The area known as Back Channel, a body of tidal waters between the 2 New Castle bridges, so-called, and Goat Island and Shapleigh Island to the north; and the Wentworth hotel bridges, so-called, to the south; said body of water being bordered by the town of New Castle to the east; and Sagamore Creek to the Sagamore bridge, the city of Portsmouth and the town of Rye to the west; is closed to all duck hunting or the discharge of firearms. This section shall apply to all islands situated within the above stated boundaries.