Using GPS to Hunt Fish

By Tom Pettengill 

It was still dark as I pulled into the parking lot near the upper end of Rockport Reservoir. I was anxious to get back on the ice because a week earlier I’d caught a mess of fat 10 inch yellow perch.

Just before I hoisted my auger and bucket of tackle over my shoulder I pulled out my hand held GPS unit and recalled the waypoint I’d saved at the hole where I’d caught the perch a week ago. Over the last 7 days we’d had a good snow storm and none of the holes or angler tracks from a week before were visible.

As I left the parking lot I followed the plotter path and headed for the waypoint icon. When I got within a preset distance the unit’s alarm began beeping to signal my arrival.

I was looking for 30 feet of water and hoping the perch hadn’t changed their travel route and feeding location. I was also hoping that the Defense Department’s selective availability tweaking of the satellite signals wasn’t putting me too far off target.

I cut a hole, put my fish finder to work and it read 30 feet. Before I could get baited and a line in the hole I noticed small schools of perch on the fish finder. Within minutes I was catching another mess of yellow perch. By saving a waypoint where I’d caught the fish the week before I was able to quickly find the fish again. I didn’t waste valuable time during the early morning feeding period searching for the right depth and location.

Saving waypoints on hot fishing spots isn’t the only useful feature of modern GPS units. You can save event markers where you catch fish, you can use the plotter to re-trace a trolling path where you marked or caught fish on a previous run, and you can use your unit to monitor your trolling speed.

Event markers come in a variety of objects. They may be shaped like a fish, an anchor, etc. They are like throwing out a small buoy marker that is only visible to you and stays put for future trips.

A few years ago I went out to the submerged island off the South Marina on Willard Bay. Another boat was already trolling there and they were throwing out a small marker buoy every time they caught a walleye. Before long several other boats had arrived and all were trolling and playing connect the dots with the first boats marker buoys. If they had saved event markers on a GPS unit rather than throwing out visible buoys only they would have known the exact location of their catches. Also as they picked up their buoys those locations were lost for reference on future trips.

I have saved event markers out in the open water at Willard Bay and returned to the same markers for the last three summers to catch more walleyes. Yet anyone else who travels across the lake doesn’t see anything because I don’t put out any buoy markers for other anglers to fish around.

I also use the plotter screen and the travel path it records to re-run successful trolling routes on a given outing. These travel plots do not stay on the screen to be followed on subsequent outings or even return trips on the same day but they are there to be followed over and over again while you stay in the same area. By combining the plot path and event markers you can detect any real patterns of where feeding fish are schooled.

Maybe you’re not following the same route or you’re randomly trolling a zig-zag route. By saving event markers you eventually notice all the fish are coming from a small area. You can concentrate your efforts in that area.

Those of you that have trolled a lot know that trolling speed can be critical to fishing success some days. Some GPS units give you Speed Over Ground (SOG). SOG is affected by the Defense Departments selective availability. You have to watch the SOG reading and compare it with how fast your boat appears to be going and how hard your rod is pulling to get a feel for whether your SOG reading is way off at a given time.

An easy way to detect error is to turn your unit on while tied to the dock or while sitting on your trailer before you launch. I have watched my unit read one mph while sitting on my trailer. Most of the time the error isn’t that far off. Usually it is pretty close. By watching the SOG reading and seeing how fast you are going when you catch fish you can maintain the right trolling speed for catching fish on a particular day.

Fish aren’t always in an active feeding mood. Some days they will hit lures just flying through the water and other days they want it just barely moving along. One of the things you have to determine during each outing is what speed is triggering strikes. Then repeat it. Once you catch a fish your SOG reading can help you maintain that magic speed.

Using my GPS has put more fish in the boat for me and I hope this information will help you as well.