Thermocline.

Thermocline.

To all you lake fishermen…
How do you react to a lake that thermoclines. By definition the water deeper than the thermocline level should be void of fish but in my experience I have just not seen it. Take for instance Dagget on the Whitefish chain. I did manage a few fish in 20 feet of water however I have been told repeatedly that there are no fish deeper than 14feet.
Any thoughts would be appreciated.
Jc

Jeremy,

I’d have to concur with your experience. On many lakes, dissolved oxygen levels beneath the thermocline remain at or above 6ppm throughoutthe summer. I also fish the Whitefish Chain a lot, and clearly, this is one system that harbors sufficient oxygen well into the hypolimnion. Only thing I’d add is that by midsummer, into late summer/early fall, the thermocline usually hovers in the 28 to 36 foot range, descending in depth as surface waters cool into September/October.

On Big Trout of the chain, for example, you’ll mark (and often catch) lake trout, pike and walleyes in 30 to 70 feet of water all summer, even though the thermocline lies between 20 and 40 feet (depending on seasonal surface temperatures). Lots of other examples out there, too.

Alas.. Content.

Thanks Schmidt.

To further this. Lets say for example we are on a classic oli-lake. Now many of these lakes have a “hypolimnion” range meaning that by all likelihood there should be few if any fish using it which leads to the whole mystery of bathyal fish. The seasonal movements from waters that extend into the deepest part of the lake or basin. Some of the old Perry spoon plugging methodologies and experiences I have been involved with complete contradict the meanings of Thermocline and hypolimnion. Now with that begin said how and why do you suppose people even contemplate them as being a factor. I assume it is a convenient excuse for not catching fish and / or gives them the reasons they need to continue to stay in depths that they are comfortable. To be quite honest I have limited lake experience and in my fish locating methodologies I have found the whole lake game to be a big joke of information filled with limitations. OK, On to the question.

How do you qualify the definite movements of these bathyal zone fish in regards to thermocline when one is present and obvious on your depth finder. You made a very valid point with the O2 level being capable of sustaining life and in discussions with quality anglers I am all but beaten off with a stick when saying that the thermocline is “there” limitation not one of the fish. If this were the case how do Lake trout survive. I am sure we are on the same page but some information to help make my case in general discussions or the other would be greatly appreciated. Heck, Maybe it should just be our little secret. –grin-

Jc

i know i have had mild sucess with trophey northerns in canada fishing what comes up on the graph as a thermocline. see…. a big northern can handle a lower dissolved oxygen level than that of their prey(shad, whitefish, perch) and the baitfish in deep water love to congregate on the thermocline when i’ve found this i snap jig 2-7 feet belowe the apparent thermocline and have done alright. I think it’s confusing in that it appears all species has a certain level they can handle. And there are also contributing factors like, water clarity in the respect to how much light is getting down. I will agreee that by growing up on the river, a big lake is a head scratcher when for me when the fish our deep.

I found just the oppposite. Lakes are typically easier to pattern. Fine tuning the pattern to a point where you are the best guy out there is on the other hand difficult no matter where you go. I was finding quality fish really deep and all the historical data said this should not be the case. Nope, Not fihsing the thermocline. Fishing about 20 feet underneath it.
jc

This is an interesting topic of discussion, since I will be going to a early to mid stage meso-lake in a week and will be trying to figure this thermocline deal out. All have had valid points here. I think the thing to remember is that not all lakes thermocline and turnover, neither does this occur at the same time in the same type of lakes in the same region. In the lakes that do thermocline this generally happens during the peak summer period to the post summer into the fall cold water period. The hypolimnion that lies underneath the thermocline can (depending on the dissolved oxygen content) sustain life, which can differ from lake to lake, and the depths at which this occurs can also differ. Again, everybody has a valid point, especially considering that every body of water is a little different, and things happen at different times and depths. Hopefully, we will help each other learn a little bit on how to unlock this mystery on the particular body of water we are fishing.

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By definition the water deeper than the thermocline level should be void of fish but in my experience I have just not seen it.

