Tuesday, August 2, 2016

The Scalloped Hammerhead Shark

photo credit : Rafael Pesantes

The Scalloped Hammerhead
Sphyrna lewini 

The scalloped hammerhead is a very interesting species, as are the rest of the hammerheads. It is also occasionally known as the bronze hammerhead, or the kidney-headed shark. Hammerhead sharks are not normally considered a threat to humans. According to the International Shark Attack Files, from 1580 - 2011, approximately only 15 non-fatal attacks have been recorded, and no fatal attacks have been recorded.

The famous hammer shaped head.
The scalloped hammerhead has the infamous hammer shaped head that all hammerheads have. It can be distinguished from other hammerheads by the "scalloped" edge of their head. They have a large, triangular first dorsal fin and a smaller second dorsal fin that is close to the caudal fin. Their coloring ranges from dark olive to brownish gray with a whitish ventral side. The ventral side of the pectoral fins darken with age, sometimes even darkening to black in larger sharks.

Kingdom : Animalia
Phylum : Chordata
Subphylum : Vertebrata
Class : Chondrichthyes
Subclass :  Elasmobranchii
Order : Carcharhiniformes
Family : Sphyrnidae
Genus : Sphyrna
Species : lewini

Similar Species and Other Family Members:
The family Sphyrnidae has eight described species, all with unique"hammer" shaped heads. Scalloped hammerheads are most commonly mistaken for the Great Hammerhead (Sphyrna mokarran). However, the great hammerhead is larger and has a shorter head with more square ends.

Scalloped hammerheads are viviparous, meaning they give placental live birth, like humans do. They tend to have 12-38 pups and typically have a 9-10 month gestation period.

Scalloped hammerhead are typically between 160-200 cm (5.2-6.5 ft) with the males being smaller than females at maturity. Females can occasionally reach up to 243-365 cm (8-12 ft).

The scalloped hammerhead tends to eat bony fish. They also eat invertebrates and other sharks. Hammerheads in general are known for their appetite for rays, including dangerous stingrays.

Schooling scalloped hammerheads
Habitat and Distribution:
Scalloped hammerheads are found worldwide in tropical and warm temperate seas. They are unique in that they migrate and school in large groups around sea mounts and islands, most famously around the Cocos Islands and the Galapagos Islands.

Life Span:
Scalloped hammerheads are believed to live up to 35 years.
The scalloped hammerhead's large fin puts it at
great risk from shark finners. 
Conservation Status:
On the IUCN Red List, the scalloped hammerhead is listed as endangered worldwide. They are heavily fished around the world, and are commonly hunted for the shark fin soup trade due to the large size of their fins.

The Shark Handbook, Dr. Greg Skomal
Sharks of the World, David A. Ebert, Sarah Fowler and Leonard Compagno 

note: none of the images are mine, however I did draw the illustrations

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