DO in relation to depth

[RobbyZ5001]

I did a lake survey last week and found DO from 0m to 11m and I only found DO to be suitable down to 5m which at that depth was 5 mg/l. Why is it that we still catch fish 20ft+ when the DO is not suitable? I have read that the lowest DO for surviving a 24 hr period was 5.5 mg/l. Any thoughts?

[islandbass]

Is DO short for dissolved oxygen? I apologize for not knowing what it stands for.

[Raul]

Did a survey ---> how many samples ? every how many sq ft ?

The degree of a survey is proportional to the ammount of samples taken.

[RobbyZ5001]

The way we did the survey might not have been the best way. We checked DO/temp/sechi disk at the shallow site where we used a trap net then we kept moving across the lake and surveyed every 60-80m. We just used a DO meter starting from 0m down to the bottom recording DO every half m. Even at the shallow site where we had our trap net it showed a decrease in DO at 3.5m where it equaled around 6-7 mg/l. I am not sure if I answered your question, but that was how we did it. This was not an official sample for the state.

[Paul Roberts]

First, I assume you are using professional equipment that is calibrated. Also, taking profiles at two locations is not likely indicative of the whole lake, or where the bass are. But, I'm gonna trust to you and your crews acumen on that.

Assuming above is kosher:

LM tend to show avoidance depending on temperature -their metabolic requirements. I just read a paper in which LM, during winter quiescence, moved out of water at 2ppm (mg/l). That's pretty darn low. In this study, the bass did not seek the highest DO. Habitat elements were probably more important. They were happy (in their quiescent state) at 3 to 6ppm.

I'd have to re-check, but off the top of my head, values below 5ppm has been shown to move bass in warmer water. This I don't believe was a survival issue as much as an activity issue. Bass gotta eat in warm water.

Your 5m depth sounds about right for a thermocline depth in a lot of waters. Below this, in a fertile water body (how many aren't "fertile" nowadays) it is not uncommon to have low to zilch DO.

Couple thoughts:

First, have you been catching fish in this lake at greater than 16feet lately? Many lakes have sufficient DO below 20feet and much more. This one may not -at this present time.

Another thought is that while we may think we catching fish in 20fow, it's possible these fish were suspended nearby.

I once held a similar mystery. We did a DO profile on a deep meso/euthrophic lake and found 0 DO at bottom. We also marked a couple large hooks down there on sonar :-?. I now have an explanation: I believe these were quiescent big pike below the thermocline, but were actually higher than the sonar displayed, due to their being at the edge of the sonar cone.

Bottom line, we aren't going to catch fish where there is no oxygen. You are right there. If you discover something new. Let me know.

[RobbyZ5001]

Paul your the man... That is some great info. I am guessing the DO will change due to turnovers. Paul I know time of turnover will vary in bodies of water due to size and other factors, but when does it usually occur in the northeast? Other then transition from turnover why would DO be different in deeper spots then other lakes in summer?

[Paul Roberts]

Timing:

You know, I wasn't on the water, taking profiles much at that time of year. But, as I remember it, turnover occurred anytime from late mid October into November (in NYS).

You can keep tabs on it by knowing when the surface (over deep water) cools to near hypolimnion (below TC) depth approaching what's called isothermy meaning all the same temperature. When the water column approaches isothermy, the density difference that kept these water masses separate erodes with it. All it takes is a good wind to mix it all up.

You can get a general idea of when turnover is imminent by noting when surface temps drop to around 60. From there it's up to wind, and/or continued cooling (which is inevitable by then). Of course not all lakes turnover, bc some do not develop a TC. And those that do vary with the depth and robustness of the TC, and the water quality below it.

As to why some lakes:

Deep areas below light penetration do not support plants (rooted or planktonic) that produce the O2. Most LM lakes are either eutrophic or mesotrophic (often with eutrophic areas) and are fertile enough that nutrients (dead organic matter -DOM) collects in the basin and supports a bacterial population that uses up existing 02. No 02 is produced down there so it isn't replenished until turnover. After 02 is used up, anaerobic bacteria take over, many of which respire using nitrate, or sulfur, instead of oxygen thus the sulfurous odor at turnover in some water bodies, and in some drinking water wells too.

Oligotrophic lakes are different in that they are infertile and so little organic matter collects in the basin, and that that does is processed by relatively small populations of aerobic bacteria, or if it's deep and cold enough, maybe not at all. Turnover in these lakes is a period when trapped nutrients get rolled back up, bringing a flush of important nutrients back up into sunlit waters. It also allows warmwater fish to move deeper than they had in summer, and exploit deeper (coolwater) preyfish. This is why many such waters can have a deep fall fishery.

