Being in Aus, we don't have those. From the looks of it, it's similar to something we have called a quoll. Did it take them from the coop, or are they free ranging?
When I was a kid we had one get into the coop and take 5 ducks (muscovy no less) in one night. Not bad for a little thing.
It tore the 2"x4" wood frame into bits and chewed through the chicken wire. So I would suggest making the coop out of more sturdy avian mesh and heavier/thicker wood if the fisher is similar?