Capt. Nick Castillo: Pharmaceuticals in Bonefish and the Fight for Ocean Health

Full transcript of the Tom Rowland Podcast, Episode 795: Pharmaceuticals in Bonefish and the State of Our Oceans, with Capt. Nick Castillo.

Introduction

Tom Rowland: Today we're talking science. If you're a fan of Saltwater Experience and watched our latest season, the 2023 season, we fished with a bonefish scientist, Captain Nick Castillo. He's a very good fisherman in his own right, and he's also a very knowledgeable scientist. He's doing a lot of work with the pharmaceutical studies you may have heard about — they're finding pharmaceuticals in bonefish. What does that mean? That's what we're going to talk about today with Nick: what does it signal about what's going on, and why are the fish being exposed to these drugs that we take? They're going through us, getting into the water, and getting into the bonefish. What does that mean for the population? What does that mean for the fish? What does that mean for us as anglers? That's what we're going to be talking about today. Stick around — here comes Nick.

Catching Up and the Hot Seat

Nick Castillo: Alright. I'm Captain Nick Castillo, and today we're going to talk some bonefish science and fishing and have a good time.

Tom Rowland: Nick, how are you, man?

Nick Castillo: I'm doing good, Tom. Good to see you.

Tom Rowland: Yeah, we hadn't seen you since we shot the show together. That was fun.

Nick Castillo: Oh, that was a good time. We had some tough fishing, but we made a good day out of it.

Tom Rowland: We sure did, and we got some good science. So you're working with FIU — is that correct?

Nick Castillo: Yeah, I'm a PhD candidate at FIU. I'm with Dr. Jennifer Rehage in the Coastal Fisheries Lab. I know you know her pretty well.

Tom Rowland: My favorite guest, man. She's been on the show a number of times and given us some incredible information on all the stuff they do there, and now you're going to be taking over and doing all kinds of stuff there as well. Looking forward to it. So, in order for the audience to get to know you a little bit — if you haven't seen Nick on Saltwater Experience, the episode we did was a 2023 episode, one of our brand new shows that just dropped on YouTube and was on Discovery Channel recently on Waypoint. But if you haven't seen him there, we're going to do a one-minute hot seat. The whole idea here is we're going to try to get through as many of these questions as possible — maybe you can set a record. I think about 13 or 14 is the number people have gotten through, so don't put a lot of thought into it, just go with whatever comes to mind, or you can say pass. Alright, you ready? We'll start the clock right now.

Tom Rowland: Inshore or offshore?

Nick Castillo: Inshore.

Tom Rowland: Rock, country, or other?

Nick Castillo: Rock.

Tom Rowland: Mountains or beaches?

Nick Castillo: Beaches.

Tom Rowland: One thing you're afraid of?

Nick Castillo: Spiders.

Tom Rowland: Fiction or nonfiction?

Nick Castillo: Nonfiction.

Tom Rowland: Audiobook, Kindle, or paper?

Nick Castillo: Paper.

Tom Rowland: The last book you remember reading?

Nick Castillo: It was A Land Remembered.

Tom Rowland: The Office, Friends, or Parks and Rec?

Nick Castillo: Office.

Tom Rowland: Three nonnegotiables in your life.

Nick Castillo: Fishing, a boat, and a movie.

Tom Rowland: The best advice you ever remember being given?

Nick Castillo: It just takes one good shot.

Tom Rowland: Technological gadget or invention you rely on the most in your life?

Nick Castillo: Fortunately, a laptop.

Tom Rowland: Something you're proud of?

Nick Castillo: This work I work on, the bonefish science.

Tom Rowland: If you could have one superpower, what would it be?

Nick Castillo: Flying. I have to go with that — it might be cliche, but let's do it.

Tom Rowland: Alright, that sounds great. We made it to 11 — maybe 12. That's close to the record, that's pretty good, I'll take it. So you're not afraid of sharks, but you are afraid of spiders — that probably leads you to doing all your research in the ocean rather than someplace where spiders live.

Nick Castillo: Yeah, I avoid it. I've encountered some bad-looking spiders in my boat occasionally, if it sits, you know.

From Watching Fishing Shows to Studying Bonefish Science

Tom Rowland: So anyway, Nick, tell me how you started. You told us on Saltwater Experience, but I'd like for this audience to know kind of what your path was to studying what you're studying, and how you ended up having what I would think is the ultimate job for someone who is a researcher and likes to fish. You get to go out there and catch bonefish, tag them, and do all these cool things and learn about them — it just seems like the perfect job. And I don't think anybody can just do that. It seems like there are only a few of those positions, and you got one. So that's pretty cool — how did that happen?

