The scalloped hammerhead (Sphyrna lewini) is a species of hammerhead shark, family Sphyrnidae. Originally Zygaena lewini, it was later moved to its current name. The Greek word sphyrna translates into "hammer" in English, referring to the shape of this shark's head.
This shark is also known as the bronze, kidney-headed or southern hammerhead. It primarily lives in warm temperate and tropical coastal waters all around the globe between latitudes 46° N and 36° S, down to a depth of 500 metres (1,600 ft). It is the most common of all hammerheads.
The scalloped hammerhead was first named Zygaena lewini and then renamed Sphyrna lewini by Edward Griffith and Hamilton Smith in 1834. It has also been named Cestracion leeuwenii by Day in 1865, Zygaena erythraea by Klunzinger in 1871, Cestracion oceanica by Garman in 1913, and Sphyrna diplana by Springer in 1941. Sphyrna comes from the Greek and translates into hammer.
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 a result of genetic testing and counts of vertebrae.
Distribution and habitat
The scalloped hammerhead is a coastal pelagic species, it occurs over continental and insular shelves and in nearby deeper water. It is found in warm temperate and tropical waters, worldwide from 46° north to 36° south. It can be found down to depths of over 500 metres (1,600 ft) but is most often found above 25 metres (82 ft). During the day they are more often found close to shore and at night they hunt further offshore. Adults occur alone, in pairs or in small schools while young sharks occur in larger schools.
Anatomy and appearance
The most distinguishing characteristic of this shark, as in all hammerheads, is the 'hammer' on its head. The shark's eyes and nostrils are at the tips of the extensions. This is a fairly large hammerhead, though is smaller than both the Great and Smooth Hammerheads. On average, males measure 1.5 to 1.8 m (4.9 to 5.9 ft) and weigh approximately 29 kg (64 lb) when they attain sexual maturity, whereas the larger females measure 2.5 m (8.2 ft) and weigh 80 kg (180 lb) on average at sexual maturity. The maximum length of the scalloped hammerhead is 4.3 m (14 ft) and the maximum weight 152.4 kg (336 lb), per FishBase. A female caught off of Miami was found to have measured 3.26 m (10.7 ft) and reportedly weighed 200 kg (440 lb), though was in a gravid state at that point.
This shark is often seen during the day in big schools, sometimes numbering hundreds. They are not considered dangerous and are normally not aggressive towards humans.
This shark feeds primarily on fish such as sardines, mackerel and herring, and occasionally on cephalopods such as squid and octopus. Larger specimens may also feed on smaller species of shark such as the blacktip reef shark, Carcharhinus melanopterus.
As of 2008, the scalloped hammerhead is on the "globally endangered" species list. Research has shown that in parts of the Atlantic Ocean, scalloped hammerhead populations have declined by over 95% in the past 30 years. Among the reasons for this drop off are over-fishing and the rise in demand for shark fins. Researchers attribute this growth in demand to the increase in shark fins as an expensive delicacy (such as in shark fin soup) and are calling for a ban on the practice of Shark finning, a practice in which the shark's fins are cut off and the rest of the animal is thrown back in the water to die. Hammerheads are among the most commonly caught sharks for finning. 
- "More oceanic sharks added to the IUCN Red List" (Press release). IUCN. 2007-02-22. http://www.iucn.org/en/news/archive/2007/02/22_pr_sharks.htm. Retrieved 2007-02-25. "The status of scalloped hammerhead shark was heightened from Near Threatened to Endangered."
- "Florida Museum of Natural History on scallped Hammerhead". http://www.flmnh.ufl.edu/fish/Gallery/Descript/ScHammer/ScallopedHammerhead.html. Retrieved December 2008.
- Quattro, et. al. (December 2005). "Genetic evidence of cryptic speciation within hammerhead sharks (Genus Sphyrna)". Marine biology (Springer Berlin / Heidelberg) 148 (5): 1143-1155. doi:10.1007/s00227-005-0151-x.
- "Scientist Finds 'Genetically Distinct' Shark". PhysOrg.com. http://www.physorg.com/news68994294.html. Retrieved June 2006.
- Ed. Ranier Froese and Daniel Pauly. "Sphyrna lewini". FishBase. http://www.fishbase.org/Summary/SpeciesSummary.php?id=912. Retrieved 10 December 2008.
- Castro, José I., The Sharks of North America. Oxford University Press (2011), ISBN 978-0-19-539294-4
- "Hammerhead Shark Makes Endangered Species List". redorbit.com. http://www.redorbit.com/news/science/1259813/hammerhead_shark_makes_endangered_species_list/. Retrieved August 2011.
- Kotas (2000). Sphyrna lewini. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 11 May 2006. Database entry includes justification for why this species is near threatened
- "Sphyrna lewini". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=160508. Retrieved 23 January 2006.
- Froese, Rainer, and Daniel Pauly, eds. (2005). "Sphyrna lewini" in FishBase. 09 2005 version.
- Scalloped hammerhead shark (Sphyrna lewini) at Wikimedia Commons
- Scalloped hammerhead shark (Sphyrna lewini) at Wikispecies
- Scalloped hammerhead shark (Sphyrna lewini) at Integrated Taxonomic Information System
- Scalloped hammerhead shark (Sphyrna lewini) at Animal Diversity Web
- Scalloped hammerhead shark (Sphyrna lewini) at FishBase
- Scalloped hammerhead shark (Sphyrna lewini) at Ocean Biogeographic Information System