Instead their internal frames are made of cartilage . Sharks have what some call a sixth sense . They can sense electrical and magnetic fields, which helps them detect prey and orient themselves using the earth's magnetic fields. Sharks' diets vary widely. The largest of the bunch, the whale shark, feeds mostly on plankton, while tiger sharks will eat most anything.
Most species grow slowly and mature late.
It can take up to 20 years for some species to reach reproductive age. This means that population depletion can be especially devastating.