Thanks for the link about horn blasts, Guest #. I had no idea.

Now, the rules on the BoatUS site are for vessels which are leaving the dock or overtaking another vessel. The tugboats in the video aren't doing anything like that, so I suppose tugs have special signals. Perhaps since the situation was unusual, the operators had agreed-upon signals just for the job in hand.

What was unusual? Enormous boat sideways in a small body of water with its bulbous bow stuck deeply in sand, probably clayey sand.

Jack, I agree about the sounds being recorded.