Authorities in Bahrain say the wooden boat that capsized Thursday night, killing 57 people, was not licensed to operate as a tour boat, and they have detained its captain for questioning.
The prosecutor's office says the man, an Indian, was also not qualified to captain the boat.
The traditional wooden boat had been chartered for a construction company party.
A British survivor, Simon Hill, a manager of the construction company, says the boat started to sway even before it left port and that some of the guests chose to get off rather than sail.
Survivors say the boat began to list sharply after it made a sharp turn about two kilometers off Bahrain's coast.
Owners say the boat was overloaded, carrying more than its capacity of 100. Officials say 126 people were believed to have been on board.
Most of the victims were foreigners.
The dead include 21 Indians, 13 Britons and five South Africans.
Some information for this report provided by AP.