Hammerhead Shark
There are currently nine recognized species of hammerhead shark alive today, each with a uniquely shaped hammer-like head that gives them their common name.
Class: Chondrichthyes
Order: Carcharhiniformes
Family: Sphyrnidae
Genus: Sphyrna, Eusphyrna
Species: S. mokarran (Great Hammerhead), S. zygaena (Smooth Hammerhead), S. tudes (Smalleye Hammerihead), S. gilberti (Carolina Hammerhead), S. lewini (Scalloped Hammerhead), S. media (Scoophead), S. tiburo (Bonnethead), S. corona (Scalloped Bonnethead), E. blochii (Winghead)
Common Names: Hammerhead Shark
The purpose of the shark’s strange head has long been a subject of interest to scientists. It is thought to give the shark a wider field of vision, but it may also help them detect electric fields created by living things, which can help them detect prey.
Hammerhead sharks are predators and consume a wide range of prey, including fish, squid, octopus and crustaceans. A favorite food of the hammerhead is the stingray.
Hammerheads prefer warmer waters, along coastlines and continental shelves. They may travel sometimes in large schools, which is rare for sharks to do.
Hammerheads breed once a year. They are viviparous and give birth to live young. The mother usually gives birth to 12 to 15 hammerhead pups, although great hammerhead litters can be even larger.
The bonnethead is the first shark known to have reproduced without a partner, a process known as parthenogenesis.
Hammerhead sharks are known for their distinctive hammer-shaped heads. Instead of the pointed snout of a typical shark, hammerheads have flattened heads with projections on either side that give it the appearance of a hammer (or in some species a shovel) when viewed from above. Their eyes are at the end of these projections. The entire structure is called a “cephalofoil”.
Aside from the head, the body plan of most hammerhead species is similar to the typical shark body plan. Their dorsal fins are large in comparison to most other shark species, and their mouths are relatively small.
Coloration is usually gray, sometimes with a yellowish or greenish tint, and can vary by species. The smallest species of hammerhead are the bonnethead and scalloped bonnethead, which grow to around three to four feet long. The largest species is the great hammerhead, which can grow up to 20feet long.
Aside from their different sizes, the easiest way to tell different hammerhead species apart is the shape of their head. Bonnetheads are also called shovelheads, and are named for the rounded shape of their cephalofoils. The great hammerhead has a T-shaped head, while the scalloped hammerhead has a series of notches in their cephalofoil. The winghead shark is named for it sextraordinarily large cephalofoil, which may be as wide as half of the total length of the entire shark.
Hammerheads have cultural significance to the indigenous Torres Strait Islanders. Hammerhead sharks are often featured in their artifacts and ceremonial dress. In native Hawai'ian culture, the hammerhead is one of the most respected species of shark. They are known as mano kihikihi, and are viewed as protective spirits.
In 2015, hammerhead sharks were found living in one of the most active underwater volcanos, known as Kavachi, in the southwest Pacific Ocean. Despite the hot temperatures and acidic quality of the water in the active volcano, the sharks appear to have adapted to living comfortably within the volcano’s crater. It is not currently known where the sharks go in the event of an eruption.
Hammerhead sharks have a fearsome reputation, but there have only been 17 documented unprovoked attacks on record by hammerhead sharks. The most likely shark involved in these attacks is the great hammerhead. However, such attacks are exceedingly rare, and while hammerheads are large and powerful sharks that deserve to be treated with respect, humans are not among their favored prey. There are no recorded human fatalities caused by hammerheads.
Almost all species of hammerhead shark are currently threatened with extinction. The smooth hammerhead is Vulnerable, the bonnethead and winghead are Endangered, and the great hammerhead, scalloped hammerhead, scalloped bonnethead, scoophead, and smalleye hammerhead are all Critically Endangered. The Carolina hammerhead, a relatively recently discovered species, does not currently have enough population data available to determine its status, but it is likely that it faces similar threats.
Hammerheads are caught in fisheries, and their fins are used in shark fin soup, and it is estimated that nearly 400,000 hammerheads a year may be caught for their fins.
Smaller hammerhead species, such as the bonnethead, are frequently showcased in captivity in public aquariums. Larger species are much more difficult to keep in captivity, but some aquariums have housed scalloped, great, and smooth hammerheads with varying degrees of success.
References
Castro, Jose I. (2011). The Sharks of North America. New York, New York: Oxford University Press, Inc.
https://en.wikipedia.org/wiki/Hammerhead_shark
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