THERE ARE many functions in the menus of our fishfinders and sensitivity is probably the most underused – and incorrectly used – of them all. This results in a high percentage of anglers getting nowhere near optimum sounder performance and, in more severe cases, virtually no useful fishing information.
Most fishfinders have a sensitivity setting scale from 0% to 100% but in reality the unit doesn’t begin to function until it’s set well past the half-way mark. Increasing the sensitivity of the set is akin to winding up a hearing aid. It allows the unit to ‘hear’ signals that are weaker, whether from small fish and objects near the surface or from big fish down deep. It also hears a lot of unwanted signals, which end up being shown as ‘clutter’ on the screen.
It’s impossible to practise setting the correct sensitivity level when the unit is in simulator mode, so do your practice out in the field. After a while you’ll be able to find the perfect setting for a given depth of water just by casting a casual eye across the screen and quickly manipulating the sensitivity level on the keypad. In the meantime, follow these few pointers:
1. Adjust the sensitivity level to 100% to start with. In water that’s less than 20m deep the screen may well black out from top to bottom. Ease the sensitivity level back a little at a time until the blackness starts to disappear. You’ll be left with a screen showing sparse single dots which begin disappearing from near the bottom first, clearing further up the screen the more you reduce that level. Once those single dots disappear from the level of the water column you wish to investigate, the unit is at its optimum setting for that depth. The smallest of objects, such as single baitfish moving into the transducer beam, may be detected and shown on your sounder.
2. Should you move into deeper water, adjust your sensitivity up to get a similar optimal result. Reduce the level of sensitivity if you’re moving into shallow water.
3. Much of the time you’ll be left with a heavy clutter across the top of the screen, extending down into the viewing area of your sounder. It is best to put up with this or clear it using surface clarity control in the function menu.
4. If you’re searching for pelagic fish very close to the surface, a reduced sensitivity level will clear the upper screen. But remember that by reducing sensitivity, the unit is basically being made deaf and won’t show deeper signal returns.
5. In deep water, a 100% sensitivity level may not black out the reading near the bottom. If you’re searching for fish and structure at this depth, maintain that level of sensitivity to get the very best out of your unit.
6. ‘Auto sensitivity’ is a function in most units that takes away the need for the operator to think. Unfortunately, it won’t allow the unit to perform to its optimum level in many situations. Should the unit be working over water that’s very turbid, suspended matter in the water will show on screen if the sensitivity is manually set high. In auto sensitivity mode, the unit will automatically reduce the sensitivity to clear this clutter to give a clear screen. This reduction in sensitivity deafens the unit and weak signal returns from shallow or deep in the water column will not show on screen. This includes signal returns from perhaps giant fish, which might only just touch the edge of the transducer beam and therefore will be shown as a single pixel dot.
So get to know your sensitive side and make sure you adjust it according the current fishing situation. Your results and sounder-reading ability will improve out of sight.