Structure Fishing and Thermocline

[NoShoes]

I’ve been fishing a little over a year now and have done well as a bank beater, but now I’m trying to expand my horizons fishing more structure further off the bank

 

My question relates to the thermocline and deep water access for fish. In my researching of the topic, I understand what the thermocline is and that fish will stay at or above it. What I haven’t quite got yet is with a shallower thermocline, will fish still prefer spots that have access to deeper water, even if it dips below the thermocline?

 

The lake I fish has a thermocline at roughly 10-15 ft right now, so obviously I’ll target that depth and a little shallower. Just wondering if finding points and humps surrounded by much deeper water would be preferable. 

[Team9nine]

My short answer is yes, relationship to deep water is always an important consideration (though not an absolute), especially since those fish likely came out of deeper water in the spring and will return to deeper water in fall and winter (much of the year when there is no thermocline restricting their movement).

[Dens228]

I can't say I've ever caught a bass below the thermocline. 

Yesterday I was fishing a very clear, very deep in spots quarry.  The thermocline was at 22-23 feet, I could see the bottom at 15 feet.  I was marking fish, all were shallower than 20 feet.  FYI I hardly caught any of them and those were tight up against the shoreline bluffs in the weeds and shadows. 

[Glenn]

For the most part, no.  I say that because "yes" they can and will go below the thermocline for short excursions, but they can't stay there long due to lack of oxygen.  For this reason, the forage won't be below the thermocline, so there's little incentive for bass to go there....even if the thermocline is "shallow".

 

Here's a video I recently did that talks about catching fish when a thermocline exists:

 

 

 

[J Francho]

Why do trout and salmon stay below the thermocline, and bass generally stay above it? It can't always be that there is no O₂?  Because it's not true on all lakes.  Below the thermocline is cooler water with greater potential for higher saturated O₂.  There is gas exchange at the thermocline, just as there is at the water's surface.  Trout and salmon require cool temps and more saturated O₂ than bass, so there must be another explanation.  My guess is it's too deep, too cold, not the right forage, and not the right structure.  In other words, not suitable for a temperate species when there better environmental conditions in summer.

[WRB]

Lakes are lakes but they are not all the same.

Natural lakes that have a bass populations that develop a thermocline or thermoclines usually do not have any current outside of wind created current. Thermocline is simply the 1st layer of fast water temperature change within a few feet, usually below top epilimnion and within the middle metalimnion layer. The  layer below is hypolimnion below the thermocline tend to transition water temperater slower. The very low DO levels are near the bottom hypolimnion layer because decaying organic debris uses up oxygen. DO (desolved oxygen) is what fish breath. 

Manmade impoundments, reservoirs, usually have incoming water and outgoing water creating some current. Current mixes the top thermal layers and often have 2 thermoclines with good DO levels, different water temperatures. Bass do not like water temperature changes of more the 10 degrees from what they are acclaimed to. 

Thermocline location or depth is more about temperature comfort then low DO levels.

Ponds or shallow lakes can be severely impacted by DO depletion below a thermocline and may need aeration systems.

I prefer looking for the fish and bait to determine the "life zone" depth, usually somewhere near a thermocline.

Tom

[TnRiver46]

Luckily most of my waters lack a thermocline because of the current. People

routinely catch monster catfish 50+ feet down 

[jimmyjoe]

   @J Francho brought up a point I didn't know, namely the one about some fish routinely staying below the thermocline. We have no salmonids where I fish, but I had thought that one local lake, which was quite deep, had yellow bass regularly hooked below the 16-foot thermocline. I wonder whether there are other species which orient themselves to the thermocline differently than bass. It might be possible to use their presence or absence as a "marker" for DO. 

   Just another reason not to abandon river fishing.   ?    jj

[OkobojiEagle]

On 9/4/2020 at 8:16 AM, NoShoes said:

Just wondering if finding points and humps surrounded by much deeper water would be preferable. 

In my local lakes this holds true during July and August evenings when the thermocline is most abrupt.  I catch many smallmouth while jigging for walleye where the thermocline meets long tapering points.  These spots aren't as productive during daytime.  I think the walleye/smallmouth suspend at thermocline depth over deeper water during daytime and follow the thermocline to the points at evening time to feed.  Every lake is unique, as my lakes are deeper than your's and the thermocline sets up at 33' depth.  I don't catch largemouth on this pattern, so take my experience with appropriate grains of salt for your bass population.

 

oe

[NoShoes]

Thanks for all the thoughts!  I’ll definitely put it to good use!  Fishing deeper is definitely a new world but I’ll get it!

[lo n slo]

this is good stuff right here 

[TnRiver46]

On 9/5/2020 at 10:29 AM, OkobojiEagle said:

In my local lakes this holds true during July and August evenings when the thermocline is most abrupt.  I catch many smallmouth while jigging for walleye where the thermocline meets long tapering points.  These spots aren't as productive during daytime.  I think the walleye/smallmouth suspend at thermocline depth over deeper water during daytime and follow the thermocline to the points at evening time to feed.  Every lake is unique, as my lakes are deeper than your's and the thermocline sets up at 33' depth.  I don't catch largemouth on this pattern, so take my experience with appropriate grains of salt for your bass population.

 

oe

That sounds like fun times on those points!