Of thermoclines and turnovers...

[crash]

Yea I know, an actuall fishing question from crash...take a picture.

OK, I've been trying to figure this out all summer and have a few theorys I wanted to toss around.

I fish a Reservoir that has a very defined Thermocline. It first shows up at around 25 to 20' and as the summer progresess it creeps up to 15', maybe even 10' if the weather is real warm like last year.

From what I have experinced, immediatly above or below it is where I want to be during the day, and as far away as I can get during the night.

From what I have researched its because of the Oxygen generation during the day, and consumption at night, of the organisms that bloom in the thermocline. Therfore they attract during the day, and force away at night.

Now for the tricky part.

Does the severity of the thermocline have any direct bearing on the sevarity of the Turnover? Last year was awful with bait kills and tough fishing for over a week. Does that mean that this years cooler summer is going to bring on less weed growth and a less defined Thermocline, hince a less severe Turnover?

Whats your thoughts? Are the two directly connected or is this just a trend in my Reservoir.

[Neal/Co]

I've noticed that when a couple of my favorite lakes turn over, wind plays a major role. If it is windy, turnover happens alot quicker. I can always tell when this happening because of all the dead weeds floating around, especially on the windward side of the lake. All the floating weeds make it almost impossible to fish for about 7-10 days.

[byron]

Its interesting that you say the thermocline moves up during the summer. My experience has seen that this line goes deeper when the surface temps rise. One thing i have learned is that thermocline is just the place where there is a lot of dissolved oxygen and the line separating warm and cold water.

Now for your question. Cooler summer temps=cooler surface temp. cooler surface temp, means the thermocline should be closer to the surface (not always though) and possibly less weed growth. Since the surface temp was cooler, the turnover should be a gradual one with the fish adapting quite easily. If there was drastic cold/heat spell or major water drawdown, the fish/bait/plants in some cases would die from not being able to adapt.

[AquaMan]

I, too, am of the understanding that the thermocline falls deeper during the summer. Since the thermocline is the term used to describe the line between warmer oxygenated water on top of cooler less oxigenated water, it stands to reason that warmer temps on the surface will drive the line down.

Might be off on this, but that is what I was lead to believe. I know that not all lakes are the same and that depth, flow/current and wind have dramatic effects on the thermoclines.

AquaMan~~~~~~~~~~~~~

--- "It all begins and ends at the water's edge"

[crash]

Thats weird isn't it?

In this case we're starting out with a Reservoir that has very little current or weeds. There is simply not enough oxygen in the water. There has actually been talk of installing huge areators on the reservoir floor. You'll run across dead spots at times, where nothing will survive, when the weather gets real hot.

When I put bait down and drift I cant run any deeper the what the Thermocline allows or I get dead bait. Is that because of the dead water below the thermocline? or am I way off here and there is another reason for the stratification other then a thermocline?

This is why I turn to you guys.

[markb(loser)]

you may be combining two animals.....thermocline...which
refers to lake stratification by temperature....and
the vertical concentraction of dissolved oxygen
within the lake....the two...oxygen and temperature...
may or may not be related....thermocline will move
downward in water column as summer season progresses...
oxygen debt...i am assuming that is what is occuring
in lake you refer to...will move up in the water
column as summer progresses....some lakes...usually
shallow, sheltered from wind, with little incoming
freshwater... a pond for example...will experience
oxygen debt without ever forming thermocline...other
lakes...usually large oligotrophic lakes...like eastern
basin of lake erie or lake ontario....have well defined
thermocline with little oxygen debt...lake trout, salmon
and others routinely live in or below thermocline...
in some lakes suffering from oxygen debt in lower
water layers...a fish kill can be associated with mixing
periods...like fall turnover...especially if a lake has
little exposure to wind or incoming fresh water during
summer period...since a large layer of water...say from
10' down as in your example...is low in oxygen...when
lake finally mixes...lake becomes temporarily low in
oxygen and fish kill occurs....this could even happen
in say august...if lake experienced a wind storm violent
enough to mix entire lake...my guess is the lake you are
refering to is sheltered from wind...has little incoming
fresh water...and has a fairly high productivity; it is
eutrophic...oxygen debt is occuring in lower water column...
a nice hot calm summer increases oxygen debt...that is why
the fish kill last year...a cooler, rain filled summer would
decrease the problem...

