Combining Sonar and GPS For More Efficient Fishing

by Ralph Martone

When my first two casts came through the water without catching any weeds I knew I must be out of position. A quick glance at the GPS told me to nudge the boat slightly to my left. A couple of small corrections by the bow-mounted trolling motor and I was in position.

I sent the big double-blade bucktail in a long arch and began retrieving it as fast as the reel would allow. Halfway back to the boat I felt the lure make contact with the first weeds when it was jolted to a sudden stop. I reared back on the rod just in time to see a huge swirl appear.

Whatever happened in the next couple of minutes is a blur. The reel's drag was screaming, the fish went deep below the boat one second and was airborne the next.

Although I know the whole battle lasted no more than a couple of minutes, it seemed to take forever. Finally, with both fish and fisherman wearing out, I was able to bring the 49-inch musky alongside the boat, slip a pair of bolt cutters up to the hooks and cut them away.

I continued to hold the fish by the tail, planning to work it back and forth in the water to revive it before letting go. The fish had other plans. I had no sooner leaned over the edge of the boat to get a better grip when the musky twisted into a tight S-shape, then lunged forward sending a drenching splash into my face before gliding off no worse for wear.

That fish and several others are the result of combining the mapping capabilities of a GPS with a sonar unit, commonly known as a fishfinder. Actually, the term fishfinder is not entirely accurate. Although these electronic units can show the location of fish, their most common use is in determining the water's depth and bottom structure.

The secret to catching the musky described above was knowing the exact location of the weed edge. This was accomplished as soon as I arrived at the lake. Slowly weaving along the transition between deep water in the main body of the lake and the shallower water of the bay, each time I passed over the edge of the weed bed, I marked its location as a waypoint on my GPS.

I placed nearly a dozen waypoints, each one marking the edge of the weeds. To effectively fish the area, I placed the boat about half a cast from the weeds and followed the line of waypoints.

Each cast starts over the weeds before swimming out toward deeper water. A musky, lying in wait at the edge of the weeds, makes a sudden attack as it prey, in this case my lure, leaves the weed cover.

The same method can be used to mark the edge of drop-offs, rock piles, shoals, fallen timber and other structure that hold baitfish and in turn attract predators such as musky, walleye, bass and pike. By knowing the exact location of these structures you will greatly improve your odds of catching fish.

Too often fishermen, anxious to start fishing as soon as possible, neglect these important steps, resulting in many casts that completely miss their mark, falling short of important structure elements that hold fish.

When it comes to trophy-sized fish like a mature musky, it is important to remember that 95-98% of the water is empty. That means fishermen looking to find a trophy-sized catch can use all the help they can get. This method puts more casts in the critical areas that hold fish, increasing your odds of making contact with Mr. Big.