Am not sure concerning the subspecies, do guess it is likely to be ssp. sinensis.
The larger group of cormorants was too quick when flying above me.
These birds are obviousely used to be hunted by fisherman who hate them for "stealing" their prey.
Thus they will fly away when seeing humans approaching.

Two trees at opposite side of river Mur, full of white guano (no snow), might be resting places at night?
May not be certain at all, could originate in grey herons as well?
You are right, am no birder at all ;-)