Great hammerhead shark
The great hammerhead (Sphyrna mokarran), is the largest species of the Hammerhead shark group. It can be identified by the shape of its "hammer" (called the "cephalofoil"), which is wide and has an almost straight margin at the front, and by its first dorsal fin which is tall, and is sickle-shaped.
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| Species: | S. mokarran
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Description
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Like all other hammerhead sharks, the great hammerhead has a streamlined body and a "hammer" on its head. They have usually been confused with the scalloped hammerhead and the smooth hammerhead shark, but adult great hammerhead sharks can be identified by their wide cephalofoil which has an almost straight margin at the front, and by their first dorsal fin, which is tall and sickle-shaped. The cephalofoil is usually around 1 to 1.5 meters long.
Great hammerhead sharks are around 2.85 to 5.5 meters long, and weigh around 450 kg, but the longest ever found was 6.1 meters long. The heaviest ever found was a 4.4 meter long female, which weighed 580 kg, and was caught off Boca Grande, Florida. But the female weighed this much because it was pregnant. The top part of the great hammerhead is gray-brown or green, and the belly is white.
Home
changeThe great hammerhead shark is found in tropical waters around the world, between the latitudes 40°N to 37°S. In the Atlantic Ocean it is found from North Carolina to Uruguay, including the Gulf of Mexico and the Caribbean Sea, and from Morocco to Senegal, and the Mediterranean Sea. It is found all along the rim of the Indian Ocean, and in the Pacific Ocean from the Ryukyu Islands to Australia, New Caledonia, and French Polynesia, and from southern Baja California to Peru. It's said to be found off Gambia, Guinea, Mauritania, Sierra Leone, and Western Sahara, but this has not been confirmed. Great Hammerhead Sharks can be found from inshore waters which are less than 1 meters deep, to a depth of 80 meters offshore. They live mainly in coral reefs, but have been found in lagoons and deep water near land.
Behaviour
changeEven though great hammerheads are apex predators, young pups have been seen eaten by bull sharks. Yellow jacks have been seen rubbing themselves against great hammerhead sharks, probably to get rid of parasites. Pilot fish have been seen swimming with great hammerheads.
Reproduction
changeGreat hammerheads are viviparous, meaning they give live birth. Females are pregnant for around 11 months, before giving birth to a litter of 6-56 pups. When they are born, the pups are around 50–70 cm (20 to 28 in) long. Males mature when they are about 2.3 to 2.8 meters long, and weigh around 51 kg. Females mature when they are about 2.5 to 3 meters long, and weigh around 41 kg. Great Hammerhead Sharks live for around 20–30 years, but the oldest Great Hammerhead Shark ever found was said to be 40–50 years old.
Feeding
changeGreat hammerhead sharks are known to hunt at dawn and at dusk. They feed on crustaceans like crabs and lobsters, mollusks like squid and octopuses, bony fish like tarpon, sardines, herrings, sea catfish, toadfish, porgies, jacks, croakers, groupers, flatfish, boxfish, and porcupine fish. They also eat other sharks like smoothhounds and grey reef sharks. Great Hammerhead Sharks have been known to eat others of their kind.
Great hammerhead sharks' favourite prey are rays and skates; its favourite type of ray are stingrays. The venomous spines of the stingrays don't seem to affect them, because a great hammerhead shark caught off Florida had 96 venomous spines found in and around its mouth.
The cephalofoil of the great hammerhead shark is said to be used to pin stingrays down, because agreat hammerhead shark was found attacking a stingray in the Bahamas; the great hammerhead first pinned the stingray down by hitting the stingray with its cephalofoil, and then it grabbed the stingray in its jaws and started to rip apart the stingray by shaking its head rapidly.
Another great hammerhead shark was found attacking a spotted eagle ray in open water; the Great Hammerhead Shark first bit off one of the ray's pectoral fins, and then pinned the ray down with its cephalofoil, and then ate the ray head-first.
Human interactions
changeAlthough they have been said to be dangerous towards humans, Great Hammerhead Sharks rarely ever attack humans. Divers have reported that Great Hammerhead Sharks are shy and avoid humans, but there have been reports of Great Hammerhead Sharks approaching divers closely and even chasing them. In 2009, the International Shark Attack File listed 34 attacks caused by a shark which belonged in the Sphyrna genus, but it is not confirmed if the shark was a Great Hammerhead Shark or not. The great hammerhead shark has been confirmed to be responsible for one provoked attack.
Conservation status
changeThe great hammerhead shark has been listed as endangered by the International Union for the Conservation of Nature (IUCN), because of fishing for its fins, which are made into shark fin soup, for its skin which is made into leather, and their liver oil for vitamins. Populations of the Great Hammerhead Shark have decreased by 50% because of fishing.
References
change- BBC-Great Hammerhead Shark Archived 2012-06-19 at the Wayback Machine
- Great Hammerhead Shark-Cool Facts and Information Archived 2012-09-01 at the Wayback Machine
- FLMNH- Great hammerhead shark Archived 2016-01-24 at the Wayback Machine