Great Hammerhead Shark
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.