My question is: Why is a dj wearing a captain's uniform?
Possible answers:
It's not a 'captain's uniform'; it's a Tattoo DJ's work uniform/costume.
If he was wearing a blue t-shirt in the photo, we'd have a hard time seeing him.
He forgot his tee-shirt the day the photo was taken.
His tee-shirt was faded and looked crappy for a photo.
He spilled something on his tee-shirt just before the photo was taken & the 'captain' loaned him his shirt for the photo.
The order for the costumes/ uniforms got screwed up....
What does it matter? It's a party boat.
Probable answer ... he was acting captain of the boat, though it may have been moored.
The other answers are ridiculous, IMHO.