# Thermocline



## NightTrain

I read a very extensive and very informative post on another site about "lake turn-over"and the thermocline and it's effects on the movement and habits of fish.Can't seem to find it,now.Would ya'll share your thoughts and experiences with this twice yearly phenomenon?Thanks.


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## Catfish

I have never had much luck during this time , however I can actually see the thermocline line on the depth finder -- I think thats cool ...


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## NightTrain

Oh yeah...you can definately see it on your graph.Just wonderin'if anyone has any informative articles or interesting stories they might share.


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## Trophycats

hehhehehe now we are learning


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## NightTrain

Hey T-cats,

Thought you might learn us since you is the deepwater wintertime catchaser.The point of the post was to learn somethin'...yep.


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## Trophycats

Well i am no expert but i did spend last night in a holiday express lol


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## TXPalerider

All I know about thermoclines is this:

If a catfish goes below it to eat the bottom bait on your jugline, and you don't check your lines every 15 minutes, he will DIE. Ah, the joys of flagging jugs. Saved many of big ole cats lives.


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## Trophycats

How can a cat going below the thermocline kill him? I fish for cats in 40/60 ft of water, and know of some guys that fish for cats in 80 ft of water on some rivers. The cats are on the bottom, the thermocline is always above them.


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## TXPalerider

Lake of oxygen below the thermocline.

I don't know about the lake you fish. But, on lakes where the water is deep and stained, like Lake Conroe in Texas , sunlight does not penetrate deep enough to have any plant life on the bottom to produce oxygen. Also, the bottom 5-10 feet or so is where everything settles to decay, thus eating up oxygen. If you fish gin clear water, this may not be an issue. We infact catch fish below the thermocline too. And I believe fish live on the bottom year round. However, it's been my experience, when a fish struggles on a hook for a long period of time, below the thermocline, he does not have enough oxygen and will die. That has been my experience.

Also, it seems that while there is a thermocline, you will catch more blues on hooks in or above the thermocline.


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## Trophycats

Well i will disagree with you on that one. I fish a very muddy river...average fishing hole is 40 ft or so, and the cats are on the bottom, you dont catch them at or above the thermocline, you catch them below it. And i have never had one die from the fight, they are all CPR..


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## TXPalerider

There may be a difference in the water below the thermocline on a lake and a river. And I am speaking specifically of fish caught on jugs below the thermocline and are held down there to fight for 30 minutes to an hour. But, I will assure of one thing, we see it on a regular basis in Texas lakes. When a fish, especially a big fish, gets hooked on a jugline hook below the thermocline and stays there for an extended period of time, he dies. We've even cosidered not baiting hooks below the thermocline if we aren't sitting in our spread of jugs. Have lost several big fish that we were unable to CPR.


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## Hawkeye

I read that in some places below dams that there isn't enough dissovled oxygen to support fish-life. I also read that some of these dams installed oxygen infusers (I think Catfish mentioned this too) to correct the oxygen deficient water situation. The reason these dams release oxygen deficient water into the tailrace is the water is being released from below the thermocline and is low in oxygen as a result. How this applies to fishing, I do not know, but it would seem that in certain reservoirs, at least, there isn't any point of fishing in water (below thermocline) that does not contain enough oxygen to support life... I'll try to find the paper I read on the subject, if anyone is interested...


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## MUDHOLE KID

I Fish On A Lake 90% Of The Time And I Will Say This.there Is A Thermocline And Fish React To It Different In Different Parts Of The Lake.you Go Down Into The Main Lake, Fish Become Harder To Catch Below That Thermocline,but You Get Up The River Arms Where There Is Alot More "current" You Get Better Results.thats Why I Think I Can Catch A Few More Blues In The Winter,because There Is No Thermocline To Deal With.once The Lake Turns Over I Have Better Luck With Blues. Flatheads On The Other Hand,the Places I Fish For Them Are Always A Few Feet Within The Thermocline.that Sweet Spot 20' To 30'.again ,this Is The Way I Fish And I'm Not Telling Anyone What They Should Or Should'nt Do


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## Guest

*Question*



TXPalerider said:


> All I know about thermoclines is this:
> 
> If a catfish goes below it to eat the bottom bait on your jugline, and you don't check your lines every 15 minutes, he will DIE. Ah, the joys of flagging jugs. Saved many of big ole cats lives.


Not looking to start anything, but I have question about jug fishing. If you are going to CPR, where is the sport in jug fishing or using a trotline? What am I missing?

Do you at least use circle hooks?

