Good question. I have never done the snorkeling for lobster thing myself, but the best dive shop in the Keys is Dive Key West - they really are awesome and can give you the best advice, I think... Bob and CeCe Holston own it. They are cool ... here's their info:

Bob Holston
Dive Key West Inc
3128 N. Roosevelt Blvd.
Key West, FL 33040
305-296-3823
Dive Key West