Great Hammerhead

The great hammerhead shark (Sphyrna mokarran) is the largest species within the hammerhead family, Sphyrnidae, typically reaching an average length of 4.6 meters (15 feet) and a maximum length of 6.2 meters (20 feet). This species is prevalent in tropical and warm temperate waters across the globe, primarily inhabiting coastal regions and the continental shelf. It can be identified by its distinct "cephalofoil," which features a wide, nearly straight front margin, as well as its pronounced, sickle-shaped first dorsal fin. As a solitary, strong-swimming apex predator, the great hammerhead preys on a diverse range of species including crustaceans, cephalopods, bony fish, and smaller sharks. Studies indicate that the cephalofoil may play a crucial role in immobilizing stingrays, which are a preferred prey item. Reproduction in this species is viviparous; females give birth to litters of up to 50 pups biennially.

Despite its potential danger to humans, the great hammerhead infrequently attacks and may exhibit curiosity toward divers. However, the species has been subject to significant fishing pressure, largely for its fins, which are highly valued in the Asian market for shark fin soup. Consequently, the global population of great hammerheads is in decline, leading the International Union for Conservation of Nature (IUCN) to classify the species as critically endangered as of 2019.

Geographically, the great hammerhead is distributed across tropical waters worldwide, between latitudes 40°N and 37°S. In the Atlantic Ocean, its range extends from North Carolina to 🇺🇾 Uruguay, including the 🌊 Gulf of Mexico and the Caribbean, as well as the waters from Morocco to 🇸🇳 Senegal and the Mediterranean Sea. The species is also found along the 🌊 Indian Ocean rim and in the 🌊 Pacific Ocean regions from the Ryukyu Islands (🇯🇵 Japan) to 🇦🇺 Australia, 🇳🇨 New Caledonia (🇫🇷 Overseas France), 🇵🇫 French Polynesia, and southern Baja California to 🇵🇪 Peru. Additionally, it may be present off the coasts of Gambia, Guinea, Mauritania, Sierra Leone, and Western Sahara, although this remains unconfirmed. Typically, great hammerheads inhabit inshore waters as shallow as 1 meter (3.3 feet) and can be found up to 80 meters (260 feet) deep. They prefer coral reefs but are also present on continental shelves, island terraces, lagoons, and in deeper waters near land. The species exhibits migratory behavior, with documented movements toward higher latitudes in the summer in areas such as Florida and the South China Sea.

The great hammerhead's body is streamlined, characteristic of hammerhead sharks, with a cephalofoil that is nearly straight-edged and marked by significant medial and lateral indentations. The width of the cephalofoil constitutes 23-27% of the shark's body length. Its teeth are triangular, strongly serrated, and become more oblique toward the mouth corners. The dental formula includes 17 tooth rows on either side of the upper jaw with two or three at the symphysis, and 16-17 on either side of the lower jaw with one to three at the symphysis.

The first dorsal fin of the great hammerhead is notably tall, sickle-shaped, and originates above the pectoral fin insertions. The second dorsal and anal fins are comparatively large, with deep notches on their rear margins. The pelvic fins feature concave rear margins unlike the straight-margined pelvic fins seen in the scalloped hammerhead. The shark's skin is adorned with tightly spaced dermal denticles, each diamond-shaped with multiple horizontal ridges leading to marginal teeth, which increase in number with the individual's size. The dorsal coloration ranges from dark brown to light gray, fading to white ventrally. Adult fins are unmarked, whereas juvenile fin tips, particularly the second dorsal fin, may exhibit dark pigmentation.

In terms of size, the typical minimum great hammerhead measures 3.5 meters (11 feet) in length and weighs over 230 kilograms (510 pounds), while exceptional individuals may reach up to 4.6 meters (15 feet) in length and weigh 449.5 kilograms (991 pounds). A small percentage of the population, predominantly females, can grow significantly larger. The longest recorded great hammerhead measured 6.1 meters (20 feet), and the heaviest, a pregnant female, weighed 580 kilograms (1,280 pounds) and was caught off Boca Grande, Florida, in 2006. Specimens potentially reaching 900 kilograms (2,000 pounds) have been reported, though not verified.

The great hammerhead is an independent, wide-ranging predator and typically avoided by other reef sharks. When threatened, the shark may display aggressive behavior, lowering its pectoral fins and swimming in a stiff or jerky manner. Juvenile great hammerheads may fall prey to larger sharks such as bull sharks, while adults are generally free from predation except by killer whales. Instances have been reported of yellow jacks using the hammerhead's flanks to rid themselves of parasites and pilot fish accompanying the sharks.

Dietarily, the great hammerhead is versatile, consuming invertebrates like crabs, lobsters, squid, and octopuses; bony fish including tarpons, sardines, and groupers; and smaller sharks. Notably, they opportunistically hunt grey reef sharks at Rangiroa Atoll and exhibit canniundefinedstic tendencies. Fossil evidence from the Gatun Formation in 🇵🇦 Panama suggests historical predation on juvenile Otodus megalodon along with contemporary snaggletooth sharks.

As apex predators, great hammerheads specialize in feeding on rays, sharks, and skates, particularly stingrays whose venomous spines do not hinder the shark despite being imbedded in its mouth. These sharks predominantly hunt at dawn or dusk, using their cephalofoil to detect stingrays buried in sediment through electroreceptive organs. The cephalofoil also aids in swiftly maneuvering to apprehend prey detected on the ocean floor. Observations demonstrate how the great hammerhead utilizes its cephalofoil for disabling prey, particularly rays, and its predation strategy mirrors that of the great white shark (Carcharodon carcharias).

The reproductive habits of great hammerheads involve viviparity; they birth live young after an 11-month gestation, with litters ranging from six to 55 pups. Breeding occurs every two years, typically in late spring to summer in the Northern Hemisphere and December to January in 🇦🇺 Australian waters. Unlike most sharks that mate near the ocean floor, great hammerheads are observed mating near the surface.

While the great hammerhead's size and predatory capabilities pose a theoretical threat to humans, actual incidents of aggression remain rare. Despite an aggressive reputation, this species is often shy or indifferent to divers. There are reports of the sharks approaching or charging divers upon initial contact. The International Shark Attack File recorded 34 hammerhead shark bites as of 2011, with 17 unprovoked. However, it remains difficult to attribute these specifically to great hammerheads. Only one provoked bite from this species has been confirmed. Caution is still advised when encountering them in their natural habitat.