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Thermocline

7/27/16 @ 5:42 AM
ORIGNAL POST
jimbo55will
User since 1/17/07

Over the years I have heard and read much about thermocline. Why it develops, its impact on fish, why some lakes have it and others don't, how deep it is, etc. Then I read other stories of fishermen down south fishing for crappies down 40 or more feet. It was always my understanding that a thermocline set up around 20-25 feet or so, maybe a little deeper on some lakes, maybe a little shallower on others. Supposedly there is very little fish activity below the thermocline due to oxygen levels but I'm wondering if anyone has other experiences that contradict these "gospel truths" or "old wives tales". On some lakes that go down to 80 feet I cannot pick up a thermocline on my graph, even with the sensitivity turned all the way up. Does anyone care to comment on this?

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8/3/16 @ 8:52 PM
river_chaser
User since 10/3/12

I have no doubt that sonar can be used to find the thermocline if conditions are right but when an author presents such statements as a constant fact I have to believe the author is using some salesmanship to fulfill his duties to  his sponsor or trying to give some impression of his expertise.  I have seen what appears to be thermoclines on my screens and given that my units are all under $200 and the results are inconsistent I dont really focus on this.  Best of luck.

8/3/16 @ 8:11 PM
jimbo55will
User since 1/17/07

Mendota and Others who responded--Thank you for your input. Mendota, I will look up that Queg-thing. It looked like you had it built into a console or something but I'm looking for something portable. I just know that I've read that a regular locator should be able to pinpoint the thermocline when one turns the gain/sensitivity way up and sees a fairly solid and level band on the screen but mine (a Garmin 312DV) doesn't show one on a lake that should have a thermocline. It's over 50 feet deep. I'm trying to eliminate fishless water. Thanks again all.

Jim

8/3/16 @ 6:27 PM
mendota
MEMBER since 12/19/01

Picture didn't work when pasted

8/3/16 @ 6:23 PM
mendota
MEMBER since 12/19/01

The product is/was the QUEG Fish Finder.  Mine was built by SANGER GmbH & Co, Germany.

I recall paying maybe $60 for it.  It records temperature in 5' increments all the way down.  Works as advertised; mine was still functioning when I went to find it last week. although I had not touched it for 5 years.  I did replace the battery afterwards (CR2032 button cell) to ensure another 10 years.

I've used it on perhaps a dozen different waters in the US and Canada.

REPORT ABUSE

7/29/16 @ 10:47 AM
jkb
User since 6/25/02

There is a product called a Fish Hawk DT. It is a depth and temp gauge that can record temp and depth.  Lake Michigan charters use them to get temp at downright ball.

7/29/16 @ 7:33 AM
mendota
MEMBER since 12/19/01

I actually built a digital thermometer with a 50' cord way back when in order to investigate this issue, as well as look for those legendary "spring holes".

Nowadays there are several available commercially, but they are not cheap.

About 15 years ago I got a castable probe, which records the temperature and depth as it sinks, every 3' or 5' as I recall.  Let it hit the bottom, then reel it in, and read back the temperature every 3-5' all the way to the bottom.  Very slick, although it takes perhaps 30 seconds to get it 60' down.

I'll have to look later and see who made it.



7/28/16 @ 8:32 PM
jimbo55will
User since 1/17/07

Since I brought this topic up I'm still pretty confused about the whole thing. Is there a somewhat practical way (read "cheap") of finding if a lake has a thermocline? There used to be a cheap thing called a "Depth-O-Therm" as I recall where you attached a line to this depth-temperature glass tube and lowered it into the water. Then you'd pull it up real fast and you'd get a depth and temperature reading. By doing this a number of times at different depths you'd get a lowering of temperature and supposedly this would be the thermocline. I don't know if it was very accurate but shouldn't there be something around now that you lower into the water that gives a temperature reading? Even if it doesn't tell you the depth one can figure it out rather easily by the old "arm-span" method of around 6 feet for every length of line you drop down. The whole thermocline and where it sets up still seems rather hit and miss.

Jim

7/28/16 @ 3:59 PM
jkb
User since 6/25/02

I guess I will have to agree to disagree.  IMO there is way too much daily temperature variation from 9-13 m for a thermocline to be set up.  On 7/24 there was an 18 degree Fahrenheit change in temp. and a more drastic change occurred on 7/22.  The hypolimnion should have more stable temperatures if indeed a thermocline has set up.

7/28/16 @ 3:06 PM
mendota
MEMBER since 12/19/01

This graph shows the thermocline beginning around 8m (26'), and also shows only mild mixing on windy days:

INFOS Yahara

7/28/16 @ 11:25 AM
fishmunkee
fishmunkee
User since 3/20/02

Lake Mendota is one of the most studied lakes in the world (perhaps second only to Lake Geneva in Switzerland) due to the UW's Limnology Dept.

No shortage of data available for L. Mendota. The graph here http://limnology.wisc.edu/lake_information/mendota/mendota.html shows the poster Mendota is correct on the thermocline for this lake.

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