basking shark

Basking shark. The basking shark is the second-largest living shark and fish, after the whale shark, and one of three planktivorous shark species. This gentle giant is a cosmopolitan migrant species, found in temperate oceans worldwide, and is characterized by its enormous, distensible mouth and highly modified gill rakers used for filter feeding. Historically targeted by commercial fisheries for its liver oil, fins, and meat, it is now classified as Endangered on the IUCN Red List and is protected in many territorial waters under agreements like the Convention on International Trade in Endangered Species.

## Taxonomy and Evolution The basking shark was first described scientifically by the Norwegian bishop and naturalist Johan Ernst Gunnerus in 1765. The genus name Cetorhinus comes from the Greek ketos, meaning "sea monster" or "whale", and rhinos, meaning "nose". The only extant member of the family Cetorhinidae, its evolutionary history is known from fossilized teeth and vertebrae dating back to the early Oligocene and possibly the late Eocene, with notable fossil finds in California and Belgium. This places its lineage as a relatively ancient one within the Lamniformes order, which also includes the great white shark and the mako shark.

## Physical Characteristics This species possesses a distinctive, conical snout and an enormous, crescent-shaped mouth that can be over one meter wide when fully open. Its most remarkable feature is the long, filament-like gill slits that nearly encircle the head, housing the intricate gill raker apparatus used for filtering plankton. The body is typically a mottled gray-brown color, with a massive, heterocercal tail fin. Adults commonly reach lengths of 7.9 meters, with exceptional individuals recorded by the Marine Conservation Society exceeding 12 meters. The liver, which can constitute up to 25% of its body weight and is rich in squalene, historically made it a prime target for hunters.

## Habitat and Distribution The basking shark is a highly pelagic and coastal species with a circumglobal distribution in temperate waters. It is frequently observed in regions such as the North Atlantic Ocean, particularly around the United Kingdom, Ireland, the Northeastern United States, and the Mediterranean Sea. In the Pacific Ocean, it is found from Japan to New Zealand and from Chile to the Gulf of Alaska. Sightings often occur seasonally in surface waters during the summer months in areas of high zooplankton productivity, such as the Bay of Fundy and the Sea of Hebrides.

## Behavior and Diet Unlike most large sharks, it is an obligate filter feeder, swimming with its mouth agape to passively collect copepods, krill, fish eggs, and larvae. It employs a method called "ram filtration," where forward movement forces water through its gill rakers. Observations by organizations like the Maine Department of Marine Resources indicate it often feeds near the surface, a behavior that gives the shark its common name. While largely solitary, they are known to form loose aggregations, sometimes in groups of over 100 individuals, in prime feeding grounds. Research using satellite tagging by the Marine Biological Association has revealed deep dives and long-distance migrations, possibly related to breeding or following plankton blooms.

## Conservation Status The global population is listed as Endangered by the International Union for Conservation of Nature. It faced severe depletion from targeted fisheries, especially in the mid-20th century, driven by demand for its oil for lamps and later for cosmetics, and for its fins for shark fin soup. Current major threats include bycatch in commercial fishing gear, ship strikes, and marine pollution. It is listed on Appendix II of the Convention on International Trade in Endangered Species, regulating international trade, and is fully protected within the territorial waters of nations like the United Kingdom, Malta, and New Zealand.

## Interactions with Humans Historically, directed fisheries operated in places like the North Sea, Norway, and California. While no longer commercially hunted in most areas, it remains a prized sight for ecotourism operations in locations such as Scotland, Cornwall, and New England. Its docile nature and surface-feeding habits make it a subject of study for marine biologists and a charismatic species for public education by institutions like the Monterey Bay Aquarium. Encounters with boats are generally harmless, though its size and sudden diving can pose a risk to small vessels. Its image features prominently in the mythology and heraldry of coastal communities, such as in the coat of arms of the Isle of Man.

Category:Sharks Category:Filter feeders Category:Endangered species