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Old 08-13-2007, 11:45 PM
snaildarter snaildarter is offline
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Join Date: Jul 2006
Posts: 160
Default 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.

Thanks
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