Scalloped hammerhead
Encyclopedia
The scalloped hammerhead (Sphyrna lewini) is a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of hammerhead shark
Hammerhead shark
The hammerhead sharks are a group of sharks in the family Sphyrnidae, 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 while the...

, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Sphyrnidae. Originally Zygaena lewini, it was later moved to its current name. The Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 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 latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s 46° N
46th parallel north
The 46th parallel north is a circle of latitude that is 46 degrees north of the Earth's equatorial plane. It crosses Europe, Asia, the Pacific Ocean, North America, and the Atlantic Ocean....

 and 36° S
36th parallel south
The 36th parallel south is a circle of latitude that is 36 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, the Indian Ocean, Australasia, the Pacific Ocean and South America....

, down to a depth of 500 metres (1,640.4 ft). It is the most common of all hammerheads.

Taxonomy

The scalloped hammerhead was first named Zygaena lewini and then renamed Sphyrna lewini by Edward Griffith and Hamilton Smith
Charles Hamilton Smith
Lieutenant-Colonel Charles Hamilton Smith was an English artist, naturalist, antiquary, illustrator, soldier and spy.-Military service:...

 in 1834. It have 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
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of hammerhead off the shores of South Carolina
South Carolina
South Carolina is a state in the Deep South of the United States that borders Georgia to the south, North Carolina to the north, and the Atlantic Ocean to the east. Originally part of the Province of Carolina, the Province of South Carolina was one of the 13 colonies that declared independence...

. 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.

Distribution and habitat

The scalloped hammerhead is a coastal pelagic
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...

 species, it occurs over continental and insular shelves and in nearby deeper water. It is found in warm temperate and tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

 waters, worldwide from 46° north to 36° south. It can be found down to depths of over 500 metres (1,640.4 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
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...

 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.
The maximum length of the scalloped hammerhead is 4.3 metres (14.1 ft) and the maximum weight 150 kilograms (330.7 lb).

Behavior

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.

Diet

This shark feeds primarily on fish such as sardine
Sardine
Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....

s, mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...

 and herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

, and occasionally on cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

s such as squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

 and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...

. Larger specimens may also feed on smaller species of shark such as the blacktip reef shark
Blacktip reef shark
The blacktip reef shark is a species of requiem shark, family Carcharhinidae, easily identified by the prominent black tips on its fins...

, Carcharhinus melanopterus.

Endangered status

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
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...

) and are calling for a ban on the practice of Shark finning
Shark finning
Shark finning refers to the removal and retention of shark fins and the discarding of the rest of the fish. Shark finning takes place at sea so the fishers only have to transport the fins.Shark finning is widespread, and largely unmanaged and unmonitored...

, 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.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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