Great hammerhead shark - Sphyrna mokarran
WHAT TO LOOK FOR
Hammer-shaped head with a nearly straight anterior margin. The first dorsal fin is very tall and falcate.
Dark olive green to brownish gray above, white below. Ventral tips of pectoral fins are not marked.
This is the largest of the hammerhead sharks. The shark grows to a length of at least 18.3 feet [5.6 m], and may attain a length of more than 20 feet [6.1 m]; however, most individuals encountered by divers are between 10 and 14 feet in length [3 to 4.3 m]. Females mature at a length of 8.2 to 9.8 ft [2.5 to 3 m]; males mature at a length of 7.7 to 8.8 ft [2.3 to 2.7 m].
Coastal-pelagic and semi-oceanic shark occurring close inshore and well offshore. Found over the continental shelves, island terraces and in passes and lagoons of coral atolls, as well as over deep water near land. It is found near the surface and from depths of 3 ft to more than 262 ft [1 to 80 m]. It often favors continental and insular coral reefs.
Prey – The great hammerhead shark feeds on a wide variety of prey, but favors stingrays, groupers and sea catfishes. It also feeds on squid, crabs, tarpon, sardines, toadfishes, porgies, grunts, jacks, herring, grouper, boxfish, other sharks, skates, guitarfish, cownose and eagle rays.
Reproduction – Viviparous, with a yolk-sac placenta. Litters range from 13 to 42 (average 20-40) following a gestation of at least 7 months. Size at birth is 20 to 28 inches [50 to 70 cm].
General – A solitary, nomadic and migratory species. Some populations move poleward during the winter.
Feeding – The shark feeds mostly at dusk. A shark was seen to use the underside of its hammer-shaped head to bludgeon and pin a stingray to the seabed, then the shark pivoted and bit a chunk out of the ray’s pectoral fin.
Mating – Mating great hammerheads were reportedly witnessed in 70 ft [21 m] in the Bahamas. The sharks ascended, spiraling slowly around each other and copulated at the surface. While synchronous swimming as a prelude to mating has been observed with other species of sharks, copulation at the surface has not. Most species are thought to mate at or near the seafloor.
The species is thought to be dangerous, though relatively few incidents have been attributed to it or any other species of hammerhead sharks. The shark has approached divers without displaying aggression. However, due to its size and broad food spectrum the shark should be treated with caution.
Danger to humans – divers have observed this shark in un-baited situations and found it to be unaggressive. Due to its large size it is considered potentially dangerous.