The basking shark is one of four types of large, filter-feeding elasmobranchs, the others being the megamouth and whale sharks, and the manta rays (Mobulidae). The basking shark may be unique in relying entirely on the passive flow of water through its pharynx generated by swimming for filtration; the other filter-feeders may assist the process of food ingestion by actively pumping or gulping water and food organisms into their pharynxes.
Adult, nonpregnant female basking sharks have immense numbers of small eggs in their ovaries, which suggests that this shark has uterine cannibalism as in many other lamnoids, with embryos feeding on the small eggs (oophagy). Feeding on smaller siblings (adelphophagy) has not been demonstrated.
Basking sharks are not considered dangerous to the passive observer and are generally tolerant of divers and boats. Despite this, its sheer size and power must be respected (there are reports of sharks attacking boats after being harpooned). In addition, contact with its skin should be avoided, as its large dermal denticles have been known to inflict damage on divers and scientists.
Occasionally known as "sunfish" or "sailfish" in certain areas of the world, the basking shark is the only member of the family Cetorhinidae. It was first described by Gunnerus in 1765 from a specimen from Norway and was originally assigned the name Squalus maximus.
The basking shark is the second-largest fish in the world, at up to five ton in weight and 15 metres in length. Once abundant on the British Columbia coast, they are nearly extinct today after the federal government began their extirpation from the coast in the 1950s, because their habit of basking on the surface often entangled them in fishing gear. Now B.C. produces perhaps one sighting a year, yet they still have no protection.
Basking sharks feed exclusively by straining plankton from seawater passed through gill rakers in their wide mouths while swimming very slowly just below the surface. The slow moving dorsal fin is diagnostic of this animal.
Despite being placid, planktivorous and the only member of the family Cetorhinidae, there are strong similarities between Basking Sharks and the more active, carnivorous members of the order. The large gill slits, torpedo shaped body and near symmetrical lunate (crescent shaped) tail are all mirrored in the White, mako, Salmon and Porbeagle Sharks.
Basking Sharks have been fished heavily for many years. Primarily hunted for its liver oil, basking sharks have also been hunted for their meat, cartilage and fins. Despite the majority of Basking Shark fisheries closing, some areas still target them, mainly for Asian markets.
Basking sharks appear to have very low reproductive rates and may be more vulnerable to overfishing than any other shark species. Pupping frequency has not been determined, but has been estimated at 18 months to 3 years, with litter sizes of about 1 to 6 pups. While some estimates are available, in reality, most aspects of their reproductive biology and age and growth are unknown or poorly understood.
There is no aspect of the movements, behaviors, population size or structure, or life history that isn't data deficient for basking sharks in the eastern North Pacific. More is unknown than known.