I do not know if there is any correlation but at least where I live mountain beavers have about dissapeared. They are a really important prey animal for bobcats.
Again I have zero evidence that Fishers caused it. In fact it is probably pretty farfetched as I don't think there are many fishers around. I don't know anyone that has caught one and they are supposed to be pretty easy to lure into a trap.
Long winded way to say I don't know.