Such lakes also have excellent water clarity and can have weedlines to 20ft or more. If you wanted a ballpark guess as to whether a lake has a deepwater fishery in summer, the first bet would be on water clarity.

Reservoirs that move water really well can keep things mixed up and oxygenated in the depths. But stagnant periods can deoxygenate the depths.

You can understand why lake associations and municipalities are so concerned with lakeside development, and associated fertilizer and sewage runoff. Many, if not most, mesotrophic lakes have been turned eutrophic by human activity.

You can also see why turnover is not always a deathknell to fishing. It can raise Caine in some waters, and some years, but it can also be an excuse almost as common as the dreaded cold front.

[RobbyZ5001]

I hope I am not the only one reading your replies paul...  This info is great.... I love trying to put all the info I learn in perspective to try to figure out why things work the way they do! I can't process it all right now in my current state I will have questions in the AM.

[cart7t]

I hope I am not the only one reading your replies paul... This info is great.... I love trying to put all the info I learn in perspective to try to figure out why things work the way they do! I can't process it all right now in my current state I will have questions in the AM.

Pauls info is great.  It also points out why another piece of equipment that was supposed to be the answer to a bass fishermen's quest to finding fish on a lake, never turned out to be the answer.  The oxygen meter.  20 some odd years ago, having an oxygen meter was a must.  The fish can't live where there ain't oxygen for them to breathe.  It turned out to be another non-answer in the end.  Fish can and will inhabit the depths even though the oxygen levels aren't considered ideal.  

[RobbyZ5001]

Well I sobered up and reread your last post Paul. Great info again! Do you find that when reservoirs release water that the DO is higher in the depths or will it depend on amount of flow, width of lake, and other factors? Do you ever see lakes that show oligotrophic and eutrophic qualities specifically showing the bacteria examples you mentioned?

[Paul Roberts]

Quote

Pauls info is great. It also points out why another piece of equipment that was supposed to be the answer to a bass fishermen's quest to finding fish on a lake, never turned out to be the answer. The oxygen meter. 20 some odd years ago, having an oxygen meter was a must. The fish can't live where there ain't oxygen for them to breathe. It turned out to be another non-answer in the end. Fish can and will inhabit the depths even though the oxygen levels aren't considered ideal.

Yeah, the words THE answer and IDEAL assume that there could be a single factor that overrides all others, and actually there can be at zero O2 ;D! Beyond that (and apparently <2ppm in winter and <5ppm in summer), there's an awful lot of real estate still left to cover. Other things weigh in more heavily in the vast majority of circumstances. You'd be much more efficient covering it with sonar and a lure, than with an 02 meter.

HoweverO2 could weigh in heavy in certain circumstances: like heavily eutrophic waters in winter and mid-summer resulting in uninhabitable areas, or time periods. One thing that pops up each year, mid to late summer, is people complaining they can't catch any fish in their favorite lake or pond. Talk shifts to trying something new, or to fears that the fish have suddenly had an IQ boost, but it may not be the anglers fault. An 02 meter might actually help in such circumstances, at least to answer a burning question, but I wouldn't run out and buy one. I'd like to have one for one particular pond I fishbut a meter worth owning is too expensive for the use I could get out of it. And I don't need another project lol.

BTW: The cheap units that you see in fishing catalogs do not measure 02 they extrapolate from temperature, assuming the water is at saturation which O2 compromised water is NOT. The whole point of measuring 02! Save your money.

Quote

Well I sobered up and reread your last post Paul. Great info again! Do you find that when reservoirs release water that the DO is higher in the depths or will it depend on amount of flow, width of lake, and other factors? Do you ever see lakes that show oligotrophic and eutrophic qualities specifically showing the bacteria examples you mentioned?

I have not done research in this. As a fisheries technician, water chemistry was standard protocol. My understanding of it is really pretty rudimentary. But there are entire fields of study waiting to be delved into. Maybe you could revisit this post in say, 2 or 3 years? ;D I'll be all ears. If you wish to pursue, on your own, at least read about nitrogen cycling in freshwater systems. Nitrogen is a key component in the interactions between plants and bacteria.

As to O2 levels in reservoirs, you might have something to offer here. Of course flow, temp, velocity, hydrography, would factor in.

Are we getting complicated yet lol? I always chuckle when I hear some non-intellectuals hand-wringing that somehow science will strip us of mystery. Get real! I think, Actually take up science, or even fishing! Then spout off, if you still can. Your head and heart will be stuffed full of mystery, much more so than all the BS that passed for it previously. And you're opinions will feel really small, instead of really big, and you might actually be satisfied with that.

Off topic now?? No, the question was, how does a terminal electron receptor (like 02) cycle through aquatic systems, related to fishing. That's as big a question as you care to make it.

