The problem isn't predators, the problem is domestic ducks were not developed to survive in the wild. They have been genetically altered to fit human needs, and that includes the inability to migrate in the winter or feed itself properly. It is cruel to release a domestic duck, and it would be much wiser, and much more kind, to try to find it a home with someone who can care for it. My town has to routinely round up the domestic ducks from local ponds that people have released, and either find homes for them or have them euthanized. Alot of towns don't take the initiative to do this, so the ducks are left to beg people for insubstantial scraps and suffer. The wild ducks at ponds tend to ignore the visitors and the scraps of bread they throw, and they are not around in the winter. Ideally, those wild ducks should be the only types people see at city ponds, and hopefully, with enough education, this will one day be the case. Please rethink your decision to release the duck.