Scientific Thermocline (lots of pics)

I did a little experiment this morning to show scientifically EXACTLY where in the water column is the TRUE thermocline and how do the fish relate to it. Is the thermocline the dense portion of the sonar returns? or just above it? Or is it at the very very start of the returns? Is my 1197SI sonar accurately measuring the depth of the thermocline? Lets find out..

Here is a pic of my initial sonar shot taken this am. Did it in several colors but chose this one.

http://i123.photobucket.com/albums/o...linesonar1.jpg

Here is one I took at a slightly different area a month prior in 3 way mode showing sonar, Down Imaging as well as Side Imaging.
http://i123.photobucket.com/albums/o...r/cline6-1.jpg

To get the thermocline to show up you need to make sure your in Split Fire MAX mode. I used 200/83 dual beam and I cranked the sensitivity up a pretty good bit.. I believe I was around 15 with sensitivity

Before I started this project I involved a buddy of mine. Some of you might know LTBama from the BFHP. I remembered a post a while back where he purchased a Cline Finder temp gauge and I asked him to borrow it.. Very well made gauge by the way. I cleaned the temp sensor and took my temperature with it by mouth and it actually showed 97.0 degrees.... Pretty darn accurate by my book. It has 50ft of cord and the cord is marked in 2ft intervals with the actual depth written on the marks which helps in case you lose your spot you can just look at the depth marked on the 2ft interval marks. It also winds up like a carpenters snake? Very solid unit.

http://i123.photobucket.com/albums/o...linefinder.jpg

Well since I only had 50ft of depth to work with on this unit (which is plenty). I went to a fairly deep place and started measuring the temperatures as I go down the water column. I was very surprised the the temp was CONSTANT down to 22ft of water. I actually thought the unit was broke but I brought it back out of the water and when it hit the air temp it moved appropriately?? So back to measuring water temps.

Here are the coordinates that I recorded and their respective depth/temperature.

0ft 88.2 F
2ft 88.2
4ft 88.2
6ft 88.2
8ft 88.2
10ft 88.2
12ft 88.2
14ft 88.2
16ft 88.2
18ft 88.2
20ft 88.2
22ft 88.2
24ft 88.1
26ft 88.0
28ft 86.4
30ft 85.0
32ft 84.6
34ft 83.3
36ft 82.8
38ft 82.1
40ft 81.2
42ft 80.8
44ft 79.8
46ft 79.5
48ft 78.8
50ft 78.4

I decided to take this one step further and graph the actual coordinates onto the image. I made the image bigger so that all my graph coordinates would fit. This way you can overlay the cline finder data with an actual sonar image and notice the effect easier. The image turned out fuzzy because I saved the photoshop things on there a few times

http://i123.photobucket.com/albums/o...linesonar2.jpg

Now here are some shots of fish screenshots from this morning so that you can piece the data together.

Looks like the fish are topping out right at the 27ft barrier just like the temp graph and sonar overlay image shows...
http://i123.photobucket.com/albums/o...inefinder1.jpg

I showed this one specifically because it shows a fish well below the thermocline. That one fish around the 38ft mark probably won't be at that depth for long due to lack of sufficient dissolved oxygen.

http://i123.photobucket.com/albums/o...inefinder2.jpg

So in conclusion the 1197SI sonar IS a good indicator of the depth level of the thermocline. It also shows that the leading edge of the thermocline returns seems to be the cutoff point for the depth level of fish and not the densest portion of the sonar returns.

So the strategy for this type of lake is to find deeper cover that intersects the 27ft depth mark. It can be offshore (ahem) or it can be 27ft deep near the shore. Bait choices are fairly easy. Anything that you can countdown and swim to the 20 to 25ft barrier but off the bottom for suspended fish. Some swimbaits, underspins and spoons are just a few good bait choices. etc

This is what you are looking for.
http://i123.photobucket.com/albums/o...linefishes.jpg

If you do everything right...

http://i123.photobucket.com/albums/o.../bullproto.jpg

Well done----Good readin

I used to know a fella named Tmike....uuuuuugggglyyy dude too. He had a penchant for swimbaits above 12", spotted bass up to 28 pounds and was really excited about tripple fish line for a while. Anyway, that Tmike couldn't be you on account of that Tmike got married, had a kid and wouldn't have been bored enought to go out and waste a whole day fooling around with a thermometer, especially for the benefit of a bunch of low rent Crappie fishermen.

