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Muskie Fishing -> General Discussion -> Sonar and thermocline
 
Message Subject: Sonar and thermocline
Alumacraft89
Posted 12/25/2016 9:41 PM (#844129)
Subject: Sonar and thermocline




Posts: 191


Has anyone checked the temperature of the thermocline line that's shows up on sonar?
it would seem like that definite line would be a certain temperature that make it show up. Does anyone have a clue what that temp is?

Edited by Alumacraft89 12/25/2016 10:38 PM
jaultman
Posted 12/28/2016 9:12 AM (#844292 - in reply to #844129)
Subject: RE: Sonar and thermocline




Posts: 1828


Someone once posted links to a couple WI lakes that were monitored at various depths in the summer (1-ft increments?). Maybe he will see this and repost.

Basically, in mid-summer, when lakes tend to be most stratified, you get a gradual temp gradient from surface down to the thermocline, which tends to be around 20 - 30 ft down in many lakes, and from that depth the temp drastically decreases as you go the next few feet deeper, and then the gradient becomes very gradual again as you continue to go deeper. Often the "bottom" portion of the water column has pretty homogeneous temp.

The actual temp in that region will be different from lake to lake, and vastly different in cooler northern lakes than in warmer southern lakes. I THINK the stuff you see on your sonar is actually particulate matter.

Likely temp profile of a MN lake in July:
surface 81 deg
-2 ft 80 deg
-4 ft 78 deg
-6 ft 76 deg
-8 ft 74 deg
-10 ft 73 deg
-12 ft 72 deg
-14 ft 71 deg
-16 ft 71 deg
-18 ft 70 deg
-20 ft 70 deg
-22 ft 70 deg
-24 ft 66 deg
-26 ft 60 deg
-28 ft 56 deg
-30 ft 55 deg
-40 ft 55 deg
-50 ft 54 deg




Alumacraft89
Posted 12/29/2016 6:35 PM (#844508 - in reply to #844129)
Subject: Re: Sonar and thermocline




Posts: 191


Any info is good. I was reading musky strategy and he talked about using temp probs for the thermocline for open water trolling. I always troll at or above my thermocline on sonar but I have never actually checked the temp of the actual depth of the distinguished line on the sonar screen. Just digging and seeing if someone has.
Pointerpride102
Posted 12/29/2016 6:47 PM (#844511 - in reply to #844292)
Subject: RE: Sonar and thermocline





Posts: 16632


Location: The desert
jaultman - 12/28/2016 9:12 AM

Someone once posted links to a couple WI lakes that were monitored at various depths in the summer (1-ft increments?). Maybe he will see this and repost.

Basically, in mid-summer, when lakes tend to be most stratified, you get a gradual temp gradient from surface down to the thermocline, which tends to be around 20 - 30 ft down in many lakes, and from that depth the temp drastically decreases as you go the next few feet deeper, and then the gradient becomes very gradual again as you continue to go deeper. Often the "bottom" portion of the water column has pretty homogeneous temp.

The actual temp in that region will be different from lake to lake, and vastly different in cooler northern lakes than in warmer southern lakes. I THINK the stuff you see on your sonar is actually particulate matter.

Likely temp profile of a MN lake in July:
surface 81 deg
-2 ft 80 deg
-4 ft 78 deg
-6 ft 76 deg
-8 ft 74 deg
-10 ft 73 deg
-12 ft 72 deg
-14 ft 71 deg
-16 ft 71 deg
-18 ft 70 deg
-20 ft 70 deg
-22 ft 70 deg
-24 ft 66 deg
-26 ft 60 deg
-28 ft 56 deg
-30 ft 55 deg
-40 ft 55 deg
-50 ft 54 deg






Pretty accurate. I believe the sonar is picking up on the different densities of the warm and cool water.
CiscoKid
Posted 1/3/2017 12:28 PM (#844968 - in reply to #844292)
Subject: RE: Sonar and thermocline





Posts: 1906


Location: Oconto Falls, WI
jaultman - 12/28/2016 9:12 AM

Someone once posted links to a couple WI lakes that were monitored at various depths in the summer (1-ft increments?). Maybe he will see this and repost.

Basically, in mid-summer, when lakes tend to be most stratified, you get a gradual temp gradient from surface down to the thermocline, which tends to be around 20 - 30 ft down in many lakes, and from that depth the temp drastically decreases as you go the next few feet deeper, and then the gradient becomes very gradual again as you continue to go deeper. Often the "bottom" portion of the water column has pretty homogeneous temp.

The actual temp in that region will be different from lake to lake, and vastly different in cooler northern lakes than in warmer southern lakes. I THINK the stuff you see on your sonar is actually particulate matter.

