Our knowledge of the many different types of reproductive strategies of sharks is still limited. This variety is precisely why it is difficult to make generalisations on their reproductive methods, although this is exactly what makes sharks so successful.
Types of reproduction
Most sharks bear live young (viviparity) and the others lay eggs. Several shark species mate the entire year, others prefer certain seasons and regions. The females of some shark species bear young each year whilst others stop reproducing at irregular intervals which can last several years.
Few people have witnessed the mating activity of sharks. In smaller, more flexible species the male coils around the female. Whereas, males of larger, more rigid species will orient themselves parallel and head-to-head with females. During mating, males of many species bite females on the pectoral fins or the middle of the back to hold onto them. Females often bear scars or marks. As a result, some female sharks, such as the blue shark, have skin on the back and flanks more than twice as thick as the skin of the male.
Claspers are modified inner edges of the pelvic fins of male sharks and rays. During copulation, the erectile claspers are bent forward. The male inserts one clasper at a time into the female. In some species, claspers contain cartilaginous hooks and spurs that "clasp" into the walls of the female oviduct, anchoring the clasper. Muscles force seminal fluid down a groove in the clasper and into the female oviduct.