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Sharks can rouse fear and awe like no other creature in the sea. Find out about the world's biggest and fastest sharks, how sharks reproduce, and how some sp...
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- National Geographic
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the Batoidea ( rays and kin).
- Overview
- Description and habits
shark, any of numerous species of cartilaginous fishes of predatory habit that constitute the order Selachii (class Chondrichthyes).
Sharks, together with rays and skates, make up the subclass Elasmobranchii of the Chondrichthyes. Sharks differ from other elasmobranchs, however, and resemble ordinary fishes, in the fusiform shape of their body and in the location of their gill clefts on each side of the head. Though there are exceptions, sharks typically have a tough skin that is dull gray in colour and is roughened by toothlike scales. They also usually have a muscular, asymmetrical, upturned tail; pointed fins; and a pointed snout extending forward and over a crescentic mouth set with sharp triangular teeth. Sharks have no swim bladder and must swim perpetually to keep from sinking to the bottom.
Shark species are nondescript in colour, varying from gray to cream, brown, yellow, slate, or blue and often patterned with spots, bands, marblings, or protuberances. The oddest-looking sharks are the hammerheads (Sphyrna), whose heads resemble double-headed hammers and have an eye on each stalk, and the wobbegongs (family Orectolobidae), whose skin flaps and protective coloration closely resemble the seafloor. The vernacular of shark names indicate colours in living species, such as the blue (Prionace glauca), the white (Carcharodon carcharias; also known as the great white shark), and the lemon (Negaprion brevirostris) shark.
Britannica Quiz
Understanding Megalodon
The whale shark (Rhincodon typus) and the basking shark (Cetorhinus maximus), both of which may weigh several tons, are harmless giants that subsist on plankton strained from the sea through modified gill rakers. Whale sharks may grow up to 18 metres (59 feet) in length, whereas basking sharks may reach 14 metres (46 feet) fully grown. All other sharks prey on smaller sharks, fish, squid, octopuses, shellfish, other invertebrates, and, in some species, trash. The largest among the more predatory species is the voracious 6-metre (20-foot) white shark, which attacks seals, dolphins, sea turtles, large fish, and occasionally people. The more sluggish Greenland shark (Somniosus microcephalus) of cold deep waters feeds on seals, large fish, and even swimming reindeer; they may also scavenge whale carcasses.
Normally, sharks feed on fish, often attacking in schools. Open-ocean species such as the mackerel (Lamna), mako (Isurus), and thresher (Alopias) sharks frequently feed near the surface and are much sought after with rod and reel for sport. Beautifully streamlined and powerful swimmers, those open-ocean sharks are adept at feeding on fast tuna, marlin, and the like. Bottom-feeding species of sharks are stout, blunt-headed forms that tend to have more-sluggish habits. The shellfish eaters among them have coarse, pavementlike, crushing teeth.
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Learn about the world's most ancient and diverse fish, from their skeletons and teeth to their diets and migrations. Find out how sharks are threatened by overfishing, climate change, and human activities.
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The oceanic whitetip, porbeagle and three hammerhead species are some of the shark species of concern for WWF, where the impact of trade is contributing to declines in populations. Millions of these sharks continue to be fished annually to supply the persistent demand for their fins and meat.
Jun 13, 2005 · Read on for more surprising shark facts compiled by National Geographic News: • Each year there are about 50 to 70 confirmed shark attacks and 5 to 15 shark-attack fatalities around the...
Introduction. The Ocean Portal Team. Reviewed by David Shiffman, University of Miami. There are more than 500 species of sharks swimming in the world’s ocean. Yet when most people think of these cartilaginous fish, a single image comes to mind: a large, sharp-toothed and scary beast.
