According to the thread here, there is an underwater hatch.
I am very intrigued by this. If the shark is not part of the tail-section group's Dharma Initiative section, could it then belong to this third bunker?
There's six stations, right? We know of two, possibly a third being underwater. I wonder where the other three are, and I wonder if Rousseau and The Others know much (if anything) about them.
I must now return to studying for my Italian exam.