Stillhouse bassman

I am new at fishing with a Depth finder, I have lowrance elite 3x, I am unsure is my transducer is set up correctly. At anything above idle the screen shows fish in the fish ID setting. I turn the fish id setting off and I have trouble identifying anything. I need help understanding how to use this device. I have researched several topics on you tube, there is limited information about the low end depth finders. This is what i have i cannot buy one more expensive for a few years.

During fall fishing the bass love shad! We all know they are preparing for the upcoming winter months. Also, we all know the shad head up river and creeks when it starts to cool off. What is a good fishing tactic if the lake has one feeder river and no other creeks and that one river is 5 miles on the other end of the lake?