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  #1  
Old 03-02-2005, 01:22 AM
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Default The Thermocline.

The link between fish behavior and water stratification

If you're an impoundment striper fisherman you must know and understand the thermocline to be successful. The thermocline can be found by measuring the water temperature at various depths with a recording thermometer.

The thermocline is a thin layer of water in a lake which is sandwiched between the upper layer of water (the epilimnion) and the lower, colder layer of water (hypolimnion). During the summer months, surface water is heated by the sun and the surface temp could be 80 degrees or more. This floats over a layer of colder more denser water called the hypolimnion. Now, between these 2 layers you have a thin layer in which the water temp drops fairly substantially. This will be the thermocline. The temp at this level may be high 60's and up in about the middle of spring.
This is the home and feeding area for the larger fish. The thermocline layer also has more oxygen and an available food supply.
The hypolimnion layer is the colder water on a typical lake, but is almost devoid of oxygen because of plant and animal decomposition. If the surface temperature is 75 degrees, then the hypolimnion will usually be anywhere from 39 degrees to 55 degrees.

In the summer the stripers cant take the high surface temperatures of the upper layer and the underoxygenated properties of the lower stratum. So hence the necessity of finding the lakes thermocline.
Each fall a lake will "turn over" the cooler top layers will displace the bottom layers and recirculate. The shallow coves are among the first to cool and the bass will begin to relate to shallow structure.
Also fish dont have eyleids and light refracts differntly at dawn and dusk so they are then more likly to surface and feed.

In shallow lakes with an average depth of 15 feet usually no thermocline will develop.
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  #2  
Old 03-02-2005, 05:55 PM
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Does that also apply to the thermoclines on my fishfinder when I'm in Saltwater...???
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Old 03-02-2005, 06:24 PM
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Quote:
Originally Posted by BB
Does that also apply to the thermoclines on my fishfinder when I'm in Saltwater...???
OK BB The answer required a little research. I always like to learn something. We can start with these two.
Fresh water stratification
http://waterontheweb.org/curricula/b.../teaching.html

The Ocean
http://www.ldeo.columbia.edu/edu/dee...s/o_strat.html
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Old 03-02-2005, 06:38 PM
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Thanks Jim...I also like to learn new stuff...

...always good to add to the mental library of fishing knowledge...
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Old 03-02-2005, 06:39 PM
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BB you'll enjoy this one too. 8)

http://www.glf.dfo-mpo.gc.ca/sci-sci...ausujet-e.html
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Old 03-02-2005, 07:18 PM
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I especailly found the part about the moon/tide phases and beach characteristics, the most useful...

Its amazing about how science can have such a large affect on your fishing...

...My science teacher is a amazing fisherman...one of the main reasons is that he understands every bit about weather, the moon, the tides, barometric pressure etc...
...I can't imagine how greatly all that knowledge could help improve my fishing...
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Old 03-13-2005, 03:40 AM
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Dan

These two paragraphs about the oceans thermocline pretty much sum it up.

Waters warmer than 10?C (50 degrees Farenheit) which dominate the sea surface do not extend much below 500 m in the ocean; the warm waters provide just a veneer of buoyant warmth over a basically very cold dense ocean. The sharp drop off in temperature with depth, characteristic of the ocean between 40?N to 40?S is called the thermocline. The waters below the thermocline exhibit much reduced temperature decrease with depth. In the salinity field the surface tropical and subtropical ocean is salty, with the deeper waters somewhat fresher. The rapid decrease of salinity with depth, accompanying the thermocline, is called the halocline. The deep Atlantic is relatively saline. This water is derived from the sinking of cooling of saline surface water in the northern North Atlantic. This is the North Atlantic Deep Water. In contrast the deep Pacific is relatively fresh, as it experiences no deep convection of cooled salty surface water, its surface layer is too fresh and thus buoyant to sink into the deep ocean, at reasonably cool subpolar SST. The deep Atlantic is also warmer than the deep Pacific, as the saline North Atlantic Deep water is sufficiently dense water to inject relatively warm water into the deep layer. Towards the sea floor temperatures reach below 0?C (32 degrees F.) marking the presence of Antarctic Bottom Water derived from the shores of Antarctica. Below the thermocline is a low salinity layer derived from the Antarctic Circumpolar Current. This water mass, made relatively fresh by excess precipitation of the circum-Antarctic belt is called the Antarctic Intermediate water. A low salinity intermediate of more limited extent forms in the North Pacific.

A parcel of sea water achieves its temperature and salinity at the sea surface in response to sea-air heat and freshwater exchange. Its surface derived T/S values change within the ocean interior only by mixing with other water parcels. Hence sea water spreading from the surface into the ocean volume can be to trace by Temperature Salinity properties. That 75% of the ocean volume falls with a narrow range of temperature and salinity indicates that only a small part of the sea surface contributes to the characteristics of the deep ocean.


Oceanographers often use a temperature/salinity (T/S) diagram to determine the origin of the sea water properties
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Old 03-14-2005, 02:28 PM
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That's excellent stuff - I'm new here but I suspect a few others besides myself fish fresh water for more than just stripers and that's useful for many fisheries. Those Quicktime movies make it so much more simple to understand. Thanks :D :D
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Old 03-23-2005, 12:23 AM
(T)angler (T)angler is offline
 
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Default Putting it in jus hatched terms....

it sounds like your saying that the Thermocline should be around the mid to high 60's, is this the temp that Stripers prefer? Right now in my area its cold and rainy, real overcast, so this means I should be surface fishing right? Get used to the name here, I will have a ton of quistions....thanks guys.
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Old 03-23-2005, 06:09 PM
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Around here...the magic number is 50 degrees, once it hits 50...its on!!!
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Old 03-23-2005, 09:50 PM
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Know the preferred temperature range of your favorite species and you'll catch more of them.


