Not compulsory if you dont have a 'required' license --- ie.: vessel engaged in 'commerce'.
Since the advent of Ch09 as the primary hailing channel, I monitor Ch16 at most times on a Tri-Scan (16/09/13) when moving. Before 09 was the primary hailing channel, I didnt want to listen to the endless cacophony on 16.
Im still waiting for boaters to use DSC -put in place place to reduce all the 'broadcast nonsense'- , but Ill be older than Mathuselah when that ever happens 'functionally'.