Little River Outfitters Forum

Little River Outfitters Forum (
-   Fisheries Management & Biology (
-   -   Trout Mortality (

snaildarter 08-13-2007 11:45 PM

Trout Mortality
Hi All,

With all the talk of high temps, low water, trout death, and Byron's canceled vacation and classes, I wondered if anyone knows of some good, real data showing the relationships of the above. I've no doubt that stressors increase the mortality of fish; I just wonder what the actual numbers are.

I've been googling around this evening, looking for such numbers. Here is what I've found:

- In the Park, 65% of trout die from weather related events every year
- In a study on the Gallatin, of 172 fish that were caught between the temperatures of 45 and 73 F, only one fish died within 72 hours of being caught.
- A study showing Brown Trout growth was maximal at temperatures between 65 and 75 F (the author noted that some other investigators found trout mortality increasing at these temperatures, and he guessed that maybe trout in warmer climates have genes for surviving warmer temperatures).
- Wild trout survive high temperatures better than stockers (duh)
- Lahontan Cutthroats live in relatively hot areas for trout, and have near zero mortality even when temperatures climb to 79 F for an hour a day
- Another study showing about the same thing with Bonneville Cuts

I've heard a lot of talk about rules of thumb like "I don't fish water above 68," but I haven't seen the data to back up a claim like that.

It seems to me, that maybe C&R in these high temps in the Smokies doesn't really cause much mortality, or maybe a better way of saying that is that maybe whatever extra mortality it causes might not be significant when compared with all the other causes of mortality. I've been told by fisheries folk that what limits trout biomass in the Smokies is mostly just the low fertility. If that's true, then maybe killing a few trout simply makes the remaining fish larger, until the next spawning creates more competition again. In fact, without that 65% weather mortality, maybe we would have even more even smaller fish! Maybe fishing 75 degree water in the Smokies is not such an awful thing. Of course I don't really know, which is why I'm asking everyone for whatever studies, or even anecdotal evidence, you can come up with. I think studies done on stockers in tailwaters would not be very relevant, but might still be interesting.


ijsouth 08-13-2007 11:50 PM

Good food for thought...and speaking of food, it probably wouldn't be a bad thing to keep a few fish once in a while. Like most people on this board (I suspect), I release almost all my fish in freshwater - in fact, I haven't kept a trout caught in the park. However, I've heard about what happens after a major mortality event, like a flood; the average size increases, while average fisherman catch rates stay about the same. So, some selective harvesting might be a good thing.

Of course, the majority of the fish I catch fall just a bit short of that magic 7 inches, so the point is often moot...;)

lauxier 08-14-2007 05:51 AM

trout mortality
I started keeping Park trout a couple of years ago because trout caught out of these waters are so good to eat--stockers and farm raised trout do not compare---you would think that Park trout losses of 65%,would be readily observed with dead fish floating up--

Rog 1 08-14-2007 08:26 AM

Anyone who has ever fished a farm pond where no harvesting occurs knows the effect....tons of tiny fish.....any water can support only a given number of fish ..... the Park tried to fish out Tremont one year for a brookie experiment....all fish but brookies, no matter the size, were required to be brought out.....could not get all the bows but the result was the next year the average size went up 1 - 2 inches.....after a while things returned to normal and the sizes dropped proportionately.....

ijsouth 08-14-2007 09:20 AM

You know, it doesn't matter what species you're talking about - wild fish taste so much better - much firmer flesh. It even extends to shellfish; Louisiana has had a promotional campaign for the last few years, encouraging people to only buy locally caught shrimp, instead of the farmed stuff from Asia. Now, the promotion is primarily aimed at helping out local shrimpers, who are getting killed by the imports, but it's true - they do taste better.

CinciVol 08-14-2007 10:15 AM

I think this is a very interesting topic as well. Is it possible that we could try to put a silver lining on the drought of '07 in that it may "cull the herd" of wild trout in the mountains and result in a period of bigger fish in the coming years just as an increase in harvest might do? Just something I was wondering about as I was driving by the (very) Little River the other day.

PeteCz 08-14-2007 04:00 PM

A very interesting topic. Here is a good study of Trout in Southern California. One point brought up is the variation is what optimal conditions are for trout in other parts of the country (Pacific NW v. So Cal). My guess is that trout here in the Southern Appalachians are closer to So Cal trout than Oregon)

The top end of good growth was almost 72 (22C)! and that growth dropped off at 77 (25C).

