Here’s how it works: When dramatic water-temperature boundaries collide, they draw plankton, debris and bait into the area, literally sucking everything in, and often amassing great areas of floating debris. This, in turn, draws game fish. The more pronounced a temperature break — and the longer these boundaries have been abutting one another — the greater the chance that roaming pelagics have had time to locate the ensuing feeding opportunity.
So what exactly catches Raguso’s attention on the charts?
“When studying the edge of the continental shelf, I’m watching for spin-off eddies around the canyon edges,” he says. “Inshore, I’m watching for filaments that break off the spin-off eddies and meander inside.”
These “eddies” and “filaments” Raguso refers to are basically warm-water pockets, displayed much as Doppler radar displays weather, in yellows, oranges and reds on SST charts, indicating their intensity (or warmth).
SST charts are generally updated every 10 hours or so, and Raguso watches them like a hawk, trying to determine whether a pattern of movement is developing and whether the temperature breaks are intensifying. When he sees a pattern emerging — whether it’s far offshore or closer to the coast via meandering warm-water filaments — he takes it to the next level.
“That means I start looking at the chlorophyll charts to see where the cleanest water is,” he says. “I intersect and overlay the charts. You might have a nice, 3-degree temperature change, say 76-degree water surrounded by 73-degree water, but is that water blue or green? The chlorophyll overlays add the next level of detail and help you better pinpoint where the fish should be.”
Some guesswork is involved though.
While the temperature charts are updated a couple of times a day, the Terrafin chlorophyll charts are updated only every two days or so, Raguso says.
“So there’s a bit of a disconnect in terms of chronology,” he says. “You have to watch the charts closely to determine movement patterns. You have to try to predict about where they will move.”
And that is where networking can really pay off.