Thread: Scientific Thermocline (lots of pics)

Originally Posted by frank lawhead

They always told me theres no oxygen down there

Frank, Good question. The answer to your question is YES and NO.. It depends on the lake.

Find enclosed a water profile for Lanier. Notice the DO levels are inhabitable up to 100ft deep. The cline is between 20 and 40ft.. So in this instance you can catch fish well below the thermocline..

Depth/Temp/DO (ppm)
surface / 86.5 / 7.1
3.3 / 86.5 / 7.2
6.6 / 86.4 / 7.3
9.8 / 86.4 / 7.1
13.1 / 86.4 / 7.3
16.4 / 86.0 / 7.3
19.7 / 83.5 / 7.9
23.0 / 81.0 / 7.9
26.2 / 77.9 / 7.3
29.5 / 73.0 / 6.9
32.8 / 68.2 / 7.4 Thermocline
36.1 / 63.5 / 7.2
39.4 / 60.4 / 7.4
42.7 / 58.5 / 6.9
45.9 / 56.7 / 6.4
49.2 / 55.4 / 6.4
52.5 / 54.5 / 6.2
55.8 / 53.4 / 5.9
59.1 / 52.5 / 5.8
62.3 / 51.8 / 5.3
65.6 / 51.4 / 5.2
68.9 / 50.7 / 5.0
72.2 / 50.2 / 4.8
75.5 / 49.6 / 4.5
78.7 / 49.3 / 4.3
82.0 / 49.1 / 4.3
85.3 / 48.6 / 4.2
88.6 / 48.4 / 4.1
91.9 / 48.2 / 3.9
95.1 / 48.0 / 3.8
98.4 / 47.8 / 3.5
101.7 / 47.7 / 3.4
105.0 / 47.5 / 3.1
108.3 / 47.5 / 2.7
111.6 / 47.3 / 2.6
114.8 / 47.3 / 2.5
118.1 / 47.3 / 2.4
121.4 / 47.3 / 2.3
124.7 / 47.3 / 2.1
128.0 / 47.1 / 1.9
131.2 / 47.1 / 1.8

Originally Posted by Wannabe...

Yer bluffin' bass boy.

Wannabe...

What you wanna wager on it???? Don't make me fling poo . LOL.

This is the best post concerning the thermocline i have ever seen,i am impressed thanks for taking the time Mike.

T-Mike brings up an interesting point on the thermocline with the Lanier example. Essentially, it can be there and it may not matter in terms of fishing. The ocean guys would define it as the greatest amount of temperature change in the least amount of depth change, which is what the chart shows. But all I care about is whether the water is mixing---whether there's a physical barrier that prevents oxygen from moving between the upper and lower water layers. A weak thermocline doesn't really accomplish much in that area. In the example I gave, there's a well-defined water depth range that shows that the water's not mixing--what I would call a strong thermocline. Not all lakes get a strong thermocline and some lakes only have one in some years, but not other years. Bottom line--if you've got a well-defined strong thermocline that prevents water mix and therefore oxygen mix, the fish can be anywhere between the thermocline range and the surface. From there, you look at preferred temp range, forage proximity, shelter, etc--all the stuff you would consider anyway, just in a narrower band of water depth. A thermocline can help you cut down on the amount of water you have to consider, but it's not the whole answer. And your sonar can help you find a well-defined strong thermocline. I'd be curious to know if the Lanier thermocline example would show up on a sonar all that well.

Hate to barge in on the scientific stuff here guys but DougV stated the wrong menu for what he did. You should use the “Lower Range” menu (and possibly the “Upper Range” menu) to set your unit up to display only part of the water column.

The “Max Depth” menu will stop the unit from listening past the menu setting point and may not allow your Humminbird to show a digital depth reading.

Exactly correct Greg...I sometimes forget the "Politically Correct" Name but hit when in Sonar View hit Menu button once and there it is Lower Range...Thanks for the correction.

Good read.

I ain't found no "Politically correct" button yet. If I do, I will surly disconnect it.

This is a great post with a wealth of information... I thought about it a good bit the last couple days. An area lake near my home is suppose to have a thermocline around 12 feet.... but I see fish on my 898 well below 12 feet. It is good to know that there is still some oxygen below the thermocline... just not as much oxygen since it is not well mixed. Also, I thought about why they like the thermocline line... Two reasons come to mind. That being oxygen and temperature... I am sure all fish have a preferred temperature kind of like us. We can live outside in 100 degree weather but we prefer 70 degree weather inside our house. Also, the more oxygen the more active they can be so it makes sense that the less active fish are deeper in the cool waters just to be sluggish. Maybe they have their bellies full and just want to sit in there easy chair a while and be comfortable.

I assume the thermocline would be stronger (greater change in temp over less depth) and closer to the surface when you have several days with little to no wind. The wind seems to be the greatest mixing factor... Also, when you have some very windy days the thermocline would be weaker and deeper.. Does that make sense?

Next time I am out I am going to try and locate the thermocline with my 898. I could not see it on Max mode last time, but I didn't realize you could turn up the sensitivity while in max mode. I thought max was max.. good to know it is not...

DoubleG

got to ask, is there a reasonably priced way to measure DO????--shu

Here's one on Cabelas Website..not sure the quality as I don't own but might be fun to play with:
http://www.cabelas.com/link-12/produ...cm_pla=Primary

Here is a whole list:
http://www.thefind.com/pets/info-oxygen-meter

Thanks for the info Doug, after looking at satisfaction results that idea will go back on the shelf for a while.--shu