I'm not an expert, and have never had a long conversation with a sonar technician (just a short one). I researched fish finders several years ago because I kept getting into disagreements with my Uncle and other fisherman over what the screen was telling us. I also scuba dive in Lake Erie, so I know what's down there.

As far as I know, sound sonar differenciates between densities of objects. The more solid an object is, the stronger a signal that bounces off (returns) to the transducer. It's also a function of distance, water turbidity, and a few other factors. Not sure about the air-filled swim bladder, as I've heard that before. The sonar has to pass through the thickest part of fish to get to the swim bladder, so not sure if that's entirely true.

I've scuba dove on sites and then crisscrossed them with boat fish finders, so I've had numerous experiences of what the screen is showing and firsthand knowledge of what it's going over and showing. Even swam beneath the boat (20' down) and had people on board watch the screen.

Anyway, as I mentioned, many fisherman don't userstand how their sonar works, and what it's really showing them. If I get time, I'll call a company tech, get the info, and write an article on it for the local Lake Erie newspapers and my web site.

West Basin