:rybka:


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## TXPalerider

Jaw:

I don't totally fish with jugs. In fact, I fish more frequently with R&R. And I enjoy both. However, the best way I know to describe it is comparing it to baiting deer with corn. Some people believe baiting deer is unsportsmanlike. Some may say the same about jugging or trotlining. If you grew up in Texas, you probably consider hunting with corn normal . Different stokes for different folks. Jugging is kind of like deer hunting with corn. You may kill a big deer without it. But, I will assure you, your odds go WAY UP if you use it. It just increases your odds of catching a big one. We catch WAY more big fish on jugs than R&R. The advantage comes in fishing 75-100 hooks at a time at varing depths and locations. However, I've known plenty of folks that can set out 25 - 3 hook jugs and not catch a dozen fish in a trip. So there is still skill and knowledge involved. The fact is, I just like catfishing by any method. Especially, if I'm lucky enough to find myself in the presence of a big ole Blue. Nothing like watching a jug disappear and wondering when and where it's gonna resurface. It's a thrill a minute.

As far as the hooks. I used to use all kahle hooks. But, most of us guys that fish together have switched almost exclusively to circle hooks. It doesn't take but a couple of gut hooked 15# blues to convince you circle hooks are the way to go.

I hope I answered your question and didn't just confuse everyone.


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## Guest

TXPale, Thanks for the enlightenment.
I grew up in the north country where it was illegle to hunt over any kind of bait, uncut grain/corn, or saltlick except for bear. No set lines (untended) were allowed either, except for up to 2 for cusk (lota lota luscustra) when icefishing.

Re thermoclines: When the ice melts on a northern lake the top is 32Â° F and the water below is warmer. Water at 32Â° F is at its densest, so the top layer gradually sinks. You should try diving into a lake in early June when the thermocline is only 4 or 5 feet down.  The shock to your body as you pass through is amazing!

Regards, -JAW-


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## TXPalerider

*ICE ON A LAKE!! Are you kidding me....really? LOL*

So far as this thermocline issue, here is a discussion I found as it relates to Lake Fork in Texas.

*"If you're a fisherman, the thermocline is something that's very important*
*you must know and understand to be a successful fisherman.*"
Simply put, the thermocline is a thin layer of water in a lake which is sandwiched between the upper layer of water (the epilimnion) and the lower, colder layer of water (hypolimnion). During the summer months, surface water is heated by the sun and the surface temp could be 80 degrees or more. This floats over a layer of colder more denser water called the hypolimnion. Now, between these 2 layers you have a thin layer in which the water temp drops fair substantially. This will be the thermocline. The temp at this level may be high 60's and up in about the middle of spring. ​
............

In full-blown summer you will have 3 distinct water temperature changes (at these approximate depths), 0 to 12', 12' to 22', and 22' to 45'. The temperature may drop by 10 degrees at each depth. Many of you have probably heard of a lake "turning over" and this is exactly what it does. During late Autumn, (usually in October on Lake Fork) the cold winds blow as the fronts start coming through. This in turn drops the waters surface temperature. As it cools this surface water will sink to the bottom of the lake. So when cooler weather arrives the layer that was the warmest (the surface layer) displaces the lower level and the lake turns over. This movement which occurs every year allows the bottom layer to be exposed to the air allowing it to be used by living organisms. In shallow lakes with an average depth of 15 feet usually no thermocline will develop. Mother nature keeps all this in check. In such cases as very shallow lakes you may find heavy cover to screen out some of the suns penetrating rays.
October is a month of water temperature changes, once again, for Lake Fork. Depending on our weather you will find water temps becoming more uniform from the surface to about 25' in most areas of the lake. The temps may vary from 69 degrees (surface temp), to 66 degrees down to the 22' mark, give or take a few feet. Fall fishing patterns have set in and you can count on nice numbers of fish with predictable patterns. Is the hypolimnion void of oxygen? At certain times of the year this may true but there are also certain times when it has more oxygen than the other layers of water. As you already know the turnover on Lake Fork usually occurs in October. The water begins to cool. The shallow coves are among the first to cool and the bass will begin to relate to shallow structure, this is why fall fishing is fantastic at Lake Fork. Generally speaking the thermocline averages 7 to 10 feet thick and is usually found at 22' of water. Fish will be caught in the upper regions of the thermocline (early October), but usually the best fishing occurs just above where the thermocline starts.

The main thing to remember is when stratification is evident the fish will be found in greater concentrations within the thermocline. Why is this? Two reasons. First the upper layer has too much light penetration to be comfortable for fish and the hypolimnion is usually void of oxygen. This leaves the thermocline where the light is just right and the oxygen is comfortable. ......... Also remember sunlight will diffuse differently depending on the time of day. Early morning and late afternoon the suns rays will be at more of an angle and not as intense. Wind will also affect the suns penetration into the water, as will the clarity of the water. Can you catch fish in the hypolimnion? Why do anglers catch fish in 40 feet or deeper water? During the late winter there is usually no stratification on Lake Fork or most other lakes. As a result the water will undergo a temporary oxygenation process. Strong winds, feeder streams feed the lake with spring rains and plant growth begins. So under normal conditions the deeper end of a water body will be quite saturated with oxygen. Since the lower layer is much colder than the surface (averages 10 to 25 degrees difference) the deeper portions can retain the oxygen molecules sent its way during the pre-stratification. Why does the hypolimnion lose it's oxygen? The thermocline and the upper layer of water are continually replenishing their oxygen supply and the hypolimnion gradually loses it for several reasons. Probably the most important reasons are is that there is very little or no plant life beyond the 30 foot level. Unless the water is gin clear the suns rays cannot penetrate this far into Lake Fork enough to grow any vegetation.

