| Great Hammerhead | |
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Shark |
The Great Hammerhead Sphyrna mokarran is the largest species of hammerhead shark, family Sphyrnidae, attaining a maximum length of 6.1 m (20 ft). Although potentially dangerous, the great hammerhead rarely attacks humans. It sometimes behaves inquisitively toward divers and should be treated with respect. This shark is heavily fished for its large fins, which are extremely valuable on the Asian market as the main ingredient of shark fin soup. As a result, great hammerhead populations are declining substantially worldwide, and it has been assessed as Endangered by the International Union for Conservation of Nature (IUCN).
Description[]
The streamlined body of the great hammerhead with the expanded cephalofoil is typical of the hammerhead sharks. Adult great hammerheads can be distinguished from the scalloped hammerhead and the smooth hammerhead by the shape of the cephalofoil, which has a nearly straight front margin (as opposed to arched), with prominent medial and lateral indentations. The width of the cephalofoil is 23–27% of the body length. The teeth are triangular and strongly serrated, becoming more oblique towards the corners of the mouth. There are 17 tooth rows on either side of the upper jaw with 2–3 teeth at the symphysis (the midline of the jaw), and 16–17 teeth on either side of the lower jaw and 1–3 at the symphysis.
The first dorsal fin is distinctive, being very tall and strongly falcate (sickle-shaped), and originates over the insertions of the pectoral fins. The second dorsal fin and anal fin are both relatively large, with deep notches in the rear margins. The pelvic fins are falcate with concave rear margins, in contrast to the straight-margined pelvic fins of the scalloped hammerhead. The skin is covered with closely placed dermal denticles. Each denticle is diamond-shaped, with 3–5 horizontal ridges leading to marginal teeth in smaller individuals, and 5–6 in larger ones. The great hammerhead is dark brown to light gray to olive above, fading to white on the underside. The fins are unmarked in adults, while the tip of the second dorsal fin may be dark in juveniles.
The average great hammerhead measures up to 3.5 m (11.5 ft) long and weighs over 230 kg (500 lb). A small percentage of the population, mostly or all females, are much larger. The longest great hammerhead on record was 6.1 m (20 ft). The heaviest known great hammerhead is a 4.4 m (14.4 ft) long, 580 kg (1,280 lb) female caught off Boca Grande, Florida in 2006. The weight of the female was due to her being pregnant with 55 near-natal pups.
Habitat[]
The great hammerhead inhabits tropical waters around the world, between the latitudes of 40°N and 37°S. Great hammerheads may be found from inshore waters of less than 1 m (3.3 ft) deep, to a depth of 80 m (230 ft) offshore. They favor coral reefs, but also inhabit continental shelves, island terraces, lagoons, and deep water near land. They are migratory; populations off Florida and in the South China Sea have been documented moving closer to the poles in the summer.
Food[]
An active predator with a varied diet, known prey of the great hammerhead include invertebrates such as crabs, lobsters, squid, and octopus, bony fishes such as tarpon, sardines, sea catfishes, toadfish, porgies, grunts, jacks, croakers, groupers, flatfishes, boxfishes, and porcupine fishes, and smaller sharks such as smoothhounds. At Rangiroa Atoll, great hammerheads prey opportunistically on grey reef sharks (Carcharhinus amblyrhynchos) that have exhausted themselves pursuing mates. The species is known to be cannibalistic.