Every shark species has its own expected life span and so it is wrong to set an average for sharks as a whole. However, very broadly speaking, we can say that most sharks live for between 20 and 40 years. The Spiny Dogfish lives for over a century, and Whale Sharks are expected to be similar.
most other animals, sharks do not care for their young. As soon as
pups are born into the water, they swim away and care for
themselves. Some sharks give birth to litters of up to 100 pups at
a time, while many species may have as few as two or three. In
almost all cases, all of the pups are healthy and well-developed.
This is in stark contrast to many other animals (such as several
fish species and some turtles), which give birth to large numbers of
ill-developed young (in effect, producing quantity over quality).
This means that sharks are defined as
In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity, or quality of offspring. The focus upon either increased quantity of offspring at the expense of individual parental investment (r selection), or reduced quantity of offspring with a corresponding increased parental investment (K selection), is varied to promote success in particular environments.
Mating amongst sharks is somewhat elusive, rarely seen by researchers and scientists. Fertilisation of the female egg occurs internally. The male’s pelvic fin (the fin on the underside of the body, close to the tail) has evolved into claspers, a pair of organs that can best be compared to a penis in mammal species.
Once fertilised, sharks will carry their young in one of three ways:
Oviparity – Some sharks lay eggs, protected within a leathery egg case.
Viviparity – This term is used to describe the sharks that have a placenta from which to feed and sustain their young inside. The young are born alive and at full term.
Ovoviviparity – The majority of sharks lay eggs inside their body. These hatch and the young remain inside for some time. Eventually, they are born alive and fully developed. Some shark species display a form of cannibalism in that the first pup to hatch eats the other eggs or pups while still inside its mother. This is called oophagy.
The gestation period for ovoviviparous species is not known for sure. However, it is thought to be anywhere from several months to over two years.
There have also been isolated cases of asexual reproduction, meaning that the female has managed to conceive and birth pups without any input from a male. The cases have all been observed in sharks in captivity. The incidence of asexual reproduction in the wild remains unknown and is believed to be a last resort method of reproduction in the absence of males.