The bottom 2 to 10 feet of a lake will also be where everything settles to decay thus eating up the oxygen. Fishermen will find Lake Fork usually has no thermocline until late spring or early summer and its this time you must understand what the thermocline is and what role it plays on fishing. Lake Fork and most all lakes will turnover in the fall. When this happens you can usually smell something that resembles the smell of rotten eggs and many times you will see particles of decaying matter in the water, this is the tale-tell sign that the lake has turned over. Some years, depending on the weather we have, the turnover will be more abrupt than others. Back in October 1994 Lake Fork experienced quite an abrupt turnover. Millions of shad were seen either dying or dead on the surface, and many fishermen reported the very strong smell of rotten eggs for a week or so. Estimates of the shad die off that year was over 12 million. Luckily though shad reproduce extremely fast and no noticeable decline in fishing occurred due to this turn over.

.................You will find some fish in the top layer, the bottom part of the top layer and at varying depths within what is called the thermocline. Most times you will be wasting your time if you fish any deeper than the thermocline. Many times your electronics can pick up these varying layers of water. On quality, high end electronics you'll see a washed out line. This will represent where there are drastic differences in the water temperatures.


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## Hawkeye

A slight correction... if I recall correctly, "fresh" water is most dense at about 39 degrees F (one reason ice floats... the other being that water is one of the only compounds found in the natural world that expands as it solidifies making it less dense as a solid than it is as a liquid)..... not that it matters.... but that's why lakes turn over... when the water on top reaches 39 degrees, it sinks and displaces the less dense water at the lower depths...


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## MUDHOLE KID

Good Info Palerider,that's How I Understand It Myself.hits The Nail On The Head .tell Me Something,you Jug Alot.i Can't Here Because It Is "unlawful By Dnr Standards".tell Me, That's The Reason Jugging Is So Good In The Summer Ain't It(the Thermocline)?


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## Bamacat

Most rivers will not have a thermocline because the water is constantly moving.


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## Guest

*Density of water*

*Mea culpa! * You are right Hawkeye. 

Freshwater at 1 atmosphere of pressure is densest at 39.146Â° F. If water, like most other liquids, just got denser and denser as it cooled then there would be no life on earth.

Why? Because ice would form on the bottom of the water body first and eventually it could freeze its way up until it was all solid. By freezing at the top first, as it does, it serves as an insulating layer that keeps the rest of the water warmer and unfrozen, and holding more oxygen. Ice floats because of bond changes when it water goes through the phase change to solidify. - Isn't God great to have thought of that? If dihydrogen monoxide weren't a polar molecule, you wouldn't be reading this! 

Thanks for catching that, -JAW-

ps: Have you ever watched ice-out on a big lake? Black ice can disappear in under an hour!

:rybka:


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## Nikonos

Hawkeye said:


> A slight correction... if I recall correctly, "fresh" water is most dense at about 39 degrees F (one reason ice floats... the other being that water is one of the only compounds found in the natural world that expands as it solidifies making it less dense as a solid than it is as a liquid)..... not that it matters.... but that's why lakes turn over... when the water on top reaches 39 degrees, it sinks and displaces the less dense water at the lower depths...


 Excellent chemistry Hawkeye, I am impressed. The density of water at varying temperatures is the main reason for lake "turnover' during the colder months.


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## Hawkeye

-JAW- 
I hope you didn't mind the interjection of the comment about water density... it's nice to know I remembered correctly at least... My highschool physics teacher (who, it seemed hated my guts for sleeping a lot in his first period class) would be so proud I remembered something.... maybe it wasn't him that planted that seed? LOL

Nikonos,
I'm sure that you'll find my head is full of all sorts of useless bits of information... stayed tuned if you were impressed by that, I'll see if I can spout some thermodynamics mumbo jumbo a little later LOL... 

In truth, I was reading about this very subject not too very long ago. I did a little net surfing on fishing close to dams... Kerr and Lake Gaston dams in particular, when I happened on an fairly extensive "read" on the subject of oxygen deficiency in tailrace water at certain Army Corps of Engineer(ed) dams.... apparently allowing the water to flow out of a reservoir from the bottom of the dam is a bad idea due to the tendency for water (for many of the reasons TXPalerider has already mentioned) in the deeper portions of the water strata to be oxygen poor. This sets up an equally bad situation for fish approaching the dam from the downstream side (to spawn or whatever), as when they approach the dam, they reach a section of water immediately downstream of the dam that is very oxygen poor... This water is fine as soon as it gets a chance to absorb some dissolved oxygen a few hundred yards downstream of the dam... SO, in an effort to correct the problem the design created, the Corps of Engineers drilled holes into the dams (simplified explanation of a complicated process to get air into the discharge of the dam) to infuse the with air making it more hospitable to fish and such...

Like I said a while ago, I think this topic was broached, however briefly in the thread regarding bait / live wells... and the keeping of shad alive.

Personally, I don't KNOW enough about the pros and cons of trying to fish above or below the thermocline (which actually appears the be THE SPOT where the fish really are) to make heads or tails of what to do. That's probably why I tend to fish in shallow water adjacent to deep holes in an effort to lure big fish into the shallows with the smell of fresh (bleeding and oily) bait... 

From where I sit, it appears both "camps" are really speaking about the same thing.... the fish like to be where they are temperature, light and oxygen "comfortable" and the "art" of finding them where ever they are is what fishing is all about.... I've never seen the thermocline on a depth finder, but I most certainly have experienced how one feels when swimming (snorkling) in lakes up in Yankee land (The Finger lakes in New York)... it feels real weird....


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## Hawkeye

P. S. In case I forgot to mention it earlier... it's good to see -JAW- over "here" talking fishin' with we catmen....


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## Bigcat

I've caught cats as deep as 120' deep in the summer on lake Travis below(about 600 yards) the dam.

How long does it take for a thermocline to set up once the water stops moving?


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## Hawkeye

I don't know the specific answer to your question, but here are a couple of things to consider. Ground water tends to run about 56 degrees, again if memory serves me correctly, so deep water would "tend" to be cooler due to the factors mentioned previously (inability of the sunlight to penetrate to depth and warm the water), but stratification is density driven, and would pretty well be a factor of the overall temperature of the flowing water and the absorbtion of heat by the bed of the formerly flowing body of water (heat sucked out by the cooler river/lake/reservoir bed).

You'd probably have to have a doctorate in physics to figure out exactly how long the process would take, but it starts immediately after the flow stops.... or at least I think it does... The greater the temperature (density) differential, the more drastic the seperation of the layers and the more dramatic the effect of stratification becomes... This phenomenon can also be seen in salt water in areas of varying salinity (specific gravity) in the water. It can be so dramatic at times, so as to actually cause fish kills as the layers "slide" in and around each other. Recently, there has been a significant croaker kill here in the Chesapeake Bay. Early on, they were blaming it on an influx of fresh water into croaker habitat, but more recently they have discovered that it appears there is a bacteria at work that is causing the fish to die. Cool stuff, this water...


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## Guest

Bigcat said:


> I've caught cats as deep as 120' deep in the summer on lake Travis below(about 600 yards) the dam.
> 
> How long does it take for a thermocline to set up once the water stops moving?


Bigcat, I think the major factor would be how great the temperature differential is in the water column (and how the weather is affecting it). Heat loss/exchange is proportional to delta T. - Oxygenation and water purity would also play a factor as will pressure. As Hawkeye points out it is quite complex. - However, once you see it over a period of time in a specific body of water you can usually predict pretty well how long it takes to get to a given depth.

:rybka:


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## NightTrain

*Now,*we learnin' sumpin'!!:idea:

Hawkeye...if you don't mind,go over to kerrlake site and git that post on thermocline Katnip posted,and bring it over here.An even better one is bein' looked for by that board.Thanks...I ain't very 'puter literate!


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## Guest

*Fish & Thermocline*

When I fish for salmon and lake trout on the deep northern lakes they are always at or below the thermocline. The landlocked salmon are generally within 5 feet of it, but the trout may be at any depth below it, usually hanging around structure. Cusk (gudgeon, eelpout) are normally on the bottom, and smelt hang below the gradient. All other fish stay above the thermocline in warmer water, except in winter when they will go to wherever it is warmest.

:rybka:


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## Hawkeye

Here's the article NightTrain wanted me to pirate:

by Dan Kibler

FINDING FERTILE WATER; USING THE THERMOCLINE, FISHERMEN CAN PUT MORE FISH IN THEIR BOATS

1,373 words 
15 August 2004
Winston-Salem Journal
METRO
15
English
(c) Copyright 2004 Piedmont Publishing Company, Inc. All Rights Reserved.

I have read the word "thermocline" and used it in conservation more in the past two weeks than perhaps in the past five years. I have read up and questioned experts about how the water in reservoirs acts during different seasons, how it contributed to the large kill of striped bass at Lake Norman and how fisherman can actually use it to their advantage.

