South of Long Key bridge there is no 3 mile limit on the Atlantic side. However, keep in mind that you probably will get stopped and inspected by: MCSO, FHP, KLPD, FWC, Home Land Security, USCG, Fish Huggers United and a few others I have forgotten. Also, there are protected areas you are not allowed to spear, areas that you are not allowed to even be in, No guns in the state parks, zones where you are not allowed to drop an anchor, etc, etc, etc.
Oh yea, I forgot. Good luck
I forgot aboutthat... I keep it simple and just get on a boat when i go down there .