But you do look a lot like that Tmike though.....maybe a touch uglier and maybe a bit thicker in the middle. Maybe you know him though.

Wannabe...

There was this one guy I knew named Wannabee. He had 2 sons. Gonnabe and gottabe and his wife's name was IS LOL. Boy he could wire a mean boat too. I still got them pics too!! Blackmale for life.

BTW this is the SAME T Mike that guided Wannabee to his infamous PICKWICK rally win. What was it. Big fish of Day 1, Big fish of the entire tournament, Biggest total weight and you ONLY weighed the only fish of the entire 3 day tournament!!! Your only claim to fame and your welcome :)~ Now you fish for fish that fight like a wet sock and live in Grenader Mississippi :). What happened to you dude? You had a bright future when I left you in Madison! :). LOL

Great pictures and explanations, but I don't see the thermocline on the last picture. Am I missing something?

Great explaination....Just wondering though if the water temp is the same all the way to the thermocline what makes the fish want to be on the edge of the thermocline?

Quote:

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Originally Posted by AUTiger

Great explaination....Just wondering though if the water temp is the same all the way to the thermocline what makes the fish want to be on the edge of the thermocline?

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Absolutely nothing keeps them at the thermocline. Unsure of this theory but I think like most fish they are "EDGE" oriented. Not only is there a temperature "EDGE" but there is also a DO "Edge" in this instance as well. The sonar image shows this pretty clearly ie fish scattered throughout.

They always told me theres no oxygen down there

T- Mike - Great Info - Thanks

Actually, it's not that there's no oxygen and not all fish respond the same way. For instance, here's a temp/oxygen chart for a local lake with the O2 levels for each depth:

D Temp Oxygen
0 82.4F° (28.0C°) 7.5
5 82.4F° (28.0C°) 7.5
10 82.4F° (28.0C°) 7.4
15 82.4F° (28.0C°) 7.3
20 81.3F° (27.4C°) 4.9
21 80.4F° (26.9C°) 3.6
22 78.1F° (25.6C°) 0.4
23 76.5F° (24.7C°) 0.2
24 75.0F° (23.9C°) 0.2
25 73.9F° (23.3C°) 0.2
26 71.4F° (21.9C°) 0.1
27 70.9F° (21.6C°) 0.1
28 69.1F° (20.6C°) 0.1
29 68.0F° (20.0C°) 0.1
30 66.4F° (19.1C°) 0.1
31 65.5F° (18.6C°) 0.1
32 64.4F° (18.0C°) 0.0

A thermocline isn't a hard line--it's a band of depth. You look for a temp drop of 1.5-2 degrees and that's the start. Above, the t-cline starts between 15 and 20 feet and is complete at 22 feet. Crappie can tolerate well down to about 4 parts per million O2. Fish like lake trout can tolerate alot less. And crappie don't always ride right on the t-cline. The other day, the t-cline was at 13 feet, but we caught fish all day long at 6-8 feet, sometimes shallower, as well as at 13 feet. The t-cline can eliminate alot of water, but I always try everywhere between the t-cline and the surface.

Thanks T. I definately saw the same stuff a little earlier on the local lake.

This is quite a good post. Very informative with great illustrations.
Thanks

great stuff guys....thanks!!

Good info. Thanks.

Quote:

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Originally Posted by T Mike

Boy he could wire a mean boat too. I still got them pics too!! Blackmale for life.

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Yer bluffin' bass boy.

Wannabe...

thanks for the info. great stuff.

this should be made into a sticky.

You are one sharp dude. THANKS FOR THE INFO

Here's a tip to maximize the use of your fish finders display area is once you find the thermocline is to maximize the screen area for "fishable" waters. Since most fish cannot survive below a thermocline since the oxygen level is too low. Instead of looking at the entire water column use the MAX Depth Feature and remove the "unfishable" water from the display and it will increase the amount details you can see in the waters fish can live.