Briefly, more than 2,500 striped bass have floated to the surface of Lake Norman since boaters and fishermen began noticing the dead fish the last week of July. Biologists believe that stripers, which prefer cool temperatures - especially during the summer - squeezed themselves into small pockets of comfortably cool water in the lake's deepest areas, and, unwilling to leave, used up what dissolved oxygen there was until they suffocated.

The great majority of the lake's stripers survived, either by moving up the lake, where river current offsets some of the effects of the summer's heat, or by finding a band of water at the lake's mid-depths that had enough oxygen and was a degree or two below the level that fish consider too warm.

The potential for this kind of fish-kill exists because of a process known as "stratification." That is, the waters in a lake are not uniform. There are areas of warm water and areas of cooler water, and those areas don't often mix. In effect, a "barrier" between those waters is created - as thick as any storm door you could erect. That's the thermocline.

Scott Van Horn, a biologist with the N.C. Wildlife Resources Commission who for years oversaw reservoir fisheries in the Piedmont, said that the division of waters is a seasonal phenomena common to most lakes and ponds.

"In the winter, the water temperature in a reservoir is going to be uniform throughout - it's all cold," he said. "And it's gonna have dissolved oxygen from the top slam to the bottom. Fish can use the whole lake.

"In the spring, as the sun warms the surface, the water gets warmer, and warmer water is lighter than colder water. The heavier water sinks to the bottom, and as the spring progresses, there comes a point when the water on the bottom is not gonna warm up any more. You get a situation that's like oil and water - they don't mix.

"The water on the bottom has dissolved oxygen, but by the middle of the summer, it's like it's locked in a box, put in a closet. It has no access to get more oxygen. And eventually, the dissolved oxygen will get used up, either by bacteria or what little plant growth there is on the bottom."

A "thermocline," Van Horn said, is the "interface" between the warm layer closer to the surface that has plenty of oxygen and the cooler layer on the bottom that lacks oxygen. The thermocline may be two or three feet thick, it may be six inches thick. But all of a lake's living organisms had better be above the thermocline or they're in trouble.

Twice divided

Almost all popular gamefish in North Carolina reservoirs require water that has at least five parts per million of dissolved oxygen to survive. You can go to coastal swamps where the D/O level is one or two parts per million and see fish like bowfins or gar, but precious few gamefish.

What happened at Lake Norman, biologists believe, was that the reservoir's waters divided twice. The upper layer, from the surface to about 30 feet, was full of warm, oxygenated water. It was too warm for stripers, except for the band from 28 to 30 feet - just above the thermocline. From 30 to 60 feet deep was cooler water with almost no dissolved oxygen, something of a dead zone. And below 60 feet, there were scattered pockets of cooler water that contained enough dissolved oxygen to attract stripers.

Van Horn called those areas "thermal refuges." But as the summer wore on, the levels of dissolved oxygen in those refuges dwindled to a point where stripers were stressed and finally, as the available oxygen was used up, they died.

Typically, Van Horn said, the thermocline will divide water into layers by temperature and also by the level of dissolved oxygen. The two go hand in hand. Where the thermocline sets up can vary a great deal from year to year and lake to lake, depending on the lake's hydrology, how water is drawn through upstream or downstream dams, nutrient levels in the water, plus the size and depth of the reservoir.

"Typically, in Lake Norman, the thermocline usually sets up at about 35 feet," Van Horn said. "At Buggs Island, it's between 35 and 45 feet. At Badin Lake, it's 25 to 30 feet, and at a shallow lake like Falls of Neuse, it may only be in 10 to 15 feet of water."

Healthier fish tend to operate better and longer in areas where the D/O isn't to their liking. And in some lakes, especially larger, deeper lakes, it takes much longer for the D/O on the bottom of the lake to get used up.

Looking for shallower water

Forget about Lake Norman's fish kill for a second. If you're a fisherman, ask yourself, "How can a thermocline put more fish in my boat?"

Van Horn knows. A confirmed catfish addict, Van Horn for years has fished for channel cats in the rivers, streams and lakes close to his Durham home. He was fishing at Falls of Neuse Lake one summer, several years ago, piddling around, not catching much of anything and noticing that very few of the bass fishermen he saw fishing in some of the lake's deeper spots were catching much of anything, either.

Van Horn happened to have a device used to measure dissolved oxygen levels. He lowered the probe over the side and found that, below the 11-foot mark, there wasn't enough D/O to support gamefish. He moved to shallower water and started catching catfish.

Van Horn said that fishermen need to determine where the thermocline is - he found it that day by noticing where the level of D/O in the water dropped precipitously. Fishermen who use temperature gauges can do it by lowering their devices into the water and noting where the biggest drop of temperature is in a short vertical distance - most likely, that's the thermocline. Or they can use a depthfinder to scan something other than the bottom.

