Pond Boss Forums INTRO Questions & Observations thermoclines??????????

Hi i am new and i was just wondering what a thermocline was and why most crappie won't go deeper than it. How do you tell where your thermoclines is in your pond so you know where to place your cover. This doesn't affect the bass any does it only like bluegill, crappie, and stuff like that right. Thank yall for your time.

josh,

The answer to where to put habitat in small ponds is to put most of it in water 3 to 5 feet deep. That is where most of the fish will be.

A thermocline is the thin defining layer between water of different temperatures. It's location will vary with the weather, size of the pond, wildlife activity, fish activity, etc.

Cold water is more dense and sinks. Warm water rises. If the difference in temperature between the two is extreme some fish will avoid the colder water and some fish will prefer the colder water (trout, perhaps some northern species). This is true only if the cold and warm water has sufficient oxygen.

If the colder deeper water is unable to be refreshed with oxygen or loses its oxygen, the cold water becomes stagnant and becomes a dead zone for all fish and organisms except anerobic bacteria. Fish are forced to live in the upper warmer layers.

Large lakes are unlikely to develop zero oxygen cold water but in small ponds it happens all the time.

The problem is when your area gets a cold front passing through and the top surface water cools quickly. The top cooler layer will quickly sink and the bottom oxygen deficient layer will rise. This is commonly referred to as a "pond turning over". Fish are accustomed to living in the top layer and many will die from a lack of oxygen. It seems that a lot of fish are just too dumb to go deep where the oxygen is. A good windy day may save a lot of the fish as the wind will oxygenate the top surface water.

Aeration will prevent theroclines and will provide oxygen to the bottom mud layer to sustain aerobic bacteria which can break down waste products better.

If you have ever swam in a pond/lake and felt the warm surface water yet your feet were reaching cold water, that area of different temperature is the thermocline.

The desity of water is dependent upon water temperature. Ponds and lakes may stratify thermally, beacuse heat is absorbed more rapidly near the surface of a water body and the warm upper waters are less dense than cool lower waters. Stratification occurs when differences in desity of upper and lower strata become so great thaty the two strata cannot be mixed by wind.

To summarize, at the spring thaw, or at the end of winter in a lake or pond without ice cover, the water column has a relatively uniform temperature. Although heat is absorbed at the surface on sunny days, there is little resistance to mixing by wind and the entire volume of the water circulates and warms.

As spring progresses, the upper stratum heats more rapidly than heat is distributed from the upper stratum to the lower stratum by mixing. Finally, waters of the upper stratum become considerably warmer that those of the lower stratum.

In lakes, a thermocline is defined as a layer across which the temperature drops at a rate of at least 1 deg. C/m of depth. The depth of the thermocline below the surface may fluctuate depending upon weather conditions, but most large lakes do not destratify until autumn.

The reason the fish do not pass the thermocline is that the denser colder water contains less oxygen than the upper waters. It does affect the bass too.

I think someone on this site mentioned a cheap way of checking the temperature other than the fancy products on the market.

Maybe someone will remember that.

The thermocline equally affects bass, crappie, sunfishes and most all warm water fishes esp if the layer below the thermocline has oxygen concentrations below 4ppm (mg/L).

joshcc , and others. I think it is an error to only place cover {habitat} in the top 5 feet of the lake . This may be true if you only fish in summer. For large parts of the year fish {bass and BG/RE} will live, feed and/or suspend in deep water {deep water is warmer has o2 and not as subject to extreme temp. change } from late fall - spring. If you intend to fish the entire year you should consider placing cover from the surface to bottom. More cover should be in the shallows but deep cover has its place for a number of reasons in addition to the one above. I have had success having several locations in the lake where cover reaches from top to bottom - then the fish can select their own comfort range and you can locate them easily. Thanks--ewest

ewest,

Excellent post. I share your thoughts also even though that goes against conventional wisdom. We built "islands" that raise up from 20 feet to within 3 feet of the surface in our larger pond along with various shallow water structure. Guess where the fish like to hang out? Yep, on and around the islands.

thanks for the help guys you all answered all my questions. thanks again

Meadowlark :
Great point , what better way to break the thermocline in the deep part of a pond than to make or have an island. It will also result in you using a larger % of your lake. Most pond owners { not those posting here} only use {fish} about 25% of their water . The portion from the pond bank out to 5 feet deep. What a waste when they have so much more they could use. An island under water or traditional with a flat area is an excellent concept. An area for the BG/RE and bass to spawn and live , near deep water for protection and the option to move up or down in the water column for temp. and o2 levels. Place some cover {brush} on a decending siope and you have the ultimate ambush point to fish all year. To all the pond owners who only use 25% of their water please note that you have many options with the remaining 75% . Learn about fish biology and why they use 95% of the pond at some point during the year. Like all animals it is about o2/temp. , safety , food and reproduction . To PONDBOSS thanks for this site for all of us to learn , share and re-learn. ewest.

