Drake has spots on his bill, what could it be?

[Ducktown]

For some time now, my Indian runner drake has spots on his bill. Otherwise, he seems to be healthy.

He's inside the pond most of the time, digging plants and checking for mud around it. Are these spots sign of physical damage (roses with nasty thorns are growing next to the pond) or could be an indicator of something else. I'm adding two photos of the young drake (9 weeks).

 

[Ravynscroft]

He might have banged it up, but it really looks like it's just getting ready to peel... duck bills will do that sometimes, some say it is dietary, but I think it is more about growth... kinda like shedding an exoskeleton...