Blue sharks are viviparous, with the males maturing at the age of 4-5, and females reaching maturity at the age of 5-6. The gestation period lasts from 9 to 12 months. During mating, the males have been known to bite the females, but their thick skin is believed to stop any pain. Pups are 41 to 50 cm (16 to 20 inches) long at birth, with females giving birth to 4-135 pups at a time, but the number of pups depend on the size of the female, with larger females giving birth to more pups. Blue sharks live to up to 20 years.