Richard A. French, a specialist in animal disease at the University of Connecticut, often comes to work wearing a lobster tie tack he bought at a shellfish conference. He's had lobsters on the brain lately, particularly the mystery of why hundreds of thousands of lobsters have died within the last year in Long Island Sound. In a sea of troubles. Photo: OAR/NURP. In the western end of the Sound, which separates Connecticut from Long Island's north shore, lobster landings went from historic highs in late 1997 to a nearly collapsed stock two years later. Beginning in the fall of 1999, …