Actually Vessels at Sea are recorded.
Sometimes!
Like you I have fisherman ancestors recorded on their boats on some censuses. Often these are when they were coastal fishing at various locations off the English or Welsh coast, so presumably coming in to land most days with their catch - no sophisticated refrigeration on board in those days.
But I also have many many a fisherman who are NOT on many many a census! Presumed to be away fishing, likely to be further afield, and not home for days at a time. For example smacks from the Essex coast went right over to the Dutch coast to fish, and I guess if one of those trips fell across census night they would not be recorded.
I may be wrong, but I would say a fisherman missing from a census ( with wife and family found at home ) was more than likely because he was out fishing!
