Fish Stories : Fish Here, Catch & Repeat

Uncover the Secret Powers of Your GPS Plotter and Discover the Best Fishfinder on Your Boat

Most of us use our GPS plotters at a rudimentary level. After plugging in the coordinates for a reef, wreck, or drop-off, we head for the structure – putting our lines in when we hear the arrival alarm. That’s great. But it means we’re using only a fraction of the GPS’ power as a fishing tool.There are a lot of features packed into even the smallest handheld, and most of them go unused. So I began asking around, talking to charter captains and gear geeks-anyone with a passion for getting the most out of electronics. Then I – gasp! – cracked open the owner’s manual for the plotter on my boat and mined the wealth of information inside. I combined all that data with a little imagination and experimentation and came up with some techniques that max out the angling capabilities of a GPS.

Screen Savers

As I said, there are a lot of cool features built into your GPS, but many of them get in the way when fishing. Although it may be impressive to have your screen show every buoy, sounding, and gas dock, it makes a cluttered mess that’s hard to read. Let’s face it – when fishing, all you need to see are the bottom contours and structures that attract and hold fish.


What this comes down to is customizing your display. Every GPS plotter, even the handhelds I toted around while doing my research, allows you to individualize what you see. Just go to the submenu labeled Display Options or On-screen Features, and turn off everything but the contour lines and wreck symbols. You may need to see navaids and shipping lane boundaries while steaming to the grounds, but once you’re there, they become distracting – so dump ’em. When your screen is clean, shift to the largest-scale chart available, which presents the most detail. This is important, because otherwise your GPS won’t be able to display the subtle wrinkles of a contour line and all the minuscule, fish-attracting switchbacks and high spots that small-scale charts can’t show. Next, start experimenting with the zoom function to expand your view of the bottom. How much to zoom in depends on whether you’re going to anchor (zoom in all the way), drift (try zooming to 1/4 to 1/2 mile), or troll (from 1/2 to 1 mile or more).


With your display free of clutter and showing the most bottom detail possible, you’re ready to begin your new life as a GPS fishing pro. Start by anchoring over a gully, hole, seamount, or wreck. Zoomed in, you can tell where your boat is along the feature. Pick a likely spot to start and mark it with an icon on the screen. If you don’t get any bites over a pinnacle, try dropping back on your rode until you’re fishing over the slope. No bites at the edge of the hole? Reanchor over its deepest sections or over the up slope on the other side. Each time, mark where you are on your GPS display with an icon. This allows you to dissect “the spot” into numerous “micro spots.” Keep adding icons until you catch something and determine what section of the structure the fish like on that day, at that tide, and at that current. This will also tell you when you need to reanchor as the current or wind changes and swings you off that hot micro spot. For grouper, tautog, or sea bass, moving just a few feet makes a difference.


You can micro-tune a drift as well. Use a wider zoom level because the boat will be moving and you’ll want to keep the structure on the screen as you head for it. A 1/2-mile zoom should work fine. Again, pick the wreck, reef, or temperature break you want to fish, and place the cursor on it. Next, proceed upwind, upcurrent, or a combination of both that you think will put you on a direct drift back to the cursor. When you get far enough off, shut down, mark where you are with an icon, and drift. Check to make sure the boat’s icon and cursor are still on the screen. If not, zoom out to the next level. As you drift, watch the bearing readout on your display. It should be the same as, or within a few degrees of, the bearing to the cursor. As a guide to how far off you can be, remember that a six-degree difference over 2,000 feet (1/3 nautical mile) will put you off the mark by 200 feet. If you see that you’re going to miss the wreck, start the engines and bump them in gear to get you back on a track where the two readouts match up or are close enough to do the job. Also check the Speed Over the Ground (SOG) readout to see how fast you’re drifting. If it’s too fast, you can slow down by using a sea anchor, dragging a bucket, or in windy conditions dropping your canvas. Too slow, crank up the engines.

