Fertilization takes place internally, the male inserting one of its claspers into the female. Most sharks are ovoviviparous, hatching the eggs within the female and bearing live young. Embryonic development takes more than six months, and in the Atlantic spiny dogfish it takes close to two years. The young are frequently born in protected inshore areas away from the males. Seeing, although less acute, allows the shark to catch dim movements of shadow and light in dark waters as it approaches its prey.
Sharks are particularly sensitive to sounds of low frequency and have fine directional hearing.
Organs along their lateral lines and on the snout enable sharks to pick up weak electrical stimuli from the muscle contractions of bony fish. This combination of keen senses accounts for the evolutionary success of sharks. When hunting in schools, sharks can incite one another into a feeding frenzy. Among the sharks most dangerous to humans are the great white shark, the hammerhead shark, the tiger shark, and the blue shark. Ecology Sharks play an important ecological role in oceans, similar to that of large predators on land.