[crash]

Thank you Thank you Thank you

AH HA!!! I SEE said the blind man to the hearing impared

learn sumtin new everyday.

[crash]

But how does a thermocline play into this? Or isn't there one?

So the movements of bait and fish are just them being restricted, Not my organism/oxygen theory?

Would this take place in some parts of the lake but not others?

See you sparked my curosity...

[Gilligan]

Wow! Nice post, Loser. So what do you think about the south basin of Chautauqua? 19'max depth, does a thermocline come into play? I'm sure with the way it blows in that country oxygen should be no problem.

[byron]

anything under 30ft will not really have any thermocline. Just too shallow. Key to remember: If you can see the bottom or sunlight can easily get to the bottom---no thermocline. Key for you might be to look for warmer/cooler surface water and try there.

[Phil T.]

Don't forget that plants not only produce oxygen from water in photosynthesis when in sunlight, but also respire oxygen into carbon dioxide (everything does to provide energy for life functions) for 24 hours each day. Excess weed growth will cause a "summer kill" because the plants use more oxygen day&night than they produce during the day. As expected, this will occur more often as the hours of daylight shorten.
For a quick summary of thermocline and its effect as an oxygen barrier, resulting in an anearobic depth and and aerobic shallows, look up the subject at www.britannica.com. The article isn't as good as my old limnology texts, but it will give a good start.

[cisco]

Yes, and on larger bodies of water the layer will actually tip under the influence of sustained winds. On Lake Michigan it is most severe in the form of a thermobar -- which are commonly referred to as "scum lines." As with a thermocline, the temp on one side will be different than the other -- thermobars collect all sorts of organisms, thus little fish move in followed by bigger fish. Isn't water wonderful?

[cisco]

It gets even more complicated with small surface area, but deep lakes -- Grindstone Lake in central Minnesota, for example. It will typically have two thermoclines, and trout will go well below the first. These are often called "two story" lakes.

[markb(loser)]

i aint wise.....thats for sure....but i do
love sarcasm....i would think that your
oxygen/organism theory is on target....fish
living in lake are controlled by oxygen content
of water...as oxygen decreases...fish are
forced into layers of water....that may not
be of their temp preference....but
have the oxygen to meet the fish survival needs...
if you cant draw breath....gonna
croak no matter what temp is...question is...are
fish forced into temperature zone that shuts them
down...causes them to stop feeding...at what point
do walleye...etc...say...too hot...i'm going to
estivate.....until temp is to my favor....or...do
certain temps occur which promote fish activity..
say at night....and other times i'm gonna park
my ### on couch.....or worse yet....do temps occur
in oxygenated area...that will actually kill
fish....now you have double whammy...fish cant
live in temps where oxygen ok....and...fish cant live
where temp is good but oxygen is low or absent....or...
the opposite....do fish lay dormant in low
oxygen water when temps in well oxygenated areas
are too high.....

[Gilligan]

Cisco,

I encountered this on east basin of Erie once 2 seasons ago. Killed the walleyes there that day.

I have heard of the charters on Lk Ontario searching out these areas to fish steelhead. What are your fishing experiences fishing around them?

[markb(loser)]

i got a real love/hate relationship with
chautauqua...i keep comin back to question
do fish move between basins...i have never
really fished enough at chautauqua to
answer that question to myself...and that
refers to walleye, panfish, whatever...
have had great days in both basins.....have had
terrible days in both basins...i also like to
tell myself...that fishing/boating pressure has
something to do with my success on chaut...again
though...i aint sure thats true....bottom line...
i'm lookin forward to ice season at chaut...for
panfish and walleyes...and i'm sure i'll be
disappointed when it's over...but it's always
FUN!!!!....

[cisco]

Gilligan --
In the southern basin of Lake Michigan we (myself and others in my club -- some 50 members) always work thermobars, or "scum lines." You will see a marked temp difference as you cross. It does not seem to matter if you are on the cooler or warmer side, simply cross in S patterns. As I understand it, the bar serves as an obstacle to planckton, zooplanckton and other good stuff fish like. And, with collection of food at one spot, fish will be looking. In my experience I have to say that yes, it is good strategy to follow "scum lines." Good fishing.