Shark Release

A group of high school friends go on vacation for springbreak on an island only by the access of a boat, there's no way in or out without a boat. Terror strikes when things don't go as they were planned. There's only one beach house on the island and nothing else. They think they're the only ones there but later they find out there are other inhabitants that are rarely seen. They would later realize that all the other people who have stayed on the island just vanished without a trace and now they would do anything to escape that death trap of an island.
The water is infested with man eating sharks that don't belong there but only in the ocean.

so the questions are: How did they get there? Who brought them there? Who owns them?

They see things, hear things and smell things that cause them to keep running until they are captured, will they survive or will they vanish like the past visitors?