[Paul Roberts]

Now I have a question for you, for clarity in the discussion:

You mentioned:

"Why is it that we still catch fish 20ft+ when the DO is not suitable?"

Were you catching fish at 20+ in this lake around the time you took those samples?

[RobbyZ5001]

Now I have a question for you, for clarity in the discussion:

You mentioned:

"Why is it that we still catch fish 20ft+ when the DO is not suitable?"

Were you catching fish at 20+ in this lake around the time you took those samples?

No I was not catching them at the same time sampling was done. I agree with you too on the mystery aspect... the more I learn the more confused I get if that makes sense. That is what draws me to fishing though...because it is a huge puzzle and if you fish large tournaments there is always a big bag brought in. Someone always figures it out and fish will always eat something,  somehow, somewhere. The hardships keep me interested in obtaining my goal of being consistent. Hopefully I find that same passion for research since that seems to be at the end of the road I am heading on.

[SPEEDBEAD.]

Now I have a question for you, for clarity in the discussion:

You mentioned:

"Why is it that we still catch fish 20ft+ when the DO is not suitable?"

Were you catching fish at 20+ in this lake around the time you took those samples?

No I was not catching them at the same time sampling was done. I agree with you too on the mystery aspect... the more I learn the more confused I get if that makes sense. That is what draws me to fishing though...because it is a huge puzzle and if you fish large tournaments there is always a big bag brought in. Someone always figures it out and fish will always eat something, somehow, somewhere. The hardships keep me interested in obtaining my goal of being consistent. Hopefully I find that same passion for research since that seems to be at the end of the road I am heading on.

I am glad Gifford Pinchot State Park and I could assist you in your hardship and confusion last weekend!!

;D

[RobbyZ5001]

Wayne between the rednecks, the boyfriends, Mr. talksalot, and old angry man it was a fun day.

[WRB]

Suggest that you search "thermocline" and read the variety of articles.

Bass can move within a 30 foot or 1 atmosphere depth change without too much discomfort and will relate to the thermocline level when it exists.

Some reservoirs will have multiple thermoclines created by current during power generations. Current affects both thermoclines and DO levels throughout any given day. Current can also be wind/wave generated and will mix the DO and bend the thermocline.

Best way to determine at what depth the bass are using is with good sonar; you can see both thermocline and bass/baitfish levels.

3-12 mg/l is well within the tolerance levels for bass and that is a wide DO band.

More important regarding bass is the water temperature; 70 is ideal, tolerance level; 40 (39.4) to 85 degrees, also a wide band. Below 40 degrees the DO level are too high, above 85 too low for the bass to survive very long. Smallmouth tend to tolerate colder water for a longer period and therefore can live further north than LMB. FLMB can tolerate slightly higher water temperatures, however prefer cooler water if available and locate under weed mats or near springs for that reason, when the water gets over 85 degrees.

Water, like air, isn't evenly mixed, there will be colder zones and warmer areas at the same depth with different DO levels. The lakes structure has a lot to do with mixing or up welling currents and one more reason bass and bait like to locate near abrupt contour bottom changes.

WRB

[RoLo]

You can also see why turnover is not always a deathknell to fishing. It can raise Caine in some waters, and some years, but it can also be an excuse almost as common as the dreaded cold front.

For many decades, the fall turnover has been ballyhooed as a time when fish are highly negative and unresponsive.

According to research of late however, the troublemaker is not fish disposition but fish location.

Once fish are located during the fall-turnover, they appear no more difficult to catch than at any other time.

During the fall-turnover however, the water temperature, water density and dissolved oxygen level

are similar throughout the entire lake. Without the constraints of a thermocline and oxycline, fish of all species

are free to scatter hither-and-yon, not only across the entire lake, but anywhere between the surface and the bottom.

Paul, as a special favor to me, do not take away my "cold-front" alibi...it's all I've got left ;D

Roger

[Paul Roberts]

You can also see why turnover is not always a deathknell to fishing. It can raise Caine in some waters, and some years, but it can also be an excuse almost as common as the dreaded cold front.

For many decades, the fall turnover has been ballyhooed as a time when fish are highly negative and unresponsive.

According to research of late however, the troublemaker is not fish disposition but fish location.

Once fish are located during the fall-turnover, they appear no more difficult to catch than at any other time.

During the fall-turnover however, the water temperature, water density and dissolved oxygen level

are similar throughout the entire lake. Without the constraints of a thermocline and oxycline, fish of all species

are free to scatter hither-and-yon, not only across the entire lake, but anywhere between the surface and the bottom.

Paul, as a special favor to me, do not take away my "cold-front" alibi...it's all I've got left ;D

Roger

;D ;D

Roger, I'm working hard at taking away ALL alibii's. Unfortunately, I just don't have the 100 fish days every time out as proof. Still workin' on that end of it.