They eat dead, sick and hurt marine life as well as just about anything else that finds it's way into their mouths. Of course, not all sharks are carnivores. Twenty of these species live in the oceans surrounding Australia. The best known sharks are the ones with reputations for vicious attacks on humans, although such attacks are quite rare. In the cooler waters off southern Australia, it is the great white shark .
All true sharks spend most of their lives in salt water.
At this time, we do not know enough about many shark species to allow us to understand their behavior or their population levels.