Note 2 of the pics. In one a drake has a cord of some sort that is hanging from the bill. No idea what it is. It looks like parachute cord? It doesn't look like seaweed or anything natural.
In another there are 2 pairs. I watched these birds for 2 hours. The drakes chased the hens, and all 4 had their rear tail feathers raised as you see. Some sort of courtship routine? When they were not chasing each other the tail feathers were not raised like this.