Knowing exactly what you are seeing on our fish finder is sort of an art. You have to know how your sonar works. You need to know how your sonar is configured. You need to know what kind of fish and bait are in the environment and how those fish and bait interact in the environment. Lastly, you need to know what your sonar looks like while your boat is stopped or moving.

Understand how your sonar works

Read the manual, watch manufacture videos, and do a bit of research on your sonar unit. Know what kind of cones your unit uses and how to control the contrast and sensitivity and generally configure your sonar. As an example, know how your units white marker works. This is a feature that let’s you select one color on the color palette and turn it bright white. You can use the white marker to turn the bottom and background bright white so any bait, fish, or other targets are very easy to see.

Bait and Fish

A sonar alone will not help you if you do not know what kind of fish and bait are beneath you. In the Puget Sound, the most popular baits will include: herring, sand-lance, stickleback, squid, and smelt. No matter what bait and fish you are after you will want to know their make up. For example, a squid has no swim bladder or bones, so it will show up very lite on your display (just a fuzzy blue color depending how your sonar palette is set up).


A herring on the other hand has a backbone and a swim bladder so a herring bait ball will show up dark in the middle of a bait ball and fuzzy on the outside. Sand-lance (also called candle-fish) will likely show up on the bottom. Sand-lance show up often in fine sand or fine gravel, so you need to know your bottom also. Like herring they may show up on your sonar as dark color ball, but that ball will be fixed to the bottom. Or sometimes if you drop your down-rigger cannonball down you may notice a dust come up from the bottom. That is actually candle-fish being disturbed from the burrows in the sand or gravel.


Fish on the other hand normally show on your sonar display as arches, diagonals, or worms. Fast moving fish through your sonar cone will show up as diagonals, while slow moving fish as worm shapes. Normally a good fish arch will be hard on top of the image and fuzzy on the bottom. A small blob on the bottom with a hard top could be a fish. Fish heavy bone structures and large swim bladders will create larger, more elongated marks on your display. Remember also that boat speed, depth of water, sonar speed, and sonar sensitivity will all have an impact on what bait and fish look like on the display.

Boat speed

If you are moving your boat too fast, objects will appear smaller…..too slow and they will appear larger. If you are anchored the more time a target will spend in your sonar cone. If there are large bumps on your sonar bottom reading, then you might be in some waves….it is not a rocky bottom. Your chart speed should be slightly higher than boat speed. Most sonar manufacturers recommends driving your boat 1 and 3mph and in a straight line, at a constant speed, to get the best picture of the bottom and fish.

How to Determine a Species on your Sonar

Determining the species of bait or fish is sort of an art. You may need to learn this over time. For example, if you are catching a certain type of fish, take a picture of your fish finder, and then study it. The next time you see it on your display you will know what you are looking at. As for bait, you can catch a fish then cut open the fishes stomach for a clue for what you are seeing on your screen. You will learn different species after a while. For instance, sturgeon will be at a large angle on the bottom angled down. Sea bass move slowly so you will likely see larger marks or even worms if they stay underneath the cone of your sonar.

dogfish and candlefish on a fish finder
herring looks like on a fish finder
salmon and herring look like on a fish finder

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