Keith Brack was on top of the world after releasing his first blue marlin, fishing with his dad and me off Bimini, Bahamas, this past June. We caught the fish trolling in 1,500 to 1,600 feet of water, tight to the island. The next day, we trolled the same zone without luck, and even stayed the same course until noon on day three. A report from Roffers Ocean Fishing Forecasting Service showed a 1-degree temperature break several miles off Bimini over deep structure. We made the move, and after three hours of trolling, Brack fought and released his second blue marlin of the trip, an estimated 250-pounder.
Such a scenario wasn’t new to us. In fact, it has played out many times for dolphin, and even marlin and yellowfin tuna. Knowing exactly where potentially potent stretches of water are prior to leaving the dock bolsters confidence, and can possibly reduce fuel consumption by eliminating a lot of searching. We call it precision targeting.
There are numerous means of obtaining water-surface-temperature readings, ranging from raw satellite imagery to detailed analyses that actually edit down the masses of water temps and highlight only the most significant ones, for simplified and quick interpretation. In addition, some of these charts also list the duration of significant, stable surface-temperature breaks, as well as other oceanic-circulation features. For decades I’ve relied upon Roffers Ocean Fishing Forecasting Service (roffs.com), a leader in turning the raw satellite data into useful information. Even though such information is spoon-fed via email or fax, getting the most from the intel requires a good understanding of how to read these analyses.
Productive zones often occur along a water-surface-temperature break. Such a break signifies either two different water masses (water types with different densities), the infiltration of a warm-water finger or filament, an eddy, or an upwelling that pushes deep layers of cool water toward the surface. When different currents lie next to each other, they often have thermal variations along with upwellings, which bring nutrients to the surface along these convergence zones. And, in turn, these often result in plankton blooms which, if stable, establish mini ecosystems, which draw tiny baitfish that feed on the blooms, followed by slighter larger baitfish, which feed on the smaller baitfish — all the way up the line to top-tier predators.
Warm, tropical-water systems carry game fish with them. Major systems include the Loop Current in the Gulf of Mexico, and the Gulf Stream moniker itacquires as it rounds Florida and heads north; the eddies from the stream that peel away and drift toward shore off the mid-Atlantic and New England coasts; and the warm, tropical water off Southern California, when it migrates northward during El Niño episodes. When these warmer blue waters meet cooler, inshore and greener continental-slope waters, they create major feeding zones. When water-surface-temperature breaks occur within the depth range of your target species, pay special attention to them.
Like that underwater hill over which Brack scored his second blue marlin, bottom structure relating to thermal edges bolsters the presence of game fish. Such structure may be small mounds, mountains, shelves, depressions, canyon edges, pinnacles, wrecks and reefs. These habitats naturally hold forage species and often game fish. When a warm-water edge or current moves over these structures, upwellings usually occur. As a general rule, water-surface-temperature breaks alone out in deep water are good zones to fish. However, a temperature-break crossing or intersecting prominent bottom structure has far more potential because of its ability to aggregate nutrients and bait.
The length of time an edge remains over structure determines its importance in pinpointing fish. Basically, the longer a thermal break remains in place, the better its potential for establishing a thriving mini ecosystem. For example, if a break has recently parked over a major structure, it will likely not be as productive as one that has been in place for a few days. Roffers Analysis notes major surface-temperature and color breaks as well as the duration of their position over prime bottom. The latter appear on an analysis chart as numerically dubbed black dots. Therefore, a “2” signifies a break that has been in the same place for the past 48 hours, whereas a “3” or “4” reveals a 72- and 96-hour duration, respectively. Shoot for the long-standing breaks.