Great Hammerhead Shark

The Great Hammerhead (sphyrna mokarran) is a very large shark with the characteristic hammer-shaped head from which it gets its common name. The font margin of the head is nearly straight with a shallow notch in the center in adult great hammerheads, distinguishing it from the smooth hammerhead and scalloped hammerhead. The first dorsal fin is very tall with a pointed tip and strongly falcate in shape while the second dorsal is also high with a strongly concave rear margin. The origin of the first dorsal fin is opposite or slightly behind the pectoral fin axil with the free rear tip falling short to above the origin of the pelvic fins. The rear margins of the pelvic fins are concave and falcate in shape, not seen in scalloped hammerhead (S. lewini). The posterior edge of the anal fin is deeply notched. This shark is gray-brown above with an off-white belly. The first dorsal fin (the large fin on the top of the shark that most people associate with sharks) is very large and pointed.

As the largest of the hammerheads, the great hammerhead averages over 500 pounds (230 kg). The world record great hammerhead was caught off Sarasota, Florida (US) weighing 991 pounds (450 kg). The largest reported length of a great hammerhead is 20 feet (6.1 m). Expected life span of this species is approximately 20-30 years of age.

In waters off Australia, males reach maturity at a length of 7.4 feet (2.25 m) corresponding to a weight of 113 pounds (51 kg) and females are mature at a total length of 6.9 feet (2.10 m) corresponding to a weight of 90 pounds (41 kg) (source: Stevens and Lyle 1989).

Circumtropical in distribution, the great hammerhead is found in coastal warm temperate and tropical waters within 40°N - 37°S latitude. In the western Atlantic Ocean, it ranges from North Carolina (US) south to Uruguay, including the Gulf of Mexico and Caribbean regions, while in the eastern Atlantic Ocean, this species ranges from Morocco to Senegal, including the Mediterranean Sea. Distribution of the great hammerhead includes the Indian Ocean and the Indo-Pacific region from Ryukyu Island to New Caledonia and French Polynesia. The eastern Pacific range is from southern Baja, California (US) through Mexico, south to Peru. The great hammerhead is considered a highly migratory species within Annex I of the 1982 Convention on the Law of the Sea.

This large coastal/semi-oceanic shark is found far offshore to depths of 300 m as well as in shallow coastal areas such as over continental shelves and lagoons. The great hammerhead migrates seasonally, moving poleward to cooler waters during the summer months.