The Sphyrna mokarran, more commonly known as the great hammerhead, is one of the most mysterious creatures that inhabits the planet. It is classified as an “Endangered” species on the IUCN Red List, 2018. Several shark divers have tried to have a great hammerhead encounter; however, this predator is quite elusive. On certain occasions, some divers were lucky enough to come in contact with the great hammerhead’s relative, the scalloped hammerhead. Even though not enough research has been carried out on the great hammerhead, it is considered to be a highly dangerous species, mainly because of its size and its feeding habits (Rogerson, 2004).
Taxonomy:
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Carcharhiniformes
Family: Sphyrinidae
Genus: Sphyrna
Species: Mokarran
(Denham et al. 2018)
Nomenclature of Sphyrna mokarran
Scientific Names: There is one other synonym that is used to describe this species. This is Zygaena mokarran, which was given to the great hammerhead, by Ruppell in 1837.
English Names: In English, this shark is simply known, as the hammerhead shark and squat-headed hammer shark.
African name: In Africa, this species is known as Groot Hamerkop.
Italian Names: In Italy, this species is known as Crozza, Pesce Pantofola, Cornuda Gigante and Scrossena.
Japanese Name: Since the great hammerhead also inhabits Japanese waters, it is known as Hira-Shumokuzame.
(Denham et al., 2018)
Geographical Distribution of Sphyrna mokarran
The great hammerhead shark is distributed, throughout different oceans around the world. Even though this shark is endangered, it can still be found in waters surrounding several countries. These inhabit European, African, North and South American, Asian and Australian waters, mainly throughout the Indian, Pacific and Atlantic oceans, as well as the Mediterranean Sea. Therefore, it is widely distributed in the latitudes, 40 degrees North and 35 degrees South and it is considered to be a migratory and nomadic species (Denham et al., 2018).
Morphology of Sphyrna mokarran
The great hammerhead is the largest hammerhead shark in the Sphyrnidae family. It has a cephalophoil, more commonly known as the “hammer head.” The cephalophoil is rectangular and straight in relation to the axis of its classically shark-shaped body. The Sphyrna mokarran has a characteristically curved dorsal fin and it has a brownish to light grey colouration, on the dorsal aspect of its body, which fades into a cream colour, on its underside. Its skin is also covered in denticles, which overlap along the frontal and lateral margins. The great hammerhead, can reach a length of around 20 ft. Like other sharks, this marine species has ampullae, which are highly sensitive electrical receptors, to detect electrical signals which are emitted from nearby prey (Bester, 2018).
Habitat, Feeding Habits and Reproduction of Sphyrna mokarran
The great hammerhead shark is considered to be a semi-oceanic and pelagic species, in both inshore and offshore regions, over continental shelves, lagoons and deep waters which can reach a depth of over 80m to 300m. It is a carnivorous fish and may feed on crustacea, cephalopods, teleost fish, elasmobranchs and it is considered to be cannibalistic, eating sharks of its own species, when food sources are not available (Campagno, 1984).
The great hammerhead shark is a viviparous species and its embryos develop in a yolk-sac placenta. The gestation period of this species is around 11 months and birth occurs during the seasons of spring or summer. The Sphyrna mokarran females, breed once every 2 years and can have a litter ranging from 6 to 40 pups (Bester, 2018).
Threats Faced by Sphyrna mokarran
This hammerhead species is faced by several threats, especially in the fisheries sector. There have been several reported catches of hammerhead sharks, due to longlining, hook and line, both pelagic and demersal trawling and trammel nets. These sharks are either caught, as a targeted species or as by-catch. However, this hammerhead shark is particularly hunted for its fins, since the latter are sold for very high prices, especially in the Asian market. In Taiwan there was shark fishery, which was carried out in northern waters of Australia. This regularly captured great hammerheads up till 1986. In Sierra Leone, the hammerhead fishery is still carried out (Denham et al. 2018). These sharks are also captured for their liver oil, since it is used for the production of vitamins, leather and fishmeal (Bester, 2018).
Conservation of Sphyrna mokarran
According to the IUCN (2018), there are no current conservation measures being carried out, specifically for this species. Since it is a highly migratory species, several states must co-manage its conservation, in order to safeguard this shark. Shark finning bans are also being carried out in countries, such as the U.S. and Australia, to decrease shark captured specifically for fin markets. In my opinion, by-catch reduction devices are a way forward to resolve several over-fishing issues, since this fishing technology can be used to decrease sharks being caught as by-catch. Marine Protected Areas should also be implemented to safeguard any shark nursery grounds, to aid in the re-population of these marine species.
Is the Great Hammerhead Dangerous to Humans?
The International Shark Attack File, has reported 17 attacks with no known fatalities, for different species in the Sphyrna genus. There is not enough sufficient data, that can be directly related to this species, since it is highly difficult to distinguish between different hammerhead species. The great hammerhead shark consumes numerous prey and is a highly misunderstood marine creature, therefore it should be treated with respect (Bester, 2018).
References
Bester, C. (2018) Sphyrna mokarran [online], Available at: https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/sphyrna-mokarran/, (Accessed on: 4/12/18).
Compagno, L.J.V. (!984). Sharks of the World. An annotated and illustrated catalogue of the shark species known to date. Volume 3. (Carcharhiniformes). FAO Species Catalogue for Fisheries Purposes No. 1, Vol.3. FAO, Rome.
Denham, J., Stevens, J.D., Simpfendorfer, C., Heupel, M.R., Cliff, G., Morgan, A., Graham, R., Ducrocq, M., Dulvy, N.K., Seisay, M., Asber, M., Valenti, S.V., Litvinov, F., Martins, P., Lemine Ould Sidi, M., Tous, P. & Bucal, D. (2007) Sphyrna mokarran. The IUCN Red List of Threatened Species 2007 [online]: e.T39386A10191938. http://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T39386A10191938.en. (Accessed on: 4/12/18).
Rogerson, S. (2004) Sport Diver, Mad for Mokarrans [online], Available at: https://books.google.com.mt/books?id=arLX-zzPoQIC&pg=PA56&dq=great+hammerhead&hl=mt&sa=X&ved=0ahUKEwjGr8bt-YXfAhWLAMAKHZ-oDAwQ6AEIOTAD#v=onepage&q=great%20hammerhead&f=false, (Accessed on: 4/12/18).
Rüppell, W.P.E.S. (1838) Neue Wirbelthiere zu der Fauna von Abyssinien gehörig. Fische des Rothen Meeres.
Image References:
Barry Peters (2018) Cuba’s Pristine Reefs are Ideal for Spotting Great Hammerhead Sharks [online], Available at: https://www.popsci.com/great-hammerheads-cuba-reefs, (Accessed on: 4/12/18).
Denham, J., Stevens, J.D., Simpfendorfer, C., Heupel, M.R., Cliff, G., Morgan, A., Graham, R., Ducrocq, M., Dulvy, N.K., Seisay, M., Asber, M., Valenti, S.V., Litvinov, F., Martins, P., Lemine Ould Sidi, M., Tous, P. & Bucal, D. (2007) Sphyrna mokarran. The IUCN Red List of Threatened Species 2007 [image]: e.T39386A10191938. http://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T39386A10191938.en. (Accessed on: 4/12/18).
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