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.
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.