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Backcast episode: How does water temp affect trout behavior? With John McMillan

Description: This week I am delighted to have biologist John McMillan back as my guest [46:00]. John gives us a detailed view on the affect of water temperature on a trout's metabolism, particularly at the upper end of their safe range. In this summer of low flows and high water temperatures nearly everywhere in North America, it's a critical topic. And as usual, John puts his critical eye on how we, as anglers, can mitigate these effects by changing our fishing behavior. John is never without optimism, and I think you'll enjoy his discussion and learn more about trout biology and how we can be more responsible anglers.
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Podcast Transcript:

Tom: Hi, and welcome to "The Orvis Fly Fishing Podcast." This is your host, Tom Rosenbauer. And my guest this week, later in the podcast, is someone I've had on the podcast before, biologist John McMillan from Washington State. I always have a fascinating time talking to John. I know you enjoy this podcasts.
And today, we're going to talk about a pretty serious subject, which is water temperature and trout, and we're going to focus a lot on the upper end of water temperatures for trout, particularly appropriate this summer because, nearly countrywide, we have both low water situations, a lot of fishing pressure, and what looks like are going to be very high water temperatures this summer.
So, we all have to make some adjustments to our fishing. And John has some excellent suggestions on what we can do as anglers to help minimize damage to our cold-water fisheries during these hot, dry times. So, I hope you enjoy. I know I enjoy talking to John, and I think you will, too.
But first, the Fly Box. And if you have a question for the Fly Box, you can send it to This email address is being protected from spambots. You need JavaScript enabled to view it.. You can either just type your question in an email or you can attach a voice file. And if I answer the question, I'll read it on the air. So, I hope you've got some good questions coming.
I've had lots of good ones lately and really appreciate the great questions that you all send in. This podcast wouldn't be as interesting as it is without your great questions and your tips that you pass along to me and the rest of the listeners, and the occasional complaints, which I enjoy as well. I really like complaints. They help me make the podcast better. So don't hold back on your complaints.
Anyway, let's start it off with an email from Nick from Pennsylvania, "A longtime fan, first-time caller. Thanks for all that you and Orvis do to promote fly-fishing education. So, I've been fly fishing for about nine years. And recently, I went out with a guide on a day-long float drip, during which time she mentioned that we needed to use heavier leaders and tippets so as not to overexert the fish. I found this comment curious because I typically think about leader and tippet gauge in terms of either, one, strength against breakage or, two, visibility to the fish. I never thought of it in terms of the exertion of the fish.
So, my question today is, how does a thicker leader and tippet that is 3X result in less stress on a trout than a thinner leader and tippet 6X? Does it have to do with the amount of stretch of the lighter gauge leader and tippet? Can one land a trout faster at 3X versus 6X? Can you please shed some light on this topic? Thanks, Tom."
Well, Nick, that's a timely question because we're going to cover that in the podcast with John. But basically, it's all about getting the fish in quicker. And you can get a fish in a lot quicker on a 3X tippet than you can on a 6X. The less time that we play a fish, the less time we handle a fish, and the sooner you get them back into the water, the better off they're going to be.
So, yeah, as John mentions in the podcast interview, you're probably going to sacrifice a few of those fussy fish that won't take a fly on the heavier leader, but it's really up to us to try to use flies that we can handle on a bigger leader. So bigger flies, bigger leader. Sometimes, you can't get 3X through the eye of a small dry fly, so you have to use a little bit bigger flies.
And you're gonna sacrifice a few fish here and there, but you're going to be able to get them in much, much quicker, and it's going to be a lot better for the fish, particularly in warm water temperatures. And kudos to your guide, who had that philosophy on the boat. We need to see that more often.
Here's an email from Matt, "In the most recent Fly Box-only podcast, a gentleman had written you with questions about getting into vintage bamboo or glass rods. I concur with your suggestions to visit The Fiberglass Manifesto, as it is one of my favorites. I would also like to suggest that your listener consider picking up an old rod that needs a little TLC as a project.
This spring, I bought an old bamboo rod from the 1930s that needed several new guides, some new wraps, the grip cleaned, a set removed from one tip, and the whole thing needed to be refinished. I found that project to be very fun and pretty inexpensive.
It isn't top of the line, but for about 150 bucks, not counting my labor, I have a cool old rod that is fun to fish and has some history behind it. I enjoy the work very much and feel a part of me is in this rod since I brought it back to life. I actually did a similar one for a friend for free. He liked mine and enjoyed the work so much that I hooked him up.
The work isn't difficult, just time-consuming. And the replacement parts, guides, and silk thread, in this case, aren't expensive. Slap an old click and pawl reel on it, and it has a totally different feel than modern rods. I don't have the distance on my cast with it as with modern rods, and it is so heavy, I think I could fight off a bear with it. But it's a blast to catch smallies with. I love the podcast, and I finally feel like I have something to contribute."
Well, thank you, Matt. That's a great idea and a great plan for anyone who wants to kind of dip their toe into bamboo rods and have a nice winter project.
Josiah: Hi, Tom. I'm Josiah, calling from Kitchener, Ontario, Canada. And I've got two questions for you today. The first one is about drying off waders and wading boots. So I was out fishing this morning, and I got home, and I took my waders and set them over the railing on my back porch to dry off. But it occurred to me that it probably isn't the best to leave waders drying off outside like that because of UV light. I could be wrong.
I'm assuming that UV light breaks down the materials in our waders a little quicker, and I'd rather not have unnecessary wear and tear on my gear. So, I'm wondering what some best practices are in terms of drying off wading gear efficiently and safely, especially, I'm wondering about the boots because those seem to take a long time to dry off. And so, yeah, if there's a week between fishing trips or whatever, I'd rather not have my boots wet and mildewy in the middle of the week.
Second question is about flying with fishing gear. So, I've got a work trip to Calgary in October, and I would be remiss if I didn't at least try to get out on the boat, river while I'm there. I know I've got some free time, and I'd love to experience fishing on the boat. But I've never taken gear on a plane before, and so I'm wondering what you typically do when you're flying with rods and waders and all that stuff. Do you usually check it? Do you keep it as a carry-on? Are there any other things that you do to keep your gear safe and protected during the flight?
So, anyways, thank you so much. I really appreciate the podcast. I listen to it every week. It's pretty much always on in the car for me and while I'm doing laundry and washing dishes. So, thank you so much, Tom. Have a great rest of your day. Bye.
Tom: So, Josiah, wader fabric is really made to be resistant to UV. You know, we wear them outside for sometimes 12 hours a day in the sunlight, and it really won't hurt it. The fabric that's used in waders is very resistant to UV. So, leaving them outside is not going to hurt them, and it's not going to hurt wading boots either. Similarly, the materials in wading boots are resistant to UV.
You can put waders in the dryer, if you want, on a light setting, not a high heat but a cool like a permanent press setting. You can throw them in the dryer and dry them off. And wading boots, again, you can just put them out in the sun, but you can also buy electric boot dryers that will dry the boots from the inside out, which is a great thing to do because it also helps kill any invasive species that might be hitching a ride on your wading boots. But, again, having them outside is not going to hurt them a bit. I leave mine outside to dry all the time.
Regarding flying with fishing gear, actually, I check my fishing gear and, yeah, I've occasionally had it not arrive. And I've been without my waders and my rods and my reels and my flies for a day or two. And I take a chance. But my problem is that I carry on my camera, a bunch of lenses, and sometimes a drone in my carry-on baggage, which I don't really want to put that stuff in my checked baggage.
So, you can carry it on, and a lot of people do carry it on. It's probably the smarter way to go. Although, I can say that in an Orvis Carry-It-All, I've never had a rod broken even though I checked the Carry-It-All, so I wouldn't worry about breakage. But, yeah, sometimes, your luggage doesn't arrive.
So that Carry-It-All, most airlines will let you carry it on and put it either in the overhead or in the front closet. But you have to be careful with airlines, you never know, it's up to the individual aircrew as to what you can carry on with you. So, you're always taking the chance. And even flies, certain airlines, mostly international airlines, won't let you carry hooks on the plane, so you really have to check beforehand. And it's probably a wise idea to carry it on.
And another option that some people do is to ship their gear, their waders, you know, the heavy stuff, the waders, and their fishing pack or wading boots. They'll ship it ahead of time to the fly shop that they're going to hire a guide with or a hotel or something like that. That's a little scary too, but it saves you the worry. You know, ship it out a week before and it saves you the worry of knowing that it's going to get there. So, lots of options, but carry it on if you can, but just double check first.
All right, another email. This one is from Tristan from BC. "Hi, Tom. I have three questions for you. My first is, what is the difference between hen and partridge? Which one should I choose? My second question is, how do I know where to find trout streams because I have many streams near me but I'm not sure if they have trout in them? My third question is, what size should I tie my ants in? Thank you for all you do for this sport and have a great summer."
