From NY's website:

Are there any reciprocal license agreements with other states where marine waters form boundaries with other states?

Yes. If a state sharing a marine water boundary with New York has an active marine license** program and grants New York recreational marine fishing license holders fishing privileges in that state's portion of the boundary water(s), then New York grants the appropriately licensed anglers from that state the privilege to fish in the New York portion of the boundary water(s) without securing a New York recreational marine fishing license. The following waters are included in this reciprocal agreement:

* Connecticut: those parts of Long Island Sound lying between New York and Connecticut

http://www.dec.ny.gov/permits/54950.html


Based on that wording my take is that the south side of Fisher's Island would NOT be included.