Low trout threshold temperature for fishing

[rrt]

When I was young, the icons of fly-fishing wrote that 40 degrees was the lowest temp for effective fishing and that 39 degrees was impossible, something I have found to be false. However, my water thermometer goes down to only 32 degrees, and that was the water temp today, and I didn't get a bite in water where I normally can catch at least a few trout. Yet, two days ago in 34-degree water, I landed a handful of fish, including several nice ones. Now for the question: What is the lowest water temperature that you think is realistic for possibly catching and releasing a few trout in a couple of yours? As of now, I think it's more than 32 degrees.

 

[pcray1231]

I've caught fish in sub-32 degree water. Thats right, supercooled, anchor ice forming from the bottom up! It's surely not as good as warmer water, but they'll feed in it.

I don't think you can define a minimum temperature. Anytime the temperature is outside of the trout's preferred range (roughly, say, 55-65 degrees), it's not the actual temperature, but rather the direction of change that matters. 33 degree water warming to 35, fish are likely to turn on. 37 degree water cooling to 35, and they'll be turned off. Same is true of water that is too warm, except your looking for the cooling trend instead of the warming trend.

One thing to keep in mind with winter fishing is that, with snow cover, it can be a little difficult to predict the trend. A warm day can easily cool the water with snowmelt.

 

[pete41]

," it's not the actual temperature, but rather the direction of change that matters. 33 degree water warming to 35, fish are likely to turn on. 37 degree water cooling to 35, and they'll be turned off." -that is a guy who knows what he is talking about-so true-
ironical if it gets comfortably warm outside the snow melt flips the switch to off-lol
see the gin clear water start to cloud enjoy the weather and scenery.

 

[WildTigerTrout]

I agree with pcray1231 and pete41. Could'nt have explained it any better myself. Fish have to eat all year even if the water is REALLY cold.

 

[Fishidiot]

I tend to agree with Pcray - it's more a matter of whether the temps are trending upward or downward. Strictly speaking, I'm not really sure what the bottom threshold is. In my experience, 42 degrees F seems to be right about the temp at which trout stop chasing stripped streamers and at which I switch to dead drift presentations right on the bottom. I've certainly caught trout in icy streams with temps at or perhaps below 32 but it's definitely tough - but they do remain catchable - just ask ice fishermen.

I also have a theory that mountain brookies are considerably more active at very cold temps (low 30s) than browns, rainbows or stocked brookies. Just a theory.

 

[jayL]

I would think the brookies would have to remain active at very cold temps. Otherwise, they'd be sitting ducks to predators.

 

[rrt]

I had used to subscribe to the temp change theory, too, when I fished almost exclusively with dry flies. I first saw that theory promoted by the late Leonard Wright in The Ways of Trout. But, I haven't found that to be so true as I have increasingly nymph fished. Still, with what you guys say, maybe I was just a lousier-than-usual fly-fisherman this afternoon.
Thanks for your replies.

 

[JackM]

rrt wrote:
Still, with what you guys say, maybe I was just a lousier-than-usual fly-fisherman this afternoon.
Thanks for your replies.

Don't blame yourself. I think the new moon tomorrow is the culprit.

 

[WildTigerTrout]

rrt, no sometimes the trout are just not hungry! LOL. Nothing more and nothing less.

 

[RLeep2]

I think the temperature trend takes primacy when we're talking changes from say, 36 to 40 or even 35 to 39 or some such.

I have considerable skepticism that the same phenomenon can be seen at work when we talking about changes where both numbers are in the low to mid-30's.

I think there is a baseline of about 35. Below that, very little happens. Right at 35, a bit more happens. If the water is 35 when I start and it goes to 39 or 40 over the course of the day, the effect on the fish is noticeable. If it is 33 when I start and goes to a peak of 35, the effect is negligible.

This has been my experience, anyway.

 

[JackM]

Cold-blooded creatures adapt to the environmental temperature by adjusting the body temperature and metabolism to suit those circumstances. We all know the metabolism slows at low temps and I would suspect this is the origin of a 40 degree benchmark. Below that, the trout will be in a slow-down and conserve physiology. They still eat, but they eat conservatively, awaiting better conditions where they can eat a little more carelessly. This can occur with a sharp upturn of water temperatures. It seems to stimulate the urge to feed more often or more recklessly. As RLee indicates, at very low temps, the difference in a very little feeding and energy expenditure and a very, very little of such is not so noticeable. Once temps have stabilzed, such as 5 days of high water temps in the mid-thirties, the temperature shock from a severe decline in water temps wears off and the fish resume their limited feeding activity.

