The 100 fathom line (600 feet deep) we call it the Edge, drops off sharply to 2000 foot and beyond. Those fingers coming towards shore are what we call canyons. That’s the structure that holds bait. Squid and small fish.
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But it’s not just structure. It’s also water temps and chlorophyll.
Here is a sea surface water temp shot. The orange is the hot water coming in from the Gulf Stream. When you drive from the yellow to the orange there is an instant change in water color from greenish to beautiful blue.
Fish both sides until you find the fish. Sometimes cold side, sometimes hot side. But just like deer they are on the edge.
Sometime there are eddy's or fingers that break off. When the Gulf Stream breaks off and hits a canyon it’s usually lights out fishing.
This late in the summer the water gets blended because of the summer heat in the shallower water It’s usually all green. Then we use chlorophyll shots to find plankton that starts the circle of life. TMI.
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A less geeky answer is hot water. Find 76 plus degree water off the edge with bait around and you’ll find Marlin.