Basking Shark Morphology

Aside from their large size, Basking Sharks are characterised by their powerful lunate (or crescent-shaped) tail, very large mouth, pointed nose and five huge gill slits which almost encircle the head. Weighing up to 7 tonnes (average 4.5 tonnes), the maximum reported size of a Basking Shark is 12m, although the existence of specimens of 15.2m length has been suggested. However, most adults do not exceed 9.8m.

Basking Shark (lateral) © Marc Dando.

Other key identifying features are the strong lateral keels on the caudal peduncle (where the tail joins the body) the bristle-like gillrakers and rows of hundreds of minute teeth that fill the mouth. The mouth can be well over 1m wide in adult sharks. Basking Sharks also have huge livers that account for up to 25% of their body weight and provide the shark with near-neutral buoyancy.

One curious anomaly is the shape of the snout of juveniles which is long and hook-like at birth and for the first year of life. It is believed that a hooked snout makes feeding in the womb, and for the first few months of life, easier by increasing water flow through the mouth.

Basking Sharks are typically greyish-brown but can range through to slate grey or black on the dorsal surface. Irregular patches, patterns and streaks mark the animals' flanks and fins while the ventral (underside) of Basking Sharks are predominantly lighter than the dorsal.