It is uncertain at what size female Basking Sharks mature but it is thought to be around 8 m. Conversely, males mature at around 5 m yet it is thought that both sexes can take up to 18 years to mature.

 

There is little data on Basking Shark reproduction with only a single reported catch of a pregnant female carrying six pups reported in 1943 (Sund, 1943) - this leads to the theory that females give birth in areas of low or no fishing pressure.

 

It is believed that Basking Sharks are yolk-sac viviparous (fertilised eggs develop within the womb until all of the egg yolk has been absorbed and development is complete, the female eventually gives birth to fully developed live young) and that, like many other lamnoid sharks (mackerel sharks – 16 species including White, sandtiger and Goblin Sharks), pups display oophagy (feeding on infertile eggs released by the mother into the uterus).

 

Gestation period has been estimated to be as long as 3.5 years  but this figure has recently been revised to around 14 months (see Exploitation & Threats). Regardless of duration, Basking Shark pups are still larger at birth than the majority of other sharks are when fully grown (around 1.5 – 2 m).