Great White Shark
The great white shark or white shark Carcharodon carcharias is one of five species in the family Lamnidae. The remaining members of Lamnidae being the shortfin mako Isurus oxyrinchus, longfin mako Isurus paucus, salmon shark Lamna ditropis, and the porbeagle shark Lamna nasus. White sharks are thought to have evolved from the extinct Carcharodon hubbelli, a species of shark that persisted in the late Miocene, 6-8 mya. Due to its attention in the media, the white shark has been villianized as is most evident in the hit movie Jaws (1975). In reality, the white shark is simply abiding by the rules of nature and fulfilling its position at the top of the food chain.
The white shark is one of, if not the most, well-known and easily recognizable fishes found on earth. The lateral and dorsal regions of the body are light to dark grey. The ventral region of the body from snout to tail is pearl white. The snout is relatively long, pointed, and contains numerous electroreceptive pores in the skin, termed ampullae of Lorenzini. The teeth are triangular and serrated, which function like a steak-knife and can easily tear through the toughest of hides. The eyes are dark black and have the ability of rolling back to protect the eyes when pursuing prey that are well-equipped to fight back like seals. The caudal fin is heterocercal and lunate and the caudal peduncle has a prominent keel, which reduces drag. Five long gill slits lie anterior to the large pectoral fins that function in generating lift. The pectoral fins also have charicteristic black markings on the ventral side where the fins come to a point. The pelvic fins lie on the ventroposterior portion of the body. The first dorsal fin is large and rectangular. Both the second dorsal and anal fins are tiny compared to the other fins. The longest confirmed white shark measured 5.944 meters long and was caught in 1984 off the coast of Western Australia. White sharks can weigh up to 3,000+ Kilograms. White sharks are late-maturing and long-lived sharks that are estimated to live 40-60 years in the wild.
The white shark reproductive mode is ovoviviparous in which the developing embryos are nourished by eggs produced by the females ovaries (oophagy). Male white sharks are estimated to reach sexual maturity at about 3.5-3.8 meters in length and 7-9 years old. Females are believed to reach sexual maturity at 4.5-5.0 meters in length and 12-17 years of age. Gestation period lasts 12-18 months. The breeding intervals (time between breeding events) is 2-3 years. Females give birth to litters of 2-17 pups, which at birth, are already 1.0-1.5 meters in length. Juvenile white sharks reside near the coast and feed mainly on other fishes.
Distribution & Movements
|Chris_huh - Compagno, Leonard; Dando, Marc & Fowler, Sarah (2005). Sharks of the World. Collins Field Guides. ISBN 0-00-713610-2.|
Distributed worldwide, with exception of polar seas, and can be found in the warm to temperate waters of the Indian, Atlantic, and Pacific Oceans. The largest populations of white sharks occur along the coasts of South Africa, Australia, central California, and the Atlantic coast of North America. White sharks are both coastal and oceanic species as they can be found inshore and are also known for small-scale migrations along coastlines and large-scale migrations spanning entire oceans. Common migratory routes include a distance of 3,800 kilometers (2,361 miles) between the coasts of California and Hawaii in the Northern Pacific Ocean. Migratory white sharks also cross the Indian Ocean from South Africa to Australia, a distance of 22,000 kilometers (13,670 miles). Other individuals have also been documented migrating from Australia to New Zealand.
The white shark is both a coastal and oceanic species, which can be found from 0-1,300 meters deep. Inshore white sharks can be found in the rocky reefs or shallow bays of coastal regions. Migratory white sharks can be observed traversing continental shelves and navigating the open ocean. Habitat use varies seasonally and depends on temperature, food availability, gender, and reproduction.
