The Basking Shark (Cetorhinus maximus) is the second-largest living shark and fish, after the whale shark. Typically measuring around 7.9 meters (26 feet) in length, they are greyish-brown with mottled skin and a white mouth. Basking sharks are slow-moving filter feeders that feed at the surface, deriving their name from this behavior. They have adaptations for filter-feeding, including a large mouth and well-developed gill rakers that trap plankton.
They can be found in temperate oceans worldwide, often alone or in small groups. Despite their size, they are harmless to humans. Basking sharks have historically been important for food, shark fins, animal feed, and shark liver oil. However, due to overexploitation, their populations have significantly declined, leading to the need for protection.
The Basking Shark is a coastal and pelagic species found worldwide in boreal to warm-temperate waters. It typically inhabits the continental shelf and prefers temperatures ranging from 8 to 14.5°C, but can be found in much warmer areas as well. Basking sharks are often observed near the surface as they follow plankton concentrations and exhibit seasonal migrations.
Adult basking sharks usually measure 7 to 8.5 meters in length, with some individuals reaching 9 to 11 meters. The average adult weighs about 4.65 tons. The largest recorded specimen was 12.27 meters long, captured in the Bay of Fundy, Canada, in 1851, weighing around 16 tons.
These sharks can be distinguished from great white sharks by their cavernous jaws, larger gill slits, smaller eyes, and hooked teeth that are significantly smaller. Unlike great whites, basking sharks are filter feeders, consuming zooplankton and small fish while swimming with their mouths open.
Basking Sharks possess highly textured skin, a pointed snout, and a lunate caudal fin. Their coloration varies, typically ranging from dark brown to black or blue dorsally, fading to white ventrally. They can be scarred from encounters with other marine animals, such as lampreys.
As slow movers, basking sharks feed at about 2 knots (3.7 km/h or 2.3 mph) and do not avoid boats. They can breach entirely out of the water, which might help dislodge parasites, although this behavior is not entirely understood.
These sharks can filter up to 450 tons of water per hour while feeding, with a preference for small planktonic crustaceans. They may gather in groups of up to 1,400 individuals, particularly in areas rich in zooplankton. Unlike other filter-feeding sharks, basking sharks rely primarily on the water column for sustenance.
Basking Sharks are ovoviviparous, meaning that embryos develop inside a yolk sac without a placental connection. Their teeth may help them feed on the mother’s unfertilized eggs, a behavior known as oophagy. Only the right ovary in females appears to function, and the reason for this is unclear.
Gestation is thought to last over a year, possibly two to three years, with young measuring 1.5 to 2 meters at birth. One documented pregnant female carried six unborn young. Mating occurs in early summer, with birthing in late summer as females move to shallow waters.
Basking Sharks reach sexual maturity between six and 13 years, at lengths of 4.6 to 6 meters, and breed every two to four years. Their estimated lifespan is around 50 years.
