Dulce, if you are in municipal waters, the municipal laws apply. In state waters, state laws apply. In federal waters...You can see where this goes, right?
I'd assume that the only "firearms discharge" rules out there would be Florda State, which usually means something in the FLorida
Statutes that can be found onlline.
However, given the range of a high power rifle, a call to the USCG regarding reckless or negligent operations might be in order. Not that I'm against shark or duck hunting at sea, but most folks don't realize just how far a "high powered" rifle bullet can travel. There's a reason cruise
ships used to offer trap and skeet shooting--not riflery.