All right, Tristan. So number one, hen is a chicken, a mottled chicken. And the advantage of hen feather is that you can get various sizes. You can get stuff that will tie down to a 16 or maybe even 18, depending on the neck, up to an 8 or a 10.
Whereas with partridge, often you really only get one size. You know, it's kind of like a size 12. You might be able to get some 14s out of it and some 10s. But it's hard to tie the smaller flies with partridge. Partridge has kind of a stronger speckling and is actually better looking. But again, it's more difficult to deal with and it's tough to get a range of sizes.
So, honestly, I have both. Partridge is expensive. And hen feathers are not nearly as expensive. So that may be a consideration for you. But they're interchangeable, and it just depends on your budget and what size you're tying.
Your second question, "How to find a trout stream?" Well, the best way to find a trout stream is to go fish it. I don't know of a better way unless your province has a list of streams that contain trout, and sometimes they do, or a stocking list. You know, sometimes states will publish those kinds of things. But the best way to do it is to check them out.
And if you don't want to go and fish them, I would suggest, probably you're talking about smaller streams, generally, you can find out pretty quickly if there's any trout in and by fishing a dry dropper, a big foam dry like a Chubby Chernobyl with a hare's ear beadhead, hare's ear or something hanging off the end of it.
But if you don't want to fish them to test them, there's a couple things you can do. One is to take water temperatures in the middle of the day. If the water is below 65 degrees, or even 70 degrees on a really hot day in the middle of the day, then it's likely that those streams hold trout. The other thing to do is to visit the streams right before dark. Typically, in the summertime, there's always some kind of insect hatch just at dark. And if there's any trout in there, you might see them rising.
But I would suggest you just go and fish them. And if you can't find out anything about a stream, nobody knows about it, and you go and find trout in it, you're going to have a real gem because you'll probably have it all to yourself.
And your third question, "What size should I tie my ants in?" Well, you know, there's lots and lots and lots of different kinds of ants falling into most streams, and some of them are really tiny. And honestly, I don't try to imitate those little, tiny ones, unless they're flying ants. If there's a fall of flying ants in your stream, the trout get kind of picky to them, and you need to match them to size pretty carefully.
But if you're just blind-fishing an ant during the day, you know, I'd try a 14 or 16. I wouldn't try anything too small, and I'd tie a parachute ant with a visible post on it, a white or a pink or red or orange post, so that you can see in the water. That's what I use. I typically use a size 16 fur ant or a foam ant with a parachute post, and, you know, you could tie smaller, but they're hard to see on the water. And I think if a fish will take a little ant, it'll probably take a big ant. And there's lots of big carpenter ants around in most trout streams which are a fairly good sized ant.
Okay. Let's do another email. One is from Roger from Washington, "You have correctly warned fly fishermen in the past the problem associated with tying a clinch knot with small tippet material to larger size flies. However, there is a modified clinch knot that has worked well for me in the past where I needed to use 3X to a size 4 Wooly Bugger in order to fool spooky late-season summer steelhead stacked up in deep clear pools on West End rivers on Washington's Olympic Peninsula.
The knot goes like this. Double the tippet material so you have a loop around 10 inches long. Crease the end of the loop, insert it through the eye of the hook. Then tie your clinch knot or improved clinch knot, whichever you prefer. However, with this knot, use only four wraps around the main line. I believe the knot is actually stronger than the main line since it contains two strands a line as opposed to one. I also use this knot for saltwater salmon and halibut fishing, where I know I need maximum knot strength.
I hope this helps fishermen who feel they need to use lighter tippet material with larger flies to fool spooky fish. Keep up the good work, Tom. I found your podcast several months ago and love it. I appreciate all you and Orvis do to promote fly fishing and conservation."
Well, thank you, Roger, that's a great tip. And I've never tried that knot, but I'm gonna give it a try. It sounds similar to the Trilene knot, but it's not quite the same. And doubling that strand over should help with that strength with lighter tippet. So thank you very much.
Isaac: Hey, Tom, I just want to send you a quick question. Thanks so much for responding to my earlier question from last podcast. I ended up using your technique, and it worked.
So, essentially, here in BC, we can only use a single barbless hook, so I can't do a dry dropper, you know, unless I technically cut the hook off. So, I ended up just using wool, like a New-Zealand-style wool, and floating a nymph through. And I shorten that up way short. So instead of going deep, I kind of floated it maybe 5, 6 inches from the top. And sure enough, yeah, I started getting hits.
So, now the problem I have is I consistently... Well, I still lose fish on a dry fly, and I still lose fish on a swing, but I seem to consistently lose more fish on nymphs. So I went out today and I kept getting hits like my wool would go down, would pop down, but I was missing the strike. So that was consistently.
Once I started getting my speed up and I started, you know, kind of striking a little bit faster, I was able to hook a couple, but I would always lose them within a few seconds of them either jumping or kind of flipping around in the water. And it seems to be the consistent theme for me.
So, I'm just wondering, is that just the byproduct of having, you know, like beadheaded flies? I know you've mentioned this before. Now, is there any way to kind of fix this or kind of, you know, compensate for that? Should I be tying my flies with maybe, you know, a lead and maybe no bead instead? Or is there any kind of techniques you recommend for either playing a fish or kind of increasing your landing rate for nymph fish because I think I lost out of like 10 or 11 strikes, you know, I only kind of hooked but probably about 3 or 4. And out of those three or four, I lost all of them.
And then later on, I went back to the dry fly, and I was able to land a couple. So, the only difference I can see is just the weight on that fly.
So anyways, I just want to kind of ask you that question, see what you think. And, you know, maybe you can give me some tips, I really appreciate it. And by the way, I was using a nymph both a size 14 and a size 16, Beadhead Prince Nymph, also a Beadhead Pheasant Tail nymph. And the third one was a small size 18 Zebra Midge, just so you know which I was using, but all three of them had a kind of tungsten bead on them. Thanks.
Tom: To Isaac, I'm glad you're finally catching fish on nymphs. And I'm glad that the shorter dropper helped out in those small streams. And yes, if you're using barbless beadhead flies, you're gonna lose fish, particularly if they jump a lot. It's just the fact that that hook can shake loose easier than a barbed hook. And also, the fact that those tungsten-weighted flies have some weight to them, and the fish can shake that loose.
So, what I would suggest is to use Orvis tactical hooks, the tactical wide-gape hook or the tactical Czech nymph hook or the tactical jig hook. These have a special bend in them that kind of curves inward, and it really helps to hold the fish. I've lost very few fish when using these barbless flies with beadheads. And then, what you might try, instead of fishing beadheads, is to just let lightly weight your nymph with some nontoxic wire and don't use a bead.
In small streams, you typically don't need a lot of weight in your nymphs. In fact, you can tie them unweighted. And that's going to help them from shaking loose. So try that, and good luck.
Here's an email from Mike from Albuquerque, New Mexico, "I've been fly fishing for about five years and recently observed some interesting feeding behavior from two different species of trout. I was fishing a small mountain stream in northern New Mexico that has populations of Rio Grande cutthroats, brown trout, and the occasional rainbow. I was fishing a dry dropper with a size 14 [inaudible 00:22:33] as my dry fly and a size 18 Pheasant Tail nymph about a foot below as my dropper.
After fishing for about four hours, I'd caught a total of five cutthroat and four browns. Every single cutthroat was caught on the dry fly, whereas each brown was caught on the nymph. I felt at first it may have been just a coincidence, but after doing some research, I haven't been able to find much information on this. Have you or anyone you've heard of experienced different species in the same water system feeding in separate water columns? Or do you just think it's a lucky coincidence? I'd appreciate hearing your feedback.
Thank you so much for all the great information on fly fishing and fly tying. It has made all the difference in my time spent on the vice in the water."
Well, Mike, yeah, I don't know of any scientific studies, but I have experienced this many times myself. And I don't doubt the experience you had. That's exactly what I would suspect would happen.
Brown trout do tend to feed...although when they were first introduced in the United States, they were touted as great surface feeders and they would feed on dry flies all the time. In my experience, they don't respond quite as well to a dry fly. Although there are some days when you'll have brown trout taking the dry fly, but you're much more likely to catch a brown trout on a small nymph in my experience.
And cutthroats are extremely surface-oriented. I'm not sure what it is about cutthroats. But, you know, a big dry fly is often better than any other kind of fly for cutthroats, even a streamer, even a nymph. And you can even catch bigger cutthroats on a dry fly. So they're extremely surface-oriented. And so that does not surprise me at all. And you know, next time you go out, you may catch more brown trout on the dry fly, but I imagine you'll still catch nearly all your cutthroats on the dry.
