What you should know about these beautiful creatures.
Dr Samuel Gruber reknown marine biologist and shark expert, Mike Rudson specialist shark diver, Christina Zenato shark diver and Walter Bernardis shark diver says, they are not freightened of sharks, but you must respect them.
Hammerhead Sharks are found in both open deep ocean and shallow coastal waters. During summer they may make small migrations towards more northerly areas. The great hammerhead is observed in deep water off the fore reef, in channels, on the reef flat and in lagoons.
Hammerhead sharks are found in tropical waters throughout the world.
Hammerheads mostly hunt at dusk and feed on fishes (including catfishes, toadfishes, jacks, herring, groupers, boxfishes occassionally other sharks), squid and crustaceans (including shrimps, crabs and mantis shrimps) that occur on or near the bottom. Larger specimens seem to have a particular fondness for skates and rays (including guitarfishes, butterfly rays, whiptail stingrays, cownose rays and eagle rays), which it has been observed chasing in shallow waters.
The Great Hammerhead is a solitary species, rarely seen with other sharks. Scalloped and Smooth Hammerheads on the other hand, form small and large schools. Scalloped Hammerhead sharks can often have hundreds of sharks in one school. All Hammerhead sharks migrate to warmer waters in the winter. Other sharks have been known to avoid Great Hammerheads out of fear of being eaten. Hammerheads may attack other sharks.
Hammerheads will often warn you with threatening postures before attacking.
Popular places to see Hammerhead sharks include South Africa, Galapagos Islands, Coco Islands, Great Barrier Reef (Australia) and some Indonesian Islands. Huge schools of Scalloped Hammerheads can be seen at the Galapagos Islands, which is a truly amazing experience!
Hammerhead Sharks In General
The Hammerhead Sharks are a group of sharks in the family Sphrynidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna; some authorities place the winghead shark in its own genus, Eusphyra. Many, not necessarily mutually exclusive, functions have been proposed for the cephalofoil, including sensory reception, maneuvering and prey manipulation. Hammerheads are found worlwide in warmer waters along coastlines and continental shelves.
Since sharks do not have mineralized bones and rarely fossilize, it is their teeth alone that are commonly found as fossils. The hammerheads seem closely related to the carcharhinid sharks that evolved during the mid-Tertiary Period. Because the teeth of hammerheads resemble those of some carcharhinids, it has been difficult to determine when hammerheads first appeared. It is probable that the hammerheads evolved during the lat Eocence, Oligocene or early Miocene.
Geneticist Andrew Marin used DNA to study all of the hammerhead species and he concluded that the first hammerhead appeared on the winghead shark, which has the largest hammer and the rest of the hammerhead sharks evolved one at a time from the original winghead shark each with a smaller hammer.
The nine known species of hammerhead range from 0.9 to 6 m long (3 to 20 feet). All the species have a projection on each side of the head that gives it a resemblance to a flattened hammer. The shark's eyes and nostrils are at the tips of the extensions.
The hammer shape of the head was once thought to help sharks get food, aiding in close-quarters maneuverability and allowing the shark to turn sharply without losing stability. However, it was found that the special design of its vertebrae allowed it to make the turns correctly, more than its head. But as a wing the hammer would also provide lift; hammerheads are one of the most negatively buoyant of sharks. Like all sharks, hammerheads have electroreceptory sensory pores called ampullae of Lorenzini. By distributing the receptors over a wider area, hammerheads can sweep for prey more effectively. These sharks have been able to detect an electrical signal of half a billionth of a volt. The hammer-shaped head also gives these sharks larger nasal tracts, increasing the chance of finding a particle in the water by at least 10 times as against the ability of other 'classical' sharks.
Wider spacing between sensory organs better enable an organism to detect gradients and therefore the location of a gradient source such as food or a mate. The peculiar head of this shark can be thougt of as analogous of an insect.
Hammerheads have disproportionately small mouths and seem to do a lot of bottom-hunting. They are also known to form schools during the day, sometimes in groups of over 100. In the evening, like other sharks, they becoe solitary hunters.
Reproduction in the hammerhead shark occurs once a year wih each litter containing 20 to 40 pups. Hammerhead shark mating courtship is a violent affair. The male will bite the female until she acquiesces, allowing mating to occur. The hammerhead shark has internal fertilization which creates a safe environment for the sperm to unite with the eggs. The embryo develops within the female inside a placenta and is fed through an umbilical cord, similar to mammals. The gestation period is 10 to 12 months. Once the pups are born the parents do not stay with them and they are left to fend for themselves. Young hammerheads are often born headfirst, with the tip of the hammerhead folded backward to make them more streamlined for birth. A world record 1,280 pound (580 kg) pregnant female was caught off Boca Grande, Florida on 23rd May 2006. The shark was carrying 55 pups, which suggests scientists had previously underestimated the number of pups per gestation.
In May 2007 scientists discovered that hammerhead sharks can reproduce asexually through a rare method known as parthenogenesis, (a direct development without the need of a sperm, similar to how social insects can reproduce). At first the announcement was considered skeptically, because a female shark can store sperm inside her for months, even years, but it was confirmed through DNA testing that the pup lacked any paternal DNA. This is the first documented case of any shark doing this.
Scalloped Hammerhead, Sphyrna
"Cryptic scalloped hammerhead" - Scalloped hammerheads are two separate species, which have not yet been officially reclassified with separate names.
Great Hammerhead, Sphyrna
Smooth Hammerhead, Sphyrna
Whitefin Hammerhead, Sphyrna
Scalloped Bonnethead, Sphyrna (Mesozygaena)
Winghead Shark, Sphyrna (Mesozygaena)
Scoophead, Sphyrna (Platysqualus)
Bonnethead or Shovelhead, Sphyrna (Platysqualus)
Smalleye Hammerhead, Sphyrna (Platysqualus)
Announcements in June, 2006 reported the discovery of a possible new species of hammerhead off the shores of South Carolina. The possible new species is referred to simply as a cryptic species until it receives an official designation. This is prolonged, in part, because the discovery is really that the "scalloped hammerhead" is possibly two different species, not that a new species has been sighted, in the normal way. The discovery that scalloped hammerheads are possibly two species is purely a result of genetic testing, not identification of physical differences.
Relationship to humans
Of the nine known species of hammerhead, three may be dangerous to hamans: the Scalloped, Great and Smooth Hammerheads.
The Great and the Scalloped Hammerhead are listed on the World Conservation Union's (IUCN) 2008 Red List as endangered, whereas the Smalleye Hammerhead is listed as vulnerable. The status given to these sharks is as a result of over fishing and demaned for their fins, an expensive delicacy. Among others, scientists express their concern about the plight of the Scalloped Hammerhead at the American Association for the Advancement of Science annual meeting in Boston. The young swim mostly in shallow waters along shores all over the world to avoid predators.
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