Just as a matter of getting things straight, that duck is neither a black duck or a mottled duck. It is a black duck - mallard cross. Admittedly, it's probably a few generations removed from a direct cross, but a black duck has no white in the speculum. The presence of white in the speculum is an indication of a mallard somewhere in its ancestry. We get a lot of them up this way. Some DEC officers will count it as a cross duck and others will count it as a black duck, so you need to get a clarification from your local officials if you start running into more of them. We're only allowed one black duck on the Atlantic flyway.
Anyway you look at it, it's a cool bird. Good luck in mounting it. Post up some pictures when you're done.
I feel slightly sorry for a man who has never patterned his gun, who has no idea how far his chosen load will retain killing penetration. But I'm extremely sorry for the ducks he shoots at beyond the killing range of his gun and load - Bob Brister