hammerhead shark
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What is a hammerhead shark?
The hammerhead shark is any of 10 shark species in the family Sphyrnidae. Hammerheads are known for their flattened hammer- or shovel-shaped head, called a cephalofoil. They are considered one of the most distinctive and unique of all sharks.
These cartilaginous fish vary in size. The small scalloped bonnethead measures only 90 cm (35 inches) long, while the great hammerhead grows to over 6.1 meters (20 feet) in length. Hammerhead sharks are widely distributed in tropical and temperate marine waters near the coasts and above the continental shelves. They may migrate seasonally, moving equatorward during the winter and poleward during the summer.
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What does a hammerhead shark look like?
Hammerhead sharks, from the family Sphyrnidae, are known for their distinctive, flattened hammer- or shovel-shaped heads, called cephalofoils hammerhead shark. The size of these cartilaginous fish varies; the scalloped bonnethead is only 90 cm (35 inches) long, while the great hammerhead can grow to over 6.1 meters (20 feet) in length. The peculiar shape of their cephalofoils appears to serve multiple purposes, including enhanced maneuverability, a keener ability to locate prey, a wider field of view, and the ability to detect the electrical impulses of prey.
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Where are hammerhead sharks found in the world?
Hammerhead sharks are found worldwide in tropical and temperate marine waters near coastlines and continental shelves. They migrate seasonally, heading towards the equator in winter and toward the poles in summer. During warm El Niño years, they can extend their range hundreds of kilometers beyond their usual boundaries. The Galapagos Marine Reserve (GMR) in the eastern Pacific Ocean is a significant marine protected area for approximately 30 shark species, including the critically endangered scalloped hammerhead shark.
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What do hammerhead sharks eat?
Hammerhead sharks consume a variety of fish, cephalopods, and crustaceans, with specific prey varying among the species. Smaller bonnethead sharks, equipped with flattened teeth, commonly feed on crabs, shrimp, and small fishes buried in the sand. Notably, the bonnethead shark (S. tiburo) is omnivorous, supplementing its diet with seagrass. Conversely, larger hammerheads utilize their bladelike teeth to prey on sizable fishes, squid, small sharks, and stingrays. The great hammerhead is known to specialize in hunting stingrays, often enduring numerous stingray barbs embedded in their bodies.
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How does the hammerhead shark’s head shape help it survive?
The hammerhead shark's unique head shape, called a cephalofoil, serves multiple purposes that aid in its survival.
- The flattened head enhances maneuverability, allowing the shark to make quick and sharp turns to capture prey.
- Expanded nostrils improve the ability to locate prey by following scents.
- The wide spacing of the eyes may provide a broader field of view and better depth perception.
- The underside of the head houses electroreceptive organs that can detect electrical impulses from prey, even those buried in sediment.
- Larger hammerheads use their head to ram and pin prey to the sea floor.
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What threats do hammerhead sharks face in the wild?
Hammerhead sharks face several threats in the wild, primarily from human activities. Commercial fishing, driven by the demand for shark fin soup, leads to the finning of sharks, where their fins are harvested, and the bodies are discarded. Hammerheads are also caught as bycatch in fisheries targeting other species, causing significant population declines.
Despite decreased shark fin consumption and finning, shark populations continue to decline due to expanding commercial fishing fleets. Habitat destruction and pollution also pose threats.
Conservation efforts include establishing marine protected areas and implementing legal protections, such as the Shark Conservation Act in the United States, to restrict the taking of sharks without their fins.
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hammerhead shark, (family Sphyrnidae), any of 10 shark species belonging to the genera Sphyrna (9 species) and Eusphyrna (1 species), which are characterized by a flattened hammer- or shovel-shaped head, or cephalofoil. Hammerhead sharks, or sphyrnids, are perhaps the most distinctive and unique of all sharks. These cartilaginous fishes vary in size; the small scalloped bonnethead (S. corona) measures only 90 cm (35 inches) long, whereas the great hammerhead (S. mokarran) grows to over 6.1 metres (20 feet) in length. Although they are considered one of the most recently evolved groups of sharks, sphyrnids are known to date back in the fossil record to at least the early Miocene Epoch (about 23 million to 5.3 million years ago). Some authorities believe that this group emerged as early as the Eocene Epoch (roughly 56 million to 33.9 million years ago).
Hammerhead sharks are widely distributed in tropical and temperate marine waters near the coasts and above the continental shelves. They may migrate seasonally, moving equatorward during the winter and poleward during the summer. In years with warm El Niño conditions, hammerhead sharks may range many hundreds of kilometres farther than normal. Some species, such as the scalloped hammerhead (S. lewini) and smooth hammerhead (S. zygaena), form large schools that may be segregated by sex or age.
Hammerhead sharks are viviparous: they retain fertilized eggs within the body and give birth to live young—from 2 to 42. Smaller species produce just a few young, whereas the great hammerhead will give birth to several dozen. Birth usually occurs during the spring and summer months, and females will usually give birth in shallow, protected coastal waters. The young will live in these areas until they reach larger sizes and can safely venture into deeper offshore waters.
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The peculiar shapes of sphyrnid cephalofoils appear to serve several purposes. First, the flattened and expanded head acts as a hydrodynamic bow plane that allows the shark to raise and turn its head quickly and sharply. This feature gives the shark enhanced maneuverability to snap up its prey. Second, the nostril is much expanded compared with other groups of sharks and may provide hammerhead sharks with a keener ability to locate prey and follow scents to their sources. Third, the extended spacing of the eyes may provide a wider field of view; it may also widen the lateral field of view and increase anterior depth perception. Fourth, the wide underside of the head—with its expanded surface area—houses more electroreceptive organs (see sensory reception), which are important for detecting the electrical impulses of prey. These organs may even detect the electrical impulses of prey buried in sediment. Lastly, many larger hammerhead species hunt stingrays and other benthic (that is, bottom-dwelling) fish; they have been observed using the wide margins of their heads to ram and pin prey to the substrate before biting them.
Hammerhead sharks prey on a wide array of fish, cephalopods, and crustaceans, but specific prey varies between the different species. The smaller bonnethead sharks have thicker, flattened crushing teeth and often prey on crabs, shrimp, and fishes buried in the sand. One species of bonnethead shark, S. tiburo, is omnivorous, because it eats seagrass. In contrast, larger hammerhead sharks possess sizable bladelike teeth and often prey on larger fishes, squid, small sharks, and stingrays. In fact, the great hammerhead specializes in hunting and eating large stingrays, and some members of this species have been found to have dozens of stingray barbs embedded in their flesh. Most species feed in relatively shallow coastal waters and may even venture into brackish bays and estuaries. A few species migrate into offshore waters to feed at night, and some of these have even developed strategies to hunt at great depths. One species, the tropical scalloped hammerhead shark (S. lewini) dives to depths of 800 metres (about 2,600 feet) or more where the water temperature falls to as low as 5 °C (41 °F); it conserves heat by stopping the flow of water through its gills, essentially “holding its breath,” as it dives.
While hammerhead sharks usually are not considered dangerous, there have been several confirmed accounts of large hammerhead sharks attacking people. Most of those attacked were spearfishing, and it could be that the blood of the speared fish attracted the sharks. Nonetheless, large hammerhead sharks should be respected and avoided by bathers and divers.
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Humans often eat the meat of hammerhead sharks; however, consumers should be aware that large specimens may have high levels of mercury and other pollutants. Fins, skin, and teeth are also harvested from sphyrnids, and many larger hammerhead sharks are prized as sport fish.