Sphyrna Zygaena, Linnaeus, 1758

Identification

This species is named “smooth hammerhead” because of the distinctive shape of the head, which is flattened and laterally extended into a hammer shape (called the “cephalofoil“), without an indentation in the middle of the front margin (hence “smooth”). The cephalofoil is wide but short, measuring 26–29% of the body length across.
The positioning of the eyes, mounted on the sides of the shark’s distinctive hammer head, allows 360° of vision in the vertical plane, meaning the animals can see above and below them at all times. They also have an increased binocular vision and depth of visual field as a result of the cephafoil. The body is streamlined, without a dorsal ridge between the two dorsal fins. The first dorsal fin is moderately tall and falcate in shape, with a rounded tip. The pectoral and pelvic fins are not falcate. The back is dark brownish, becoming lighter on the flanks and the belly is white. As with all sharks and rays, hammerheads have small pores or “ampullae of Lorenzini”, distributed along the ventral surface of their head and serve as highly sensitive electrical receptors that are used to detect the electrical signals that are emitted by potential prey items, including those that are buried under the sand such as stingrays.

Biology

The second-largest hammerhead shark, can measure up to 5m. The smooth hammerheads is an active-swimming predator that feeds on bony fishes, rays, sharks, caphalopods and crustaceans. The species is viviparous. Females bear large litters of 20-50 pups after a gestation period of 10-11 months. Unlike other hammerheads, this species prefers temperate waters and are observed worldwide at médium latitudes. In the Summer, migrates following cool water masses and forming schools with other sharks. It is a pelagic species that habits coastal and oceanic waters.

Behaviour

The hydrodynamic shape provides greater speed when turning head. The smooth hammerhead stays closer to the surface, in water less than 20m deep. However, it has been recorded diving to a depth of 200m.

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