How to Read Fishing Graphs

"Fishing graphs" are the visible display on sonar fish finders. The sonar emits sound pulses, or "pings," into the water below a boat, and the fish finder charts the echoes that return on a small, monochrome screen. The results of each echo scroll across the screen, and when viewed side by side all these images "graph" the lake, river or ocean bottom, including weeds, rocks and shipwrecks and also the fish between the bottom and the boat. Some models include a "Fish ID" that marks the fish with fish icons. Other models show only smudges and jagged lines that you must interpret.

Instructions

    • 1

      Determine the changing depth under the boat by reading the current depth display, which is usually on the left side of the display screen.

    • 2

      Evaluate the bottom contour by watching the graph. The harder the bottom, the darker the shaded area will be. Rocky bottoms appears as very dark circles on the bottom. Trees look like spikes, and weeds will appear as a thick uneven band with no gray inside it.

    • 3

      Read horizontal bars on the graph as "thermoclines." Thermoclines are sudden changes in the temperature of the water.

    • 4

      Interpret any arc as fish. Either the fish move under the sonar or the sonar moves over the fish, but the result is always an arc that is darkest in the middle and faintest at the ends. Turn on your Fish ID feature, if your model has one, when you see an arc.

    • 5

      Find schools of baitfish by looking for balls or blobs in the water above the bottom.