"So far we have seen seven attacks off Nigeria this year and one off of Benin. So that makes eight since the beginning of the year and we believe many more attacks may have gone unreported."
Two weeks ago, pirates fired on a cargo vessel off Nigeria, killing the ship's captain, according to the IMB.
Choong said that vessel's chief engineer died from a fall during the attack, correcting earlier reports that he also had been shot dead.
That ship was Panamanian-flagged but its owners were Taiwanese, he said.
The IMB has said other recent attacks in the area included a tanker that was hijacked south of Nigeria earlier in February. Nigerian vessels intercepted that ship and rescued its crew.
The IMB, which is funded by shipowners, warned in September that the seas off Benin, Nigeria's neighbour, were emerging as a new piracy "hot spot" due to the weak enforcement capabilities of governments in the region.