfishes, have this ability to strikingly change color, become iridescent, become darker, become lighter in very short time scales. I'm not studying that explicitly. I think it still needs to be studied in more detail, but I would not be surprised if they're employing a similar sensory system as these hogfish or camouflaging flounders — that the skin itself acts as its own sensor for their color change abilities. There's not a lot of places to hide in open water. And so these animals having this phenomenal vision to be able to see predators at a great distance, and the ability to change color to try to hide in with their surroundings — they're just pulling out all the tricks to try to survive in that open environment.

Tom Rowland: On one hand, you're thinking maybe a dolphin is changing colors to hide from what he's trying to eat. But on the other hand, even a 20- or 30-pound dolphin is by no means top of the food chain out there, and there are all manner of things. So while they're going to hunt other fish, they're also putting themselves at risk of being hunted themselves. Maybe they're changing colors to protect themselves as they're leaving the school. I never thought about it like that. Maybe that's something going on too — they're going to that blue color to match the sky so that they're not as visible to the marlin that might feed on them. I don't know what's going on, but there's obviously a lot more going on than we once gave these fish credit for, with their vision, with their skin, with their ability to change colors.

Where the Research Goes Next: Bioluminescence

Tom Rowland: So for that point, where does your research go from here? What are you excited to study? Are you going to go further into fish vision? Are you going to take some of the things that you've learned here, and does that open some curiosity to some other fields? Where do you go from here?

Dr. Lori Schweikert: That's a great question. As scientists, we all have a plan, and then we're just inspired as we have experiences going forward. We talked about this extreme light environment that fish have to survive in, and some adaptations of their eyes to be able to survive in that environment. Light can be very limited in an underwater environment, and especially as you get to great depth. So another branch of this story that I am moving into with my research is the role of bioluminescence — the natural ability to create light underwater — and how that has to do with marine animal ecology. I had not known this, but when I'd given a talk at the fishing seminar the other day, there were gentlemen talking about how they're using these underwater light beacons to attract billfishes to their lines. It's very interesting to me — that's very reminiscent of maybe what some of these animals are going to encounter in the water, as so many organisms in the marine environment can create and emit their own light of different colors and different intensities.

Dr. Lori Schweikert: So my research at Florida International University right now is going toward that branch of it, which is this emission of light and how that could be perceived by predators and by prey.

Tom Rowland: Well, certainly in the swordfishing world, those guys — it was thought for a long time, when everything was nighttime swordfishing, that it was all about the light. They had these big lights on the surface, and then there were lights all up and down the leaders. Now things are streamlined. They're catching these fish in the daytime, obviously. Daytime swordfishing is really popular now, and obviously catching lots of them. But the lights — first of all, the lights have gotten better, they've gotten smaller, they can handle going down into the depths. You'll talk to some of the captains that are big-time swordfish captains, and they wouldn't even put a bait down without a light on it. And others don't feel like that, just like every other type of fishing. Whatever it is that someone feels strongly about, there's another fisherman or captain that feels strongly the opposite way, and both seem to work sometimes, which is also kind of interesting as it comes to fishing.

Tom Rowland: But that bioluminescence is probably something that could be studied not only at depth, but we see that stuff in Key West Harbor when we're night fishing for tarpon. It's all over the place, very cool looking. I don't know if it has anything to do with the way the tarpon are feeding, but I'd like to know what it is.

Dr. Lori Schweikert: Exactly. I've had the privilege of going bioluminescence kayaking. You're out on the water in those warm end-of-summer months, early fall, where that water is so warm, you get this bloom of what are called dinoflagellates — these plankton in the water that, when they become agitated, emit this beautiful blue-green light. Being out there in the kayak in these Florida backwaters and spooking schools of mullet with my kayak, and seeing the whole school in dark left, dark right, and just seeing these streams of light in the shape of a fish — it's hard to think how the predators are not so effective during those times. This blue-green light does fall in the direct color sensitivity of many fish, including the tarpon. So it's going to be making these prey in the shallow waters more visible.

Dr. Lori Schweikert: At the same time, as you have a predator moving through the water, they then become more visible to prey at a distance. You see this big glowing mass coming at you from a distance. And so that really complicates it for these animal interactions under those circumstances.

Tom Rowland: That's kind of an interesting thought. Earlier, you were talking about how tarpon can see so many different colors that are invisible to us. Would it be a stretch to say that a shrimp in the water on a dark night is creating some types of light that are invisible to us but incredibly visible to the tarpon? We assume that a tarpon has this incredible night vision and they can see shrimp on a black, dark night. But could it be that maybe there's some bioluminescence that's getting agitated, like what you were talking about on the mullet, that's very obvious to you? Is it possible that there could be some sort of light on the spectrum that we're not seeing that the tarpon is seeing very clearly?

