Dead Zone Fish...

We rarely see fish on drop-offs because the closest “bottom” to the transducer is the drop-off so the fish are not seen. All sonar displays is echo strength of the target and the distance the target is from the transducer. The first example has the fish a farther distance from the transducer than the bottom so the fish echo is added to the “bottom “echo and not seen. The “bottom” under the transducer is 25 ft, fish at 23 ft, and the drop off “bottom” is 20 ft. Now visualize what the sonar will show you. The picture is my rough drawing so it is not to scale; it is just to get you thinking.

The second example shows a fish in the dead zone.

I have only captured one recording like this so the conditions have to be perfect.
I am drifting very, very slowly on a sharp drop-off. Notice how flat the fish arch is. The drop-off is a fast taper and not a ledge. I think the reason you can see the fish in the dead zone is because of the sharp drop which causes less return from the bottom so it displays the bottom as red for echo strength. The fish echo is added to the bottom so the fish arch becomes yellow when it is in the dead zone. On a slower drop-off, the “bottom” would return stronger echoes so it would be yellow and the fish would not be seen in the dead zone. The bottom is sand and I have never seen fish on the side before. The top was loaded with fish. I just think there were a lot of fish so I got lucky capturing this recording.