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Smooth Hammerhead Shark (Sphyrna zygaena)

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The smooth hammerhead shark (Sphyrna zygaena) is also known as the common hammerhead and the round-headed hammerhead. These sharks are are one of the 9 species of hammerhead sharks - species that all have unique hammer or shovel-shaped heads.

Description:

Smooth hammerheads are about 8 feet long when they are mature, and can grow to about 13 feet. Their maximum recorded weight is over 880 pounds.

Smooth hammerhead sharks have a large head, which doesn't have a notch at its center - a feature that allows one to distinguish this species from the great hammerhead. Smooth hammerhead sharks have an olive-gray or brownish-gray back. They may also have dark spots on the posterior (back end) of their underside, and the underside of their pectoral fin tips are a dusky color. The first dorsal fin of smooth hammerheads is tall, and they have a small 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: zygaena

Habitat and Distribution:

Smooth hammerhead sharks have a fairly wide distribution throughout temperate and tropical waters. They live both inshore and offshore, and on continental shelves in the western and eastern Atlantic and Pacific Oceans. In the U.S., they are found along the East Coast of the U.S. to the Caribbean, and from northern California to South America, and off Hawaii. They have even been seen in freshwater in Indian River, Florida.

Feeding:

Smooth hammerhead sharks eat fish, sharks, skates, rays and invertebrates such as crustaceans and cephalopods.

Reproduction:

Smooth hammerheads become sexually mature when they are about 8 years old. They are viviparous - they give birth to live young after a 10-11 month gestation. The pups are 19-24" when born and there are 29-37 pups per litter. Young sharks may gather in large schools, and these sharks may migrate north to cooler waters in the summer. These sharks are thought to live for 20 years or more.

Shark Attacks:

Hammerhead sharks are not generally dangerous to humans. The International Shark Attack File lists as #8 (hammerheads not listed as specifically as species) 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:

The smooth hammerhead is listed as vulnerable on the IUCN Red List. Threats to this species include fishing, harvesting for their fins, and bycatch.

References and Further Information:

  • Bester, Cathleen. Smooth Hammerhead. Florida Museum of Natural History. Accessed June 30, 2012.
  • Carpenter, K.E. Smooth Hammerhead: Sphyrna zygaena. Accessed June 30, 2012.
  • Casper, B.M., Domingo, A., Gaibor, N., Heupel, M.R., Kotas, E., Lamónaca, A.F., Pérez-Jimenez, J.C., Simpfendorfer, C., Smith, W.D., Stevens, J.D., Soldo, A. & Vooren, C.M. 2005. Sphyrna zygaena. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1. . Accessed June 30, 2012.
  • Compagno, L., Dando, M. and S. Fowler. 2005. Sharks of the World. Princeton University Press.
  • Florida Museum of Natural History. 2012. ISAF Statistics on Attacking Species of Shark. Accessed June 30, 2012.
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