Scientific Thermocline....

[Doug Vahrenberg]

A good friend of mine Mike Bucca did a neat experiment on Thermocline using his Humminbird and said I could share:

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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.

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.

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.

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

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...

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.

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.

If you do everything right... :newyear: :newyear:

Thanks again to Dugald for allowing me to borrow his cline finder unit..

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Now here's what you can do to maximize you screen area when you find a Thermocline.

Using Lower Range to your advantage especially with thermoclines to view only the "Fishable Waters"

He is an image of in Auto Depth Control on a 798c:

Now look at the size of the details when you cut out the "Non-fishable waters" in this case I set Lower Range to 40'

[motoman]

Great post Doug, very interesting!

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And to be friends with Mike Bucca! I'm saving my pennies for some Bull Shads!

[snagged in outlet 3]

Very cool Doug!!

And I don't even have a bass boat.

I think you did a great job on your experiment. Just like a good chemistry experiment, simple with easily documented results.

And it paid off.

SIO3

[Chris King]

Awesome post!

[Flippin]

Doug thanks for sharing that info. I think it was great and I enjoy learning details like this.

[Stragler]

Doug: Thanks for this great info. We read so much about the Thermocline and you have showed what is really is all about, once again thanks.

[sportshop]

so the difference between the surface temp and the thermocline is just 2 degees? or am i missing something.

[wallin]

That looks correct-lol I think, you sure do think it would be more-but I bet every lake is different.

Tom

[Matt Henry]

Thank you very helpful.

[techo]

Wow! That was an awesome lesson. A question I have is...do you really have to fish at the thermocline for the fish. We know where they are from the depth finder, but depending on their condition (how hungry, spawn...) they will come a long way to eat your bait won't they?

So say you are at a 27 foot thermocline.....if they are hungry and the surface water isn't too hot, they hit top water if the rest of their food is there. I guess i am asking if the thermocline is important by itself or more important to determine where the food is in relation to the thermocline to determine what depth, speed of retrieve and method of fishing that particular bait?

Poop! I think I just confused myself! Thanks for explaining and showing how to find it!