Modern Humminbird sonar, left, identifies lake depth with a color selection system, while Mega-360 sonar imaging, right, provides a 360-degree view of bottom structure and fish all around the boat.

“Cast that way, about 40 feet,” said Lake Michigan fishing guide Capt. Chris Noffsinger, pointing off the bow at roughly 10 o’clock. I readily complied, flicking a drop-shot-rigged worm to the spot ...