They wouldn't. Those are sand tiger sharks, and they are- oddly- one of the most gentle species of sharks out there. Just not very aggressive or dangerous, but undeniably mean-looking. If you were a small fish, or maybe a crab you'd be in serious danger.
They have attacked humans, but each documented case has been a shark defending itself when grabbed. Smart people, eh?
This type of shark was obliterated in Australia after "Jaws" came out- so much so that the author of the novel had to go down there to tell locals that his book was fiction, and that wiping out sharks was a bad thing.
http://animals.nationalgeographic.com/animals/fish/sandtiger-shark.html
:hatsoff:
H