Examples of all three reproduction methods are found in sharks living in Australian waters. The Port Jackson Shark (Heterodontus portusjacksoni) lays spiral shaped eggs that young hatch from (oviparous), the Smooth Hammerhead Shark (Hphyrna zygaena) gives birth to live young (viviparous) and the Grey Nurse Shark (Carcharias taurus) gives birth to pups after they have hatched from eggs within the uterus (ovoviviparous).
Most sharks are ovoviviparous, meaning that the eggs hatch in the oviduct within the mother's body and that the egg's yolk and fluids secreted by glands in the walls of the oviduct nourishes the embryos. The young continue to be nourished by the remnants of the yolk and the oviduct's fluids. The young are born alive and fully functional.
Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs. They choose such areas for protection from predators (mainly other sharks) and the abundance of food. Dogfish have the longest known gestation period of any shark, at 18 to 24 months.