Ray makes a good point. I have, however, logged several QSOs in LSB mode that were almost certainly marine traffic in that band, going by the topics discussed (OMs talking about how much fish they caught, things like that). Those transmissions were in Spanish however, not Portuguese, and were on other frequencies, not 6925 kHz. I imagine a lot of the transmissions heard in the 6-7 MHz region are freebanders or outbanders though. The line blurs when you have fishermen talking to land-based stations. Lots of husbands talking to their wives on these frequencies.
I know the 6900 LSB and similar frequency crowd are land-based. I believe that some marine radios do have LSB an option, but others are USB only.