"If you'll turn the sensitivity way up on your depthfinder, sometimes, it will mark the thermocline on the screen - well above the bottom."

The "echo" will be fainter than the bottom reading, but it will still be there, Van Horn explained, because the sonar signal that your depthfinder sends out is looking to bounce off something. The bottom is obvious, but Van Horn said that the cooler, heavier, more dense waters below the thermocline will often reflect a sonar signal enough for it to show up.

Once located, it's a simple matter of fishing no deeper than that level. For cool-water lovers like stripers or, in the mountains, walleye, fish barely above the thermocline. Ditto smallmouth bass. Largemouth bass can tolerate higher temperatures, so they might be found anywhere from the surface to the thermocline where the right kind of cover or structure is located. The same thing goes for crappie and bream.

But by eliminating a huge percentage of the lake's infertile water, you've won half the battle. All you have to know is where the battlefield is. 
*Email:* [email protected]


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## NightTrain

Hawk...Thanks,dude.


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## TXPalerider

Mudhole;
I don't know that the Thermocline makes fishing better with jugs. I think it is probably why fishing with jugs is more successful than R&R during the dog days of summer though. You can fish the entire water column until you find the fish. I think fishing is probably better in the early fall. And certaily in the Spring when fish are really easier to pattern. However, I no expert by any means. There are certainly folks on this board that have forgotten more about catfishing than the sum of my knowledge.


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## NightTrain

My experience with summer jug fishing or for that matter R&R,too,has been to fish 'em shallow(7-9')around the spots that shallowup near the channel(ie-old riverbluffs,humps,flats edges)where the mussels and baitfish would naturally be...combine that with thermocline effects....and dare day is!!:fish:


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## fishomaniac

Bigcat, I'm not sure about lake travis, but I do know the water stays really clear compared to most lakes, so maybe the surface layer doesn't absorb as much heat. I've swam and dived in it, and the water is much cooler than most lakes, even at the surface. When I lived in east Texas, an issue that concerned thermoclines and lake "turnover" was the buildup of methane gas in the bottom dead layer from decomposition of whatever settled down there. You could have a turnover that would kill all the fish and was smelled from miles away(methane, not fish). If I remember correctly, some guy invented a "bubbler" that was placed on the bottom. Sort of like an upside down tub that was hinged on one side and fed by a small air compressor. When it flled up enough with air it would tip up and release a large bubble, which kept the two layers mixed up enough that that you didn't have gas buildup.


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## redneck

Thermoclines do not exist in a river. River water is constantly moving and the movement oxygenates the water, as well as helps filter it. Thermoclines only exist in lakes.

There most definately IS a thermcline in lakes, and it most definately DOES effect the fishing. The fish will go below the thrmocline to feed, but they cannot stay there long because they will die due to lake of oxygen.

This the reason jug fishing and holding them below the thermcline will kill them in warmer months.

Here is an excerpt from an article I did for an outdoors publication a few years back.

++++++++++++++++++++++++++++++++++++++++++

Many of the lakes and reservoirs see temperature rises as much as 20 degrees in just a few weeks, and our area lakes have reached very warm water temps as of this writing, and it will only go up until late September when the weather begins to cool.

With this hot weather the lakes stratifies. Basically what this means is that in deep water, there becomes a point where the deep water is much colder than the more shallow water above. What this does is creates a deep layer of water that is cold, and has a poor oxygen content and the temperature decreases rapidly as the water gets deeper. The warmer water above it will have higher oxygen content.

In deep water when the lake stratifies a thermocline is created. The thermocline is the point where the water has stratified, and will be an almost definite line where the water changes from the cold oxygen poor water, to the warmer oxygen rich water.

You are probably asking at this point "what does this have to do with me and catching catfish?". Well the point if all this scientific rambling is that fish require water with high levels of oxygen. If you are fishing the area lakes this summer in the deeper water (15 or more feet) you need to have good electronics or "depth finders" on board to be on the lookout for the thermocline. The thermocline will present on your electronics like a hazy line down towards the deeper water.

There is no magic depth to know where it presents in every lake because it is dependent on water temperature and depth, but several things hold true, it will be in the deeper water, and if you look for it you will see it. Your electronics will display the bottom and top of the water, and somewhere in between you will see a definite line, this is the thermocline.

++++++++++++++++++++++++++++++++++++++++++++++

Now if you wanting to drift in hot water with a thermocline in a lake, I have two things to say. 1st, I think this is the worst time of the year to drift a lake. You can catch em like this but I am just not crazy about it. It is NOT the most productive way to fish in hotter months. 2nd, if your gonna drift, try to find areas with humps and structure that are just above the thermocline and drift them.

Just my .02 for what its worth.