Nick Castillo: Super cool. Well, you're right — they are far and few between, but they're there. I think they present themselves to somebody who's passionate about that work, because the work we do, you really need to be passionate about it. I mean, yeah, we get to be on the water, but there's a lot of stuff behind the scenes that's maybe not as enjoyable, behind the computer. As far as how I got here — I grew up in Fort Myers, Florida, and for whatever reason I was always obsessed with fishing. As we mentioned on the show, I was watching you guys back in the day laying on the carpet on Sundays, probably on Sun Sports at the time. I was just enamored by fish, and I was a really hyperactive kid, so my parents would make it such that I'd try in school by bribing fishing ability to go out — straight A's, please, and then you can fish this summer. But I didn't really know what I wanted to do. I knew I was passionate about fishing, so I went to college. I did my undergrad at Duke and studied environmental science, but only after a late-night 3 AM exam experience when I was a junior. I was studying neuroscience at the time, and I was with a friend and I was like, I'm not passionate about this — I like the environment. I don't know what the career path was, which is probably what kept me from doing it at first — it's not clear cut. You study neuroscience, you study economics, you'd be a doctor, you'd work in finance or something. So it didn't make sense, but I said, alright, I'm gonna go for it. I graduated and then came down to Big Pine Key and taught at Sea Camp there — a lot of listeners probably have kids that go there, it's a really cool place. I taught there for a year, but I'd been fishing in the Keys my whole life, so from Fort Myers it was a quick trip. I really knew one guy down there well, Captain Mark Johnson, so I fished with him a bit. The funny way I got to know him was that story we mentioned on the show, where I went on the computer when I was about 10 — my parents said straight A's, fishing trip, and mind you I'm in Fort Myers, so they figured we'd just go down the road. But I hopped on the computer and booked a trip with Rich. My parents were like, what? We went down, and unfortunately Rich was sick, so he called that night before and set us up with Mark, and I just stayed in touch with him. He helped facilitate my enjoyment of fishing down there, and next thing I know I was in a position to start guiding. After I finished Sea Camp in 2015–2016, I started guiding out of Islamorada — mostly running bay boats, but still skiff fishing. Then Irma came through, and I found myself with a mold remediation crew tearing stuff out, and I thought, let me apply to grad school. So I applied, and this is the part of everyone's journey where sometimes luck comes into play — it's just timing of things. You can take advantage of these lucky opportunities by working hard and setting yourself up, but the PhD program I'm working on now, with Bonefish and Tarpon Trust, was looking for somebody who could study bonefish, and that's a unique fish to study — you can't just go out there and say I'm going to sample ten today. You need a little know-how, and I had the angling experience. So it really wasn't the direction I was planning on following. If you'd asked me a year prior whether I'd be doing this, I wouldn't have had a clue. But it worked out, and it ended up being one of the best things I could have done, because I get to do research that I feel has real-world implications. It's not just going to be published and put on a shelf — I feel like all of our fisheries, not just the bonefish fishery, could in one way or another be benefited by the research I'm doing in our lab, with Jen and all the other work we do in the Everglades. So that's a little bit of a long story as to how I'm here chatting with you right now.

Tom Rowland: Well, it's super cool. And I think one of the things that might be interesting to talk about today is how the work you're doing might benefit other fish and other anglers, not just people who like to bonefish — the real pharmaceutical work you've been doing. I'm sure a lot of people listening know that you and others have found pharmaceuticals in fish, and these bonefish can be like a harbinger or a bellwether — a canary in the coal mine for what's going on. So if we're finding them inshore in bonefish, maybe we should be looking for them somewhere else, and how widespread is this? And maybe that could lead back to how the pharmaceuticals are getting into the water in the first place, and what could happen, and what the next course of action would be to fix that. Tell us about how that program started, and why someone would even look for pharmaceuticals in fish. I found that really interesting when we were fishing together.

Why Scientists Started Testing Fish for Pharmaceuticals

Nick Castillo: Well, pharmaceuticals are relatively new compounds — our pharmaceutical industry has increased dramatically since the 1970s. I'll pull up a quick figure here — this is, in a nutshell, why we're studying pharmaceuticals now. This figure shows the proportional change of things we care about with the environment: CO2, human population, and then that orange line is the increase in drugs we've been making. So we've dramatically increased how many drugs we're producing, and it happened so quickly that we didn't have the ability to understand what was really happening outside of us taking those drugs — what was happening elsewhere.

Tom Rowland: Just to be clear, it starts at 1955 and goes to 2015, and it seems like right where you're pointing, that should be about the 1980s or so.

Nick Castillo: Probably just about the eighties, yeah.

Tom Rowland: But then it goes up pretty substantially right where your mouse is — where's the bottom of that trajectory, is that 1995?

