i am not aware of any specific dividing line. here on the east coast, NMFS has three regional councils, the New England Fishery Management Council, the Mid-Atlantic Fishery Management Council and the South Atlantic Fishery Management Council. the MAFMC is represented by states as far south as North Carolina. interestingly, the SAFMC also has North Carolina reps. the different councils don't manage different waters, they manage different species. those regulations are then set coastwise (beyond 3 miles, since inside of 3 miles is left up to state jurisdiction).
various species will have varying regulations based on geographic dividing lines, but to the best of my knowledge these are species specific and there is no general dividing line use for all species.
might want to take this topic over to the Reel Talk forum.
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Capt. Adam
Karen Ann II