Great Hammerhead Shark

The great hammerhead shark (Sphyrna mokarran) is the largest of the 9 species of hammerhead sharks. These sharks are easily recognized by their unique hammer or shovel-shaped heads.

Description

The great hammerhead can reach a maximum length of about 20 feet, but their average length is about 12 feet. Their maximum length is about 990 pounds. They have a grayish-brown to light gray back and white underside.

Great hammerhead sharks have a notch in the center of their head, which is known as a cephalofoil. The cephalofoil has a gentle curve in juvenile sharks but becomes straight as the shark ages. Great hammerhead sharks have a very tall, curved first dorsal fin and a smaller second dorsal fin. They have 5-gill slits.

Classification

• Kingdom: Animalia
• Phylum: Chordata
• Subphylum: Gnathostomata
• Superclass: Pisces
• Class: Elasmobranchii
• Subclass: Neoselachii
• Infraclass: Selachii
• Superorder: Galeomorphi
• Order: Carcharhiniformes
• Family: Sphyrnidae
• Genus: Sphyrna
• Species: mokarran

Habitat and Distribution

Great hammerhead sharks live in warm temperate and tropical waters in the Atlantic, Pacific, and Indian Oceans. They are also found in the Mediterranean and Black Seas and Arabian Gulf. They undertake seasonal migrations to cooler waters in the summer.

Great hammerheads may be found in both nearshore and offshore waters, over continental shelves, near islands, and near coral reefs.

Feeding

Hammerheads use their cephalofoils for detection of prey using their electro-reception system. This system allows them to detect their prey by electrical fields.

Great hammerhead sharks primarily feed at dusk and eat stingrays, invertebrates, and fish, including even other great hammerheads.

Their favorite prey is rays, which they pin down using their heads. They then bite at the ray's wings to immobilize them and eat the entire ray, including the tail spine.

Reproduction

Great hammerhead sharks may mate at the surface, which is unusual behavior for a shark. During mating, the male transfers sperm to the female via his claspers. Great hammerhead sharks are viviparous (give birth to live young). The gestation period for a female shark is about 11 months, and 6-42 pups are born live. The pups are about 2 feet long at birth.

Shark Attacks

Hammerhead sharks are generally not dangerous to humans, but great hammerheads should be avoided due to their size.

Hammerhead sharks, in general, are listed by the International Shark Attack File #8 on its list of species responsible for shark attacks from the years 1580 to 2011. During this time, hammerheads were responsible for 17 non-fatal, unprovoked attacks and 20 fatal, provoked attacks.

Conservation

Great hammerheads are listed as endangered by the IUCN Red List due to their slow reproduction rate, high bycatch mortality and harvest in shark finning operations. The IUCN encourages implementation of shark finning bans to protect this species.

_{References and Further Information}

• _{ARKive. Great Hammerhead. Accessed June 30, 2012.}
• _{Bester, Cathleen.Great Hammerhead Shark. Florida Museum of Natural History. Accessed June 30, 2012.}
• _{Carpenter, K.E. Great Hammerhead: Sphyrna mokarran. Accessed June 30, 2012.}
• _{Compagno, L., Dando, M. and S. Fowler. 2005. Sharks of the World. Princeton University Press.}
• _{Denham, J., Stevens, J., Simpfendorfer, C.A., Heupel, M.R., Cliff, G., Morgan, A., Graham, R., Ducrocq, M., Dulvy, N.D, Seisay, M., Asber, M., Valenti, S.V., Litvinov, F., Martins, P., Lemine Ould Sidi, M. & Tous, P. and Bucal, D. 2007. Sphyrna mokarran. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1... Accessed June 30, 2012.}
• _{Florida Museum of Natural History. 2012. ISAF Statistics on Attacking Species of Shark. Accessed June 30, 2012.}
• _{Krupa, D. 2002. Why the Hammerhead Shark's Head is In the Shape It's In. American Physiological Society. Accessed June 30, 2012.}
• _{ScienceDaily. 2010. Hammerhead Shark Study Shows Cascade of Evolution Affected Size, Head Shape. Accessed June 30, 2012.}