Dr. Lori Schweikert: Potentially. I think potentially. There's another phenomenon that's called fluorescence, and you've probably seen this yourself. You put a black light over your chartreuse lure, and you'll actually see, when you have that certain blue light going on, this emission of greens coming out of your lure. That's called fluorescence. It's reactive. It's not the generation of light, but it is the emission of one color of light under certain conditions, and we're finding so many marine organisms are also fluorescent. So when these shrimp are getting lunar light or moonlight onto them, they could be fluorescing at certain colors that the tarpon are picking up as well.

Dr. Lori Schweikert: But I almost get this vision invoked of the Predator movies, right, with Arnold Schwarzenegger — you see this incredible night vision ability to see a target in the background. Tarpon, with their extreme sensitivity to light at night, are probably able to silhouette these prey against that background moonlight far better than we're able to. So that's playing a role too. Plus they're able to smell their prey. So it's this whole combination of things working together.

Tom Rowland: Yeah, it's fascinating.

The Bonefish and Its Built-In Goggles

Tom Rowland: One more question about a different fish. Have you ever had an opportunity to study the bonefish and its vision?

Dr. Lori Schweikert: Bonefish are closely related to the tarpon. They're in the same order. I have not, but I had a colleague who did. Just as you would expect, they're a shallow-water species, a clear-water species. I think they have complex color vision on par with us, but their color vision does not marry to that of the tarpon with these five cones that let them see fairly broadly. So it's in the work. It's been studied and definitely tied to trying to better understand these fish, their ecology, and to conserve them.

Tom Rowland: That's important. But the first bonefish that I ever caught, it was pointed out to me that they were wearing goggles. I looked at this fish, and if you look at a bonefish from the top down, they are essentially wearing a scuba mask. They have a membrane that goes over their eye. And unlike the tarpon, unlike the snapper, unlike the amberjack or any fish like that, you can't touch their eye. You can run your finger over the top of this lens that goes over it, but you can't touch their eye. I was just kind of wondering, how or why does a fish adapt like that? Obviously a bonefish is mudding — they're going down into these holes, they're putting their eyes in the mud. So I guess over time they just kind of adapt this lens that protects their eye and allows them to see in those conditions where they literally have their eye in the mud. Is that what's going on there? Are there other fish that have that kind of membrane, that kind of lens across their eye?

Dr. Lori Schweikert: I think you hit the nail on the head. I know exactly what you're talking about — it's pretty thick, this thick clear membrane essentially protecting the layers of the eye. We also see that on mullet. And the connection there is, mullet are eating what we call detritus off of the bottom — dead matter, decaying matter — they're down in there rooting around, foraging off the bottom. I wouldn't be surprised if that membrane exists to protect their eyes, as it potentially would with the bonefish. And you're right, you don't see that broadly across other animals.

Dr. Lori Schweikert: Think about the tarpon — it has this beautiful upturned jaw, and they very much attack their prey from beneath, ramming beneath them and capturing their prey. So they're looking above. They're less so, perhaps less often, eating within the sand, eating off the bottom, and so they may not need that membrane, maybe just to be able to see in that upward line of sight. In fact, once we study their retina and their ability, we see that their sharpest visual ability is in that upward direction. Just like our own eyes — you have central vision, and then you have peripheral vision that's not as sharp. The tarpon's central vision really is in that upward line of sight. So it's that sensory biology again marrying to ecology: how are their bodies built, and how does that building plan really inform us about how they survive in their environment?

Tom Rowland: It's interesting when you apply that to another fish like a redfish, that is kind of a combination of the two. It often feeds down, but its eyes don't have the lens over them like the bonefish does. But it'll also feed up, and has particularly good vision that way too. That seems like an interesting fish to study. You said you had done some redfish research, right?

Dr. Lori Schweikert: A little bit, and that is ongoing. It's really interesting. They have these mounds on the bottom, and they can eat off the bottom. But I'll tell you, some of the most amazing experiences I've had on the water were topwater fishing for redfish using pass crabs in Sebastian Inlet. And man, can they see those crabs at the surface and just roll on top of them and strike them. It's incredible. So it'd be interesting to see what's happening there with their eyes.

How Scientists Measure Where a Fish Sees Sharpest

Tom Rowland: How would you know — when you say the tarpon, there have been studies done where you can clearly see that they are most visually acute looking up like that — how can you tell that? And you'd be able to tell that a bonefish maybe is best looking down. Is that part of the eye structure? How would you know that?

Dr. Lori Schweikert: That's a great question. Bottom line, just like in our own eyes, one key indicator of the sharpness of vision in a certain direction is the density of rod and cone photoreceptors in that retina. So if you take a fish retina and look at it under a microscope, and you count cells in the different regions, the streaks where you have the highest, densely packed area of cells is what's indicating to you the direction in which they have pretty focused vision. So for fish, that's exactly what's going on. We have a fovea — an area in our retina where we see very sharply. In those terms, fish also have a high density of cells.