Nick Castillo: Looks like it's just about '95 — I couldn't say exactly what incident happened there, but there was just a dramatic increase in pharmaceutical production. Since then, year after year, it's exponential, the amount we're producing. In the United States, we have about six billion different prescriptions dispensed every single year. That's a ton — we're taking all these drugs, and inevitably it's making its way into the environment. And you asked me a moment ago, well, if it's in bonefish, what about elsewhere, what about offshore? People have found pharmaceuticals at concentrations that could disrupt ecosystems in the Antarctic — they found them in phytoplankton, the basis of the food web there, at concentrations that could change the composition of that food web, so it could have a ripple effect. We're finding them anywhere. I haven't tested, say, a dolphin or a tuna, but odds are it's there — we can find it in open ocean water, and you can really trace it back to us taking these drugs and improperly treating them. As we mentioned with that figure, we've been producing them so quickly — remember the line at 1975? Our wastewater infrastructure, say in Miami, was built well before we had all these new contaminants that would be in the water. So it's not so much that we were ignoring an issue — we didn't know it was something to consider when we built all our wastewater treatment plants. And now we're taking so many pharmaceuticals, and there are other chemicals that just can't be removed with the way the plants work now, so they're making their way into the water.

Can You Filter Pharmaceuticals Out of Your Drinking Water?

Tom Rowland: On these pharmaceuticals and some of the other chemicals you're referring to — can those be removed from your own drinking water, like with a Berkey filter or some other type of filter? I've read that some filters claim they can remove things like pharmaceuticals, but I don't know — is it possible, or is it too difficult? It seems like it must be difficult, because they're not getting it out of the wastewater.

Nick Castillo: It's definitely difficult. The wastewater treatment was really designed for biosolid waste — bacteria, viruses, things that would directly hurt us — that bio-active kind of removal. These compounds don't fall into that category, so they weren't targeted. As far as your own drinking water, there are a few things that can help a little: some wastewater treatments use charcoal or activated carbon filters, which can remove some of the pharmaceuticals. UV — if you were to treat your water with UV — can remove some of those as well. One of the other chemicals I was referencing is PFAS, which are used in anti-stick coatings for pans and in flame retardants. They're finding now that those are essentially forever chemicals, and they can be dangerous at really low concentrations. A scientist I was chatting with said the best thing you could do would be a reverse osmosis system for your drinking water, but it's tough — these chemicals are everywhere: drinking water, produce, seafood if you're eating seafood. There are just so many different routes of exposure that it's really hard to avoid, unfortunately.

Tom Rowland: Yeah. So that's us — now let's talk about the fish. As it applies to the fish, we're finding them in bonefish — so what's the concern? Obviously it's strange that you'd find them in there, and if it changes our behavior at some concentration, it would possibly change a fish's behavior too. Is that what you're finding, or what's the concern when we find pharmaceuticals in fish?

How Pharmaceuticals Change Fish Behavior

Nick Castillo: Yeah — pharmaceuticals as a compound are designed to do something at a really low dose, because we don't want to be taking bucket loads of a pill for something to happen. So they're really active at low concentrations, and those are the concentrations we find out in the environment for some of these drugs. And they're not toxic — the amount there isn't going to kill a fish, it's not some toxic compound where you see dead fish floating everywhere. But what is changing are important behaviors for survival. There's also feminization of some fish — if they're exposed to birth control, for example, which is really active at a low concentration, it can change physiological things that are really necessary for successful reproduction. So it's really changing behavior, not killing the fish, but these are important behaviors for surviving — like evading a predator, when we think of fish that have an issue evading sharks or other fish. Those are the things we're concerned about: this change in behavior that could lead to an entire population having difficulty surviving. And unlike you and me — I take Tylenol and six or seven hours later it's out of my system — the problem with these fish in the water is they're constantly breathing in water that has that chemical, so it's a constant dose. It's not like mercury that stays there forever, but they're constantly getting a dose, and it's multiple drugs. If you go to the doctor, they ask what else you're taking, because they're worried about what drugs do to each other — and some of the bonefish we've tested had 17 different drugs. That's 17 different drugs that could all be doing something, and they could be doing the same thing on the same receptor, having a pretty profound effect. The concentrations we're finding are high enough to do something — some are above what we call the therapeutic concentration, the concentration your body needs for that drug to do something. Once it hits that, whatever it's designed to do can happen, and we're finding those concentrations in the fish we're testing in the wild.

Tracing Contamination Back to Its Source

Tom Rowland: Wow. And so when you find these — another thing we were talking about when we were fishing was finding higher concentrations in certain areas that might indicate additional exposure, maybe a leak somewhere. Explain how that works, and how you use that information.

Nick Castillo: We're working on a paper right now focusing on Tylenol. Tylenol is one of the drugs that's actually really well removed — almost 100% — through wastewater treatment. Some drugs pass through untreated, sometimes even in higher concentrations than when they went into the wastewater, but Tylenol is really well removed and doesn't last long in the environment. So if we find it, we can say that was a recent release of untreated water, or a septic system release, because septic systems won't treat it. We are finding it in certain areas — we find it in Biscayne Bay, and a little bit in the Upper Keys, maybe one or two fish out of 20. In the Lower Keys it's completely absent in Key West, but really prevalent in fish from the Dry Tortugas, which is super surprising. Basically, every step of the way in this study I've been surprised — we hypothesize things as a scientist, and pretty much all of those were wrong. I looked at Biscayne Bay and was excited to include the Dry Tortugas thinking we'd have a comparison, but it just showed us this is a water quality issue, and even remote areas that aren't urban aren't spared.

