We do not yet know much about the reproductive strategies of sharks and rays. Sharks have probably been very successful through evolution because they have adapted their reproduction to many different conditions.
Many sharks bear live young (viviparity), others lay eggs (oviparity). Several shark species mate the entire year, others prefer certain seasons and regions. The females of some shark species bear young each year, others stop reproducing at irregular intervals which can last several years.
Approximately 30% of all sharks lay eggs, that can have many shapes and colors. These species are oviparous. The egg size can vary strongly: from a few centimeters of the catshark to even 25 cm in length. The eggs have a yolk that nurtures the embryos sufficiently with nutrients. By laying their young in well-protected, stable egg capsules with sufficient nutrients, the female sharks shorten the time needed to care for their young.
Other sharks bear live young: the eggs hatch inside the female’s body and the babies are fed by a placenta which transfers nourishment from the mother to the babies The number of pups in a litter ranges from 2-20 or more. Sharks like a.o. bull sharks are viviparous.
In other shark species, the eggs hatch and the babies develop inside the female’s body but there is no placenta to nourish the pups.
The pups eat any unfertilized eggs and each other (they are oviphagous). Very few pups in a litter survive until birth due to this form of sibling cannibalism. This is called aplacental viviparity (ovoviviparous). A.o. great white sharks reproduce this way.
The reproduction of sharks and rays is slow. They mature late en their litter is small. They are therefore also excellent indicators for overfishing: the worse the situation of elasmobranchs is getting, the worse the situation for other fish stocks probably is.
Some sharks do breed in captivity, and Sweet Pea, a bowmouth guitarshark, gave birth to seven pups in the Newport Aquarium.
This historical achievement was made possible through Newport Aquarium’s revolutionary Shark Ray Breeding Program (SRBP), which was established in February 2007 with the introduction of what was, as the time, an extremely rare male shark ray named Scooter.
The SRBP expanded with the introduction of a second female shark ray, Sunshine, in 2009 and a second male, Spike, in 2013. You can see the birth of the pups in the video below: