Turnover?

[bchen]

Mike, Can you explain fall turnover for me? When does it start to happen? Thks

[Mike Bucca]

Bchen, Alot of folks don't know that turnover actually happens twice a year. Right now the surface of a lake the water will be very warm and stays warm down to a certain level. For example, the surface might be in the 90 degree range while 15 feet deep it is 80 degrees. From 15 to 20 feet the temperature will drop fast - several degrees in a few feet, from 80 to 60 degrees in this example.

Below 20 feet the water might be as cool as 60 degrees and it will stay that cool all summer. Unfortunately for the fish, this deep, cool water is very low in oxygen. Fish can not live long in it. A good depthfinder will show the thermocline because algae and protoplankton will form a layer there, and the deeper, colder water is much more dense.

Here is a temperature graph showing temp as it relates to depth. Another name for the thermocline is Metalimnion

Fish are limited to spending most of their time in the upper levels of the lake and this is a good time for the striper guys to U rig as they can cover that thermocline depth very effectively by trolling U rigs.

But as the surface cools in the fall, the top layer will suddenly mix with the lower layer, breaking the thermocline, when the surface layers get as cold as the lower layers.

Within the past few days you can tell that fall is coming. The temps are nowhere near as hot. Lots of wind and overcast. This very well could be the very start of our water temps starting to drop.

When turnover occurs the stale deeper water mixes with the upper levels, and the whole lake may take on a murky look and have a bad smell or you might see alot of bubbles for several days the fish don’t feed much. Then, after things settle down, the fish will scatter. After turn-over the whole lake has good oxygen content and fish can move anywhere and feel comfortable at any depth. They are hard to pattern because they roam a lot for a few weeks before setting up on deeper winter structure. This is where running and gunning is at it's best.

Here is an article I wrote on the subject a few years ago. It's got a couple of paragraphs on turnover and the thermocline.


www.insideline.net/2005/bucca-thermal-refuge.htm

[bfriendly]

BCHEN, that is a great question! Especially here where we 2 turnovers. Maybe even a better answer(Simplified) from the pro! I have been trying to figure this thing out and must have missed or forgotten how the coolest deep water has low oxygen levels and that is why it is not so great for the fish.