Tom Rowland: Right — so let's talk about that. Completely absent in Key West means maybe their wastewater treatment is solid, no leaks, doing what it's supposed to do. But then you find it out in the Dry Tortugas — lots of tourists go out there, it's an island 70 miles off Key West, but lots of tourists go out every day on float planes and boats, and people have to go. Maybe that's an antiquated wastewater treatment out there, or none at all, because it's probably not even set up for that many people. There were soldiers there for a while, and Dr. Mudd was there — that's the doctor who treated John Wilkes Booth after he shot Lincoln, and they sent him to the Dry Tortugas to serve his time. At that point they probably didn't have much sewage treatment, and it probably just went straight into the water and didn't hurt anything — you had maybe 70 soldiers out there, the ocean can easily handle that. But when you have 700 tourists going out there every single day, that's a bigger problem, a big difference. Is that the conclusion to draw — that that septic system needs some work because you're finding Tylenol in the water?

Nick Castillo: I think it's telling us that — you mentioned 700 people, that doesn't sound like a lot, but if you've been to the Dry Tortugas, it's a tiny little spot, maybe one or two square kilometers. So 700 people peeing in the water and taking their boats out — maybe they're disposing of their waste too close. It's kind of telling us that when you compare 700 people to Biscayne Bay with a few million people in Miami, a few people in a very concentrated area can still have a big effect on that ecosystem. So it's about being conscious that even though we think this is super remote, we can still have an impact there. I think you were spot on saying that — it's just a small area, and we likely have some people not disposing of their waste properly, just peeing in the water. As far as the Dry Tortugas is concerned, as a visitor you're supposed to use a porta-potty and that waste is shipped out — it's like a dry porta-potty with sawdust and everything. So it's likely a point source of exposure, probably from tourists, and not any fault of the Dry Tortugas — we're just now recognizing that a few people can have a big impact.

Tom Rowland: Don't forget the cruise ships go through there too, and who knows what they do.

Nick Castillo: There are studies showing that open ocean areas near shipping channels can have higher concentrations or presence of pharmaceuticals and contaminants. If you're near a shipping area, like a cruise ship route — and I'm sure the Dry Tortugas gets passed by a lot from ships going to Key West — that can be a source, an open ocean source.

How Scientists Test a Fish for Pharmaceuticals

Tom Rowland: So tell us the process — the screening process for a fish, whether it's a bonefish or any other kind of fish. How do you determine there are pharmaceuticals in that fish?

Nick Castillo: You can test it, but it has to be a tissue — you could test muscle, or if you were killing the fish you could test internal tissues, liver, brain. But what we use primarily is blood — we take a blood sample and release the fish on their way. Blood is a really good medium to detect a bunch of different drugs, because regardless of whether it's an anti-anxiety drug that goes to the brain or a drug distributed throughout the body, one way or another it's in the blood. We take a blood sample, keep it free from sunlight, freeze it preferably on dry ice, and keep it super cold. Then we use a mass spectrometer to analyze the sample — it looks at the weight of every molecule, there's a comparison and a curve, and we can say this curve matches this drug, matches that contaminant, and get an ID for that drug and its concentration. It's pretty cool — we're able to look at 102 different drugs in one sample, and it's just point-two milliliters, a super small amount. We can learn a lot from that.

Tom Rowland: And when we were fishing, you had quite the kit — a Pelican box that was ready to go, and we had this thing, I don't know what you call it, it was like an inflatable — it was basically a net, a pool floaty.

Nick Castillo: Yeah, I made a fancy sling out of PVC — I went to Home Depot and got all this stuff. Then Dr. Ross Boucek, who works for Bonefish and Tarpon Trust, showed up one day with this pool floaty he picked up at Publix, and that worked perfectly.

Tom Rowland: That was perfect. It really was, because the way it worked — a lot of people have seen this on social media — you catch a bonefish and you don't even have to touch it. You just slide the bonefish in, and there's an inflatable ring around it with some mesh inside that happens to be blue, which is a perfect color for it. The fish just sits there in maybe three or four inches of water — it's absolutely perfect.

Nick Castillo: Submerged, yeah.

Tom Rowland: And the fish just chilled out — like when you put bait in a live well that's blue, there's a noticeable difference from one that's square and white. In corners, the bait kind of freaks out, but in rounded live wells with no corners to run into, they just chill out. People say blue makes a big difference. When I saw it on your setup, that pool floaty, the fish really chilled out, and the depth was perfect for you to do your work. Then you had another machine you brought with us — explain what that process was for somebody who might have seen the show. It's a twenty-two-minute-and-thirty-second show, so we did a lot of talking on the boat that didn't make it into the show about exactly what you were doing. I think it's interesting to know what goes into sampling the blood, and how much we can learn from that one sample.

