These Beach Warning Signs have been copyrighted since 1986 by the Hawaiian Lifeguard Association. Attacks on people from sharks are very rare and usually it is a case of mistaken identity. The attacks are very nearly always on the surface, often in water with low visibility, and often where fresh water enters the ocean. The chances of a person even seeing a shark in Hawaii are very small. The chances of being attacked by a shark in Hawaii are very likely less than being hit by lightning.
Current thought seems to be that attacks that do occur are cases of 'mistaken identity'.
There really isn't a lot of good information on shark behavior, especially the large, deep ocean dwelling species. A few popular 'shark avoidance' rules are to not swim in areas where a stream empties into the ocean or during the hour around sunset. Moray eels are fearsome looking creatures, big gaping mouth with long sharp teeth, and a body that reminds us of a land dweller we all know and love, the snake. They are also, generally, shy animals that live in holes in the rocks or coral by day, and hunt on the reef at night. The big gaping mouth is the eel breathing.