Here's an email from Matt from Framingham, Massachusetts, "Hi, Tom. Thank you for the podcast. There's always a lot of talk about trout and smallmouth bass. Where I live in Massachusetts, I have access to quite a bit of largemouth bass in local ponds. What would you recommend for flies for pressured largemouth in summer and fall? I'm always looking for a new pattern to try and tie up."
Well, Matt, I don't think it's so much the pattern for largemouth that are in pressured waters as it is the presentation and maybe the size of the fly. What I would try are some trout-sized streamers, things like Willy Bugger, Muddler Minnow, Marabou Muddler, crayfish imitations, but I'd fish them on the smaller size. I would fish in the sizes that we typically recommend for smallmouths, particularly during the day. Because in pressured waters, a largemouth, most fish are a lot less suspicious of a small fly. Maybe they don't see it as well. Maybe all the lures and other flies they see are big, and they've been caught and released on them.
But I would try smaller flies, I would try subsurface, I would try fishing them relatively slowly, and I would fish them at dawn and dusk. But, you know, as far as specific patterns are concerned, you know, largemouth there are pretty opportunistic predators, and it's more a matter of the size of the fly. But try some crayfish patterns. Largemouths like crayfish just as much as smallmouth do. You always hear about smallmouth loving crayfish, but largemouth love them too. And sometimes, the crayfish imitation will work quite well in pressured waters, so give that a try.
Here's an email from Andy from New Jersey. And I have to apologize. Andy wrote this back in June, and I'm still catching up on some of my Fly Box questions, and this was a Father's Day-specific podcast, but I guess better late than never, Andy.
"Hi, Tom. First, thanks to you and Orvis for all you do in support of this sport. I love the podcast, and I've been relying on Orvis fishing reports for years. You and I met at the Orvis New York City store a few years ago. You held a short seminar on reading small streams. I took a selfie with you and sent it to my son, Alex. He texted back and asked if you were a good guy or a weenie. I told him you are a good guy." Well, you know, you don't know me well enough.
"Alex and I took the fly-fishing course at the Orvis school in Manchester, Vermont, at least 15 years ago. It was a great way to introduce him to fly fishing. And as an intermediate angler, which unfortunately I still am, I improved my casting knowledge, and we had a blast.
Today, Alex is in his sixth year as a fly-fishing guide in Montana. While I really miss him being so far away, I'm really proud of him and happy that he gets to live his dream. And for me, knowing that we're both enjoying the same sport, it helps me feel connected to him.
This past Easter, for the first time in two years, I had all my boys together as Alex flew back East for a few days. I asked him if he liked his job. His response, 'I love it more every day.' Wow. I almost cried. It's great when one of your kids is doing what they're meant to do. This summer, his brother Drew is moving to Northern California for a job that he's really looking forward to.
I'm looking forward to trips out West, visiting and fishing with both of them. So again, thanks to you and Orvis. I don't know if Alex would have gotten the bite if we had not attended the school together. So, if you don't mind giving a shout-out to Montana. I love you, Alex. I'm proud of you. Go get them. And to you, and to all the dudes out there, happy Father's Day."
Well, sorry for the delay, Andy, but such a nice note. I just read it this morning, but I did want to read it. So, happy belated Father's Day to everyone and Mother's Day.
Here is an email from Jeff from Michigan, "While I will always favor dry fly fishing, your excellent program on Euro or contact nymphing with George Daniel convinced me I needed to give it a try. You described how this method keeps nymphs in the strike zone much longer. Would that be true if you Euro nymphed from a drift boat or a float tube? Can you keep the flies in the strike zone for an extended drift?
Thanks much to you and Orvis for the podcast and your other educational programs that have made fly fishing so much more enjoyable and accessible."
Well, Jeff, I have seen firsthand with my friend and coworker, Jesse Haller, on a drift boat on the Missouri River, just how effective Euro nymphing can be from a drift boat. And I can guarantee you that not only were my eyes open, but the guide that we fished with was just blown away. It's not done an awful lot, and it's not easy to do from a drift boat, but it can work extremely well. So, yes, it can work, if you're in the right water.
Now, from a float tube, it's going to be a little bit more difficult because you're much lower to the water in a float tube. And it's going to be tougher to keep that line off the water. Not that you can't do it, but I would use as long a rod as you have for that. It's gonna be a lot tougher from a float tube. But from a drift boat, where you're standing up and you're high above the water, it works quite well. So, anyway, yes, it'll work, and give it a try.
Okay. Another email from Oliver from Spokane, "Hey, Tom, I have two questions for you. How do you mend your line on a FireCast? I'm fishing with a dry dropper, and I'm casting about 30 feet out there. Once it lands, I'm not able to mend upstream because I can't pick up the whole line from such a far distance. Any tips?
Two, when fishing a Chubby Chernobyl, how do you get the legs to separate more? When I tie them in, they just fold up so they're almost touching. How do you fix this?
Here's my tip. When fishing any nymph with hackle, like CDC or partridge, and your fly start to drag, let them drag, and turn your drift into swinging your nymphs. This might not be the best thing to do, but I've caught fish like this, so I thought I would share."
Yeah, it's funny, Oliver, how flies with a hackle collar all the way around swing much better than a nymph without that partridge or soft tackle collar. And I'm not sure why, but it just must be the way they're oriented in the surface film, but it does work quite well at the end of the drift.
As far as your questions are concerned, you should be able to mend all the way to the dry fly with 30 feet of line out. You know, a couple things to check out. One, is your line floating okay? If it's not floating that well, clean it. Just next time, before you go fishing, just soak in a little soap and water and then run it through a nice, dry paper towel. Put some pressure on the line, and you'll both remove any algae and dirt on the outside of the line. You'll kind of rejuvenate that lubricant that's in the line. That should help keep it floating.
The other thing that I do, when I'm fishing a dry dropper like this, is I will put some fly dressing, some dry fly paste or dry fly gel on my leader all the way up to the dry fly. I don't think it bothers the fish at all. And it's a lot easier to mend a leader that's floating on the surface than it is a leader that's slightly sinking. So try that.
The other thing is a longer rod is going to help. You didn't say what length ride you use. But, you know, the longer your rod, the easier it's going to be to mend because you can lift more line off the water. So, I think that you should be able to mend the whole fly line, 30 feet. If you still can't, don't worry about it. If you can just mend part of the line, you're going to increase your drift. So, mend as much as you can and take it from there.
As far as tying Chubby Chernobyls, yeah, the legs sometimes fold up so they're touching. And typically, what I often do is I just put one set of legs instead of two in my Chubby Chernobyls, you know, just two on each side, one piece of rubber that forms two legs. And if they're sticking together, you know, typically, when you tie a Chubby Chernobyl, you put some dubbing on the thread after you tie in the legs, and then you wind that over the legs. And if you're careful where you put that dubbing, you can kind of place the legs anywhere you want by locking them in place with the dubbing.
So, I hope that helps, and thanks for the tip. And there's a lot of videos online. I think Tim Flagler has one in the Orvis Learning Center on tying Chubby Chernobyl. You might see how he puts in his rubber legs. And I know I tied one for the Orvis Facebook Live session, and it's somewhere in the Orvis Facebook Live archives, but it's probably way, way back there somewhere because it was over a year ago.
Here's an email from Aaron from Washington State, "With little experience fly fishing, I've been having what I consider great success pulling quite a few young rainbow and one cutthroat. I've been on the river almost every day after work for the past couple of weeks. However, today was a little rough, which generated some questions. Some you may have answered before, but I haven't had the time to go all the way back into your podcast yet. I'm working on it.
Question one. While fishing, if you see a predator in the water like a beaver, otter, would you move on to a new section or just wait a little while and keep fishing? Question two. I seem to be catching myself and my rod on my fly, is this lazy casting or something that just happens? And my final question, what's your favorite river, lake you've fished in the Lower 48? Thanks, Tom, your podcast and YouTube channel have been a great help in starting me out."
All right, so I'll answer your questions in order. Number one, if you see a predator in the water... Now, beavers are vegetarians, and they're not trout predators. And I'm not sure if a trout can tell the difference between a beaver and an otter. But I have seen both. I've seen beavers spook trout. And I have seen places where trout used to live and beavers moved in and the trout moved out. I've also seen places where trout will feed right alongside a beaver in the water.
So, I think it's a matter of...eventually, some of them get used to the fact that a beaver is not going to bother them at all. But, you know, it's situational, and I can't give you a definite answer on that. It really depends on the individual trout and the size of the stream and everything else.
Now, if you see an otter in the water, you might as well pick up and go somewhere. They're incredibly efficient predators. And they're really good at it. And any fish that hangs around and doesn't get out of the way of an otter real quick is going to be dinner. So, you know, if you see an otter in the water, I'd go somewhere else. I'd move as far as you can because an otter is really going to both clean up the fish and also spook all the fish in the area for quite a while.