Nick Castillo: Yeah, that machine is a centrifuge. Once we take the blood sample, it's got the blood cells in the plasma, which is the liquid the blood cells are in, so we have to centrifuge it — spin it really quickly with an anticoagulant that keeps the blood from clotting. After spinning it, we have all the red blood cells on top, a little layer of that anticoagulant gel, and then all the clear liquid — blood, gel, and then that clear liquid. Once that's all done, it's really clear, maybe a little creamy-colored liquid, and that's what has the pharmaceuticals we're looking for. So we can test the pharmaceuticals in that, but as we're expanding the study — we figured out yes, there are drugs in fish, it's everywhere, and it's a meaningful concentration — now it's a question of what is that doing. We can also use that blood to look at other indices of health — reproductive health, general fitness, is it a healthy fish, does it have certain levels of stress — and look at the levels of these pharmaceuticals and contaminants alongside those health metrics to try to get a better idea of what's happening to the fish. We know from the lab that there can be health effects and differences in growth rates or body size, and behavioral changes, but we don't know that's definitively happening in the wild yet because we haven't tested for it. We have all the evidence that it has the capability of happening — so really the next step is, is the movement changing, can we do a telemetry study, what's happening to the health. It's pretty crazy how crafty scientists are — taking a scale or a fin clip and telling you what a fish eats and what it supports in the food web, what's in the fish.

What Bonefish, Permit, and Tarpon Really Eat

Tom Rowland: You can do that from a scale? Just a single scale, you can tell what a fish has been eating?

Nick Castillo: We do it most often with a fin clip — we took a fin clip on the show, not a big piece. In the fin there are rays, and we take a clip down two of those rays, just a little fin clip. What we'll do is dry it out and look at stable isotopes — nitrogen and carbon most often — and there's a ratio of that in everything. You can look at the ratio of carbon and nitrogen and say that's like a fingerprint of seagrass, or the epiphytes, or a fingerprint of eating pinfish, and then trace the pathway in the food web to see what's the most important energy source. In Florida Bay, our lab has sampled everything — seagrass, the epiphytes, all that brown stuff living on the seagrass, everything at the bottom of the food web all the way up to the top — and looked at what's the most important resource for supporting this, and does that change in winter and summer. And it does — is that important resource changing with different environmental changes, is water quality changing, the availability of the most important resource. So we can learn all that from a fin clip.

Tom Rowland: So you're obviously talking to a whole bunch of fishermen right now, and everybody's on the edge of their seat — what is the most important thing that a bonefish eats, or a permit eats, or a tarpon eats? If you sampled a hundred fish, would there be a primary food source, a secondary food source, a third food source?

Nick Castillo: As an angler yourself, what do you think?

Tom Rowland: I think it probably changes over the year, and probably even flat to flat. But I think there'd be three or four things that, whether they're first, second, and third on one flat or reordered on another, are gonna be present in the top few things they're eating. I've seen behavior out of fish on certain flats that I don't see anywhere else — chasing bait, or doing things that are different than other fish. Maybe they're eating snails out of the grass, doing something different, and they don't act the same on that other flat. That's just an observation, bro-science at its best — I think they're eating some sort of fish over here because they're scooting around, and over there they're tailing very slowly, so they're obviously not eating whatever they're eating on that other flat because they act different.

Nick Castillo: Spot on. We've done a couple of studies — you mentioned Mike Larkin, so I'll chat about his study. He did a ton of work with bonefish in Florida — really, everything we know started with what Mike did over the course of his PhD. He looked at Islamorada, the Florida Keys, and Biscayne Bay, and the diet is different for bonefish on the ocean side versus the bay side, which makes sense — maybe they mud more on softer bottom because they're rooting around for something else. And this is another interesting thing about what we can do with just a little sample — in most of the fish we sample, we take a little swab, and we're all really familiar with this now after COVID, the little swab that goes up your nose or in your cheek for a DNA test. We take the same thing and put it in the fish's cloaca, run it through DNA analysis, PCR, and look at what it was eating — we can estimate the diet that way, and we just recently published a paper on that with bonefish.

Tom Rowland: Can people read that? Where are they eating?

Nick Castillo: We can provide a link, I guess.

Tom Rowland: Yeah, that'll be in the show notes. I'm sure lots of people would love to read that.

Nick Castillo: So for the anglers listening who are bonefishing — what are they eating? I don't know if we're tying flies for a lot of what they're eating. A lot of what they eat are mollusks, snails — I've analyzed the gut contents of a few bonefish, and in Biscayne Bay there was one bonefish that had its stomach completely stuffed with tiny black snails, completely full. So we're not throwing a tiny black snail, but I know some pioneer fly fishermen who use worm flies, and that's top of the diet — annelids, worms.

Tom Rowland: Listen, man — I've got one, it's called the green worm, the simplest fly in the world. I've taken it all over — I took it to Christmas Island, and the guide totally laughed at me, said no man, we're not throwing that. So when he wasn't looking, I tied it on, and this fish just piled on it. He said, let me see the fly, and I pulled it out, and he was like, oh, you didn't do that. And then he wouldn't let me take it off for the rest of the trip. They pile on a worm in some places. But I also went — I was in Exuma — and they didn't really like it that much. They ate it, but not like they do in other places.