Now you can make precise drifts, going back to that marked spot and drifting over the wreck each time – that is, until the morning’s light airs become breezes, and the currents speed up, slow down, or change direction. When these things happen, you can miss the structure altogether. Don’t get lazy. On each drift, watch your bearing and SOG. They may tell you that it’s time to pick up and run to a different starting location so you can hit your mark. In addition to the drift’s direction and speed, you should also micro-tune for time. Say you intend to drift and chum across a set of wrinkles in a depth contour for mako or bluefin. You’d want to start upwind and get the chum flowing, making sure you reach the spot before the chum runs thin and has time to work its magic.

Do this by marking the structure as a waypoint and using the Estimated Time of Arrival (ETA) readout to determine when you’ll get there. If, in your experience, that time is too long, use the engines to “power drift” and speed up. Too short? Start farther away or use a sea anchor.


Electronic Marker Buoys

Your drift is like a run down the interstate toward a main crossroads where fish gather. But that doesn’t mean there isn’t a lot of action on the backroads. Off to either side of your drift, fish may be balling bait, finding a warm-water eddy, or congregating about a tidal rip. As you see or come across these targets of opportunity, mark them. This way you’ll find them again on a later drift. Do this with an icon, usually a fish symbol or skull and crossbones, included in the GPS’ software for that purpose. If your GPS has a notation feature, use it to alphanumerically identify these potential hot spots as “Bait Fish” or “East Rip.”

Now you can use your micro-tuning technique to hit not only the primary structure but secondary possibilities as well. Turn on the engines and adjust your drift direction, zigging and zagging to cover all your marked territory. Now you’re using your GPS to map a small section of the open ocean into a patterned, highly detailed-and more understandable-fishing ground.


Troll With It

During the day, you’ll notice a pattern of where fish live as evidenced by your catches and hookups. There is also a pattern of where they may soon be living, which you can predict from observations and knowledge of your quarry’s habits. GPS lets you tap into these patterns with one of its most underused features – the plot trail.

This is a line made by the boat’s icon as it moves across the screen. More accurately, it’s a series of dots laid down at intervals of either time or distance that the unit’s software connects to make a line. The plot trail transforms a featureless expanse of water into a detailed record of where you’ve been and where something has happened.

Most likely, the factory setting won’t be right for your situation and will have to be changed. This is easy to do, and even portable units allow for trail memory customization. For instance, my Lowrance Global Map 100 can be set to update the trail anywhere from once per second to once every 30 minutes. It also lets me update by distance, leaving a dot once every hundredth of a mile or every 10 miles. The trick in choosing the right update rate is to balance your need for a detailed history against having so much information that the screen looks like an Etch A Sketch in the hands of a dyslexic on speed. If you’re trolling a specific area, update by time. A bigger area will need a slow update rate; a smaller area, a fast one. Experience will soon teach you what’s right for different trolling speeds. The point is not to run out of trail until you’ve established a pattern. Combined with icons you drop at every strike, this will tell you where the fish were and also in which direction your baits were moving when they struck.

Changing the update rate from units of time to units of distance is useful when fish are spread out, such as during migrations or when baitfish are scarce. In this case, wide-area, high-speed trolling is called for. So it’s best to set the plot trail to update, say, once every mile if you’re dragging baits over an area that covers 20 miles of deep blue. When you get hit or come across an uncharted structure or temperature break, drop an icon. This will help target the productive area, at which time you can increase the update rate to provide more detail.

Whether you use time or distance, there’s a limited amount of memory allocated to plot trails within your GPS. If you’re updating too fast, you risk having the line run out before finding fish-or worse, after finding them so you can’t track your pattern back to success.

Another Brain

Some anglers will argue that these techniques can be used without the aid of a GPS plotter. And they’re right, provided your navigation skills are razor sharp. But you’re not out here to navigate-you’re here to concentrate on fishing. When you use your GPS with any of these techniques, you’re free to concentrate on other things, such as lure selection, bait rigging, and choosing who gets the rod when the cry of “fish on!” rings out from the cockpit.