Thread: 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.



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...

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?

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?

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.