Here's the additional info on dredging .......

More on dredging

                The question of licensing depends on where you live.  Some
states may prohibit other-than-commercial dredging operations altogether.
Others may prohibit  the taking of commercially important species at all, or
the taking of them without a commercial license.  You'll have to check with
your local fisheries
department.
                If you are using a winch, either a power winch or a hand
winch, to retrieve the dredge, the tension of the tow line during actual
dredging should not be on the winch itself.  You should have a strong metal
cleat, designed for tying off a rope,  attached firmly to the boat
(preferably with bolts, not screws that can pull out).  While dredging, the
tow line should be tied off on the cleat.  Once the dredge is full, or the
dredge run is completed, allow a bit of slack to develop in the line, being
extremely careful not to let the tow line become entangled in the boat
propeller, then untie the line and use the winch.
                It is also important, if you are using an outboard motor,
not to have a bigger motor than you need.  You can only dredge at very slow
speed - otherwise the dredge comes up off the bottom.  Therefore, a small
motor is adequate for the actual dredging.  Of course, a bigger motor gets
you to the dredging site faster.  However, you have noticed that hanging an
outboard motor on the stern of a boat pushes the stern down somewhat.  You
have also noticed that running the motor pushes the stern down even more.
As you might imagine, towing a dredge along the bottom pulls the stern down
somewhat too.  Get the picture? Combine a big motor and a heavy dredge with
a small boat, and you may push/pull the stern of the boat right under the
surface.  This is especially true in the scenario you mentioned - if the
dredge suddenly gets caught on a large rock or other immovable object.  So
make sure you have a good clearance between the top of your stern and the
surface of the water while dredging. Some dredgers use a breakaway device on
one side of the dredge.  For example, with a rectangular dredge, you can
attach the upper and lower corners of one side to the tow line with strong
rope or light chain, but attach the other two corners with heavy twine.  The
theory here is that if the dredge gets hung up, the twine will break,
allowing the dredge to slide around the obstacle.  Of course, after that it
has to be retrieved, and new twine installed.  I don't do this myself.  On
the few occasions I have gotten hung up on the bottom, I have gotten loose
by circling back and pulling in the opposite direction. Again, make sure the
rope stays away from the propeller, or an annoying problem may turn into a
really bad problem! One final note - if the bottom is sloped (for example if
you are dredging toward shore or away from shore), it is much easier to keep
the dredge on the bottom if the dredge is moving uphill rather than
downhill.

Where to dredge

                My methods of picking dredging sites are not very
sophisticated - it pretty much depends on where I can find boat-launching
facilities, in an area where the bottom is not too rocky.  As you said,
coral reef bottoms would not be suitable for dredging - but here in the
northeastern United States we don't have to worry about that.  There is only
one species of coral here, and it grows in little flat patches on rocks - no
branches or brambles, and no reefs.
                The rocks themselves are the main problem to be avoided.
Here in New England (for those who might not know, New England is a
collective term for six states located at the northeast corner of the USA)
there are many rocky shorelines.  In some cases, the rocks are fairly small
(egg size to fist size) and smooth.  But in other cases the beach is covered
with rough boulders ranging from basketball size to truck size.  Usually
(though not always) the nature of the substrate just offshore resembles that
of the intertidal area - rocky bottoms off rocky beaches, sandy bottoms off
sandy beaches, muddy bottoms off muddy beaches.  Even off rocky beaches
though, you can usually find sandy or muddy bottom if you get far enough
offshore.  A good quality depth finder or "fish finder" is useful in
assessing the bottom type, as well as the depth.  I don't have one however.
I get my depth information the same way Columbus did - with a weighted
"sounding line".  Specifically I use a fishing reel with braided nylon line
that I have marked at intervals with various colors of fluorescent paint.  A
16 ounce (450 gram) lead weight takes it straight to the bottom, and I can
read the depth by the colored marks where the line enters the water.
                Trying to dredge on a rocky bottom is not usually
worthwhile.  The dredge bounces and bangs along, often gets damaged, gets
hung up on large rocks, and may become irretrievable either by filling with
rocks, or more likely by getting wedged between two large boulders. Actually
it is the chain which leads the dredge that is most likely to get wedged
somewhere.  There was one fellow I corresponded with years ago who did have
some success dredging brachiopods ("lampshells") off rocky bottoms in the
northwest.  Brachiopods look superficially like bivalve mollusks, but they
live very differently. They attach to rocks by means of a stalk, and the
shell sits atop the stalk like a golf ball on a tee.  Apparently they were
quite abundant in his locale, and the dredge would clip off enough of them
as it bounced over the rocks to make the effort worthwhile.  However, he
also told me that he carried three dredges on the boat, and at least once he
lost all three of them on one trip.  I only lost one dredge ever, while
dredging on a flat mud bottom, 80 feet deep.  I'm not sure what I "caught"
(or rather what caught me) but I suspect it may have been a sunken fishing
boat known to be in the area.
                Dredging on grass beds can be somewhat productive.  A small
dredge like I described in my previous posting won't rip up grass by the
roots like a large commercial dredge or trawl would.  On the contrary, it
just bends the grass down as it moves along.  This prevents the dredge from
digging into the bottom, and actually even from touching the bottom.
Therefore you won't pick up many burrowing bivalves; and, you won't get many
gastropods that crawl on the surface of the sediment.  What you will get is
small snails that live on the actual blades of grass (in some areas there
are amazing numbers of these), and also bivalves that swim, and come to rest
on the grass, or attach to it by a byssus (in this area, primarily pectens
and small mussels).
                Dredging isn't just for deep water.  You can snorkel over a
sand or mud bottom in a few feet of water and not see a thing.  Yet a small
dredge towed along the same path may yield many interesting specimens that
were hidden just below the surface of the sediment.  In such shallow water
you don't necessarily even need a boat - you can tow the dredge manually if
necessary.  Make a large loop and put it around your waist - or tie the tow
rope to the middle of a sturdy pole, and two or more people can work
together, holding the pole horizontally and pushing on it like a yoke of
oxen.  Two variations on this theme are - a hand dredge (sort of a mesh
scoop attached to a pole, that you can use manually, with a raking action);
or screening - shoveling sediment onto a flat screen of suitable mesh, and
sifting it through by shaking the screen (easier if the screen is held in
the water while sifting).  With either method, as in dredging, you don't
have to dig in deep - most specimens of interest are in the top inch or two
of sediment.
                What are you likely to get besides shells?  Here's a partial
list from my experience - sand dollars, sea urchins, sea cucumbers,
sandworms, lugworms, tube worms, bloodworms, scaleworms, starfishes, brittle
stars, sea robins, toadfish, pipefish, sculpins, flounders, cunners, skates,
lobsters, spider crabs, hermit crabs, green crabs, rock crabs, blue crabs,
horseshoe crabs, sea spiders, barnacles, amphipods, mantis shrimp, grass
shrimp, coral, sea anemones, jellyfish, comb jellies, sea squirts, sea
porks, sponges, seaweeds, dead shells, rocks, bricks, broken glass, bottles,
cans, plastic bags, wood, a grapefruit, a Batman action figure, a pair of
pliers, a Boston Red Sox hat - I guess you get the idea.  That's why I
recommend rubber gloves while picking through the catch.  Note: before you
toss back the wood, check for piddocks and shipworms.  Before discarding
dead shells and bottles, check them inside and out for limpets of various
kinds, and chitons.

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