Lowrance Fish Finders use sonar (SOund NAvigation and Ranging). Sonar functions by utilizing an electrical impulse, converted into a sound wave and beamed through the water. The sound wave hits an obstruction, like a fish, or a submerged tree and bounces back to the fish finder device. The device works out the distance by calculating the time it takes for the sound, or echo to come back from the fish---or submerged tree.
Turn the a Lowrance fish finder on. The lights will flash and the display will show the Fish ID mode by default. The Fish ID mode is an interpretation of the actual sonar arches and is not the sonar map.
Examine the screen. The first set of digits at the top left is the depth. Below that is the water temperature. The little fish icons are the Lowrance fish finder Fish ID images. The line below that is the bottom signal. You'll see a gray line below that---defining a hard or soft bottom. The depth range at the bottom of the depth scale is below that.
Interpret the image to mean that where there are fish icons, there are fish. However, all may not be as it seems. The fish icons in Fish ID mode are machine interpretations of the actual arches created by the sonar. Arches are the actual maps created by the sonar and are more reliable. Fish IDs can be false readings. Bubbles and tree limbs extending outwards from clumps of submerged trees are notorious for causing false readings.
Learn to read sonar arches. Turn off the default Fish ID mode and look at the display. The arches you see are the schools of fish. Surface clutter, including bubbles that showed as fish icons in Fish ID mode, are represented by pixelated dots, as is bait fish. The arches are the real fish.
- fish on image by Mitchell Knapton from Fotolia.com