Big bass after the spawn

TCB,

I can say that in a river due to the moving water there will not be a thermocline. Even on the St. Johns which has fairly slow water. It is enough to mix up the water sufficiently to keep thermoclines from forming.

Here is a definition courtesy of Wikepedia:

The thermocline (sometimes metalimnion) is a layer within a body of water or air where the temperature changes rapidly with depth.

Because water is not perfectly transparent, almost all sunlight is absorbed in the surface layer, which heats up. Wind and waves circulate the water in the surface layer, distributing heat within it somewhat, and the temperature may be quite uniform for the first few hundred feet. Below this mixed layer, however, the temperature drops very rapidly—perhaps as much as 20 degrees Celsius with an additional 150 m (500 ft) of depth. This area of rapid transition is the thermocline.

Thermoclines can also be observed in relatively shallow lakes. In colder climates, this leads to a phenomenon called turnover. During the summer, warm water, which is less dense, will sit on top of colder, denser water that sinks to the bottom, with a thermocline separating them. Because the warm water is also exposed to the sun during the day, a stable system exists and very little mixing of warm water and cold water occurs. One result of this stability is that as the summer wears on, there is less and less oxygen below the thermocline, as the water below the thermocline never circulates to the surface. As winter approaches, the temperature of the surface water will also drop until it approaches 4 °C (39 °F), which is the temperature at which water is densest. 4 °C is, generally speaking, the temperature of the water below a thermocline. When the entire body of water is at or close to 4 °C, 'fall turnover' begins - the thermocline disappears, (or, to say a different way, it reaches the surface) and the water from the bottom of the lake can mix freely with the water from the top. This process is aided by wind or any other process that agitates the water.

As the temperature continues to drop, in those locations where it does, the water on the surface begins to get cold enough to freeze and the lake begins to ice over. A new thermocline develops where the densest water (4 °C) sinks to the bottom, and the less dense water (water that is approaching the freezing point) rises to the top. Once this new stratification establishes itself, it lasts until the water warms enough for the 'spring turnover,' which occurs after the ice melts and the surface water temperature rises to 4 °C.

TampaCountryBoy said:

Thanks Tom Although I believe I understand thermocline, can you explain that term a bit more. When it occurs, is it just when the lake turns over or does it exist all year long? Clarification would be helpful. Lately I have been hearing conflicting theories regarding the position of Bass to the thermocline. In Florida deep is based on the water you are fishing. Deep could be a little as 10 feet on some of our lakes, but then we have lakes with much deeper water. How about rivers does thermocline exist there as well. Just some clarification would be helpful. Thanks for your time and information

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Jim can define this condition better than I can, however let me give it a try. Thermocline as I understand and apply the terminology is the first water column temperature break below the surface water temperature. Temperature break is usually measured in about a 3 to 5 degree change within a few feet. Summer stratification creates a dense temperature break of warm surface water to cold deeper water that is easily located because of the abrupt change. Thermoclines exist whenever there is a water column temperature break. The reverse is usually the situation in winter where the colder surface water meets deeper warmer water. In most thremocline temperature breaks the dissolved oxygen level are ideal for bait fish and bass. The dense thermocline can hold dissolved oxygen from mixing down into deeper layers colder layers during the warm water periods, unless wind or current mixes the layers. In Florida you have a lot of lowland reservoirs and natural lakes and rivers, all spring feed. Altough the lakes are shallow compared to other reservoir types, a thermocline can still exist. Springs located in deeper water may be your best choice because they provide the same condition for prey and bait fish as the thermocline does for the deeper reservoirs.
Good sonar can pick up the water density change and the life zone associated to the thermocline is also easy to meter with sonar. Thermocline looks like a dark line in the water column on sonar and bait fish look like clouds of suspended fish. If you see the bait fish at 10 feet all over the lake, you should be able to tune the sonar to define the thermocline dense water break line. Power generation lakes create current and mix things up when the current is running, similar to a river. However in any body of water the life zone is there and the big bass tend to locate very close to the lower levels of that depth.
Tom

TampaCountryBoy said:

Thanks to both of you, This is going to take some time to absorb, I appreciate the info but for some reason the ole brain ain't absorbing the info. ld: Thanks again

