Fishfinder Depth Sounding Sonar Tips

Water Bottom and Topography

The transducers packaged with depth finders send out sonar waves that bounce off of the lake or ocean bottom and are received back by the display unit. When the sonar waves are received, the display screen indicates flat black lines indicating the water's bottom. If the bottom is muddy or soft, the display will show a thick solid black line. If there is brush or floating sediment, displays show large groups of pixels. Look for a depth number (locations vary depending on unit) that tells you the depth of the lake bottom, how deep the brush or sediment is or how thick the mud is.

Scuba Uses

Scuba divers use sonar depth finders to locate sunken ships or boats, vegetation or coral beds for diving. To get these results, they often use a manual for the Legend sonar depth sounding device. Make a copy of the Legend to keep next to the display unit to interpret symbols displayed in the screen. The Alaska Science Center, funded in part by the USGS, uses sonar depth finders to locate kelp beds, and sunken boats for diving salvage or scientific studies.

Fish Readings

Using a sonar depth finder to locate schools of fish is practiced by sport and commercial fishermen. Most displays have a fish symbol that appears when there are either single large fish under the boat and within the sonar wave zone, or schools of fish. Look for numbers next to or around these symbols. These numbers tell you the depth the fish are at, helping you determine how much line to let out, if sinkers are necessary and sometimes what species are present. Almost all modern sonar depth finders have a magnification button allowing you to zoom in at least two times to visibility helping you determine how many fish are present or potentially what species.