In the early 2000's I was lucky enough to help out on a project to see if fishers and martens inhabited the islands.  The NPS boated us to half a dozen islands where we walked transect lines through the woods, placing tent-shaped "track boxes" (that my dad designed) along the way.  There was a chicken wing hanging in the middle, with white contact paper beneath it and soot on either end.  An animal passing through would leave their tracks for us to see.  Plenty of fishers and martens, though most boxes got smashed by bears.  Best job ever.