 

[Stone_Fly]

Trout metabolism slows to nearly nothing below 40 degrees, they burn little energy and they take in only what they burn so they are much less active, when it get much below that it's barely worth the time it takes to get to a stream and get your stuff on for the number of fish you catch. I can be catching trout easily at 39 degrees, but let the afternoon warm up a few degrees above freezing and snow melt enters the water then the trout will suddenly turn off, the only reason I can connect to this behavior is water temerature change.
How do I know this? I take the temerature when I arrive and take it regularly during an outing.

 

[troutslammer]

I fished yesterday and the water temp was 36 deg. The trout were feeding real well and even chasing nymphs & eggs out of the fast water into the tail outs to get them , so i would have to disagree. Bottom line is if you come across hungry fish they will eat if the fly is presented to them in such a way that they don't have to move real far to get it (their feeding lanes narrow greatly )

 

[afishinado]

NOTHING is absolute in fishing, but with the temperature issue, I see a trout's activity level as a bell curve. The further away the temp is from the ideal which is 55* (+/- depending on the species of trout), the less activity / feeding. If the temp takes a swing to the center (more ideal temps) the fishing usually improves. If it swings away, the fishing declines.

 

[osprey]

Lakes in Minnesota frozen to the point where you can drive your car out there , ice measured in feet not inches , and they still catch fish , sometimes alot of fish. All the rest of the theories considered , fish like any other organism , eat when they are hungry and they have food available PERIOD.

 

[JackM]

afishinado wrote:
NOTHING is absolute in fishing, but with the temperature issue, I see a trout's activity level as a bell curve. The further away the temp is from the ideal which is 55* (+/- depending on the species of trout), the less activity / feeding. If the temp takes a swing to the center (more ideal temps) the fishing usually improves. If it swings away, the fishing declines.

What is the Y axis measured in terms of? My bell curve is like that but is squashed down significantly in the middle, which I would place in the upper 50s or low 60s after I consult my notebooks.

I also think when temperatures stabilize after having gone low, activity will pick up regardless of upswings in temperature. That is, the third day of fairly consistent water temps, even below 40 degrees will be a marked difference in activity from the first day at that temp.

Keep in mind....

 

[pcray1231]

Afish, if it were a curve, it'd be a skewed one. You list 55 as the optimum, I think it's probably closer to 60, but either way, we'll use 55. That would be saying things are equal at 40 and 70, 35 and 75, etc. In all of those scenarios, I think the colder temp is clearly better, I'll take 35 over 75 in a heartbeat. I think the right side of that curve would stay strong through the 60's and be nearly vertical above 70.

In the 50-65 range or so, I don't think temp matters all that much. Outside of that, I still subscribe to the rising or falling theory, though I do think that there's some dependence on absolute temperature. For instance, I'll take 35 and rising over 35 and falling in a heartbeat, probably even over 40 and falling, but perhaps not over 45 and falling. Likewise, 45 and rising certainly beats 35 and rising. So yeah, absolute temperature means something.

Of course, even then, temperature is only 1 variable. Time of day, hatch activity (both current and recent), water fertility, streamflow and clarity, cloud cover, and a host of other things still all come into play. For instance, I'd take a drizzly 40 degrees combined the first strong BWO hatch of the year over a sunny 58 degrees and nothing going on.

 

[afishinado]

THERE-ARE-NO-HARD-AND-FAST-RULES-WITH-TROUT, but IN GENERAL the best fishing is when temps are near the ideal (mid 50's - low 60's). I just cut and pasted a bell curve graph for demo purposes. Of the thousands of FFing trips I've made, on average, I caught more fish when temps were in or near the ideal range.

Jack and Pat, your mission is plot the activity levels and temps by .01 degree increments and mark it on the X & Z axis. Factor in the hatch quotient squared (of course) and mutiply by the 7.892 of the population density / hectare liter and divide by the square root of the macro density per square meter of stream, and we'll finally nail this thing down........:roll:

 

[pcray1231]

Now you're talking my language.

As always, using science for trout fishing is exceedingly difficult because of the numbers of variables and inability to isolate them. In those situations, the only way to learn anything is LOTS OF OBSERVATION. I think I'll go fishing.

 

[afishinado]

pcray1231 wrote:
Now you're talking my language.

As always, using science for trout fishing is exceedingly difficult because of the numbers of variables and inability to isolate them. In those situations, the only way to learn anything is LOTS OF OBSERVATION. I think I'll go fishing.

There ya go!

I'm goin' fishin' this AM! I'll prepare report on the temp and the correlation of trout activity and get back to ya....NOT!.....lol