The great hammerhead has worldwide distribution in tropical waters. It is the largest of all hammerheads, attaining a maximum length of 20 feet. Its unique feature to other hammerheads is its nearly straight hammer-shaped head. They are apex predators, solitary and migrate long distances. In terms of growth rate, this species has a faster growth rate than other hammerhead sharks. Great Hammerheads, or Sphyrna mokarran, are vulnerable to extensive fishing.
Due to the global shark fin trade, they are particularly threatened. More than 90% of great hammerheads die after they are captured during fisheries. Currently, they are listed as endangered species vulnerable to extinction. Due to their size and unpredictable nature, they should be treated with caution. The expected life span of the great hammerhead is 20 to 30 years of age.
Morphology
Great hammerhead can easily be confused with the smooth hammerhead based on their similar sizes. They have a flat hammer-shaped head with a notch at the center situated along the front edge. The head is nearly rectangular. The first dorsal fin is extensively curved, while the second dorsal and pelvic fins are high with deeply concave rear margins. Regarding coloration, they are light gray or gray-brown on the dorsal side, while they do not have observable markings on the ventral side.
Adaptation
They have special sensory organs such as the Ampullae of Lorenzini for detecting changes in the chemical, physical, thermal and electrical fields of prey species, such as those buried in the ocean floor. They are able to scan a wide area during hunting because of their hammerheads.
Feeding
Great hammerhead sharks feed on stingrays, sea catfishes, small bony fishes and lobsters. For some unknown reason, they are cannibalistic. They particularly prefer stingrays above all other foods.
Habitat
The great hammerhead is considered highly migratory species. They are found in coastal warm temperate and tropical waters. They can venture as far as depth of 984 feet below the sea. However, are often found in shallow coastal areas including the continental shelves and lagoons to the depth of 262 feet.
Reproduction
The species engages in viviparous mode of reproduction. The period of gestation is 11 months. Birth occurs during the summer in the Northern Hemisphere. The females breed once every two years. Litter size can range from 6 to 42 pups each measuring 1ft 7 inches.
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References
Florida Musuem (2019). Sphyrna mokarran. Great Hammerhead. Retrieved from https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/sphyrna-mokarran/
Kennedy, J (2019, May 25). Great Hammerhead Shark. Facts about the largest hammerhead shark species. ThoughtCo. Retrieved from https://www.thoughtco.com/great-hammerhead-shark-2291445
Long, D (2019). Hammerhead Shark. Encyclopedia Britannica. Retrieved from https://www.britannica.com/animal/hammerhead-shark
MarineBIO (2019). Great Hammerhead Sharks. Sphyrna mokarran. Retrieved from https://marinebio.org/species/great-hammerhead-sharks/sphyrna-mokarran/
OCEANA (2019). Great Hammerhead Shark. Retrieved from https://oceana.org/marine-life/sharks-rays/great-hammerhead-shark