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If you had a thermometer with a weight and lowered it down into the water, the surface temperature during the winter would be cold, lets say 50 degrees. As you lower the thermometer and could read the temperature while it was going down the temperature would start to rise if the water was warmer deeper. If the temperature climbed from 50 to 53 within a foot or so, say between 11 and 12 feet, that would be the thermocline. If the temperature fell from 50 to 47 degrees, that would also be a thermocline. Whatever depth the reading changes quickly is where the thermocline is located. We don't use thermometers anymore with weights to lower into the water, so we use our electronics to see where the warmer water meets the colder wate. The colder water is heavier, more dense, so the sonar signal shows this transition as a dark line. The bait fish and bass tend to locate at the temperature break and the sonar picks up the fish locations and I call that depth the life zone. The life zone and thermocline are usually the same depth. Clear as mud?
Tom

TCB,

Most of our lakes here in Florida except some of the deeper ones in Central Florida do not get Thermoclines. Our weather is not drastic enough to create them here. So for us thermoclines rarely play a factor in fishing here in Florida.

Now if we had winters that stayed in the 40's for a long enough time to drop the water down into the 40's and then as it began to warm in the fall it would create a thermocline. Typically the fall is when thermoclines become apparent in lakes. You will know too when a lake has turned over. It will stink and you will see clumps of bottom material floating on the top with lots of air bubbles. This means the water temps is the same at all depths and the fish are spread out at all depths. Some are on the bottom some are mid level and some on top. This is why it is tough fishing during these conditions.

But fishing lakes that are less then 10 feet deep like what we have plus having mild winters means we don't see thermoclines here. But some lakes that are in the 20-30 feet depth and like what happens on Kingsley lake in Keystone Heights thermoclines can develop. But like I said we just don't get extremem weather one way or the other really to create major thermoclines. Heck in some lakes there are 2 thermoclines going on at the same time. This can be seen by increasing the sensitivity on your graph and a solid black line will appear on the sonar. When you see this it is a thermocline.

In warm months when I find the thermocline depth I've eliminated all water below it, narrowing my search to a tiny fraction of the total lake. If it happens to be at 21 feet below surface, I pay attention to any water at or above that mark. That includes from thermocline depth to mainlake shore, humps in mid lake that at at least poking shallower than 21 feet, or any cover or structure poking up into the top 21 feet of water. A bridge piling might stand in 40' of water, but the top 21' of it will be the life zone.

That isn't to say no big mama bass won't go deeper. She will to escape danger, but can't survive down there long enough to consider fishing there. Some species of fish can last longer deeper, so seeing some on the sonar at 30 feet doesn't alert me to think 'bass'.

The contact zone between upper warmer and deeper colder/denser water, the thermocline, can be many feet wide. The thermocline in my instance might start at 21' and show on the graph to extend to 30'. Thick zones like that can hold DO deeper. The main limitation is there is practically no DO, not enough for bass health, in the lower cold water outside the mixing zone. There is likely some DO, just not enough unless there's a 'forest' of vegetation in that cold water. Plants oxygenate water above them, so in that case the thermocline mostly suggests a comfort zone depth rather than a matter of life and death concerning O2.

In those south Florida spring fed lakes there most likely is a thermocline. Maybe it doesn't show up since it occupies practically the whole depth. The immediate area around a spring can be a little deeper, the incoming spring water cold and flowing under the warmer surface water. Maybe the cold water (hyperlimnion) is only 6" thick compared to 9 feet of upper warmer water (hypolimnion) with a mixing zone (metalimnion) of only 1 foot. In order to view a sonar horizontal dark banded thermocline the high sensitivity setting needed often produces other viewing problems like false bottoms and erratic depths.

Next time out during post-spawn try to stop beating the shoreline for "used" bass and try fishing those outer waters for a change, down to about thermocline depth. Right now, during the spawn, bass are bottom-oriented eating crawfish, so stick to shallow. In post-spawn they will be shad-oriented off the bottom, so fish out there wherever the shad are. If you find shad there's enough DO for bass too. Crappie spawn very close to bass timing and places, so find some crappie/bluegill beds where bass feed on the fry and later fingerlings. It's revenge time for the bass.

Jim