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I don’t know what you call the definition of thermocline (that sounds like the “some guy at the boat launch definition” ), but I’m pretty sure the real definition is only related to rate of temperature change wrt depth change. Anyway having a thermocline doesn’t mean there’s insufficient DO below that level.
Look at it this way colder water can have a higher level of DO, so before the lake develops the thermocline there is good DO in that volume of deeper water, now after it stratifies the DO gets used up a little at a time by fish and other organisms. So whether or not the levels drop significantly during the summer has a lot to do with the initial DO level,total volume of water below the thermocline vs. the amount of DO being consumed by fish etc.
Anectdotally most big deep clear lakes support populations of ciscoes, whitefish etc. which you can consistently mark big schools well below the thermocline all summer long. And where there’s baitfish…

I am not sure I gained anything here other than different lakes do different things at different times. Care to expand…
jc

OK superfluke,

Definition: Zone of water in a stratified lake in which temperature and oxygen concentration drop precipitously with depth which brings us to the zone (hypolimnion ) I am trying to understand. The water underneath the thermocline that does not get enough light penetration to support many of the creatures we associate Bass with. Without light penetration and / or warmth the ability for life in any stage is limited aspecially in waters that are man made or altered. Fish that suspend and use deeper water often have immediate availability to food sources and O2.

The dock definition that SuperFluke mentions is very accurate. Most guys say that you will not find bass under the thermocline depth. To date I am not hearing much debate other than to talk about these fish in or around thermocline. I should have called this post, Way The Heck Down There.
Jc

Its been my experience that when a lake stratifies, you don’t necessarily focus on water above the thermocline. I tend to focus on structure which is at the same depth as the thermocline. It is true the bottom layer will not necessarily be devoid of oxygen and you will see fish below the thermocline. Shallow, weedy lakes, would be more capable of having a hypolimnion void of oxygen as plant or other matter uses oxygen as it decays. Fish that are less tolerable of warmer waters such as walleye, pike or trout will still seek out the colder layer if oxygen is present. But it would be unusual to see large schools below the thermocline. When diving in a lake that has stratified, I’ve seen many fish swimming at or above the thermocline, but not below. Also, its possible for some lakes to turn over more than once during the summer because of weather. Interestingly, when diving you can actually see the thermocline – and feel the drop in water temp! Burrr! And the thermocline isn’t just a line across your sonar screen, its usually a few feet thick.

I guess what I am saying is, some lakes are deep vs. shallow, clear vs. dirty, oli vs. meso vs. eur., and so on. All these variables have to be taken into account when talking about thermoclins and turnover. Just for an example lets say you have a deeper meso lake that has clean water and thermoclines. I would venture to say that below the thermocline in the hypolimnion there may still be some weeds that get good light penetration and give off oxygen, so the DO level would be high enough to sustain a population of baitfish or prey and therefore there are gamefish present as well. Versus a deeper and dirtier meso lake, which may not be able to generate enough DO to do this. DO content depends on things to give it livable conditions, like water temp, weeds, and light penetration to make it all work. Like I said there are a lot of variables present in each lake and situation, it just depends where you’re fishing at and the calender period the lake is in. Remember, these are my thoughts on this right or wrong, but would like to learn more on this subject.

check this out, it sort refers to some of the things we are discussing. Some refers to saltwater, but there is also freshwater in there as well. Just click or use the scroll on your mouse to go through, it looks to be in a power point presentation. http://www.bedford.k12.ny.us/flhs/science/apes/ecology/aquaticecology.ppt
The one page shows the thermocline and other zones with the amount of DO oxygen at each level. This may bring up another question. Fish are usually thought of wintering in the lake basins or close to it, according to this the DO is at a low level, whether or not it is enough to sustain life, ?. Fish obviously use less energy in the winter, would the fish in this zone during the summer we are talking about, not move around as much and conserve energy ?, thus being enough DO to live comfortably?

Okay… this is hitting home for me (and my dad), as we have just returned from a clear Canadian Shield lake that exceeds depths of 150 ft with many bays bottoming out at 30 ft with shallow areas… We found the lake’s surface temp to be steady for the 5 days we were there at 60.5 degrees… no thermocline seemed to be apparrent, as we searched with electronics. We did manage a few Smallies during VERY low light times, otherwsie we focused our attention on Largemouth which were shallowed up and feeding quite nicely… though, we were in search of some 6 lb smallies. We failed… miserably. We graphed fish down near rocky points at 35-45 feet… schooled fish. We tried many different techinques, but found nothing that wanted to bite… even livebait! Would you speculate that these fish were Smallies? Its our assessment that we hit the lake during turnover, as there was debrie floating everywhere and the lake just didn’t possess its normal “gin clear” clarity.