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## mudd_catt

*Now my 2 sense worth.*

Now I get to show how stupid I can sound.

I agree that there is probably little or no thermocline in swiftly flowing rivers. 
I agree that fish are gonna stay 75% of the time ABOVE the thermocline.
I also agree that if you leave a fish on a line that is ANCHORED to where a fish can't get above the thermocline, when there is VERY little o/2 it, such as warm water southern lakes with little or no current, they will die after a WHILE.
I know for a fact that in mid-tier lakes, with current, I have had catfish on trotlines for as long as 12 hours in 40 ft of water.

HOWEVER, I don't believe that we should let this get into hard feelings, as it is only a matter of science, and a lake in Texas will be vastly different than a lake or river in any other part of the south.

I also DO believe that I didn't know that Hawkeye had that much knowledge lost up in that head of his.  :slimer:


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## NightTrain

*******:You are correct,imho,about the fishing above humps and other structure that is above the thermocline...do it all the time.

MuddCatt:You ain't stupid, bro...and neither is Hawkeye!I told ya'll after I went fishin' with that dude,don't believe all of that" I don't know nothin'"stuff....The boy is a genius and a sponge for knowledge.


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## Hawkeye

I agree that this topic is not something that should drive a wedge between the folks that participate on the board. 

Water is a very curious liquid. if you have a body of water, and it does not matter if it is a lake, river or ocean, and it has temperature gradients (it works a lot better in slower moving or water that isn't moving according to conventional thinking), then it will stratify. Stratification is nothing more than the seperating out of the water in layers based on each layer's density. The speed at which the water will stratify is a factor of the differential density of the "layer" of water. There have been many great posts in regard to the "thermocline" but you have to seperate thermocline from the notion that just because there is one, doesn't mean that there's oxygen deficient water beneath the point at which two laters of water of converge (thermocline). There are too many other variables at work to assume there will be insufficient dissolved oxygen below the area of convergence... again, it also doesn't mean that there WILL be dissolved oxygen there either.... did I just muddy the water a little more? 

Being aware of the way that water settles in layers is enough to get thinking about the possible influence the layering may have on fishing. I have always tended to look for fish suspended at depth, and have rarely sought them out on the bottom in really deep water, only because I didn't know any better... There's no reason a fish can't be directly on the bottom anywhere in a body of water, regardless of the dissolved oxygen in that region. I'm sure fish can tell when they have selected an area in which there is insufficient oxygen to breath, same as we can when we're awake... A large, healthy fish may choose to spend time in a oxygen deficient location if there is something else there (food? sex? cooler water?) that the fish finds to be appealing... I don't know. There are a lot more things that I don't know about fishing that the list of things I'm sure of. I do know that I really like it when we talk about things that make me THINK about the hows, wheres and whys of fishing, and I am grateful for the large number of responses to this thread... keep it friendly and keep those thoughts and opinions flowing in.... 

Learning is a very funny thing. If we only work (or fish) in the "zones" we understand, or if we always do things the same way we always do them, then there is no learning going on. It is only when we take a chance and think, fish, or do whatever else it is we set out to do, outside of our personal "box" that real learning takes place. Take a chance and try something a little different... I know I try things in different ways every time I fish because it is the only way I can be more successful... as some person a whole lot smarter than me once said, "Doing the same thing over and over and over again, and expecting a different result is the definition of insanity." Don't be insane... try a slightly different fishing technique... it just might be the trick to boating that personal best cat you've been looking to catch... Once you've tried something a little different with success, you can come back here where we can tell you that you can't catch fish like that LOL>.............


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## Guest

*A Slightly Different Topic*

First off, I didn't know anyone was taking offense to an open exchange of thoughts on a fascinating topic that should be of importance to any fisherman who fishes large bodies of water. I hope that everybody is learning something and no one is getting angry.

Second, one small correction; moving water can stratify and form layers, but when this happens in river situations (or the ocean) there are usually other important factors that affect density involved besides temperature.

Finally, another topic, *oxygenation*: Which can hold more oxygen, hot or cold water?

I realize that under fishing conditions water above a thermocline may contain more O2 than the colder water below it, but is this due to physics or just local conditions? - I thought cold liquids could theoretically contain/hold more dissolved gasses than hotter ones. Do I have this backwards? I know hot air can hold more moisture than cold air (_that is what makes for a dew point and relative humidity_), and that more sugar will dissolve in hot coffee than in cold, but I swear that a warm soda (*OK*_ a warm _ :brew: ) will go flatter faster than a cold one. (_Isn't that what fractional distillation is about?_)

What say you? It is Friday, so please conduct your own experiments, mellow out and don't fight (_Chill, don't get hot_), and report your findings back here upon more sober reflection.   

