For the price of a dozen goggle eye baitfish, monthly subscribers to SiriusXM’s Fish Mapping can access a wealth of satellite-based information that could dramatically improve their chances to catch fish offshore.
Unlike inshore fishing, which is often oriented around structures, successful offshore fishing depends on a series of changing variables the average angler isn’t equipped to predict. SiriusXM’s Fish Mapping uses a constellation of satellites to gather the latest data, then interprets it to
predict where specific species of fish are likely to be gathered.
For $100 a month, anglers can bundle Fish Mapping with SiriusXM’s Marine Offshore Weather package — which costs $60 a month by itself. The Marine Offshore subscription can be accessed by owners of Garmin, Furuno, Raymarine and Lowrance/Simrad/B&G displays, when those displays are equipped with satellite receivers that cost $450 to $800. Seasonal anglers can drop the Fish Mapping part of the bundle for six months a year without having to pay a reactivation fee.
Finding the Weed Lines
Well-formed sargassum weed lines found offshore are the closest thing anglers have to a sure thing for species such as mahi-mahi, and are like an oasis that small fish use for cover, attracting predators. To locate these weed lines, SiriusXM Fish Mapping analyzes water reflectivity. The weed lines are noted on the screen as magenta outlines, and the information is updated every 24 hours.
By clicking on each weed line, users can see when the information was gathered, and a loop can be shown of the past three days of sightings, so general movements and trends can be determined. Weed lines 25 miles or farther offshore are shown.
Finding the Hot Zones
Under the layers menu within SiriusXM Fish Mapping is the sea surface height anomaly detector. It operates like radar, using microwaves from satellites that bounce off the water surface to identify areas where sea height differs from surrounding seas. These differences can be upwellings, represented by negative numbers (and typically higher in nutrients than downwellings), or they can be downwellings, represented by positive numbers.
Anglers can look for areas showing a zero value, where the lines of demarcation are close together with a negative number on one side and a positive on the other. This spot is called a convergence zone, and it usually provides the hottest fishing.
Finding the Species
Most people who fish want to know the sea temperature, since various species have temperature preferences. Typically, a stronger variance in temperatures means more baitfish are present, which usually means the best areas for fishing.
The sea surface temperature contours feature within SiriusXM’s Fish Mapping shows breaks where temperatures change in 2- degree increments. The lines are color coded, with the lighter version of red showing lower temperatures, and the darker version of red showing warmer spots. To enhance this color differential, a user can narrow the temperature range on the legend.
Users also can select the surface front strength tab, which allows them to see boundaries where the strongest temperature changes occur. These areas usually hold more nutrients, which attract baitfish and predators, and create barriers to fish movement. These fronts are numerically rated by strength from one to four. Anglers who target the higher numbers will usually find more fish.
SiriusXM Fish Mapping also has a menu item called 30-Meter Subsurface that shows the sea temperature about 100 feet below the surface, where apex predators spend a lot of their time.
Finding the Plankton
The plankton concentration feature, when used in conjunction with the sea surface temperature contours feature, can identify where predators are likely to be feeding.
Plankton, measured by milligrams per cubic meter, is shown on the map by contour lines. Darker green represents the densest population. The fronts tab shows areas where the highest plankton concentrations are located, next to the lowest plankton concentrations, graded on a scale of one to four.
Users can view the plankton contour lines over the temperature gradient lines. Any convergence of dark red and dark green lines identifies areas where the best fishing is likely.
The Fishing Recommendation tab ties all of these features together, with recommendations from oceanographers who consider all the above data, as well as the makeup of the seafloor and currents. The recommendations show the likeliest places to catch bluefin tuna, marlin, mahi-mahi, yellowfin tuna and wahoo.
These recommendations are made twice a week and are color coded by fish species. Spots where multiple hot zones of different species overlap usually are the best overall for fishing.
This article was originally published in the February 2021 issue.