Basking Shark Biology

Basking Shark © Charles Hood.Despite their size, and visibility during summer months, researchers are only just beginning to piece together the life history of the Basking Shark; yet there remains much we don’t know about the largest shark in UK waters.

It is believed that males reach maturity at around 4.6–6.1m in length, at an age of 12–16 years. No data for female maturity or the longevity of either sex is available, although extrapolation from other Lamnoids would suggest a female maturity of around 20 years and a life expectancy of at least 50 years.

The Basking Shark belongs to the order Lamniformes and is the only member of the family Cetorhinidae. Basking Sharks are ovoviparous, which means the female produces eggs which she retains until they have absorbed the egg yolk and completed their development, they will then hatch inside the female, before she gives birth to fully developed young. Like many other Lamniformes, Basking Sharks are oophagous, which means that infertile eggs are produced to nourish the growing young. 

Gestation periods of 1–3.5 years have been proposed though this figure has recently been revised to around 14 months. Estimates of the size at birth range from 1–1.7m, making Basking Shark pups larger at birth than the majority of other sharks are when fully grown. 

There is little data on Basking Shark reproduction with only a single reported catch of a pregnant female carrying six pups reported in 1943. This leads to the theory that females give birth in areas of low or no fishing pressure, possibly segregating from the general population.    

Basking Sharks appear quite social animals and are seen singly, in small groups or in schools of hundreds of individuals feeding in areas of high plankton concentration. Fisheries captures of Basking Sharks off the British Isles during the summer revealed that the individuals present were predominantly adult females, outnumbering males by as much as 40:1. However, the few individuals that were caught during winter months were mostly male. Throughout the geographical and vertical migrations that Basking Sharks make there are many reports of groups of same size and sex individuals, suggesting a strong sexual and age segregation within the species.