Dredging is a term that we use in Montauk to describe the way in which we use sinking lines to fish flies deep. This is not sightfishing, although sighting fish and bait can play a part, as we will see.
Normally I use lines in the 350- to 450-grain weight range, as I find that these lines give me adequate depth and will cast well with the 9- to 10-weight rods that we typically fish with during the fall.
Fly choice depends on the bait.
In the spring and fall, when I would most use the dredging method, the bait is usually large herring, shad and bunker, so the fly of choice would be a large deceiver or herring fly. If the bait is smaller, match the hatch accordingly.
Other choices include flies that will have a neutral buoyancy, thus holding their position in the water; heavily palmered flies, like a Seaducer or even a Gartside Gurgler, which most people use as a top-water fly (but with a foam body that makes it a useful choice for deep water, as well).
As always, casting is very important. The further the cast, the deeper the penetration and the longer the fly will remain in the strike zone.
If there is a strong moving tide, cast up current and let the fly sink into the strike zone before stripping. A short cast will be pulled straight off the bottom within a few strips. Note, that stripping depends on the conditions, but a slow, irregular strip often is the most effective.
The first and obvious choice on where to fish is structure. Look for structure on charts or your GPS, pay attention to local knowledge and scan for other boats that may be trolling or using bait.
Use your fish finder to locate bait over structure and to help determine the depth of the fish. Otherwise, fish the current across a reef or shoal making sure that your fly is in the strike zone at the down-tide drop-off, where predatory fish will wait out of the current for the bait to be washed over the rise.
The up-tide side of the rip also can produce, so look out for working birds and rising fish.
Another choice is to look for schools of bait; the stripers, for instance, may be feeding deeper under the shoal, picking up scraps and injured baitfish from actively feeding bluefish higher up in the water column.
A good technique in this situation is to wait until the school of bait and feeding blues have almost passed, then fish deep and behind the school, where the big bass will be following.
These big fish tend to stay out of the melee to pick up the injured fish.
Tidal rips present another opportunity, as the rip often will hold the bait. Look for bird action and fish across the rip from a distant up-tide position until the fish are located.
In the presence of blitzing bass, try a sinking line deep under the fish feeding on the surface, as this will often produce larger fish.
In the absence of any indicators, use the dredging technique anywhere in locations that you know hold fish points such as Montauk point, depressions in the sea bottom and anywhere your fish finder indicates fish or bait or simply along migration lines where the fish are known to run.