Reading Your Fish / Depth vinder

[West Basin]

Saw a post in the fishing reports section about a fish finder. Over the years I've seen many fishermen misread their fish finders. From my experience, many people don't really understand how these instruments work, or what they really are showing you on the screen. Just a few things to remember about fish finders, although today's models technologies may have improved on this. You may already know these things, but most fishermen don't.

Often, what you see on your screen is not neccessarily what you think it is:
1. Your screen is two-dimentional. The sonar pings are three dimentional. There is no certain way to know where the target mark is in relation to your boat (left, right, forward, backward).
2. Solid, or strong, sonar returns will show up as large marks, weak returns will show up as small marks. A small fish 20 feet down directly beneath the transducer will return a very similar mark (strong signal but small fish) as a big fish at 20 feet just at the far edge of the sonar beam cone (big fish but weak signal). The computer and the screen cannot tell the difference, so the marks will look the same. Just because you get big or large marks on your screen doesn't mean they are large fish.
3. The highest object on the bottom marks the bottom on your screen. If the bottom is 20 feet, and there is a bolder coming 8 feet off the bottom, as long as that bolder is in the sonar beam cone, your screen will show the bottom at 12 feet. There is no way to know what is below that 12 foot depth because the bolder return covers up all the other sonar returns in that depth zone. There could be fish all around at 18, 16, and 14 feet, but you won't see them. When graphing rocky or varired bottom areas, make right angle passes to get a better idea of what is really down there.

There are other things to know about how your fish / depth finder really works. Take some time and learn these things and you'll get much better (real) information out of your unit.

Hope this helps someone.

West

[Gettin Jiggy]

My understanding of the sonar is that the sonar picks up the swim blatter of the fish. henz bigger swim blatter bigger fish. When they test the units they run golf balls under the transducer on a string. I was told this by an Executive of Standard Horizon.

[West Basin]

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