Finding fish in cold water, part 1: Using Humminbird Side Imaging's Sharpness Feature
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Once fall water temperatures dip into the mid-40s, I observe very predictable shifts in walleye and sauger locations in most of the rivers that I fish...especially the Mississippi River near Red Wing, MN. As the usual higher flows associated with fall rains begin to drop back into typical winter ranges, I see quality fish move to locations near deep "wintering holes". Fishing in the middle of these very deep holes (30+ feet deep) will generally provide an endless supply of 1-2 year old walleye and sauger, and most anglers will avoid these nurseries. However, the deep flats that are located near these holes (flats that are 20-25 feet deep), along with the edges of these holes, can provide a very nice run of quality fish. Finding pods of catchable walleye and sauger on these flats can be a challenge, as the pods of fish can be quite mobile. Therefore, before I ever drop a line in one of these deep flat areas, I scout for fish using my Humminbird Side Imaging fishing system.
Dr. Jason Halfen 
Professional Walleye Angler
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Not every pod of fish will reveal itself quite so readily. With certain combinations of bottom composition, water clarity and turbulence, fish that are closely associated with the bottom can sometimes be challenging to identify...even if present in very large numbers. Under these conditions, the Sharpness feature, found in the SI Enhance menu, can make a BIG difference in your ability to find, and subsequently target, these fish. For example, consider the screen capture below. It was taken with the same sonar settings (SI range = 100 feet, chart speed = 5, SI sensitivity =10, SI contrast = 10) as above. An experienced Side Imaging user may be able to see the fish, particularly towards the far edge of the left Side Image, as well as in the upper half of the right Side Image. Can you spot them?
Depending on the composition of the bottom, pods of fish can often be made quite visible by making some simple adjustments to Side Imaging sensitivity and contrast. For example, consider the red zoom window in screen capture below, generated by my Humminbird 1198c. This screen capture shows a small group of a dozen or so fish, lined up in a small depression in the bottom that is to the right of a large tree (the tree is casting a dark sonar shadow to the left). I was able to clearly see these fish by adjusting my Side Imaging sensitivity to 10 and my Side Imaging contrast to 10 (with a Side Imaging range of 100 feet, chart speed = 5 and boat speed = 4-5 mph). Those bright white returns from the fish in the depression stick out like sore thumbs in this screen capture.
Those fish may be apparent now...but a casual glance at your 1198c in the field, with the sun on the screen and other boats on the water that require your attention, may allow those fish to go undetected...and unfished. However, the Sharpness feature will help to make these fish more noticeable, so that you can swing around and catch them. Sharpness is set to "off" above. However, the next screen captures show the same pod of fish with Sharpness set to High. Those barely noticeable fish are now much more apparent, as brighter white spots on both the left and right Side Images. This deep flat is littered with fish, and the best part is that there were no other bots fishing them. Undetected by traditional sonar, and missed after a casual glance at Side Imaging, a quick adjustment to the Sharpness feature turned these walleyes and saugers into sitting ducks!
Using the Sharpness feature does tend to make the rest of the Side Image somewhat grainy, so I only turn Sharpness to Medium or High when I am looking for bottom-hugging fish. Once you start rolling Sharpness adjustments into your bag of tricks, you will find your Humminbird Side Imaging fishing system to be even more valuable for finding, and catching, cold water walleyes and saugers like the ones below. 

Be sure to check out Part 2 of this series which covers the use of Dual Beam sonar for vertical jigging!
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