Nice catch. I've heard these guys on several different frequencies, usually in the 6500-6800 kHz or so range, but they have popped up in the 6765 kHz - 7000 kHz band as well. They seem to be fishing fleets or maybe charter services using their own "private channel" or "side channel" or general chat. I've also heard some of them chatting with their wives or girlfriends. LSB and USB seem to be used about equally, even in the 6525 kHz - 6765 kHz aeronautical band and the 6200-6525 kHz marine band.