Food & Feeding Habits
Lamnid sharks have a heat conservation mechanism termed counter-current exchange system. Heat generated by muscle contractions is retained by juxtaposed capillaries that run counter-current to each other and the heat diffuses down its concentration gradient. This gives C. carcharias and other lamnid sharks the ability of sustaining elevated levels of activity when in cooler waters. White sharks are mega-predatory oceanic fishes that will feed on marine mammals (Cetaceans and Pinnipeds), seabirds, sea turtles, crustaceans, cephalopods (squid and octopus), and fishes including other sharks. When closing in on a prey, the white shark lifts the upper jaw and drops the lower jaw to maximize gape. When prey is captured in the mouth, the upper jaw is rotated forward and down and the lower jaw is lifted forward and up, thereby articulating the jaws to actually thrust the jaws outward towards the prey. Prime conditions for seal hunting include cloud cover and turbid waters, which gives white sharks the element of surprise, key for capturing highly agile prey. White sharks use vision to locate and identify potential prey. The cryptic coloration of the white shark acts as counter-shading, allowing the shark to go undetected by prey when viewed from above. Large white sharks can be found hunting near islands where marine mammals like seals congregate. The most infamous feeding strategy of white sharks is "breaching", in which white sharks attack prey at the surface from below, propelling themselves many meters above waters surface.The high blubber content in seals makes them rich in energy when consumed. White sharks also have a low oxygen consumption rate relative to other large fishes, thus, a diet consisting of high energy prey and a low oxygen consumption rate allow white sharks to endure extended periods of time without food.
White sharks have low natural mortality rates as humans and orcas Orcinus orca are their only natural predators. White sharks are routinely caught as bycatch from commercial fishermen, due to entanglement in fishing nets that are targeting other species of fishes. Unless freed from entanglement, the white shark will perish as they need to continuously swim to respire. Tuna farm owners have also been known to dispatch white sharks that have endangered the stock of farm raised tuna.
Economic Importance for Humans
White sharks caught as bycatch are utilized for consumption from their fins and meat. While the fins are not considered high quality by the Chinese market, commercial fishermen will still take the fins of any large shark, regardless of species. White sharks have also been harvested for their jaws and teeth to be utilized as novelty items by collectors. White shark jaws have sold for thousands of dollars (depending on size) due to a high demand from private collectors. White shark teeth have been sold for hundreds of dollars (also depending on size). Cage diving with white sharks has become a popular tourist attraction particularly in South Africa, Australia, and California where numerous cage diving vessels lure tourists seeking a thrill. Steven Spielberg's 1970's hit movie JAWS starred a man-eating white shark off the coast of the Northeastern United States and has grossed $430,000,000.00 USD since its release in theatres.
Threats & Conservation Status
The first country to protect the white shark was South Africa in 1991. The white shark was listed as Protected by the South African fisheries legislation, making it illegal to capture or kill white sharks in South Africa. The Australian federal government's Environmental Protection and Biodiversity Conservation Act 1999 lists the white shark as Vulnerable. The white shark was also listed at Vulnerable in 2009 by the IUCN Red List of Threatened Species.The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) lists the white shark under Appendix II, meaning that the species is vulnerable to endangerment.
- Compagno, Leonard, Marc Dando, & Sarah Fowler. 2005. Sharks of the World. Princeton University Press, Princeton and Oxford.
- Department of Sustainability, Environment, Water, Population and Communities (2013).Carcharodon carcharias in Species Profile and Threats Database, Department of Sustainability, Environment, Water, Population and Communities, Canberra. Available from: http://www.environment.gov.au/sprat.
- Duffy, Clinton. 2004. International trade in white shark Carcharodon carcharias products from New Zealand. Shark News: Newsletter of the IUCN shark specialist group.
- Ehret, Dana J., Bruce J. Macfadden, Douglas S. Jones, Thomas J. Devries, David A. Foster, & Rodolfo Salas-Gismondi. 2012. Origin of the white shark Carcharodon (Lamniformes: Lamnidae) bason on recalibration of the Upper Neogene Pisco Formation of Peru. Palaeontology Vol. 55: pg. 1139.
- Fergusson, I., Compagno, L.J.V. & Marks, M. 2009. Carcharodon carcharias. In IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>.
- Johnson, Ryan. 2003. The behavioral ecology of the white shark (Carcharodon carcharias) at Dyer Island. Faculty of Natural and Agricultural Sciences, University of Pretoria.
- Spielberg, Steven. 1975. JAWS. http://www.imdb.com/title/tt0073195/.