When used right, modern sonars with side-scanning capabilities are awesome and powerful fishing tools. Imaging technology is leading to some of the most innovative catfishing tactics being used today.
Time was big-river steamboats had a man sounding bottom with a leadline and singing marks to the pilothouse. "Mark Twain" was a go-ahead — safe water, twelve feet (two fathoms) above the lead. "No bottom," four fathoms or more, full steam ahead.
The skilled leadman spared many paddlewheelers from chugging up onto a sandbar or cracking a hull on a rockpile. The leadrope had easy-to-see depth marks woven in, the end tied to a section of pipe filled with lead, except for the bottom end. What got stuck or didn't get stuck in the hollow part as it pounded below told of river bottom conditions.
Early mapping efforts took some of the mystery out of big rivers, details mainly marking safe travel for navigation. Beyond the heavily used routes — off into remote riverbends, across no-man's flats, and into wild side channels — things were much less formally charted. Some early river maps showed bottom content, as well as depths marked at transects across the river, sometimes a mile or more apart. A rough contour map could be made by connecting the dots, but a dangerous game of extrapolation it was making assumptions about where the contours should run.
This wasn't as much so in reservoirs, where early on the topography of the flooded land was translated into fairly accurate contour maps. Anglers could know the locations of underwater humps, points, channels, and the like. Some maps inventoried even more novel fish-attracting goodies — roadbeds, buildings, ponds, grave markers, and more.
This left the river catfisherman to rely on what could be told from limited information on charts, and in uncharted territory the various clues the river gave up — current speed and direction, visible cover, shoreline materials, and formations like islands — to decode how the forces of moving water sculpted the river. This led to discovering a milk run of catfishing spots. Still, reading a river was left much to interpretation, and without an eye into the underwater world, catfish for the most part were unrevealed, at least those that didn't get caught.
Packaging sonar for catfish into something small and affordable to anglers goes in the books as one of the Seven Great Wonders of the Fishing World. It changed how we approach fishing and the odds that go along with it. In big rivers, never-before-seen structure, submerged cover, and depth details were revealed. Even bottom content could be deduced by the strength of sonar signals. Interpretation remains part of the game, but fewer catfish remain concealed.
Another leap into the techno age and we find big-river anglers with the ability to see below the surface with almost photolike precision. Side-scanning and down-scanning imagery, once only affordable to government agencies and university researchers, has been shrunk and integrated into sonar-GPS units available to anglers on retailer's shelves. What the U.S. Navy utilized to find submerged H-bombs and sunken Russian submarines is now in your hands and the guy's next door.
With stunning vividness, individual fish, exact shapes of boulders and trees, details of slopes along structural elements, and more, are no longer in the mind's eye. Like a spy using nightvision, the details of the eerie dark space under a rusting parked barge come into view for the first time ever — six broken dockpilings, a pile of rubble, a half dozen submerged logs, a 55-gallon drum, and three big catfish. Three more catfish unconcealed.
As technology advances and more anglers become skilled at new breeds of electronics, expansive rivers such as the Mississippi are becoming smaller. It once was unimaginable that catfish could be overharvested from large, productive waterways, yet we've seen that exploitation can take its toll where harvest pressures are high. Now, as anglers become better at rooting out cats from their lairs with unprecedented clarity, how will populations fare, particularly larger fish? Rivers can even the playing field, as habitats and bottom features are constantly changing. Overharvest is something that often sneaks up slowly, though, something to constantly keep under watch.
And so it goes. Once just a dark, deep pool. No Bottom. Then, the hidden boulder field in 40 feet of water near the tailout is discovered. Between two of the largest boulders a big blue cat appears. The river revealed. Another catfish unconcealed.