When sharks mate, the male grabs the head of the female with his teeth and inserts pelvic fins called "claspers" into her reproductive area. The male has sacs that are filled with seawater that help to shoot his sperm through the female to ensure reproduction. The two sharks stop swimming and have to stay connected for several minutes. They sometimes fall to the ocean floor in the process.
After the mating process is complete, both sharks are exhausted and must rest for several minutes, taking time to replenish the oxygen they lost. The female shark sustains injuries from the male's teeth and claspers that heal after a few weeks.
For some species of female sharks, the ova is fertilized immediately after mating. Some species are capable of storing the sperm for up to one year before the ova is fertilized and they reproduce. Some sharks lay eggs. Other young sharks develop inside a placenta and have live births. Most sharks nurture and hatch eggs internally, giving birth to live young.
The hammerhead shark and three other shark species are capable of both asexual and sexual reproduction, meaning that some of the young are born with no father. Asexual reproduction does not produce as many young and is less common.