Question two. What's happening here is you're pushing and pulling your cast, probably, instead of dropping that rod tip out of the way on your forward cast. A little bit tough to tell without actually seeing you cast. But one of the things that really helps is that when you make your forward cast, drop your elbow down to your side. It doesn't have to go tight to your body. But when you make that forward cast, if you drop that elbow, you're going to get your rod tip out of the way. And it's probably going to go over your head and over the rod and not hit you.
There are many things that can cause this but dropping that elbow abruptly on the forward cast and not pushing the rod out in front of you with a straight arm is probably going to help you in that situation. So, I hope that helps.
Oh, and my favorite river, lake that I've fished in Lower 48, I honestly don't like this question because I don't have a favorite. I really don't. I have streams that are close to home that I love. I have streams that are in various parts of the country I love. But I actually don't have one favorite, so I can't answer that question.
Nate: Hey, Tom. This is Nate in Colorado. I have an 8.5 foot 8 weights that I ended up inheriting. It's a few years old, but I really like it. I was using it the other day to just throw a size 6 frog pattern on a local lake here. And I wasn't able to get a ton of distance, I felt it flexing okay. It's probably only about the second or third time I've been able to use the rod.
After seeing that there wasn't really any surface action to speak of, I ended up switching to a bigger size 2 articulated crawfish pattern and seem to get quite a bit better flex on that and a little bit better distance, not a ton more because of the fact that, you know, my fly casting is nowhere near Pete's. But whose is, to be honest?
Is the size 2 about the smallest that I can go with an 8 weight in order for it to be to be flexing properly? Or does that have more to do with just more practice with my fly casting? And then, if I'm wanting to use a size 6, or like a smaller "bass pattern," would it be better to use a 5 weight for something like that? Any feedback would be helpful.
And then, my second question just has to do with sinking leaders. I like the Versileader that I have right now. It's just a full sink leader, I should say, I believe it's about an inch and a half per second. If I'm wanting to switch from just dry flies or indicator fishing to either a blob fly or something like that, another streamer that I'm wanting to get down a little bit deeper. If I was going to use that leader for bass, because it's specifically designed for trout, would you be worried that there wouldn't be quite enough to handle a bigger largemouth or a pike that I may end up getting into? Is there another sinking leader specifically for those larger warm-water species?
I appreciate the podcast, hope to hear your answer to my question. Thanks, Tom.
Tom: Oh, Nate, floating frogs are very air-resistant, and they don't cast as well as a sinking fly. Generally, sinking flies are a little bit slimmer, and they provide less resistance in the air. And it has nothing to do with the flex of your rod. The fly that you're using is not going to affect the flex of your rod. That's going to be determined entirely by your casting.
So, a couple things you can do with that frog. One is to cut back on both the diameter and the size of your leader. A short, 3 or 4-foot leader that is stiff and heavy, when you're fishing frogs, you don't have to worry about a light tippet. So you want a short, stiff, heavy leader using that frog.
The other thing is you can open up your casting loop a little bit by making your casting arc - the distance, the power stroke - extend on your cast a little bit wider. That will open your loop. And that'll help a little bit to get that frog out there. But they're just hard to cast, you know, hair frogs or plastic frogs, or hard plastic poppers or whatever, they're just hard to cast. Your 5 weight is not going to do any better at all. You're much better with the 8 weight because the mass of that 8-weight line is going to drive that popper out there much better.
And then, finally, that trout sinking leader will be plenty strong for bass and pike. There's no real reason to use either, you know, a trout-sinking leader or a salmon-sinking layer. The trout leader just sinks a little bit a little bit slower. It's not quite as heavy as the salmon-sinking leader. But for your 8 weight, you could use either one without any problem at all.
Teal: Hi, Tom. This is Teal Tan, you know, from Calgary, Alberta. As always, I loved the podcast and everything you do for fly fishing, fly-fishing community. I have a question regarding some videos I've been watching due to your suggestions. I've really gotten into "Jazz & Fly Fishing." I think the content is great. And it's very entertaining to watch.
One thing I've noticed is these Scandinavian boys seem to lose a lot of fish once they've hooked up. I've also noticed that they tend to hold their rods well above their heads. At some points, the rod is above their head, full arm extended, and they're leaning back to get even more reach, I suppose.
Now, you must know that I'm also absolutely infatuated with Dave and Amelia Jensen. And something I've learned from them that I find very useful is the side rod. They're always suggesting to play the fish with the rod, load the water, and off to the side.
I used to always raise the rod up in typical trout set, if you will. And I found that the rod to the side makes it a lot easier to keep a fish on the line and land the fish. I'm wondering why do the boys in "Jazz & Fly Fishing" hold the rod so high in the air? Is this a Scandinavian technique? Or am I missing something? Is that beneficial? Is it just a preference of style? What's going on? Could you maybe explain a little more the benefits of holding the rod so high? Or do you feel that the side rod technique is better?
Thank you for your time, and I hope to hear this on the podcast.
Tom: So, Teal, I don't know why Scandinavians hold the rod so high, but the fact they hold the rod so high is probably why they lose a lot of fish. I don't know if it's a cultural thing or... You know, there's no right or wrong way in fly fishing, everybody has their different styles. Generally, we find that by keeping your rod at a low angle, it's much easier to control a fish. And it's much easier to fight a fish quickly, play them quickly and efficiently, and get them into with a low rod angle.
The only thing I can think of is, perhaps, when I watched those same videos, I think there's a lot of weeds in the water. And if you have a lot of weed in the water or logs or things, you do sometimes have to keep your rod high to keep the fish out of the weeds. So, that may be why they're doing it just to keep the fish from burying their heads in the weeds and twisting your leader around the weeds.
But again, you know, there's all sorts of different styles of fly casting and playing fish and choosing flies, and there's no right or wrong way. So, Scandinavians have their way, and we have our way.
So my guest today is John MacMillan. John has been on the podcast a number of times because I love talking to John. We always have such fun conversations. John is a fish biologist, a world-renowned fish biologist. And today we're gonna talk about trout and some [inaudible 00:46:21], and water temperature. How's that sound, John?
John: It sounds awesome. And, Tom, thanks for having me on again. You know, I think the feeling is mutual. I have a Tom Rosenbauer admiration place in my mind and heart for all the good stuff you've done.
Tom: Oh, thank you, John.
John: Yeah, you deserve it. You deserve it. You know, I mean, yeah, you're just a quality human being, Tom.
Tom: Well, thank you. Thank you. You haven't fished with me yet. I'm a real jerk on trout stream, though.
John: That's what I've heard though. I mean, I guess, you know, people would say the same about me, "It's all good on the phone until you get on the river. You're a jerk."
Tom: Yeah. All right. So let's start talking about water temperature. And we'll talk about trout and water temperature in general.
John: Yeah, I mean, to me, it's interesting and it's really topical. I mean, I think out here, where I live in the Pacific Northwest, we just had the worst heatwave, you know, in recorded history, right? Temperature is up to 117 degrees.
Tom: Oh, my God.
John: And our stream is going up to and exceeding 70 degrees already. In fact, we had... And I don't want to be all negative news, but, you know, I think the Chehalis River got over 80 degrees, and there were fish kills on the Chehalis. So, you know, it's an interesting time, right? As we talk about this, with you and I having a history of being anglers and trout fishing in lots of places across the West, I'm always amazed on how rapidly things are changing.
But I go back to, I think, water temperature, and I always call this. To me, it's kind of the master variable for all fish because it really does control their metabolism. What I mean by that is that metabolism is kind of the fish's ability. Once that food goes down its mouth and into the stomach, it's basically how efficient and how quickly an individual converts all of that food and calories into growth, right, so whether it's gonna grow and put on some muscle mass, or maybe store some fat.
And generally, what we see is that, as water temperatures increase, the metabolism, of course, of these fish tends to increase, which means that they need more food as water temperatures increase. And vice versa, as temperatures get cooler, you need less food because, you know, the motor is not running as hot.
Tom: Yeah. What's the minimum temperature that trout will feed? Will they feed right down to 32?
John: Yeah, they'll feed right down to 32. Now, it's interesting, there does appear to be a really narrow set of conditions in which I've read, and this isn't well studied, but it's kind of cool, right, because it's fun to talk about those extremes that people might not know about.
But there is evidence that in small streams, or even large streams, that when you get ice over, you know, like if the whole stream ices over, maybe like in Russia, Alaska, and then the solar radiation from the sun is not penetrating the ice very well, and at that point, some salmon will go into what, almost a state of torpor, kind of like, yeah, almost like hibernation.
They're not hibernating, of course, but it doesn't look like they're really feeding. They're just barely moving. If anything, kind of hiding under rocks and in log jams, or maybe at the bottom of the river somewhere.