Enjoy your weekend (_and the other end too_)!! :an2:

:rybka:


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## Hawkeye

-JAW-
I don't remember exactly, but I believe cold water is capable (key word) of "holding" more dissolved oxygen that warm water. When you heat water it "tends" to degas the water. I don't recall the exact reason why it's true, but again, if I recall correctly you are correct. The way water in a lake, river or in the ocean acquires dissolved oxygen is it is in contact with the atmosphere and is able to pull oxygen into itself through contact with the air. The ability to absorb oxygen is generally a function of exposed suface area. The larger the surface, the greater the potential for absorption of O2. If you have two bodies of water with the same mass, the one with the greater surface area will be able to carry more aquatic life. The reason colder water below the thermocline tends to be oxygen deficient is the lack of contact with oxygenated air. That's why the dams I spoke of early on had a problem with a "dead zone" downstream a few hundred yards... it took several hundred yards of contact with the air in order for the flowing water to (again) become able to support fish... While I am convinced that the possibility of stratification of water of differing densities is real, it is also likely a lot less frequent than in standing bodies of water and probably occurs to a much lesser degree... probably most common in deep holes, less affected by current and such, but real none the less... I would also expect that oxygen depletion or deficiency is much less of a concern as the mixing of "layers" would be a more common occurance and the temperature differential and hence density difference in the water between the upper and lower segments of the water column would tend to be much more subtle. That's probably why (if in fact it is true) there isn't much of a chance that the water below the thermocline in a river would be nearly as oxygen poor as the deep water in a reservoir or lake.... also, I believe the dissolved oxygen from the upper layer would transfer to the lower colder water in a river more easily because I would anticipate the thermocline "wall" would be less well defined and less likely to block interaction between the stratified layers as you would expect to see in a standing body of water... 

Bottom line is I'm not POSITIVE of any of this.. it's just s bunch of stuff that flowed out of my head while I was writing.... sometimes I can't shut it off... I guess that's why I can't sleep at night.


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## TXPalerider

Cold water can hold more oxygen than warm water. However, the thermocline and the upper layer of water are continually replenishing their oxygen supply while the lowest layer gradually loses it for several reasons.

One reason is, during the summer, hot surface water forms a thermal energy that resists wind energy. Thus, water does not mix very far down. This creates the barrier that causes stratification in the lake and isolates the cold water below the thermocline. 

The isolated cold waters on the bottom lose oxygen in proportion to the amount of phosphorus coming into the lake. What happens is: 
-Phosphorus input causes algae to grow in the upper warm and sunlit waters. 

-Algae die after a short life and drift to the bottom cold waters where they are decomposed by bacteria. 

-This decomposition uses up oxygen. When oxygen reaches low levels, cold water fisheries are threatened and a chemical reaction may cause additional phosphorus to be released from bottom sediments. This is known as phosphorus re-cycling. 

As the surface water cools in the fall, the surface water becomes heavier and begins to sink and forcing bottom waters upward. This is what is referred to as a lake "turning over." If it happens to quickly and the water below the thermocline is to oxygen-deficient, it can cause large scale fish kills.

BTW....I haven't taken offense to anybody's posts. This is good stuff. While I've always understood the thermocline to an extent. I've learned a great deal more here. And, this discussion, has forced me to seek out more info to support what I thought I understood.


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## NightTrain

JAW and TxPaleRider....I never read anything "offensive"here....it's all good.Agree wholeheartedly that the more you know about the battlefield,the more likely you are to win the battle.....and....that fractional distillation is the reason a warm beer goes flat!!!:cheers:


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## Hawkeye

NightTrain said:


> JAW and TxPaleRider....I never read anything "offensive"here....it's all good.Agree wholeheartedly that the more you know about the battlefield,the more likely you are to win the battle.....and....that fractional distillation is the reason a warm beer goes flat!!!:cheers:


And all this time I thought warm beer went flat because I didn't drink it fast enough LOL....


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## TXPalerider

I wouldn't know. Mine never gets warm.


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## NightTrain

Bumped for Jimmie Blue's question about Thermocline.


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## shadslinger

On Lake Livingston the thermocline sets up usually the first week of June, even the last week of May sometimes.
It happens within a few days. Three or four days after the morning surface water temp is 80 degrees for about three days running and it hits.
The fish act funny, running about in small schools and not staying put for very long at a time and suspending, usually for the first time since warm up in late February or early March.
The cat fish drifting I like to do with R&R is no good at that time, unless you are willing to make very short specific drifts around long points.

The deep water(24 to 45") drifting I like is good on the south or main end of the lake starting when the thermocline breaks up, usually in October, sometimes later.
And is good until the water gets colder and then the big cats move up the lake where the average depth is 20' instead of 40' and stack up in 35' holes and drifting is excellent.
Just how it goes for the cat fishing I do on the lake.
I don't fish for small fish any more, but I bet they follow the same pattern.


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