Most of the gear we take off entangled whales we find to be actively fishing gear when we are able to trace it back to the fishery that set that gear. Sometimes all we find is just a length of rope, in which case we can't trace it, but there are efforts to recover the gear and find out where it was deployed and if it was actively fished or not. Actively fishing gear is definitely a problem.
Ghost gear is as well. In the case of one whale that was entangled in the Gulf of St. Lawrence this year, the fisherman captaining the boat we were on said that the kind of gear found on the whale hadn't been used for a couple of decades. It is part of the problem, but actively fishing gear is the primary part of the problem.