Nick Castillo: Well, maybe there just isn't the bottom to support the worms there — it backs up what you're saying, flat to flat. Worms are really important. Honestly, I feel like what we mimic when we're bonefishing is lower on the diet of what they find — they're not seeing those big shrimp we use to catch our bonefish day in, day out. They're seeing smaller pistol shrimp, snapping shrimp, mantis shrimp — so annelids, shrimp, mollusks, that's the top of the diet, but they also really love toadfish. I bet part of our bonefish patterns — we think they're mostly mimicking a crustacean, but if you put marabou or rabbit on there, it can look like a toadfish, and they like to eat toadfish a lot too.

Tom Rowland: Do you think tarpon eat toadfish a lot too?

Nick Castillo: I bet they do.

Tom Rowland: There was that fly for a long time, the toadfly — it was kind of a Merkin body with marabou or a rabbit strip behind it, and then we took that same type of fly and made it smaller, and it was a great bonefish fly too. That made more sense, that it was toadfish. I just didn't know — maybe a tarpon is such an omnivore, an opportunistic feeder, that if it looks pretty good there's a good chance they'll eat it, or at least they would a long time ago.

Nick Castillo: I'd say they would.

Tom Rowland: Now they're a little more closed-mouthed on the ocean anyway. But the toadfish is a really important thing, and I'd assume permit eat those as well.

Nick Castillo: Yeah, I haven't looked into that myself, but it's a similar environment, so I'd imagine the permit as well. Bonefish and permit are really interesting — have you ever taken a peek in the back of a bonefish or permit's mouth and seen those crushers? That's also why I think, with fly, we're doing a strip set, but when you're throwing shrimp you don't really want a strong hook set, at least in my experience — because of those crushers, if you set the hook immediately you're kind of bouncing off it. If there's a little less tension, it finds purchase in the softer mouth of a bonefish. Those crushers are just crazy looking — that's how they're eating snails, clams, mollusks — sea urchins, sea cucumbers, they're crushing all of it down. They're designed to eat a very specific type of prey, similar to redfish too, rooting around and eating all the crustaceans.

Tom Rowland: That's cool. So a couple things — have you ever fished with Mike Larkin?

Nick Castillo: I've not had the pleasure yet — I've had a beer with him, a couple of conferences, but I've not fished with him. What a nice guy.

Tom Rowland: I think it would be so awesome to get you guys together on a boat — Mike is a great guy with so much knowledge, that guy has forgotten more than most people think he has. Having both of you together, doing this research at two different time periods in history, I think would be very interesting — just to pull you guys around and listen to you talk. And the second thing — you mentioned that bonefish that was absolutely stuffed full of little snails. Have there been a few other fish, doesn't have to be bonefish or permit or tarpon, that surprised you with what's in their stomach?

Nick Castillo: My work personally, I haven't done too much gut content with other fish, but I'll speak to two. In my lab we do a lot of snook research up in the Shark River and the headwaters and the Harney River, and they rely heavily on sunfish and a lot of exotics since they're there, but also peacock eel — I don't know if you've ever seen that one, it's cool, kind of has a little elephant trunk. They're another invasive thing up in the Shark River and the headwaters now. When we do research up there we do electrofishing — it shocks, puts electrical current in the water and stuns everything for a moment, so we scoop it up in a net and can do gastric lavage to get some stomach contents out. We're finding a lot of eels up there. As far as diet, I haven't done a diet analysis study, but with lemon sharks — sometimes here in Florida, if you're seeing bonnetheads, it doesn't necessarily mean there's a ton of bonefish up there, but juvenile lemon sharks might mean there are, because their diet overlaps a lot with bonefish, even though they're not big enough to eat one — they're up there feeding on the same crustaceans. So that's one thing I think is interesting — bonefish and lemon sharks, when they're smaller, have a really similar diet.

Tom Rowland: That's interesting, and it must be a similar diet to redfish too, because I was just telling you we were fishing in the Everglades recently and there was a hatch of juvenile lemon sharks — weeks old, days old, 18 inches to two or three feet long, and there were zillions of them. It's crazy how many there are. They're not going to eat your fish, but there are so many, and if you're redfishing they can look a lot like a redfish — if their fins stay down they throw a similar shape, though when they start wagging their tail you can tell the difference. They even have a similar color when they're really little, so we're paying close attention to everything we're seeing — is that a shark, shark, shark, that one looks good, that's a redfish. I guess they hatch this time of year — is that when lemon sharks—

Nick Castillo: I'm not certain about that — they breed all year long.

Tom Rowland: It was a very successful year for the lemon sharks — they did very well. So that's interesting with the different things they eat. With all the different things we've talked about — finding pharmaceuticals in the fish, the tagging and studies you're doing with the fin clips — what happens from here? We know this is happening, we know it's in the fish, but what do we do from here?