And so, I think they'll feed. And it depends, of course...this is the other interesting part is it depends on the temperatures that they grew up in as a juvenile, right, because there are some genetic effects, you know, whatever their parents may have experienced. And I think you and I have been to like, you know, we can go to some of these cold streams and fish that live in a relatively cold stream tend to feed down to colder water temperatures. They've kind of evolutionarily adapted to those temperatures.
And fish in the warmer streams, on the other hand, will probably feed at much higher temperatures. So there is some local variation that these fish can evolve and adapt to, to kind of fit. But I think when we go into all of this, with temperature, my concern is, of course, the stress during these warm, hot, long summers and the droughts we're facing.
For example, I was reading a study the other day that was just a repeat of a study that came out 20 years ago that suggests that California may be heading into 100 to 200-year-long drought. And that we're maybe 20 years into that, you know. So, you just never know what's going to happen and how stressful those temperatures can get during the summer months.
Tom: So, John, what happens to a trout when water temperatures get too warm? And let's talk, what is too warm? There's a too warm for survival and then there's too warm for fishing, right, because fishing adds additional stress to the fish's respiration. So, what do you view...and maybe you want to cover this by species, but what do you view as the as the upper end lethal temperature and then the upper end where you gotta quit fishing temperature? And why?
John: Tom, yeah, and so I'll go through probably rainbow and brown trout first, which are pretty thermally tolerant, right? They're kind of like at the flexible end. And they're lethal temperatures are really pretty high. You're talking in the high 80s for those fish to die out, right, low 90 degrees.
So, now, in order for them to persist... Like there's evidence of juvenile steelhead living and growing successfully in California streams that are running up to mid-80s to low 80s during the summer, and they don't grow during that summer period, they just hang on. And then they grow during the winter, if the winter is warmer. So, they can shift. You know what I mean? Just because the summer is hot, they can kind of put off growth then. Just like a fish in Alaska doesn't grow much during the winter because it's so cold. They grow more during the summer.
So, you know, brown trout or rainbow are pretty similar that they have these really warm water temperatures that are lethal to. But generally, you start to see stress effects once you get to 68 to 70 degrees. And that's when the fish starts to show physiological signs in the bloodstream, right? Those are things that scientists can measure.
I don't want to get too far ahead of my skis because I'm not a physiologist. You know, I'm more of an ecologist, but I think I can give the general. So, on the other end of the spectrum, we'll have char, like bull trout or Dolly Varden, right? And those are really cold-water obligate fish, right? So those things will feed right down to freezing. But as soon as that temperature gets over 60 degrees, that's when they start to feel stressed. They're quite a bit...
Tom: Sixty? That low, huh?
John: Sixty, yeah, for some of those cold-water char. And that's where you have brook trout is kind of being in the middle, right? Like brook char, kind of interesting, and they are char, but they can also persist in warmer water temperatures or at least do better in warmer water temperatures than bull trout and Dolly Varden can.
And so, I'm not exactly sure of the upper lethal temperatures for the char, but I think they're in that mid-80-degree range. Again, you know what I mean. The lethal temperatures end up being pretty similar. It's just that they're lower for the coldest char. For brook trout, I think they're in between those two, somewhere in that low to mid-80-degree stuff.
Tom: Okay. So, as far as stressing in a brook trout stream, stressors, where you would want to stop fishing, what temperature would you estimate for a brook trout or recommend?
John: Brook trout... Yeah, and I go to about that 66, 65, 68-degree range. You know what I mean? If I get above 68 for rainbow trout, I start getting concerned. I'm fishing in that warmer water. And for brook trout, it's about 65, and I start to get concerned, so I'll drop it down a few degrees.
And then, you've got a species like cutthroat. We have coastal cutthroat and westslope and all these different subspecies, and they're closer to kind of a mix between brook trout and rainbow trout, right? Some subspecies of cutthroat are very thermally tolerant, but a lot of those species we're not even fishing for because they're so endangered, you know?
You know, but lahontans are really thermally tolerant as a subspecies of cutthroat. And on the other hand, westslope and coastal cutthroat, you know, don't do as well in higher water temperatures like the lahontan do. So, the one thing with cutthroat is it really does vary. But I go back to cutthroat and just kind of treat them like rainbow because their thermal tolerances are pretty similar. And once I get above 68 to 70, I get concerned.
And personally, for me, once temperatures get to 70 degrees, I stop fishing. Because what happens to a fish—and this is kind of the interesting part—is people wonder, "Well, how bad can the stress be?" And that's a great question because I think there's a range, right? It's not an absolute. So what happens with a fish in warm water is kind of a similar response to how we are. And I'll give you an example.
Like, if you're a really a fair complexity of a person, right, your skin is really light colored. I have a couple of friends who are redheads. And I think I've mentioned this before, they tend to burn really easily when they go out in the sun. On the other hand, I heritage is a lot of Scottish, a little Turkish, so I'm kind of in the middle. And then, I've got some friends that are more darkly complected. And the point is, is what they find in humans is that the really pale skin exposed to hot sun produces a sharp cortisol response, right, like that stressful.
So if you think of us, you know, in this recent hot spell that we all had, when it gets to 100 degrees and you start not to feel good, that's because there's cortisol running through your system, right? Your body is stressed. And so your blood chemistry has changed because your skin doesn't deal, you know, with that solar radiation if you're really pale. And on the other hand, it shows how, if you're more darkly complected, right, you get a less of a stress response and you get more of a response of melanin that is beneficial to the skin.
So, you know, you put this out there because fish can respond very differently, right? In other words, I just want to explain to people that when you're sensing that stress on a hot day, people don't really think about that or put it in the terms of a fish, right? But if you're not feeling that well on a hot day, and you're tired, and you're kind of crabby, a lot of that's because of the cortisol. Your body is just stressed by the warm temperatures that it's not used to.
And so, what I like to think of in fish, and in most of our fisheries that have become really popular, you've got trout, and they're out there feeding during these warm water temperatures, and they've got to feed more frequently so their body can keep pace. They've got to bring in more calories, right?
Tom: Because their metabolism is increasing with the temperature.
John: That's right. It kind of goes from a 4 cylinder at 50 degrees up to a 6 cylinder at 60, and then you're at a V8, you know, so you just get worse and worse gas mileage. And what that means is that puts them at more risk. It makes those fish more vulnerable to being caught by us as anglers.
And if you're in a place where there's not a lot of fishing pressure and the populations are really healthy and abundant, kind of like we experienced in the '70s and '80s in a lot of these places, right? In those cases, fish, you know, there's probably almost no measurable effect of us catching all those fish, right?
Because a fish might be caught once every week, once every month, right?
It's when we get into these uncharted waters of climate change where our streams are warming, the thermal regimes are increasing, and so the fish need to increasingly feed to keep pace with that. And we have so many anglers that are so effective now, right, that maybe some of these fish are being caught, you know, once every two days. Some fish might be caught multiple times in a day, right? We don't know the frequency.
And so, I'd like to say, like, this is how you start to erode at the genetic diversity. So, if we had 100 of us out in the field, and it was 108 at my house the other day, I'm going to be one of the first people that died at 108, right? It's just the way it is. I don't do well in 108 degrees. Most of the people will be fine. But that's the point, is, you know, the cumulative impacts. Even losing a few of these fish can erode genetic diversity because each of these fish has genes that, you know, show different resilience to different thermal regimes, different food sources.
And so, the hard part is if fish are being caught multiple times and things like, you know, exposing them to air, that can induce a much greater physiological response. And so it's a little rambly, but the point is that in these places where there's a lot of fishing pressure and we're catching lots of fish, we're seeing declines in fish abundance, I get concerned that maybe the encounter rates could be too high as these fish try and to keep pace with warm water temperatures.
Now, at the same time, I love angling. And so, I think it's best to find a balance as we move forward, because I think we're moving into a new time. You know, it's a strange time, but things are changing so rapidly that I worry, you know, because I want to keep kids fishing in on rivers. But it also might mean that we have to increasingly maybe shift away from some of our favorite cold-water fish during these hot summer months, you know, to give them a break.
Tom: Yep. Yep. I'm personally going to do a lot more carp and bass fishing this summer and trying to encourage people to do that to keep the pressure off the cold-water fish.
John: And I mean, gosh, it's so hard to think of but it's better to think about it now. And I don't know what the future holds. But I don't know if you saw the report that came out maybe a month ago talking about the declines in brown trout in some of our favorite Montana streams.
And it was like, "Wow, that is remarkable how fast they've been depleted." And you start to think about just how you balance that. And I don't know if anglers are the problem, right? I'm not leading there. I'm not looking at the information.
My only knowledge is that the populations have declined. And when I see that, it's kind of you don't have as much money to spend in your bank account, so my tendency is to want to be conservative, right, so I don't overspend when the fish are struggling.
But it's a strange frontier that we face as anglers because I think we're kind of always optimists. And as a scientist, you know, the science is kind of starting to scare me more than it did 10, 15 years ago as these changes unfold.
