Finding walleye

[West Basin]

Seems I post this little sonar education every year about this time.

Sonar technology is advancing rapidly, so some of this may have changed, but the principles are the same.

Determining what you are seeing on your screen is all important. Many people think they know, but unless you understand how sonar works, you won't be certain.

The marks on your screen are determined by the strength of the return sonar (sound). The sonar transducer sends out an acostic (sound) wave through the water column in a "cone" shape (think like a flashlight beam). Any object that sound wave hits bounces back a return signal to the transducer. The transducer then sends that return signal to the fish finder and the software "makes sense" of or translates it into a mark on the screen. Your screen is two dimentional, but it's displaying three dimentional data. In most cases your screen is not showing where around your boat that mark is, just what depth it is at and how strong the signal was.

Return signals can vary and can create the same mark on your screen. Example: in 30 feet of water a small fish directly under the boat at 10 feet depth will send back the same signal strength as a large fish at 25 feet depth way out at the fringe of the signal cone. Those two signals will show up as the same kind of mark on your screen. But they are not the same size fish and in some cases one may be a fish and the other a clump of free floating vegetation.

Another thing to know is once an object comes into the sonar cone, it will continue to be marked as long as it stays in the cone. A fish swiming through the cone at the same depth will mark as a continuous line or the same mark moving from left to right until it leaves the cone. It may change it's mark as it moves from the edge of the cone to the center and back to to other side edge. If you are staying still in the boat (say at anchor) and a fish just hangs under the boat, it will appear as a solid line across the screen. The screen displays the new data in a left to right moving format. Newer units may recreate the entire screen each time it updates, but it's still working the same way. Newer units also have the ability to show a more three dimentional view. It depends which setting you have it on.

Generally what you want to look for is consistancy. Same type and size marks at the same depth zone, over say a minute or so time length. That's how schools of walleye should look.

Believe me when I say a lot of what people think they are seeing is not what is down there. I've seen things on fish finders that we through were fish only to scuba dive that spot and find out it wasn't. There is a lot of "stuff" out there that can show up as fish or fish schools. Or you think you are looking at one fish species marks when it's actually another. I will be putting out underwater cameras this season to match up what a fish finder is showing with what is actually there. I should know alot more by September.

There is a lot more to this to tell here. Look up some online videos or articles on fish finder sonar to learn all the details.

[itsbob]

Thanks West Basin for the great info on how our sonar works.

[captainshotgun]

Thx