Facts about hammerhead sharks
Most distinctive of all sharks
These peculiar fish are common worldwide. Although, like most sharks, they have bad press; they do not include humans in their diet, attacking only while provoked. Despite, or maybe in fact because of, their peculiar look, their numbers systematically deteriorate.
1Hammerhead sharks from the family Sphyrnidae.
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.
2Sphyrna derives from Greek and means “hammer.”
Eusphyra means “good” in conjunction with “hammer.”
3There are a total of ten species of hammerhead sharks.
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).
4Hammerheads are common in warmer waters along coastlines worldwide.
5Their length ranges from 0.9 to 6.1 meters, and their weight ranges from 3 up to 580 kilograms.
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.
6The distinctive structure—a hammer-like head—is called a cephalofoil.
It allows sharks an increased binocular vision and depth perception.
7The quaint structure of their hammer-like heads may have been an evolutionary way to enhance their vision.
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.
8Hammerhead species tend to swim in schools.
It is uncommon for sharks, however. During the day, hammerheads prefer company, but they hunt solitarily at night.
9Their average lifespan ranges from 20 to 30 years.
10Mostly carnivorous, some hammerhead species are omnivorous.
They feed on stingrays, small fish, and octopuses, however, 90% of bonnethead sharks’ diet consists of seagrass.
11Great hammerheads tend to engage in cannibalism.
As the most aggressive of the genus, great hammerheads occasionally eat their own species, even their own pups.
12Hammerheads are resistant to stingrays stings.
Stingrays are among the most preferred food of most hammerheads.
13Hammerhead sharks use their heads to tire down prey.
14Hammerheads do not have natural predators.
They, however, fell prey to orcas, and occasionally other sharks.
15Hammerheads are viviparous.
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.
16Pups are not taken care of after birth.
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.
17In 2007, a bonnethead female reproduced without mating.
Although parthenogenesis occurs in vertebrate species, usually in reptiles, it was the first documented case in sharks.
18Hammerhead sharks are timid.
They get scared of oxygen bubbles, so divers should not exhale while hammerheads are nearby.
19Hammerhead sharks swim at a slight angle, due to differences in their fins length.
Their pectoral fin is shorter than their first dorsal fin, and tilting allows them to use longer fin to swim efficiently.
20Hammerheads do not attack humans.
According to the International Shark Attack File, there are 17 recorded cases of hammerhead attacking humans unprovoked since 1580.
21Juvenile scalloped hammerheads can get a tan.
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.
22Most of the hammerhead species are at risk of extinction, either endangered or critically endangered.
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.