Now, all of that said, in the scheme of things, there could also be some benefits to anglers. If we can learn to work around these warmer summer temperatures, we should probably have better shoulder fishing, right? Yeah, like winters won't be as cold. You know what I mean? Maybe the following spring will be a bit more mild, so there might be opportunities to shift our fishing away from those, you know, more stressful situations to take advantage when the fish are not that stressed.
Tom: Yeah. Unfortunately, it's when most people want to take their vacation.
John: I'm with you. I mean, it's like, yeah, you know, go fish in January. That's just not that much fun. You know, you're right.
Tom: So, John, tell us what happens to a trout, a brown or a rainbow, that's happily feeding at 70 degrees, feeling pretty good, physiologically not bad, a little of that, I guess, the cortisol starting to creep in, but no problem, and then that fish gets caught by an angler. So what happens to that fish?
John: Well, the cortisol shoots up dramatically, all the stress hormones. And I use cortisol because I'm not a physiologist, I can't break down all these, you know, corticoid hormones and steroids that are in there. But the main point is, it goes up, just like it would for you and I if we're being chased by a cougar, right? It's life or death, right? And it triggers the fight or flight and so they fight, as we know, like crazy.
And their cortisol levels can go up dramatically, you know, 4, 5, 6, 10 times, depending on the fish. It's quite variable. And the cortisol levels will go up and remain elevated at more, you know, harmful levels, and remain there at longer periods the warmer the water is, right?
So as you get over that 70 degree, that effect of being caught and released, and then the stress on top of that, the effect is worse. The cortisol levels are heightened. And the duration and intensity of that is worse. Generally, we see that a lot of fish go back to background cortisol levels between 24 to 72 hours.
Tom: That's a long time.
John: That's a long time. And 24 hours tend to be in that 50 to mid-60 degree range, right? And then as you increase past that 66, 68 and into the 70s, mid 70s, you start to get up there to two days and maybe even three days, you know, for the cortisol levels to come back to normal. Now, three days would be an exceptionally long period of time, but I'm just providing the range of how long that cortisol, those elevated levels, can remain in the blood system.
And I go back to this, it's very similar in humans. We had 3 days over 100 degrees, which was a record for us. And I think our temperatures got to, like, 107, really hot. And I felt those effects for at least another three or four days. You know what I mean? You don't feel good, right?
And all of that, again, is just stress response, right, that your body's feeling as it tries to deal with a situation that is abnormal. And if abnormal events come very infrequently, your body is usually pretty resilient enough to stave them off, right?
And so, I think that's where the trouble comes in, is where you see what happens when some of these fish get stressed multiple times in a row. And that's the point where you can see these effects resulting sometimes in mortality. There's been some studies on warm water fish and variety of species, right, where they induce know, they kind of fake, like, it's a fishing response, you know, chase it around a tank, do all that, do in different water temperatures.
And then some fish, they try and basically mimic what would happen if you had multiple encounters in the same day or the same week. And those tend to be the worst-case situations, right? So the fish is caught and released once and that's really infrequent, like, that happens once a month, or whatever it is, you know, there doesn't...
Again, there's not a lot of science on...because we're not catching fish, taking their cortisol level, and then measuring that over months or weeks, right? What we usually do is catch the fish, you measure its cortisol, and then, some of these people might take the fish back and put them in a holding tank for 24 to 72 hours to see how long it takes, the cortisol levels to go back to basal stasis, right, pre catch and release level.
And that's important too, because people have to remember that when we're looking at these duration of cortisol, we're not usually measuring the fish back in and putting it back in nature. We're taking it out of nature to put it in a tank, right? So we can then monitor it. So the stress levels likely would be worse if you're back out in nature, right, where you're gonna have to deal with predators and competitors and more warm water.
Tom: And...
John: So the cortisol... Yeah, go ahead, Tom. I'm sorry.
Tom: So, what are the elevated cortisol levels do? Do they just increase their metabolism to the point where they can't get enough oxygen? How does it kill the fish?
John: Yeah, so first of all, the blood is circulating at a much faster rate as their... And so, that makes their heart have to work harder and faster, just like anything. So, it's kind of like revving your motor, right? And fish are, at this point, kind of unlike us, and that their heartbeat can, basically, the rate at which it pumps is directly correlated with water temperature, right? So ours is, we have control over that, right? Ours is not going to do the same.
So basically, you can rev that motor up to the point where they could have heart failure, right? And that has happened in really warm water temperatures. Some of these fish just cannot handle it, and their hearts will fail.
Now, the effective cortisol is something that I have a very hard time breaking down just in plain language, right? But to me, what is happening is that this is triggering a different set of chemicals. So, it starts in the liver, you know, the bloodstream goes to the liver that alters the blood chemistry. The blood chemistry goes back up to the brain. And the brain triggers these responses, like, "Oh, you've got to put more hormones out into the blood system."
And so, what that does is twofold. First, as you mentioned, it increases their metabolism. But the second thing that the cortisol does in their body is that heightened stress response makes everything have to work a little bit harder, right? So, it's kind of like going uphill. And that's the easiest way I can put it. It just makes the motor have to work harder, and it makes it less efficient.
So it's a risky proposition, right? Cortisol is really important because it can help us break down some of that stress response, right, in there. It's a normal, healthy thing. But prolonged periods of cortisol are unhealthy... I wish I could explain it better, but I'm not a physiologist.
Tom: No, you're explaining perfectly. You're explaining it perfectly.
John: I mean, I run up against these points where, like, as a physiologist, I can't break down what's happened at the cellular level. I just don't know enough in terms of the molecules but...
Tom: I don't think any of us want to break it down on a molecular level. You're doing a good enough job to get the point across.
John: Cool. But, you know, we all have our specialty. And I think that I always just say, you know, cortisol is both helpful and harmful, right? Nature has evolved cortisol to be very useful to us, right? It helps us survive really difficult situations. It provides us with a jumpstart in terms of energy and response time and our ability to think quickly.
But that comes with a drawback. And I think the difference in nature is that when animals experience these pulses of cortisol for a flight or fight, you know, they're usually really shortened duration and intensity. You know what I mean?
But it's this chronic stress that I think we're starting to see in fish. Like there's evidence that, you know, in human populations, like if humans are driving to work every day in big cities like LA, that the smog creates chronic stress in these humans and being crowded, right? I mean, we kind of all experienced that.
And so, we can see how that kind of chronic problem leads to like heart disease in humans. And because our lifespan is 68, 65, 85 years, it takes a long time for those to unfold. A fish's lifespan is much more condensed. As a trout, it's four to seven years, probably right, somewhere in that range.
And so, those effects are manifested at a different timescale than the human scale. But I think, maybe what we don't always appreciate is that how much of this chronic stress in our lives contributes to our own health problems, like unhealthy eating. I fall into that at times, trying to get a project done and writing. And I'm like, "Oh, my God, I'm gonna eat really terribly."
Or you think about those times when you're trying to get to your fishing spot, and you're just driving hours and hours, and it's just coffee and donuts or something to stay awake, whatever it takes. So, I think about the chronic stress that we endure and how heat makes our lives that much more difficult.
And for a fish, it's worse, of course, because the temperatures that they could experience are outside of, in many rivers now, are exceeding those limits that they can even survive in.
Tom: Yeah, it's interesting. It's a lot more complex than I thought. My theory, or whatever, was always that as water temperatures rise, especially above 70, their respiration increases. But water holds less oxygen as it gets warmer. So they can't get enough oxygen because their respiration is going at such a rapid rate. It's like, you know...
John: Well, that is true. And I didn't even get into the oxygen, Tom. So you're not wrong there, right? In fact, when we measure metabolism at these temperatures, it's about oxygen respiration—how much oxygen is left over to metabolize food versus the basic stuff? And so, yeah, I didn't know how much you want it, but you're right. I'm gonna let you finish.
Tom: No, no, you go ahead. We do want to talk about the oxygen level as well because warm water holds less oxygen than cold water. Yeah, I mean, I think you're right. And, I must admit, you know, you go through these different phases of what you're focused on, but dissolved oxygen is a measure of how much oxygen is available to fish in the water, right?
And so, salmon usually need dissolved oxygen levels that are minimum of like 8 milligrams per liter. And so, once you get below those levels, even below 10 milligrams per liter, you can have issues depending on the fish. So you're right, as water temperature increases, there's less oxygen available unless it's really turbulent, which is why we see fish in warm rivers nosing up into those really oxygenated whitewater areas, you know, because those small areas can contain brief pulses of higher oxygen levels because it's, you know, being oxygenated by the turbulence.
