Thermocline

[Rusty Lee]

I read a lot about crappie being really deep in summer/winter then I read elsewhere that fish don't generally go beneath the thermocline because of oxygen levels. Am I missing something?


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[Speck Beck]

I fish the Green River Lake in Ky and when the water temp gets in the high seventies I pull up the lake info from the Core of Eng and look at the dissolved oxygen level which will show the depth of the thermocline. If you look at where greatest change in temp there will a decrease in dissolve oxygen and most fish will not sustain life for very long period of time below the thermocline however base on my electronics the thermocline is different in different parts of the lake.
By looking at the COE info and electronics I see the crappie above the thermocline.

[doggone]

Once you get use to seeing it on your sonar then you can experiment with that on your own body of water. Say the thermocline is at 26 ft in 32 ft of water,then in a lake that the average depth is 30 ft or so....I would say that fish found on a brush pile in 24 ft of water as "deep". Generally speaking though remember that fish will use deeper water in lakes that are clearer and deeper,and shallower in dingy water with an overall shallower depth.Typically in a lake with deepest water of 60 ft say I would expect to find the "deep fish" around 30 ft or so. A lake with 100 ft water or more maybe 40 to 60 ft is possible. I generally do not find fish in the absolute deepest water...except in a really shallow lake (or river) say 30 ft deep or so deepest water.

Some species like catfish will hang out around the thermocline,you can't see them on some graphs sometimes...won't separate the return of the thermocline and the fish.

Several things factor into that,clarity,actual temp difference,actual water temp average, how close the cline is to the bottom ,the bottom type ,etc.


This is a good thing to experiment with and learn on the water .

[CrappiePappy]

I read a lot about crappie being really deep in summer/winter then I read elsewhere that fish don't generally go beneath the thermocline because of oxygen levels. Am I missing something?
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No, you aren't missing anything. Thermoclines set up at different depths in different bodies of water, and in different depths of the same body of water. They don't set up until the upper water column gets much warmer than the lower water column, which is mainly a Summer deal. When Fall temps start dropping, the upper water column gets colder (cold water is heavier than warm water) and drops down into the lower water column, mixing the temps & oxygen content. This is called "turnover". The thermocline won't appear again until the following Summer warm up, so it's not a concern during the late Fall/post turnover time thru the late Spring/early Summer warm up time.

And, yes .... you are correct that fish will not stay "below" the thermocline depth, as there is not enough dissolved oxygen at that depth to sustain much activity.

[Cane Pole]

Some folks confuse thermocline with plankton migration.

[NIMROD]

Thermacline sets up different in some lakes . Nimrod being a shallow lake if one sets up it ends to be about 8'. I see Shad and predators (Crappie) in very shallow water even in 100 + degree temps . Trotliners must float lines or Catfish die very quickly in summer.

[Crestliner08]

While it's true that warm water fish will stay at or above the thermocline, not all fish do. Char (lake trout, brookies and even big pike) prefer going below that level, as they are what we refer to as cold water fish. Best bet (for panfish/crappie) is to target points, humps and other such off-shore structures that are at least the same level as the thermocline and above.

[wicklundrh]

Crestliner is spot on in his statement. CrappiePappy has a good explanation of what happens however, every fish is different and every lake is different. Some lakes, the fish simply cannot live in the warmer water above the thermocline. It is just too warm for them. In lake Michigan, where we have thermo changes all the time, in mid summer, the top 50 feet of water can be as much as 60 to 70 degrees. Way too warm for a salmon, steelhead, or Lake trout to survive in. They simply boil in the heat. They will be around the thermocline simply because that is where the bait is at. For lake trout, they live on the bottom soooo, they are always below it. Same with many other bottom feeding fish. Not all fish are created equal and about the time someone says "you cannot catch them here" you will catch 50 of them.

[NIMROD]

It depends on the lake as some are void of oxygen below the thermacline . The decomposing vegatation and things eat up all available oxygen in some lakes making it impossiable for fish to survive below it . Most warm water fish like Crappie can tolerate very warm water if there is plenty of oxygen . The bait fish will also be there in shallows or suspended above the thermacline .