Or it could be that Natalee was killed up at the lighthouse and was dumped in one of those old mine pits filled with water, which diving experts have said is a dangerous place to have to search. But if they threw her body into the sea by the lighthouse, that's in the vicinity where sharks feed on offal dumped by local fishermen. Joran and his pals would know this.
I wouldn't think sharks would eat a whole human being, would they? Wouldn't some remains or pieces of clothing wash up? These are probably not the size of sharks that could eat a whole person.