Tom Rowland: Wow, that's fascinating. That's really cool. There are so many questions and so many things I'd like to learn. I really want to have you on again, especially as we get some particular subjects on different fish that you could help us understand.

Funding, Conservation, and Learning From Nature

Tom Rowland: This has been amazing. The research that you're doing is really cool. I have one following question about the research. One of the challenges to any research, I would imagine, is getting it funded. So on a study like fish vision, is there a particular fish or a particular direction that is kind of the path of least resistance? Or do you have the ability or freedom to study any particular fish that you want? Is there a path of least resistance to getting the funding to do the studies that you want to do?

Dr. Lori Schweikert: I really appreciate that question. The bottom line is that scientists — or anybody who are trying to get funds and support to be able to ask the questions that they'd like to ask — have a responsibility not only to pick things that are interesting and inspiring to themselves, but also something that generally can benefit society, will improve and advance our knowledge that could be leveraged for other important fields. And so studying fish vision is something that can be very well supported both by people and by funding sources, because nature has already done hundreds of millions of years of research and development. Over that time, it has really curtailed the designs of certain systems that work very optimally in our world.

Dr. Lori Schweikert: By simply studying something like tarpon color vision — which you can ask, by the way, in a live animal, you can put an electrode on a sleeping tarpon's eye very gently, same as you do with a human, flash different colors of light into their eye and see what they're able to see — figuring out that they have what we would call hyperspectral vision, incredible color vision, might one day allow us to build and design better underwater color sensors for our own technology. Or trying to understand, for example, how an animal like that changes the structure and function of its eye over life and regenerates it after damage — how maybe we can leverage that to improve or repair our own vision, or to cure people who have had the degeneration of their own retinas. So we look to nature, which has already found so many solutions to our problems, to then try to improve our own. That's what keeps us motivated, and that's the end goal.

Tom Rowland: Wow, that's fascinating. That's really cool, because oftentimes you may have certain research that will be for a particular food fish — we need to know this so that we can sustain the population, or fish for them more effectively, or understand what's sustainable. And then a fish like a tarpon or a bonefish doesn't get studied. That's why I was interested in that, because they don't really have food value, but they do have high economic value. I was just kind of wondering what led you to those fish. Your response was awesome.

Dr. Lori Schweikert: And what you said is completely true too. Yes, they're economically important fish. They're also ecologically important fish, being major predators. So understanding fish biology, to then understanding how they survive, to then being able to improve their conservation, is by far an underlying thing.

Tom Rowland: And have you had any communication with Bonefish & Tarpon Trust or any of the conservation groups that are tagging and doing different studies on tarpon? Do they look to you for some of your research?

Dr. Lori Schweikert: Absolutely. I've had the privilege to essentially go to them, really, and I gave a talk in years past at a meeting of Bonefish & Tarpon Trust. We talked about what I know about these animals' sensory biology, and how that adds to the larger web of what we understand for these animals. So I know some folks there. They're doing some phenomenal work, particularly recently trying to understand and improve bonefish stocks, perhaps to be able to aquaculture these animals. So I've connected with them, and we're familiar with how our work all ties together.

Closing

Tom Rowland: Well, it's fascinating. I love all of your research, and the fact that you're an angler and applying it out there for yourself on the boat is the best part of the whole story for me. As an avid angler, I'm always trying to learn more about the quarry, and this has been great. I learned a bunch. I'm sure the audience did as well. I'd love to have you on again. And also, as we spoke before, I'd love to do a feature on Saltwater Experience on fish vision at some point. So we'll work on that, and maybe we can get that done for next year. I just want to thank you for all the research that you're doing and for taking your time out today to be on the show. If people want to follow you and learn more about your research, how would they do that?

Dr. Lori Schweikert: Well, you could just Google my name. I'm fortunate to have a very unique name there that I married into, and my information will come right up, including my email. I also have a Twitter, @LoriSchweikert. And I would love to hear your stories, your anecdotes out on the water that you've seen with these fish — questions you want to know about their ability to see the things you want them to see, or to hide the things you don't want them to see. I'd love to be able to answer your questions and to learn from you. And yeah, Tom, this has been phenomenal. I've had so much fun. I'd be very happy to keep this conversation going.

Tom Rowland: Great. We'll do it. I always have lots of questions, and people write in all the time and ask questions too. So next time that we decide to do a podcast together, we'll put it out to the audience that we're going to do this, and I'm sure people will have some very specific questions on fish vision that maybe we could answer, or at least attempt to. So until next time, thank you so much for being on the podcast. I really appreciate it, and we'll do it again.

Dr. Lori Schweikert: Thank you.

Tom Rowland: All right. Bye.

Dr. Lori Schweikert: Bye.