After reviewing how bounties work, I'm going to have to add a couple 0 to Bluebeard. A Petty Officer being defeated in a duel would land 30000 on you. 
When the highest bounty in East Blue is 10,000,000 (before Luffy) and the lowest is 5 for chopper being a pet, 30,000 means. You're a threat, but not too much of a threat.