When I’m at the helm of my boat staring at my fishfinder screen, I feel like a predator with the keen vision of an eagle – even though my old eyes can barely make out the print on a prescription bottle held at arm’s length. Luckily, modern fishfinders can give old salts the keen vision of their youth. Underwater vision, that is. But in order to take advantage of what your fishfinder has to offer, you’ve got to know how to adjust it, and how to read it. Use these tips, to make your underwater vision as sharp as possible.The marks seen here are from 50-pound class black drum, passed over at about four MPH. Note that they don’t arch, at all.
1. Learn to differentiate between bait, and predators. On most decent fishfinders, bait looks like blobs while single large fish appear as boomerang-shaped arches. Except when they don’t – see #2, below.
2. Certain types of fish, like pods of big black drum, won’t necessarily create an arch on the fishfinder. They’re so big and create such a dramatic return that the arches turn into big, blocky triangles. When you’re looking at fish in the 50-pound range which move slowly, and your boat is moving slowly, don’t be fooled into thinking these marks are bait. (If either the fish or the boat are moving quickly, however, they’ll arch on-screen).
3. Ignore whispy single-color returns (usually green or yellow, on most machines) on color finders. Things as subtle as jellyfish, thermoclines, and even plankton masses can create these light marks, which many anglers believe to be baitfish. If it really is bait, there will almost always be one color in the center of the return, and a secondary color surrounding it.
4. Remember that the scale of what you’re looking at on-screen changes with depth. A 50-pound drum may look like a monster in 20′ of water, but a 100-pound bluefin tuna looks one-fifth as big as that drum, in 200′ of water.
5. Always keep your fishfinder set at the highest screen speed possible. Yes, you may miss something if you’re not paying attention, but it will give you the most up-to-date, accurate view possible at any given time. On top of that, experience has shown that if you see fish on the screen’s history long after passing over it, you have little chance of turning around around and re-locating them, anyway.