Neat find, somebody had a sad loss. Was it open or closed when you found it? I continue to find 1960-70's drink can tabs, man we did toss a lot of those things away. Seldom anything this nice.
Did you just see it laying on the bottom (not frequent in Floroida unless some one dropped it fairly recently) or did you "shoot" it with some sort of metal detector?
I do like that sort of little gentleman's knife.
=kBob