Thermocline Question

[CAPP]

This may have been asked before but I missed it.What exactly is thermocline,the reason I ask is it sewemed to show on my depth finder recently at 14' in 18'-20' of water.Problem I don't understand is we caught fish right on the bottom.Puzzled??

[sparkie51]

SInce you caught fish deep that is the preferred water temp for the fish in your lake. The thermocline is a band of cooler water. You may have been catching fish at the bottom of it. Or the fish may have been feeding on something special that is assocaited with the bottom. As long as there is oxygen avaiable the fish will than seek out the preferred water temp. Get yourself a cheap window therometer and tie a line to it and drop it over the side. Let it sit a couple of minutes at the depth hat you are marking fish. Bring it up fast and check the water temp. You may be surprized at the difference the temp can be in just a few different feet of depth.

[das speck hunter]

I was thought to think of your lake having different layers. These layers have different oxygen levels and temperatures. Fish will hold at these levels simply cause that is where they are comfortable IE. the suspended bass that Bill Dance loves to talk about, when hes not pitching a product. hahahahhaha

[Lowellhturner]

This method is also useful for locating underwater springs. the significance of locating springs is they pour 56 F water into lakes that is HEAVILY oxygenated all yr long. In the dead cold of winter they tend to hold the most active fish and are the "warmest" water in it. During the hottest "dog days" of summer it is generally the "coolest" area in that same body of water. If cover is present (or added), they can be OUT STANDING fishing areas...

[BigRiverMarine]

I've always thought you catch more fish above the thermocline also, but in this case, I think the right answer is your lake must have sufficient oxygen below to support the fish, and most likely the baitfish as well, along with being in the right comfort zone for those fish. Hey, if you're catching em, Just Do It. Who cares why or where. ;-)

[jpdawg]

What did the thermocline look like on your depthfinder? Can the thermocline be seen on all depthfinders or just some of the newer ones?

[crappiedoc]

Interesting, but believe it or not, we simply call it a thermocline. However, in freshwater the correct term is actually chemocline and the water is stratifying due to it's chemical composition and abilty to concentrate DO. Ex: ever notice the strong rotten egg smell when a lake is high or flooded, that's H2SO4 or hydrogen sulfide an acid derived from decomposition of organic matter, it's forms a very strong chemocline. One that most freshwater species can't tolerate. Then there's the tannic acids or tea formed from the same decomposition, except it generally a wood by-product. It's more tolerable than hydrogen sulfide. There are others like fertilizers, fecal matter, metals, just about everything thats water-soluble. Having said this, YES it is possible for fish to be below a chemocline if DO levels are sufficent. Your clear lakes allow sunlight to penetrate deeper and plant life does it thing. Depth is another thing that 'naturally' causes stratification. Ex: Lowells 56* water temp through a spring, which is a general constant, however it's been my experience that spring-water along with well-water generally have low DO content. But, upon mixing, if the stratum allows, will hold more DO than the water around it due to it's lower water temp. These are also the same factors involved in turn-overs. But, with all science there are some exceptions. As a rule, the colder the water, the more DO. These are the reasons that we're catching walleyes out of 40'-60' here locally, it's also our clearest lake. A true thermocline is a term PhD's use for the oceans were the temp doesn't vary +/-1* through-out the year, which by the way is 41'@39*. WHEW!!! NOAA has very good info, along with some others.

[mbhutton]

What does the thermocline look like on your graph. I may have seen it but never known what I was looking at.

[crappiedoc]

Generally depending on your sensitivity settings there will be a weak, thick broken line with heavy shading under it. If it's a strong one, it will be distinct solid line and darker underneath it. On most lakes you'll notice that there a very few fish below this line. Also with a strong one the surface temp might be 90* and down to the top of the line it might be 85*, but below it the temp might be 65*. And yes some lakes will have a strong line and fish below it, these lakes are generally clearer lakes that have excellent light penetration which allows strong plant growth, thus raising the DO level and allowing the fish to live there. Those fish if caught generally can't go back down for a few different reasons.

[FishnLine]

Here is a thermocline on my unit at 30 feet.