Facts about hammerhead sharks

There are two genera in the family Sphyrnidae, Sphyrna, and Eusphyra, with most hammerhead species belonging to the genus Sphyrna, and only one—the Winghead shark—to the genus Eusphyra.

Eusphyra means “good” in conjunction with “hammer.”

There are:

Winghead shark (Eusphyra blochii), Scalloped bonnethead (Sphyrna corona), Carolina hammerhead (Sphyrna gilberti), Scalloped hammerhead (Sphyrna lewini), Scoophead (Sphyrna media), Great hammerhead (Sphyrna mokarran), Whitefin hammerhead (Sphyrna couardi), Bonnethead (Sphyrna tiburo), Smalleye hammerhead (Sphyrna tudes), and Smooth hammerhead (Sphyrna zygaena).

The biggest of the genus is the great hammerhead. The record holder is a female caught in 2006 who weighed almost 581 kilograms. The reason for her unusual weight, however, was pregnancy.

It allows sharks an increased binocular vision and depth perception.

Their eyes are located on the sides of their flattened heads, allowing them a 360-degree vision, apart from a blind spot in front of the shark.

It is uncommon for sharks, however. During the day, hammerheads prefer company, but they hunt solitarily at night.

They feed on stingrays, small fish, and octopuses, however, 90% of bonnethead sharks’ diet consists of seagrass.

As the most aggressive of the genus, great hammerheads occasionally eat their own species, even their own pups.

Stingrays are among the most preferred food of most hammerheads.

They, however, fell prey to orcas, and occasionally other sharks.

After a long gestation, females give birth to living, fully developed offspring. They reproduce once a year, and birth usually up to 15 pups. Great hammerheads can birth up to 40 pups per litter.

They are fairly independent, usually grouping with the rest of the pups in the warmer water, until they are large enough to survive on their own.

Although parthenogenesis occurs in vertebrate species, usually in reptiles, it was the first documented case in sharks.

They get scared of oxygen bubbles, so divers should not exhale while hammerheads are nearby.

Their pectoral fin is shorter than their first dorsal fin, and tilting allows them to use longer fin to swim efficiently.

According to the International Shark Attack File, there are 17 recorded cases of hammerhead attacking humans unprovoked since 1580.

Since they swim close to the water's surface, they are exposed to sun rays, and, as a result, turn from light beige to brown.

In some parts of the world, their fins are considered a delicacy. Moreover, despite prohibiting in various countries shark finning—removing fins, and tossing the rest of the fish back to the ocean, which results in them being unable to swim and suffocate, or falling prey to other predators—shark fins trade value is estimated at US$540 million to US$1,2 billion. What is more, they tend to get captured by targeted or incidental fisheries, resulting in a high mortality rate.