Species Profile: Hammerhead Shark

Scalloped Hammerhead Shark

The Scalloped Hammerhead Shark

A quick glance at this shark species will give you a clue as to how it got its name. The hammerhead shark group are identified by their unusual and distinctive head structure. Their heads are flattened and laterally extended on either side into a hammer-like shape called a cephalofoil.

1. Scientific Name

Sphyrnidae

2. Scientific classification

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Chondrichthyes
  • Order: Carcharhiniformes
  • Family: Sphyrnidae
  • Genus: Sphyrna (except for the winghead shark which is placed in the Eusphyra genus).

3. Life Expectancy

The life expectancy for hammerheads is between 20 and 35 years.

4.  Average/Maximum Length

They average in length from 3 feet (0.9 metres) to about 13 feet (4 metres). The maximum length known is attributed to the Great Hammerhead Shark.  When fully grown, it can measure up to 20 feet (6 metres).

5.  Average/Maximum Weight

The Great Hammerhead Shark tops the scale here again. It can weigh up to 580 kg (1,278.7 lbs.). Others weigh from 3 kg (6.6 lbs.) upwards.

6. Maximum Swimming Speed

It moves at speeds of up to 40 km/h (25 mph)

7.  Danger To Humans

Due to the fairly small size of most hammerheads, they are generally considered harmless to man and are not known to attack humans habitually. Although, like most carnivorous animals, they can be aggressive in close contact. The Great Hammerhead, in particular, poses a threat to man owing to its large size, aggressiveness, and fierceness. However, few attacks have ever been recorded to date.

8. Reproduction Details

Reproduction is viviparous and occurs once a year. Mating takes place with the male biting the female violently until she concedes to mate with him.

The male transfers sperm to the female through claspers leading to conception. The embryos develop within the mother’s body and are born alive in a litter of about 12 to 15 pups for other species and 20 to 40 pups for the Great Hammerhead species. After birth, the baby sharks are not cared for at all by the parents. The babies huddle together and swim to warm waters till they grow old enough and large enough to survive in the wild on their own.

The bonnethead shark in particular displays a unique reproductive trend at it was discovered to be capable of asexual reproduction in 2007. This was the first recorded instance of a shark having this ability.

9. Diet

Hammerhead sharks eat a variety of prey including fish, squids, octopi, crustaceans, and even other sharks. Their pattern of hunting is to swim along at the bottom of the sea stalking their prey from under. They use their sensory organs to detect electrical fields from potential prey and also use their uniquely shaped heads as a weapon of attack. The fact that they can make very quick and sharp turns and bends give them an edge also. They particularly favor stingrays and attack them with their heads then pin them to the sea floor till the fish are too weak to fight.

Again, The Great Hammerhead, being larger and more aggressive will occasionally engage in cannibalism, by eating other hammerhead sharks, and even its own young.

10.  Alternative Names For The Hammerhead Shark

  • Winghead shark
  • Scalloped bonnethead
  • Whitefin hammerhead
  • Carolina hammerhead
  • Scalloped hammerhead
  • Scoophead
  • Bonnethead
  • Smalleye hammerhead
  • Smooth hammerhead

11. Population And Conservation Status

The constant demand for shark fin soup has been linked with the sharp decline in shark populations especially the Hammerhead sharks. In fact, the scalloped hammerhead shark became the first species of shark to come under the protection of the U.S. Endangered Species Act.

Studies on hammerhead populations show severe scalloped hammerhead population declines in many of its known habitats. In parts of the Mediterranean Sea where hammerhead sharks of all kind were once flourishing, they haven’t been observed since 1963.

In other regions like off the coast of South Africa, reports indicate population decline of up to 99% and sharp declines too along the coast of the northeastern U.S.A.

Presently, the Winghead shark and the Scalloped bonnethead are classified as threatened, the Scalloped hammerhead and the Great hammerhead are endangered. The Smalleye hammerhead is classified as vulnerable along with the Smooth hammerhead.

12. Ancestry And History

DNA studies on the hammerheads indicate that they are closely related to carcharhinid sharks.  Carcharhinid sharks are known to have evolved during the geologic time of the mid-Tertiary Period. The ancestors of the hammerheads most likely thrived in the Miocene epoch of about 20 million years ago.

Mitochondrial DNA studies on a phylogenetic tree of hammerhead sharks show the winghead shark as its most basal member. Since the winghead shark has the largest “hammer” of these sharks, it could be concluded that the first ancestral hammerhead sharks also had enormous hammers.

13. Distribution And Habitat

Depending on the species of hammerhead, they inhabit temperate or tropical waters all around the world. Their favourite dwellings include coastal lines and continental shelves. They dwell at the Mesopelagic zone, between 660 feet (200 meters) to 3300 feet (1000 meters) beneath the ocean surface and are common in waters up to 80 meters deep.

Their most common habitats remain reefs of shallow waters, and they occasionally visit brackish waters.

References

1. http://animals.nationalgeographic.com/animals/fish/hammerhead-shark/

2. https://a-z-animals.com/animals/hammerhead-shark/

3. https://en.wikipedia.org/wiki/Hammerhead_shark

4. http://www.sharks-world.com/hammerhead_shark/

5. http://www.sharksider.com/hammerhead-shark/

6. http://www.huffingtonpost.com/2013/07/03/hammerhead-shark-decline_n_3537932.html

7. https://www.scientificamerican.com/article/scalloped-hammerheads-become-first-shark-species-on-the-u-s-endangered-species-list/

Photo Credits

1. https://commons.wikimedia.org/wiki/File:Hammerhead_shark.jpg

2. http://flickr.com/photos/63766699@N00/193358031

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