by Stefani Andrews

Created on: August 01, 2011

For as long as humans have been studying the fascinations of sharks, scientists have discovered relatively little about their lives. While we may know how sharks reproduce and how a lot of them give birth, the details of when or where they mate is entirely unknown. And except for species that can be bred in captivity for the most part there is no information about how long gestation is or even how many pups some species give birth too. 

All species of shark are sexually dimorphic. What this means is that there is a visual difference between male and female sharks, so distinctions of sex can be made in mere seconds. Males have a pair of pelvic claspers, located between the pelvic fins near the sharks tail. Females do not have these claspers so it is very easy to differentiate males from females. The claspers are two rolls of cartilage that protrude from the male's body and are used for sperm delivery during mating. When a male shark becomes sexually mature these claspers will become stiffened by extra calcium. Males also have a pair of internal testes. The right teste will always be more developed than the left, which is often missing entirely. When a male shark is in the presence of females during mating, the sperm will travel down a groove in the claspers in preparation for mating. This is a key way that scientists determine if it is almost a shark species' breeding season. They can catch the shark and look for the presence of sperm in the clasper groove, and if it is present than the male is sexually mature and ready for mating.

Female sharks do not have claspers and their reproductive system is entirely internal. They have a cloacal opening that is located between the pelvic fins that are connected to an internal pair of ovaries. Like the testes of the male the left ovary is often reduced in size and will produce little to no eggs. 

Sharks are considered K-selected breeders, which is very different to most other fish. What this means is that instead of producing a large number of poorly developed young, sharks will produce a fewer number of highly developed young. The mortality rate of young sharks is still extremely high but they stand a better chance by being born completely developed and ready to hunt and defend themselves. Sharks also reach sexual maturity very slowly. Usually sharks reach sexual maturity when they reach a certain size, which can be as few as 5 years in the case of smaller sharks or as long as 30 years for large species like

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