Yes, the biting is probably part of a mating ritual.
How old are your ducks?
In my experience young drakes (about 6mo to two years) are bad at breeding.
Keep an eye on the behavior. If the drake hurts her bad enough that you think she is in danger, separate them. Drakes can over breed ducks to death.
I’m not sure what your pen set up is, but if you’re able, you might consider separating a part of your pen off with a small door (small enough the larger drake can’t fit through but large enough the smaller hen can). This will allow her to get away from him if she wants to.
Another solution is to get more hens (again if you have space available and want more hens) in my experience a drake with several hens won’t hurt them because his attention is split between them.
And as oldhenlikesdogs said the easiest solution might be to get a different drake.
As long as you’re not too attached to your current drake.
Good luck!