But you're right. So, as the temperature goes up, there's less oxygen available. That creates more stress on the fish, which is related to these cortisol levels, right? That's one of the metrics that the body is responding to, to produce cortisol, right, is lower oxygen levels and the labored physiological response that you need to kind of keep your motor going then, right, because it becomes more difficult. You've got to work harder, right? Less oxygen, you've got to work harder for it to keep going.
And it's one of those, you know, self-fulfilling prophecies, which is the harder you breathe, the more oxygen it takes to breathe, right? And the less you get in because the less it's available. And so, when we measure things like metabolism in a fish, we have what is called a scope for activity. And if you can imagine, on the bottom of the axis on the very left-hand side, it's like 32 degrees. On the right-hand side is like 90. And there's a bell curve in there, right, where rainbow trout and cutthroat is somewhere between 55 to 65 degrees. They're at their max ability to have oxygen to set aside for growth.
And then, once they get above 65, they're on the downhill side of that, right? And once they get the 75, it's really tough. And one of the additional hard parts is the body has to break down food at warm water. And that's very stressful to do.
So, a few years back, I think it was 2015 or '16, we had another really dry year out here. And there were huge fish kills in the Columbia River of adult sockeye, but also a lot of adult sturgeon were dying. And the sturgeon were dying, they're like 7 or 8-feet long, because they were eating so many sockeye that it's really stressful. It's like sitting there on a 100-degree day and you've just eaten a whole pizza.
And you're like, you know, that feeling we all get like, "I probably ate too much, right?" This is not going to work out well. And so, what do we do after we eat? We go inside somewhere cool, you lay down. You know, that's the difference. The fish can't do that. They have to keep swimming. They have to keep moving.
And so, as you lose oxygen, the body responds in a bad way. It's just, you know, increased stress makes your life so much more difficult. But I don't think a lot of anglers are aware of that when those fish have to eat at those warmer water temperatures, that it can make it even more difficult for them. It can create additional stress because it requires, depending on how much food is in their stomach, potentially a lot of energy to break that down.
If you're a rainbow trout that's eating like a bunch of little mayflies, it's probably not as bad as a brown trout that's kind of this big-meal eater, right? If a brown trout gets two small fish in his stomach, or decent-sized fish, that is a lot of stress, which is one reason that brown trout, after they eat these big meals, tend to go rest and hide for long periods of time.
You know, I think we've always talked about I think brown trout are pretty smart because they like to eat a very... You know what I mean? They have to have something they like to eat. They like to eat something big that looks wounded. That's gonna give them a good meal.
And we call those animals gorgers because they tend to eat once or twice a huge meal. And then they go hang out and break that stuff down. While we have grazers that are like rainbow trout, you know, like they just sit there or cutthroat, right, they just sit there and feed on the surface or they're eating nymphs all day long.
So, the gorgers, and that's why I worry in Montana, I say, gorgers are likely more susceptible to these heat effects and repeat catch-and-release effects because their stomach, at any given time, can be really full of very valuable food that is also really hard to digest.
Tom: So, that may be why the brown trout in Montana are in trouble, more trouble than the rainbows, with these high temperatures.
John: It's possible. And this is just, you know, kind of thinking out loud, right? So, I don't want anybody to think that I know what's going on in Montana because I don't, but it's fun to think, right? This is fun to think about what are some of the possible ideas.
It's a possibility, for example, that brown trout that feed more infrequently, that the more they get caught and released, the more they have to then eat. The more risks they're going to have to take. So you could imbalance the frequency of their feeding. You could mismatch their natural tendency to feed once every couple of weeks or a month on a big meal and force them then to have to feed more frequently because every time we catch them, they're burning energy.
Consider how many times anglers have caught a fish only to have that fish puke up the big fish on us. You know what I mean? That means that fish just lost its whole meal, right? That was its bank account. So, it's going to have to go back out and take a bunch of risks to try and get another one of those.
And that's one of the reasons I think brown trout are a more difficult fish to manage for anglers than rainbow trout, which are kind of grazers, you know. And, even if you catch one on a mayfly, it's got a thousand other mayflies to eat.
And, yeah, so, again, I'm not sure, but it's based on the science that's out there. That is a possibility that, you know, angling in warmer water on those fish could have worse effects. But again, you know, I'm sure somebody smarter than me will try and answer that at some point.
Tom: I know some interesting theories, though. One of the theories I have, and this is not scientifically proven, in streams that hold both browns and rainbows is that the rainbows tend to be a lot more fluid. They'll move. If things aren't to their liking, they'll move. Whereas a brown trout, unless the habitat totally disappears, the water gets so low, they can't live where they've been living, they'll stick it out. And I think that the rainbows may have a better ability to find cooler water and more oxygen, or maybe less fishing pressure, than brown trout because they do move around a lot.
I have a little stream in my backyard. You know, it's probably 20-feet wide. And it's got wild browns and rainbows and a few brook trout. And the browns are always there in the same place. The rainbows, they're there one day, they're gone the next. They show up for a while, then they leave. And, you know, I've seen that and other rivers too where rainbows really do migrate throughout the season based on water levels and, I guess, temperatures.
John: I think it's a great point, Tom. I mean, you know, and it's likely true. I must admit, there's a ton of good science on brown trout movement survival in Europe, and I've read quite a bit of it, but not as much as I would like to. But generally, I think you're right.
You know, these animals that are gorgers, once they find a good place, and they tend to be stream resident, they tend's kind of like you're an apex predator, you're going to choose the place you like the best. And if that place has worked for them for a number of years, why move because you might go through a hot period, but you've been through a hot period before?
And the hard part now is that these hot periods might be longer. The animal just doesn't understand, right? It has never experienced anything that prolonged and that hot. So, you're probably right. I think that, you know, animals that are not as mobile are far more susceptible to getting caught in what we call ecological traps. Those are areas that appear to be really profitable for periods of time, but over the long haul, are not going to be consistent enough for you to live there.
So, animals can get sucked into that trap because it might have really good food or cover for a period of time, and then it disappears. You know, maybe it's seasonal, maybe it's annual.
But I think they're like humans. It's kind of like getting an email from somebody in Nigeria that says, "We're gonna offer you a million dollars from my grandma. You just need to give me your email." "It sounds great, man. We're gonna be rich." But animals, for all their survival instincts, just like we have, they can be trapped too and tricked by nature's conditions.
Tom: Yeah, yeah, sure can.
John: But I always think—I go back to oxygen, water temperature—that those are really strongly correlated. And just, you know, oxygen is fundamental to so much of the life that we have on this planet. That it's going to be an interesting next decade to see how climate change effects unfold, to see what this does to fish, and then to figure out how we're going to have to adapt as anglers.
Because we can persist through this, but we're going to have to give the fish some space to make it through this so that they have diversity and abundance to get through a tough time. And it doesn't mean not fishing, but it means thinking more carefully about how we fish and when we fish.
Tom: And we're probably going to have to accept some regulations. Hopefully, fish managers will be smart enough to institute regulations that we may not like.
John: Yeah, I mean, it's true. I would love to fish every day of the year in any method possible, right? You would love to have that option available. Unfortunately, it's not, right? And so now, I mean, I think of this too, and I always go back to one thing is I will take a sacrifice now to increase the odds that some other kid, 40 years from now, gets to fish with these things. That's not a problem for me at all. You know what I mean?
In the scheme of things, whatever it takes, because these fish have given us so much. You know what I mean? That it's a small ask to get back to them a little bit and take a few days off the river. You know what I mean? But it can be controversial. We're a nation of opinions.
Tom: Yeah, it will be, for sure.
John: Absolutely.
Tom: We're gonna ask you a couple more questions, especially regarding high water temperatures, John. If someone is fishing at 67, 68 degrees where, you know, it's okay. But you're getting on the cusp of problems for the trout. Give people some recommendations for how they can safely fish and release those fish. What kind of things should they do?
John: Yeah, and I mentioned this, I've learned through experience. I've killed fish by fishing in warm water, even when I knew it was too warm. You know what I mean? I've been a kid like everybody else, you know what I mean? We're all human.
So, I say this through my own experience is first, I fished mornings and not the afternoons. So, if they're up in that warmer stuff...and the reason I fish mornings instead of the afternoons is because even though afternoon temperatures may drop down into the acceptable range, they're just coming off a really hot day, right? It's been a long day for them at work. And so, I want them to experience a cool evening, you know what I mean, so that their cortisol levels are lower. So, I like to fish in the morning on hot days, rather than the afternoon.
And I also just try and make sure, you know, to me, this is where the sportiness, right, if I'm going to use smaller rods and go for lighter gear. I'm going to shoot that stuff at this time of year, you know what I mean, and try and use stuff that I can get the fish in a little faster.
And if that means I have to go up 1X in tippet and a little bit bigger fly and catch fewer fish, I'll do that, right? That's okay, because I want to be on the river. So you know what I mean? You're using gear that is appropriate, so you're not worried about breaking a bunch of fish off, right? You're just trying to... And maybe that sacrifices a couple that you catch, a couple of those really picky ones.