Just like humans, fish have a defined temperature range in which they feel most comfortable. But unlike humans, that range varies - often considerably - from species to species. Therefore, the angler who knows the exact comfort range of the fish he's looking for has a definite edge.

Since fish cannot add or remove layers of clothing to stay comfortable, their only option is to move to another area when they find the temperature too warm or too cool. fish are essentially cold-blooded creatures (although some tunas are slightly warm-blooded), which means they can't regulate their body temperature internally. This makes them extremely susceptible to rapid fluctuations in water temperature. For example, plummeting temperatures can stun or even kill large numbers of fish before they're able to move to another area. Even subtle changes in temperature will affect the behavior of fish. In some cases, a degree or two can alter the feeding habits of a species without causing them to leave the area.

Get a Thermometer!

A quick glance at the thermometer will let you know if you should bother targeting a particular species. Striped bass, for example, typically head for deeper water when the shallows are too hot or cold for them. So why beat your brains out trying to catch stripers near shore in midsummer when the water temperature is over 75 degrees? Better to be looking for bluefish, which are happy as clams until the water passes the mid-80-degree mark.

Of course, there are some exceptions to this rule. For example, a high abundance of food will often keep game fish in an area that's a few degrees outside their preferred range.

Optimum Temperatures
Fish are, of course, happiest when they're in water of their optimum temperature range. This is especially true of many inshore species, such as striped bass, bluefish, bonefish and tarpon. Tarpon, for example, can often be found in deep channels when the water temperature is barely 70 degrees, and will only move onto the flats to feed when the water is within their optimum temperature range.


Offshore Temperatures
Modern satellite technology has enabled us to determine offshore sea-surface temperatures accurately and in excellent detail. There are even several companies that provide this information in chart form for subscribers.
http://www.weatherunderground.com/MAR/
When a large body of warmer or cooler water moves into an area where those temperatures are not normally encountered, it often brings "exotic" species with it. This is why many tropical and subtropical game fish were caught from California to northern Washington during the 1997 El Ni?o. During this same period, overly warm water off some parts of Central and South America pushed those same species out of areas where they are normally abundant.

But if you wait for the next El Ni?o or La Ni?a to cause unusual fish movement, you'll be missing out on a lot of action. On the East Coast, large fingers or eddies of warm, tropical water often break off from the Gulf Stream and move into cooler water, bringing with them warm-water game fish. Billfish appear off New England every year because of this phenomenon.

On a more day-to-day level, noticing the change of a degree or two that delineates the edge of a current can pay big dividends. Such current edges, or rips, tend to concentrate baitfish, and fishing on the side of the rip where the temperature is best for the species you're seeking can make all the difference in the world. This is why no savvy offshore skipper would ever leave the dock without some sort of water temperature gauge.

Sudden Changes
A rapid decrease in water temperature can chase fish away or bring them in. Even a strong breeze that lowers the water temperature a few degrees can affect the presence or behavior of fish.

If the temperature of the water drops too fast, fish will sometimes leave the area, even if the temperature remains within their range of tolerance. Why? They simplydon't like the sudden change.

In some cases, the water temperature can plummet ten degrees or more overnight due to the passage of a cold front. Even if it's calm and sunny the next day, the ocean may seem like a biological desert. That's how important water temperature can be.



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Old 04-24-2005, 09:04 AM
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one aspect of water's thermo dynamics is often over-looked by anglers, that can be, and often is, the 'holy grail' of fishfinding..

that is the somewhat false thermocline a river mouth has during the ebb and flow of the tides... the colder ocean waters that lay in the bottom layer of the river bottom quite often a ways up-river (often cleaner..see: key to holy grail) most times is much cleaner.. ever fish an outgoing tide that looks like pea soup?... ever wonder where the fish went when this occurs? most times one needs to find CLEANER water to find fish. A lot of times that is in the trenches of the bottom... fish will lie just below this 'false thermocline' just because it's clean enough to breath and a bunch of food drifts thru just over their heads. they'll dart in and out of the muddy stuff to chow but won't hang in it for more then a few seconds before they retreat back to the clean layer... most times it's tough to get a sonar reading past the goop to see the clean layer at the bottom or the fish lying there for that matter.. but it's there and so are the fish ... when you have this situation, don't call it quits... find a trench near where you were catching them before the ebb turned to goop.. and fish it deep with a bit of chartruese or black colored jigs.. also jigs with a spinner like "stump jumpers" can be the only thing they'll touch.. been there.. done that..
don't tell anyone.. it's one of my deep dark secrets..
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Old 04-24-2005, 09:50 AM
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Default thermocline

finally out of the thermocline! hope all is okay with you jigman!



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Old 04-27-2005, 03:35 PM
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alls cool, now but I been in the trenches the last few months... dude I came in just to see that avatar and you changed it to jed!.. WTF! :D ol' Jed just doesn't do it for me... the can lady was better :roll:
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Old 04-27-2005, 10:21 PM
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sorry jethro, will change it back in the morning, jd must be upset, he never replied about my goof



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