Just called Canal Control out of curiosity/boredom.
No fishing within the Canal itself (which everyone knows)
No fishing in channel limits.
Outside the bouys in Hog Island Channel.
The piling structure is considered part of the channel as its for holding barges and whatnot.
The officer on duty was unaware of any restrictions around MMA, but if they're docking/undocking (or planning on it) a patrol vessel will be out and will ask all boaters to leave the area.
Its definitely about safety, if you're drifting across a channel and a barge is bearing down on you and you can't start your engine. Buhbye boat.
Pamphlets with this info are available at Canal Control and apparently at the area ramps that are on/near the canal.
And a link to the navigation regulations:
http://www.nae.usace.army.mil/recrea...ion/navreg.htm