I'll take an educated guess here, looks like a floating musk rat trap. My dad used to trap with one of those, anchored to the bottom, the rats enter the feeding cage, then fall in to the submerged trap cage, unable to come back up (there is a one way hinged flap on the floor of the trap), they drown and the trap stays active. Pretty ingenious design if you ask me, a local trapper in Bathurst catches well over a thousand of those critters every year with such a contraption. Carrots and potato skins are great attractors for such a trap.
Hope this helps...