Meadowlark :
See the prior post and let us know more about your island. Do the bass/BG spawn on top? What is its size -- base and top ? Do you think it added productivity to the pond { using more of the lake area}? What % of the total pond volume { acre feet} does the island represent? How much more productive , as a % do think your pond is with the island. Is the top clay or gravel or hard packed? Does it have cover on the descending slopes ? Do the fish , over the year , move up and down the slope based on o2 , temp. and light penetration ? Any info from ML or others would be very useful and informative. Thanks--ewest

ewest,

I'll try to answer as many as I can.

First, I built three of these deep water islands. They are probably equivalent to a circle of 30 foot diameter at the base. The base is made of clay and extends upward about 12 feet or so from the bottom to a diameter of probably about 20 feet. On top of this clay base, I added permanent structure which reaches on up to the surface level and just below.

The pond is 3.5 acres. Its hard to estimate the % of the total pond volume, but I would say the islands do represent a significant % of the pond's volume in the deep water. Yes, there's no doubt it added significantly to the pond's productivity. They provide a sanctuary for small fish, fatheads love them, and also a great place for the predators to hang out. No, I don't believe it promotes spawning, at least for predators.

A side benefit, one of the islands can not be reached by fishing from shore...only by boat and I don't hardly ever allow anyone out in a boat. It has become a "sanctuary", a free zone for fish from fishing pressure. My idea was to try to lesson the impact of fishing pressure on LMB learning. That's a whole other topic.

My main objective in these islands was to make use of the deep water that is otherwise "fishless", especially that water in the thermocline areas. I rejected the conventional wisdom that says only place structure in shallow water. I placed my aeration stations as close to the islands as I could.

I wish I could say that from the beginning I intended to stock HSB to use these islands areas but I came upon that idea later, thanks to George and Bruce on the Forum. Guess where the HSB hang out? Yes, exclusively around the islands.

Do I recommend these islands now that I've had them for three years...yes, absolutely! What would I do differently? I think I would place gravel on at least one of them instead of all the structure. I've got a feeling that would really entertain the forage fishes.

One last thing, a soap box, don't be bound by conventional thinking all the time. Everything about ponds has not already been discovered or written about. For example, show me the books on bass management that talk about Tilapia. There aren't any that I know of

Think out of the box sometimes...you will make mistakes, but you will also learn more. If you aren't living on the edge, you are just taking up space. End of soap box. and thanks for your interest, ewest

Meadowlark :

Thanks much for your response and for your wise comments. I agree there is much left to learn . Every pond is different and we need to think outside the box. The thought process must be based on the facts gathered from the pond in question and a basic knowledge of fish/lake biology and pond management. A great topic for this forum that I have been thinking about starting is developing a short { 4 or 5 sentence} guide or check list on the process of making correct pond managment decisions ( or how not to make a major mistake}. I would hope that with enough imput from others it would be useful. The thought process would start with following :

1--Think about what you want your pond to be { realistic pond goals}.

2--A basic knowledge of the pond ecosystem {biology of fish,land and water}.

3--Gather the important facts.

4-- Seek input from others .

5--What are the possible + and - outcomes of your decision and can you and the pond live with them.

This is a rough start.

Thanks-- ewest

Drought is another reason to build "deeper" structures. My ponds are between two to three ft. below the overflow pipe already and it isn't even May. My water can drop by 7 ft. over the summer.

Dave Davidson :

That is a very good point to keep in mind . Even our lakes drop 2-3 feet from spring to fall from evaporation and we get plenty of rain . When your lake drops that much do you have a problem with fish concentration , o2 depletion or nutrient overload ? If so what do you do about the problem? Thanks--ewest

Ewest, yeah, I guess the fish get concentrated but it hasn't seemed to cause any problems. Since I quit fertilizing I haven't had any DO problems.