Normally we head up ‘nort in July and fish Smallies in 8-15 feet of water and KILL them… this year nada there… so, as mentioned above, we tried other stuff.

Thoughts on what we might have done wrong? Please, be blantently honest… I’m learning… just try to be a little gentle!

Smarter anglers than me can probably give you a better answer. But I bet those fish were Walleyes. As for the overall bite problems. The north country pretty much sucked all year. It was a wild weather year and for the most part much colder than normal. We did horrible the 2nd week of August with stacked cold fronts, 40-50 mph winds, rain and temps dipping to the low 30’s at night and topping out in the upper 50’s during the day. From what I heard weather was more unstable than stable all year. So my guess is that it was just a weather anomoly and you were doing everything right the fish were just really screwed up from the weather. For us we talked with many locals before, during and after our trip including guides paid for putting people on fish and they all concurred that the fishing stunk. May want to start with that approach with some locals to see if it was just you that had a rough time or if it was just a bad week/month/year period. Misery loves company and it did help a little to find out that the bad bite was not just us doing something wrong.

Reel Guy,

If these fish were smallies, given the water temps(60),
I’d say that these fish had transitioned to their
winter basins, or were in transition to their winter
basins. In this period, given a good supply of pelagic
forage, like whitefish/ciscos, they will forage on
these oil/fat rich fish, almost to the exclusion of
any other forage. On a late fall
tournament on Lake Superior, we encountered something
that sounds very similar to what you found in Canada.
To our misfortune, we did catch one nice fish in shallow
veggies, and I believe that was the last smallie
to leave the summer pattern(grin). After much
frustration, and searching, I finally headed to deep
water, and found the smallies tearing into ciscos, in
about 30′ of water at the end of a breakwall. About
the only thing they would hit was a light mojo weighted
4″ blue pearl senko(looks like a small cisco). We had
only 30 minutes of fishing time, and pitching in 4′ waves,
kept us from really exploiting our discovery, but
it left an indelible mark on my memory. It has paid
dividends since then. So, I believe, if you could have
located pods of cisco, and were fortunte to find a place
where “traplining” smallies were pinning this forage to
deep structure, and you put something down that looked
like wounded cisco, you would have found those big
smallies. These fish are very tough to locate, and in
these conditions I don’t even try. I find forage, near
deep structure, and wait for the smallies to find me.
Usually about every 30 to 60 minutes, a pod will move
in, feed, and hopefully I will boat a couple before
the pod moves off. Then I wait for the next pod.
Not exactly a favorite technique, for a Type A personality,
but if big smallies are what you are after, it can
be worth the wait.

Big Bass Bane

One thing to remember the thermocline must be idenified by a fish graph not info. from other anglers or info. from a map.I will use a map as genral info.Bass will never be below the thermocline at any time of the season.Jeremy remember what E.L Buck Perry preaches was the deep water home of bass is 60 feet if oxegen is availibal, if it is not the bass will go as deep as they can and will not bite [they feel sick]
The best example I have seen of a changing themocline is in the fall on Lake Bylsby.This Lake is stained and turns green.Maps say there is no oxygen below 12 feet.So most of the bass are caught off the banks in one or two feet of water.When the fish can not be caught off the bank then I look for suspended fish off ten foot banks,it is hard to caught these fish because of the stained water[Buck Perry sez fish will only suspend off structure they can see]so it is like finsing a spot on top of a spot,But as the water clears in the fall from weekend to weekend it is like clock work,the fish will be in 12 feet,a week later 15 feet and so on and so on.I am suprised this is the first time I have seen Buck Perry talk about on the bass fourm for anyone that does not know the teachings of E.L. Buck Perry buy the book Spoon Plugger it is the Bible of bass fishing.Of all the fishermen and experts no one ever will have a true grasp on bass fishing like Buck Perry.Buck wrote the bible,and left it for us to study.A student of buck is Don Dickson a great videio collection is made by Pro Structure Fishing Consultants,Don Dickson Structure Fishing Workshop

In the words of Forest Gump… “And thats all I have to say about that.”
jc