Maybe we are overly concerned about temperatures. I think the most worrisome aspect of our weather is the drought. I think that has much more to do with stress than water temp.

kytroutman 08-14-2007 07:46 PM

I know this is probably going to step on someone's toes, but after fishing in the Smokies for more than 35 years, the issue of trout mortality is real and its unfortunate that it is not taken seriously. If the issue of mortality was not a factor, there wouldn't be a need to schedule stream times such as now is occurring in Yellowstone and many of the other streams. Trout are extremely sensitive to stress and their ability to survive a five minute fight in low water and stressful temperatures is greatly diminished in the circumstances now facing the Smokies.

snaildarter 08-14-2007 09:55 PM

Thank you all for your opinions! I think, to come to a truthful position about something like this, you can't worry about stepping on toes. So don't worry about that in this thread. The world is full of unanswered questions and correspondingly bad policies simply because people are afraid to rock a boat (Bay of Pigs comes to mind...)

So far, we've only dredged up one more study (thanks PeteCz!). It would certainly be nice if more of us could cough up some more numbers, if you have them.

Kytroutman, it would be wonderful if we could find what data they base such a strong policy decision on. I'll look for that. If I find it, I'll report it back here. I will say that what happens in large western rivers with their sparse tree cover and large, sprawling acreage doesn't seem nearly as like our small-mountain-stream-Smokies as say, So Cal streams. It may be that small trout survive high temps a lot better than large ones, as some bass studies show. And well, the Smokies are full of 6-8" fish, as opposed to 15-18 " fish everywhere in the Yellowstone area. It could even be that that some of the factors causing the lethality in the Yellowstone area could be the same factors causing the fish to grow so large and abundant! Like say, the Firehole keeping the Madison at better growing temperatures for some of the winter, and the higher fertility loads (and thus higher pathogen loads) of western rivers.

As an example of something that people have long believed, and strongly, we could point to fishing for spawning bass. For many, many years it was common wisdom that you don't fish bass on nests, because that would impact their numbers. So streams were closed until after the spawn. Yet many studies have shown exactly zero impact on bass numbers when anglers are allowed to fish them off nests. The reality of that situation is that when you have a lake with a billion eggs, 99.9xxx percent of them die anyway. Killing a few million eggs just doesn't hurt anything. Slowly, policies have changed to reflect reality (I'm headed to NY in a few weeks and have read about locals being mad about biologists eliminating the spawning fishing bans on their local creeks and lakes. What that really means is that no amount of data can convince some people).

I feel that surely someone has the numbers that we are looking for. Policy decisions based on gut feelings are wrong more often than those that have good facts backing them up.

If we really are impacting the fish population during these high temps, then shouldn't our fisheries folks be closing our streams too? Or at least issuing some kind of official opinion? Also, does anyone know if the closures in Yellowstone are official, or if they are some kind of voluntary mouth-to-mouth thing controlled by the fly shops? I'm not passing judgment on it; I'm just curious.

Byron, if you are reading this thread, it would be interesting to hear your take on it. One can tell that you are very concerned about the fish, and it would help to know what things you've seen, heard, and read to come to the conclusions you have. Your opinion carries a heavy weight!

ijsouth 08-14-2007 10:16 PM

I think it has to be taken on a stream-by-stream basis. While Little River has been extremely low most of the summer, and Cosby almost dried up totally, to give two examples, the N.C. side had plenty of water and good temperatures, at least where we fished. If the water is low and warm, don't fish that area; chances are, you won't get a fish to rise anyway. If the temps are still in the "go" range (low 60s), it's a different story. Most of the time, I get a fish to hand in a matter of a few seconds - I keep my casts as short as possible. Just use a little common sense.

On the good side, I did see on the water vapor satellite loop that there actually is some moisture working its way into the atmosphere over the Smokies; the last few days, the air has been bone dry. It's pretty pathetic to be cheering for humidity, but you take whatever small victories you can. In the meantime, we might have a pretty decent storm (Dean) to deal with next week.

All times are GMT -4. The time now is 04:42 PM.

Powered by vBulletin®
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.