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Hammerhead Shark (SPHYRNA ZYGAENA)

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SHARK, HAMMERHEAD / SPHYRNA ZYGAENA
10 20 31.50 69.7 Lanzarote Canary Is. 081094 H. Lehmkuhl
24 50 113.00 249.2 Faial Azores 170893 N. Gibbs
37 80 110.00 242.8 Gran Canaria Canary Is. 280893 B. Olsson
60 130 161.00 354.15 Gran Canaria Canary Is. 110783 D. Weber
AT AT 161.00 354.15 Gran Canaria Canary Is. 110783 D. Weber

The hammerhead shark (SPHYRNA ZYGAENA)

is found worldwide in temperate waters. In the western Atlantic Ocean, this species is found from Canada south to the Virgin Islands and from Brazil south to Argentina, while in the eastern Atlantic it occurs from the British Isles south to Côte d'Ivoire, including the Mediterranean Sea. In the western Indian Ocean, the smooth hammerhead occurs off the coasts of South Africa, India, and Sri Lanka. The distribution within the Pacific Ocean includes from Vietnam to Japan and Australia and New Zealand in the west, the Hawaiian Islands in the central region, and California (U.S.), Panama, Galapagos, Ecuador, and Chile in the east.

Preferring shallow waters less than 65 feet (20 m) in depth, the smooth hammerhead lives close to shore over continental shelves and in inshore waters including bays and estuaries. However this species has been reported in depths from 0-656 feet (0-200 m) including those reported from offshore locations. In some areas, juveniles may be abundant and form large aggregations. Adults occur either singly or in small groups.

During summer months, smooth hammerheads sometime form schools during migrations northward to cooler which is later followed by a return south in the winter. During hot summer weather, adults and juveniles can sometimes be seen swimming along the surface with their dorsal fins exposed.

The smooth hammerhead gets its common names from the large hammer-shaped head. This compressed head is also referred to as a "cephalophoil", allowing for easy distinction from other types of sharks. The cephalophoil is broad and flattened with a broadly rounded unnotched anterior margin. The eyes are located on the outer edges of the cephalophoil with the nostrils also spread far apart. The head is scalloped with a depression opposite each nostril. The ventrally-located mouth is strongly arched. It is thought that the head structure may give the shark some sensory advantages or that perhaps it improves maneuverability or increases lift.

Within the hammerhead family, several species are differentiated from each other by variations within the cephalophoil. The great hammerhead (S. mokarran) is distinguished by the T-shaped head that has an almost straight front edge and a notch in the center. The scalloped hammerhead (S. lewini) is a smaller species with a rounded anterior margin and notch on the head. The bonnethead (S. tiburo) is much easier to identify with a shovel-shaped head.

hammerhead shark (sphyrna zygaena)

The body of the smooth hammerhead is dark olive to brownish-gray in color with a white underside. This is in contrast to the brown coloration that is common to many other species of hammerheads. Some individuals have dusky or black edged pectoral fins.

The average size of the smooth hammerhead ranges between 8-12 feet (2.5-3.5 m) in length with a maximum total length of 16 feet (5 m) and maximum weight of 880 pounds (400 kg). Although maximum age has yet to be determined for this species, it is believed the smooth hammerhead may have a lifespan of 20 years or longer. At birth, smooth hammerheads measure approximately 20 inches (.5 m) in length. Females reach maturity at approximately 8.7 feet (2.7 m) and males at 7-8 feet (2.1-2.5 cm) in length, depending upon locality.

Primarily a piscivore, the smooth hammerhead feeds on a variety of bony fishes including clupeids and small scombrids as well as elasmobranchs such as smaller sharks (as well as its own species) and stingrays. In fact skates and stingrays make up the majority of its diet in inshore locations. Invertebrate prey includes benthic crustaceans and cephalopods. In northern Europe, this shark feeds on herring and bass, while in North America Spanish mackerel and menhaden are commonly consumed fish. The smooth hammerhead has also been observed scavenging from surface longlines in the Mediterranean Sea.


Information supplied by http://www.flmnh.ufl.edu

 
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