Expanding the Research: Redfish and the Statewide Picture

Nick Castillo: Yeah, so as far as our research goes, we've already completed what our next step was. Step one was this bonefish study, which is the first of its kind in a marine environment anywhere, really, looking at a sport fish or a large fish like that. A lot of what's sampled elsewhere is water, or mussels used as a sentinel species — it's called Mussel Watch — looking at what's in the water. But what's really interesting is that these contaminants are at concentrations so low in the water we can't even detect them, but a fish that's breathing in that water is accumulating it to a concentration we can detect. Our most common drug in bonefish was an anti-anxiety drug, and we didn't find that in any water sample or in any of our prey samples — so if we'd taken a water sample and said, okay, we found X, Y, Z, this is what we need to be concerned about, that's not really the case, because when we sampled the fish, X, Y, Z wasn't even in the water. So the next step is to do more sampling of the higher-level organisms accumulating these drugs or contaminants that don't really bioaccumulate, or are in really low concentrations in the water, so we get a better idea of what's out there. Then it's kind of expanding — so we did bonefish, and we expanded into redfish across the entire state of Florida. We did 113 redfish from nine different estuaries — Apalachicola, Pensacola, Cedar Key, Charlotte Harbor, Tampa Bay, Florida Bay, Indian River Lagoon, Jacksonville, and St. Augustine — so we went all over the place and looked at the pharmaceuticals the same way. Out of the 113, only five fish didn't have any.

Tom Rowland: Did those all come from the same place?

Nick Castillo: No, those were a scattering from different areas. We found some surprising drugs — in one of the more rural areas, Apalachicola, I think it was fourteen out of fifteen fish that had tramadol, which is an opiate, a pretty powerful one you'd likely be administered at a hospital or prescribed for severe pain. So it's another case of a rural area having a high concentration or prevalence of drugs, maybe just because the wastewater isn't being treated correctly. It showed us both rural and urban areas can be at risk and threatened by these contaminants. So that was step two — expanding it and seeing whether it's really all coastal species. Next, we're working right now on looking at those health indices, and then you can zoom out and look at behavior and do some tracking studies. But I guess those are the next steps when it comes to the fish and the fisheries. Then there are next steps when it comes to solving the problem, because at a certain point we know enough, but we need to compile this information so we can solve the problem on the other end, which is wastewater treatment. So now we're gathering evidence saying it's there, it's at concentrations that can do something, and now we're going to figure out what sort of effects they might be having. Then, on the back end, it's conversations like this and promoting better wastewater treatment in the public sector, so we can protect our fisheries and protect ourselves, because as we mentioned in the beginning, we're being exposed too — and we don't know what happens over the course of a whole life. When people started smoking it was cool for a number of years, and then it turned out to be doing something — that could be the case here. Some of these drugs have only been around for a couple of years, and we don't know what happens when you're exposed to them your whole life at a small dose.

Turning the Science Into Policy Change

Tom Rowland: It's one thing for you to develop all these studies and mount all this evidence, but it's another thing to present it to city planners or whoever and have them listen. Do you think that's a challenge? Because what you're presenting is an incredibly expensive overhaul on sewage systems or water treatment plants, which is probably not what anybody wants to hear — that money is probably already set aside for something else, and this could be a big problem, or it could be an opportunity to really clean up the city. I don't know — or it could be, we don't want to spend money if we don't have to, and you're not even detecting this in the water, so how do we even know? What if these bonefish got it some other way? Do you think that's a challenge, mounting a case that's basically undeniable, that people have to pay attention to?

Nick Castillo: That's definitely a challenge. You mentioned that these are fish that move, so it could be one municipality saying it's being exposed by the wastewater treatment plant of another municipality, and then there's all that legislative red tape. But as a whole, the response I've gotten has been really positive. We were invited to present this information a year ago in Tallahassee to legislators, and they're listening. We've been communicating with news outlets, and one of the coolest things I've done so far with this research is help out with some litigation in the city of Marathon, trying to better understand how their wastewater treatment affects the ecosystems there. So it's being received well, but you're pretty spot on about all the barriers — there is a cost, and it can be expensive up front, but in the long run it can actually save money too, because some of these new technologies can reduce the biosolid waste, which is something we deal with. I didn't know about this until I was communicating with a lawyer in one of the rural counties in Florida — all of the biosolid waste from Miami-Dade County gets trucked out to another county, where they pay landowners to spread it on their property, under the pretense that it's fertilizer, but it's not really fertilizer — there are contaminants in that biosolid waste, and it can leach out into local water bodies. If we had newer technologies — the one I'm most referencing is ozonation — it can reduce the amount of biosolids and is really effective at removing PFAS and other contaminants and pharmaceuticals. It's a new technology but it's being used elsewhere — it's just a matter of tweaking and tailoring it to every single wastewater treatment plant. So there's a barrier, but once this evidence, and I think we're getting there, becomes insurmountable, there needs to be action. At one point there wasn't any wastewater treatment at all, and people recognized what was going on — it's a progressive process that way. I'd say the response has been great, and it makes me optimistic about the future.