Here is an image of the Humminbird 798c in Auto Depth Mode:

http://i36.photobucket.com/albums/e6/imonem/S00001.png

If your targeting fish or thermocline is at a know depth you can set a MAX Depth like I did in this image at 40 foot and increases the size of the details and makes it easier to target the fish.

http://i36.photobucket.com/albums/e6/imonem/S00059.png

IF you set Max Depth it will place an "M" next to the Bottom Depth Reading to show you are setting the Maximum Depth to view. Make sure you reset to auto if you want to navigate and see the bottom.

Thats great stuff, but is it a thermocline or a chemocline? Some say they
are analogous, I've been reading alot about this and NOAA is doing a very
intense study. That whole crowd is split, some say a thermocline is 39* with
only a couple degrees varience through-out the year. The chemocline guys
say its the specific gravity that seperates them, with hydrogen sulfide
being the main ingredient, along with others including tannic acid. Basically
the by-products of decomposition. Anyhow you look at it we're about to get
even more advancement and a better understanding of what exactly we are
seeing with our electronics. I think of the water as a pair of "photogray"
glasses, the deeper you go, the less light there is. Clarity and turbidity
affect plant growth, which in turn relates to DO, but I'm no rocket scientist.

Quote:

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Originally Posted by frank lawhead

They always told me theres no oxygen down there

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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

Quote:

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Originally Posted by Wannabe...

Yer bluffin' bass boy.

Wannabe...

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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.:p

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

Quote:

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Originally Posted by DoubleGobble00

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?

DoubleG

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Yep, temp matters, as does proximity to cover, especially objects that provide alot of shade, and a nearby food source.

Here's something that I can't remember being said--the depth of the thermocline can vary in different portions of a lake. It'll be stronger and establish earlier further from rivers and other water sources and in shallower portions of the lake. Once established, it can take alot to break it up--thus the famous fall turnover that happens when surface water cools and sinks below the thermocline, eventually mixing the water sufficiently to destroy the thermocline. I don't think a few days of wind will do it, as wind essentially just affects the first few feet of water and most thermoclines set up at least 10 feet deep or deeper. That's also why you seldom get a thermocline on very shallow lakes (I'm talking 10' or less average depth)--the wind won't let it set-up.

Lot of good info here, thanks guys ;)

I have never seen a thermocline here on Ky Lake.

Thermoclines normally occur in lakes with little or no water movement. Since Kentucky RLake is more a River Lake you probably won't see a Thermocline. I rarely see them on Truman Lake in Missouri when we have normal releases do to the amount of inflow and outflow of water. There are clines but not Thermoclines.

True; we've got them on river lakes in Ohio right now, because we haven't had enough rain or water flow to prevent it (dam flow is very low and water levels are actually dropping a bit).

Very good info. I don't turn my switchfire on set the sensitivity pretty high to get the thermocline.

Very good read....there are some smart guys on this site.

One of the most difficult things to figure out is if is a Water Density Change, Temperature Change or actual Thermocline (Absence of Dissolved Oxygen). The easiest way is to see where the fish and baitfish are since they can't live in low oxygen leaves very long. If they are above the Cline you might very well have a Thermocline.

Some would say this image has a Thermocline...I doubt it because the presence of fish below the line...

http://i36.photobucket.com/albums/e6/imonem/S00304.png

or this Humminbird Side Image...

http://i36.photobucket.com/albums/e6/imonem/S00294.png

Sometimes it's plankton and microscopic organisms rising in the water column.

Great read guys. Alot of good info. Fished-out, thanks for chiming in on the river lakes. I fish one of those OH lakes you speak of, EF, and always wondered why some summers the fish will be found deeper than.....well....this year. Guess it's the presence or lack of a strong thermocline from year to year. I guess I always assumed that since the lake was always "moving" that a true thermocline wasn't there. This is the first year I've payed much attention to it really. This post clears up a lot of questions. Definitely needs to be made a sticky.

Doug is correct about seeing fish below the cline. Here is what made me want to do this study. This was taken a few weeks earlier

http://i123.photobucket.com/albums/o...r/cline1-3.jpg

Now are you confused??? LOL