Likely temp profile of a MN lake in July:
surface 81 deg
-2 ft 80 deg
-4 ft 78 deg
-6 ft 76 deg
-8 ft 74 deg
-10 ft 73 deg
-12 ft 72 deg
-14 ft 71 deg
-16 ft 71 deg
-18 ft 70 deg
-20 ft 70 deg
-22 ft 70 deg
-24 ft 66 deg
-26 ft 60 deg
-28 ft 56 deg
-30 ft 55 deg
-40 ft 55 deg
-50 ft 54 deg






I have not checked temp versus "line" on graph as author is requesting. I do know where the link jaultman is asking for is though.

http://muskie.outdoorsfirst.com/board/forums/thread-view.asp?tid=76...

I personally do not look for the thermocline on the graph, nor get hung up on it. I have a base depth per lake I tend to stick to based on readings like in the link and experience.
Alumacraft89
Posted 1/5/2017 6:09 PM (#845214 - in reply to #844129)
Subject: Re: Sonar and thermocline




Posts: 191


I checked that link out that's some interesting info. I know a lot of people say focus on the thermocline as seen on sonar for a good base point. Do you guys know of a temp probe that is fairly cheap?
tyler k
Posted 1/6/2017 12:23 PM (#845292 - in reply to #844129)
Subject: Re: Sonar and thermocline




Posts: 409


Location: Almond, WI
The couple probes I know of are over the Catalina Technologies Cline-Finder and the Fish Hawk TD Probe. Both are around $150 last I checked.

Lake associations on a large spread of Wisconsin lakes do volunteer monitoring of water quality which includes secchi readings, temp profile and dissolved oxygen profile. It's available on the web, go to WI DNR's lake search find the lake you want and select water quality monitoring and if it's done on that lake there will be info there.
nar160
Posted 1/6/2017 12:23 PM (#845293 - in reply to #844129)
Subject: Re: Sonar and thermocline




Posts: 408


Location: MN
Fish Hawk TD https://www.amazon.com/Fish-Hawk-Electronics-At-Depth-Temperature/dp...

Only does 5' increments so not super detailed, but easy to use. Next summer I intend to take some measurements and confirm the question you are asking here. On one lake that I fish I see (on sonar) what appears to be the thermocline at something like 45' down. Will be nice to verify that.
Alumacraft89
Posted 1/6/2017 8:39 PM (#845324 - in reply to #844129)
Subject: Re: Sonar and thermocline




Posts: 191


I'm located in southern Michigan, I fish Michigan, Ohio, Indiana. I'm sure different lakes all probably have different temps where they show up on a graph as a line. But I was just curious, id like to do some testing myself as well. It would be interesting to see how clarity ad other factors affect temperature of the seen thermocline line. Basically thought if that temperature range that makes a seen line on the graph was the same lake to lake that would be easy baseline for trolling depth but I doubt it's even close lake to lake.
DaleL
Posted 1/13/2017 1:18 PM (#846001 - in reply to #844129)
Subject: Re: Sonar and thermocline





Posts: 10


Location: MN
I just heard someone speak about this and the plankton show up right at the thermocline. That is the line you are seeing (plankton). Adjust sensitivity as needed to get the reading. The temp and oxygen vary from the top to bottom of the thermocline. No need to fish deeper than the thermocline as it will be void of fish due to lack of oxygen. Until turn over occurs some of those mid lake humps could be worthless. Every lake is different and some lakes don't have a thermocline.
nar160
Posted 1/14/2017 3:41 PM (#846144 - in reply to #844129)
Subject: Re: Sonar and thermocline




Posts: 408


Location: MN
^ I've considered that possibility and I don't think it is correct, at least for the scenarios I have encountered. Both plankton and a thermal gradient are detectable by sonar under certain circumstances. However, on the water where I've seen this, the line on the graph does not move up or down throughout the day. Phytoplankton definitely move up and down throughout the day and everything follows. My conclusion is that the line is a thermal gradient and not plankton. FWIW I used to design sonar transducers and discussed this with some colleges with a lot more experience than me and they agreed that was most likely. Still have to get out and measure it to be sure though! And it could be that you are picking up plankton on some other bodies of water too.
NPike
Posted 1/14/2017 5:12 PM (#846160 - in reply to #844508)
Subject: Re: Sonar and thermocline




Posts: 612


If you really want to know use a probe. It the most certain way to tell where the rapid transition in temperature takes place. BTW it varies from lakes to lake and week to week. Many factors. I used to fish for trout and the probe is worth it weight in gold if you truly want to locate the thermocline. It can generally vary from 3 to 5 feet in height the water column, sometimes a bit more.
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