A nice little pro-shark article this week by Florida's Capt. Rob Kraut.
I have been diving in South Florida for 7 years now and have never seen a Bull Shark or a Tiger Shark. I know they are out there but I and most of my dive buddies have never seen them.
Tiger Shark are very identifiable because they have faint stripes like a tiger. Bull Sharks have this huge chest cavity that make them look like Arnold Schwarzeneger if he were a shark.