Few people have witnessed the mating activity of sharks.
In smaller, more flexible species the male coils around the female.
- In larger, more rigid species the male orients himself parallel and head-to-head with the female.
- 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. Upon examination, these marks show they have been made by upper jaw teeth. In some elasmobranchs, males have longer, narrower teeth than females. In some female sharks, such as the blue shark, the skin on the back and flanks is more than twice as thick as the skin on the male.
Shark and batoid eggs are fertilized internally, as opposed to external fertilization in many bony fishes. Internal fertilization is a key adaptation for energy-intensive reproduction.
When born or hatched, young sharks are fully formed and physically able to fend for themselves.
- Because these independent shark pups have a better chance for survival, the number of sharks produced in a litter is rarely more than 100. The majority of the species bear far fewer pups.
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.
Smaller species may reach sexual maturity in as few as three or four years. Larger species like dusky sharks (Carcharhinus obscurus) grow slowly and may not reach maturity for 15 years or longer.
Researchers at SeaWorld study growth rates, blood chemistry, and reproduction in sharks. A milestone for shark breeding occurred at SeaWorld Orlando in 1995 when brown shark pups were conceived and born in the main aquarium. This was the first time that such an event happened in the United States. SeaWorld San Diego was the first aquarium to successfully breed Pacific blacktip sharks. SeaWorld recently assisted the NMFS and Albion College with the most extensive study of the reproduction of collected nurse sharks ever undertaken. Ultrasound and intrauterine endoscopy were used to document the pregnancies of two nurse sharks that were brought to SeaWorld Orlando. When the tests were completed, both the females and their offspring were tagged and released back to the wild where their mating activities were originally witnessed and filmed.