You can also distinguish between fish and cover because fish have a different density than wood, bamboo and weeds, etc. Probably the easiest identifying feature of a sonar return made by a fish that stays in your “view” for any length of time is that it has a constant thickness or “volume”, which shows as a consistent line across your graph. Bigger (thicker) and shallower fish will show up as thicker lines because the ping comes back louder than it does on a smaller (thinner) or deeper fish but each fish will show a consistent thickness or volume as it’s sonar return is displayed across the screen.
As the fish moves towards the edge of the cone its sonar return may be somewhat lighter or thinner because it is farther from the transducer than when it is in the center of the view but it won’t change much. Tree limbs on the other hand vary in thickness and therefore show up with an inconsistent thickness or volume. Bamboo is not very dense so it has a fairly light but consistent sonar return and shows up very similar to a school of baitfish so it’s very easy to see sonar returns (arches or lines) made by fish that are down in bamboo cover.When you are confident that you can distinguish between fish and cover you may want to turn your Fish ID back on and set the Fish ID sensitivity so it only shows fish symbols on some of the better fish returns. I use the Fish ID on my Humminbird 797c2 SI so I can glance down and quickly see the depth of fish on the screen by the target depth shown with each fish symbol. In bamboo and other cover that isn't too dense I can still see the actual sonar returns to verify that the computer generated fish symbol is actual a fish. Once properly adjust, I trust that when my sonar shows fish symbols it usually is a fish. In heavy cover or steep slopes the actual sonar returns of fish are harder to distinguish because they are obscured by other sonar returns so using Fish ID can be an advantage if it is properly adjusted.
Depending on what graph you have you may or may not be able to set it to show both fish symbols/depth and actual returns. If you have to choose between one or the other you definitely want to turn off the Fish ID so you can see the actual returns.
One useful method for fine tuning your overall sensitivity and your Fish ID sensitivity is to use a 1/16 to 1/8-ounce lead head jig suspended in the view of your graph. The width of the view of a 20-degree cone angle transducer is only about one-third the depth of the object your seeing so if you’re looking for your jig at a depth of 10-feet it will have to be within about a 3-foot diameter circle centered under your transducer. It’s easier to keep your jig in the cone if you put it down 15 or 20-feet but even then it will need to be within a 5 or 6-foot diameter circle directly under your transducer.
To adjust your overall sensitivity turn your Fish ID off and suspend a jig in the view of your transducer and slowly move it up and down a foot or two at a time. It should show up on your graph as a line that moves up and down on the screen just like you are moving the jig with a split second delay as the graph processes the information and displays it on the screen. If you have a flasher bar on the side of your screen it should show the jig moving up and down in real time.
If you don’t see your jig, slowly increase your sensitivity JUST until it starts to show up as a faint line. If your jig shows up real dark then reduce your sensitivity until it only shows as a faint line. Now your overall sensitivity should be about right but you can make minor adjustments from there if needed.
Most graphs now have an “Automatic Sensitivity” setting, which adjusts for different water conditions and depths. Even with the Automatic Sensitivity turned on you can manually set the desired sensitivity range. The Automatic Sensitivity then makes adjustments for different depths and conditions so your display is consistent but with a bias towards level you have chosen. If you’re going to use your Automatic Sensitivity then be sure it is turned on before you make sensitivity adjustments.
If you are going to use your Fish ID turn it back on after you have adjusted your overall sensitivity. Now move your jig up and down as before. If you’re graph shows fish symbols along with the line depicting your jig then reduce the Fish ID sensitivity until it no longer shows fish symbols. If your jig no longer shows up as a line then you may have to increase your overall sensitivity if you are going to use your Fish ID. If your jig still doesn’t show up as a line or if it only shows up with your sensitivity set so high that you can’t distinguish between cover and the bottom then you probably want to turn your Fish ID off and reduce your overall sensitivity until your jig is just a faint line again.
With even a lower end graph properly adjusted you should be able to move over a brushpile or other cover and quickly determine how deep the bottom is, how tall the cover is, whether or not it is holding fish and how deep and how close to the cover those fish are holding.
With that information you should have a good idea about how deep to start fishing and whether or not the fish are actively feeding. If you’re not marking very many fish and don’t get a bite within a few minutes knowing that you are presenting your bait at the correct depth then you can either move to another location or sit and wait for more fish to show up or the few that are there to start feeding. On the other hand if you are marking a lot of fish all up and down the water column you may have to try several different depths to determine which fish if any are actively feeding.
Taking the time to learn how to properly use your graph will save you a lot of time and help you put a lot more fish “in the box”.