Oh - I see the subj changed. It was a predator attack.
Okay. Tighten up nighttime security. Get them in the duck house at dusk. I don't know where you live, but there are all sorts of nighttime predators in the city, suburbs and rural areas. Ecotone.
Try to identify what's attacking the ducks. Here's a website that might help:
Poultry DVM Predator Identification
Sadly, the chance of losing a duck to predation is high, but happily, ducks tend to be pretty hardy and might recover even when things look dire.
Please let us know how
you are in addition to your duck.