Elsewise, I mean, keep the fish wet, right? I love what keep them wet is doing. I think this is really important because I've got enough pictures of fish out of water, right? I did it as a kid. We've all done it. I don't need another fish picture out of water. And I don't want to judge everybody for that. But so for me, just keep them in the water. And most of the time, I'm not even taking pictures on hot days at all, right? I just want the fish in my hand really fast, or maybe I don't even touch it, just grab the hook with some pliers while the fish is in the water.
You're doing all the baby steps, right, you're treating them with kid gloves. So, you know, again, if I net, I'm going to use that knotless net. And that's great. I'm going to try not to really touch that fish that much, right? I use my pliers a lot or forceps during warm water so that my hand doesn't have to touch that fish and risk yanking some of the slime off, maybe pulling a few scales off.
And then, I think, the other part, for me, is that I do stop fishing even in the mornings, if we go through a week where it's getting up above 70 degrees during the heat of the day, every day. And it's just cooling down to 66 or 68 in the morning. So, I have that threshold.
But generally, I would just say again, fish the mornings because they've had appropriate, you know, a longer period of time to recover and cooler evenings. Second, use the right gear. That means you might sacrifice some of the smaller stuff because you just want to land it as quickly as possible. And three, is just minimize the handling, try and keep the fish wet. You know, whatever it takes.
I think those, to me, are kind of the three things that I try and adhere to. And I remind myself all the time that we participate in a blood sport, too. Even with the best behavior, some fish will die, unfortunately.
Tom: Yeah, they will. Another question. Are you done with your answer? I'm sorry if I cut you off.
John: No, yeah, I was done. Thank you so much.
Tom: Okay. So you're on a stream. And the water temperature is 70 degrees, so you're not fishing. Maybe you're doing some research or observing trout or whatever, and you see somebody fishing. And this person catches and releases a fish, and the fish swims away, and you say, "You really shouldn't be fishing, you know, it's 70 degree water temperature." And the person says, "Well, that swam away fine. It's going to be fine." What would you tell that person?
John: You know, that's a great response, and that is the most common response. My first response is, "Anybody who has been a big game hunter or a bird hunter, how many animals have you shot that looked like they ran away or flew off just fine?" Lots of them, right?
I mean, very rarely, birds... If you're a pheasant hunter or a duck, lot of times they'll keep flying. I mean, maybe you see a feather or two drop, right? And then, you wound up 400 yards down the road, and there the thing is dead as a doornail.
So, I just go back to is that it's really hard to kill the fish. You know what I mean? You had to have gone to extreme conditions and poor handling and whatever else to get that fish to roll over on its belly. So, it's normal for a fish to swim away, even if it's in really, really bad shape, right? Just because it swims away doesn't mean it's in good shape. But it's a notion that sometimes people get.
And I would say this, "This is why we have science because what we do know is that when those fish swim away, their cortisol is higher or remain higher in their body for a longer period of time." We also know that if people handle them poorly and expose them to air for longer periods, if the fish is already been compromised, that can result in worse effects, even lethal effects.
So, I go back to I think the science has answered that even though they swim off, we know they're impaired. And that's one of the reasons they're swimming off so rapidly, right, because they literally they thought they were going to die? You know what I mean?
And so, I go back to that, you know, just a lot of things that we do, animals will run away or go away, and they can be entirely compromised and still run for quite a distance because that fight or flight instinct and the adrenaline rush is so powerful.
But we know that even when they swim away, there's some impairment. Unfortunately, most of the time these impairment levels are pretty low. But yeah, you know what I mean. It's a hard argument to make, but I've heard that one a number of times.
And it took me a while to understand that. I get what they're saying now. At the same time, we know from science that, you know, there is some effect when they swim away.
Tom: Yep. Yep. How do you feel about barbless hooks?
John: Well, I think they help. I only use barbless. And that's mainly because that's what my dad used growing up, and I release almost all the fish I catch. Now, the times that I have used barbed tend to be when focused on hatchery summer steelhead.
But for trout, I think it does cost you some fish at times, you might lose a few more on a barbless hook. But I think the handling, you know, the ease of removing the hook is so much simpler. It's a lot easier to remove a barbless hook on a fish.
And I think we've all been in those situations where you forgot to pinch the barb and you go to just, you know, pull it out with your forceps, your finger. And then you're like, "Oh, no, the barb is in there." And then you're squeezing the fish, right? You're moving its jaw around. People may not appreciate probably how bad those injuries can be, because that's just cartilage in most cases in the fish, and that's how these fish end up with their torn maxillaries, for example. Right?
So I love barbless, I just think, you know, if there's something I can do to make it easier on the fish and reduce the amount of time that I have to handle them after I've had the exciting part of hooking and catching one, then that's really something that I'm going to try and do to get back to them. And I also think that if you're dry fly fishing and sometimes those fish, they can just engulf that down the tongue and I'll end up cutting my fly. I think it's easier for that hook to work its way out on its own.
Tom: Yeah, they fairly get out quite easily within a matter of minutes, particularly a barbless hook.
John: So, yeah. And so, I come back to the...I don't think a barbed... I mean, it's like all these things. I don't think, you know, in and of themselves as one single effect, they don't really create horrible, miserable effects on fish. It's the cumulative impact of a little thousand paper cuts. You know what I mean?
And so, what you're trying to do is just minimize all those little cuts, so that we can give them the best chance possible to continue on living their life as they were and hopefully be caught by another person and still reproduce successfully so they can continue the next generation.
Tom: Hopefully not caught by another person the next day when their cortisol level is still high, right?
John: This is where we get to and there's work on bass on this, like they found that you can actually select genetically against really bold animals by catching and releasing them so many times. You know what I mean?
And bold animals usually do pretty well in nature, right, because aggression often works out pretty well in nature. And so, there are these tradeoffs that we have to think about once the level of catch-and-release mortality starts to, you know, reach the mortality level that we had when we were killing fish then that's a problem, right? So, one of the issues in Montana is just simply the crowding, you know, that is happening now.
And so, I think these are the things... We see it in the steelhead world, too. How do you balance this? Which is why there are places... I go back to Atlantic salmon, how many of those places have limited entry now? And that's kind of how their fisheries have ended up.
And I don't know what the future looks like for us as anglers, I would hate to think that it's going to be a bunch of private property and pay-to-play beats. I don't think that is the future, I think we've got a lot of public land. But at the same time, if we want to ensure that fish remain on those public lands at fishable levels, I always go back to, "We have to take care of the fish and then the fisheries take care of themselves."
So give them some of your best effort in terms of just taking care of those paper cuts, I think, when the fish are going through tough times.
Tom: Yeah. Well, John, that is a great discussion. And I think a lot of people learned a lot. I know I did. And I'm certainly going to change my habits this summer. And I hope that everyone who fishes for trout or any cold-water fish pays attention to this and treats each one of those fish as though they're precious gems, because they are.
John: Yeah, they really are. I don't know what the future holds. But I do know that, again, if I can reduce my impacts for one or two months in a summer here or there and that really helps ensure that we're going to have fisheries 10, 20, 30 years down the road, I'll take that to ensure we have something left. But, yeah, I'm with you. It's just increasingly made me need to rethink my approach to fishing as climate change effects unfold.
Tom: Yeah, yeah, me too. Absolutely.
John: Well, thank you so much. You know, I always... Tom, I can't say how much I love talking to you because I could sit here and yap forever with you, but that's the way you want.
Tom: I know. It's so much fun.
Tom: Well, you bring in the fishing perspective that I think all these decades of experience you have, you're really reconnected back to fish. And I think that's important because the reason that we do all of this research isn't just... I mean, I love fish, right? I would do this even if I didn't fish for them. But at the same time, the reason we're doing most of this work is so that we can take care of the fish because people love to fish for them, you know?
And so, that's the value of continually finding out a little bit more about the fish is, "Oh, the cortisol might do this or that. Maybe we have to rethink about fishing. Or maybe the cortisol isn't that bad here. Maybe the fish don't get caught as frequently here. We're all okay."
But I do think it's a time for all of us to probably look a bit inward and think about it, what do we want our future to look like, and how are we going to go about, as Gandhi said, I guess, "being the change we'd like to see"?
Tom: Yeah. All right, John. Well, thank you so much. We've been talking with John McMillan. John, where do you live? It's in Washington, right?
John: Yeah, it is, near Port Angeles, Washington. So, I'm out here on the very western tip of the Lower 48.
Tom: And John is a lifelong angler and fishery scientist. So thank you for sharing your vast knowledge with us today.
John: Thank you, Tom. I always appreciate it, and it's just a blast talking with you.
Tom: All right, John. I'll talk to you soon, hopefully.
John: Thank you.
Tom: Okay. Bye bye.
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