Tom Rowland: One thing I forgot to ask earlier — you were talking about UV light as one of the ways you could get pharmaceuticals out of the water, and it seems like on a flat in the Florida Keys, that water is exposed to tremendous amounts of UV light. Is that not doing it — is that not enough to degrade it on its own?

Nick Castillo: If there's a constant influx of more, that's maybe where the problem is — and then, let's say it goes into the sediment, we've eliminated the sunlight exposure. So it could be in the sediment. We try to estimate how long these contaminants will last in the lab — we can use UV, organic matter, temperature, and control all these environmental variables, and we found that one drug's half-life was twelve days in the lab. But continuing the experiment out in the actual environment, it was over a hundred days. So these drugs are surprising — they don't behave the way you'd expect. Sunlight can degrade it, but it's that constant supply that keeps coming back and making the issue persistent.

Life as a Field Scientist

Tom Rowland: How much time do you get to actually be sampling fish, rather than writing reports on your computer? I'm sure people are interested in that — seems like such a cool opportunity.

Nick Castillo: At least at the beginning of my study, it was go, go, go, sampling — it's not an easy task to get over a hundred bonefish from areas across Biscayne Bay all the way through the Dry Tortugas, and in Puerto Rico, The Bahamas, Belize, and Mexico — we did this throughout the Caribbean as well with bonefish. At the beginning it was rapid fire, let's get all these fish, and that took about one to two years to get done. Then it's toiling away on the computer, but that's kind of where the magic happens, honestly, because we're figuring out what's going on. It was a love-hate relationship for a long time with coding and doing all of that, but once I got the hang of it, I understood what the story was. So it's a lot of time out in the field, and that's kind of where the passion comes in, that toiling away behind the computer — if you're passionate about these fisheries, it makes it go down easier. As a scientist, we spend a lot of time in the field, but then we go back to the lab, process samples, run analyses, write up papers. I think I can speak for everyone in our field — it feels meaningful, because we know we're learning more about the fishery, we're helping anglers continue to sustainably fish for these fish into the future. So that's what keeps the gears turning in the background.

Tom Rowland: Super interesting. I think you're doing good work, and I don't know what the result is going to be, but I hope people listen to you as it comes to being a canary in the coal mine for potential problems, and addressing them before they become major problems. Doing good work, and the FIU lab has been such a good friend to the podcast and given us such good information — so thanks for coming on. If people wanted to follow your research — we mentioned there's one paper that'll be in the show notes — is there anything else you can supply, or ways for people to follow you individually, or the FIU lab, or just anywhere people can learn more about what we've talked about?

How to Follow the Research and Get Involved

Nick Castillo: All of the above, really. To follow our lab, I can give you the email, the website, and our Instagram, which is fiu_fisheries_lab. And myself, I'm Nick and Two Fish — you could follow that to stay up to date with our research, and follow Bonefish and Tarpon Trust, who funded all of our research, to keep up with that too. And as anglers in the Keys, there are ongoing projects you can help with — right now there's a permit fin clip project. If you're in the Keys fishing for permit, you could stop by probably any fly shop down there — I know Florida Keys Outfitters has it, probably Seven Mile Fly Shop in Key West, probably the Angling Company — and pick up a little manila envelope to put a fin clip in, for the stable isotope work to understand their diet. So if you're an angler passionate about protecting these fisheries, there are ways to get involved. And reaching out to us, you can learn how to get involved. That redfish study, we were only able to do because of local anglers — none of us are from Apalachicola, I don't know the first thing about redfishing there, but all of our samples came from local guides and local anglers who helped out. So there are plenty of ways to get involved if you're concerned, passionate, or just think it's cool.

Tom Rowland: Okay — and if you get involved in that, do you have access to some of the data that's collected? Because I'm sure as fishermen, that's what you're really most interested in — if you caught this fish, could you learn more about where it's been, where it's going, or what it eats?

Nick Castillo: That's a super fun aspect — the answer is yeah, absolutely. If you get involved and you catch, say, redfish number 43, we can tell you later what was in it, what its health was, what it was eating. So if you get involved, you can be along for the ride through the whole process.

Tom Rowland: That's super cool, I'm sure many people will want to do that. Nick, thanks for coming on, man — I really appreciate it. We learned a lot, and I'd love to have you on again, and we're gonna try to get you and Mike together on the boat — I think that'd be super fun.

Nick Castillo: Yeah, that would be a blast for both of us, that would be awesome. Thanks again for having me — it's great to have some ears listening to the research we're doing, and bring it to life, make it feel super meaningful. So it's awesome, thank you so much.

Tom Rowland: You're welcome. Alright, that's another awesome show. We'll be back with another great guest just like Nick next week, so tune in for that.