Get the most out of your fishing sonar unit by understanding what you see on the screen. Sonar technology has come a long way in recent years. Even the least expensive fish finders can provide great results if used properly. Before continuing it is critical that you learn how to adjust sonar sensitivity manually.
Distinguishing Bait, Fish, and Bottom
Once your sonar unit is properly tuned you should be able to see the following:
- Small bait (shrimp, sand eels, etc.) will appear as clouds either suspended in the water column or just off the bottom.
- Larger bait and fish will appears as arcs either suspended or just off the bottom (where they can be confused with rocks and structure).
- When you are moving slowly (drifting) and fish linger beneath the boat the arcs will be even larger and stretched horizontally.
- When you are moving quickly the arcs will be compressed even to the point where they appear as spikes off the bottom or wide vertical lines suspended in the water column.
- Multiple fish will appear as overlapping arcs.
- You may seem partial or faint arcs when fish are on the edge of your sonar cone. These should not be ignored.
- Rocks and structure will be clearly defined. The echo beneath the bottom can help you determine whether you are seeing bottom structure or fish directly on the bottom.
- Flatfish such as fluke and halibut are virtually impossible to detect on most machines (more info below on that).
Detecting Bottom Fish (Fluke/Halibut) with Your Fish Finder
Fluke and Halibut are nearly impossible to read because they lay directly on the bottom (often partially buried in the sand). However, the fish are more aggressive than they appear. Experienced anglers target areas where they see significant concentrations of bait. This can make a big difference when trying to determine what depth to target along a slope or ledge.
Fish ID Features
If your fish finder has a fish ID feature, turn it off and NEVER turn it on again. Those features are made for anglers who do not have the time or skills to properly tune their sonar units. The fish IDs are almost always misleading. It is critical that you see the actual composition of the makrs on your screen so that you can determine exactly what they represent.
Watch Your Fish Finder When the Bite Is On
Pay careful attention to your sonar unit when the bite is on! When the bite is on and fish and bait are under your boat it is critical that you pay careful attention to how they appear on your fish finder. That is the only time you can be absolutely certain what you are seeing. Anglers often miss this opportunity because they are so excited catching fish, they never look back to the sonar unit.
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Frequently Asked Questions
Once your sonar unit is properly tuned, small bait like shrimp or sand eels appear as clouds suspended in the water column or just off the bottom. Larger bait and fish show up as arcs, which can be stretched or compressed depending on boat speed. Rocks and structure are clearly defined, helping you distinguish them from fish. Paying attention to these details helps you interpret sonar readings accurately.
Fish ID features are designed for anglers who lack time or skill to manually tune their sonar units and often provide misleading information. Turning off this feature allows you to see the actual sonar marks, enabling you to accurately interpret what is beneath your boat rather than relying on inaccurate automated symbols.
Fluke and halibut lie directly on or partially buried in the bottom sand, making them nearly impossible to detect with standard sonar. Experienced anglers instead look for significant concentrations of bait in the area to target likely depths along slopes or ledges where these flatfish may be present.
When moving slowly or drifting, fish arcs on the sonar display are larger and stretched horizontally, indicating lingering fish beneath the boat. As speed increases, these arcs compress, sometimes appearing as spikes or wide vertical lines. Understanding this helps anglers interpret fish size and position accurately.
It is critical to closely observe your sonar unit during the bite since that moment confirms the relationship between what you see on screen and the actual fish presence. Many anglers miss key learning opportunities by focusing solely on catching fish and neglecting to watch sonar feedback during successful bites.
Manually adjusting sonar sensitivity ensures that your fish finder provides the clearest possible image of the underwater environment. Proper sensitivity tuning helps differentiate bait, fish, and bottom structures by optimizing the unit’s responsiveness to different sonar returns, leading to better fishing outcomes.
