The Great Hammerhead Shark (Sphyrna mokkaran) taxonomy :
Filum : Chordata
Class : Chondricthys
Ordo : Charcarinifer
Famili : Sphyrinidae
Genus : Sphyrna
Species : Sphyrna mokkaran
The great Hammerhead Shark (Sphyrna mokarran), one species of Sphyrninidae that have the largest size of body usually founded in the warm water especially on the warm temperate ocean around the world like Pacific and Hindia ocean. This species can we found on the lagoon, coral reef, embayment, coastal water, sea mount, and island chain. They also found on the schooling but not on the large schooling scale.
The hammerhead shark commonly observed from coastal water to continental shelf and at depth ranging from 1m to 300m under the sea surface. They are high migratory species and nomadic. They distribution area such as Andaman Sea, Arabian sea, East china sea, Indonesia sea, gulf of Mexico,
Mediteranian sea, etc.
Like the other species of shark, the hammerhead shark is one of top predator on the coastal ecosystem that need a good condition for the live. They diet includes demersal fish (prefer), crustacea, otherelasmobranchs, and chepalopods. Grouper and catfish also the prefer food for great hammerhead shark.
Today, the great hammerhead shark is one of shark species commonly targeted for their large ddorsal and tail fins which are highly valued on Asian fish market. The impact for this condition is decreasing
population of great hammershark. IUCN give ENDENGARED status for this species.
| Common names: hammerhead (English), shark (English), tiburón (Espanol) |
Sphyrna mokarran (Rüppell, 1837)
Great hammerhead, Great hammerhead shark
A hammerhead shark with broad, narrow-blade side extensions on the head forming a hammer (width 23-27% of TL); front margin of head nearly straight in adults, with shallow central and side indentations; front teeth blade-like, with 1 point, lower teeth straight, upper teeth oblique, deeply notched on rear side; rear teeth like front teeth; first dorsal fin very tall and curved, with pointed tip; second dorsal fin large, height > length of 3rd gill slit; second dorsal and anal fins with strongly notched rear edges, their bases about equal; pelvics large, with concave rear borders; transverse pit above tail base crescent shaped, a pit below tail base; tail fin strongly asymmetrical, notched under tip of top lobe, large lower lobe.
Grey brown on back and sides, whitish below; no prominent markings on fins.
Said to reach 610 cm and 450kg, but uncommon above 350 cm; size at birth 50-70 cm.
A coastal pelagic and semi- oceanic species.
Depth range 1-300 m.
Circumtropical distribution, in the eastern Pacific from southern Baja California and the Gulf of California to northern Peru, Malpelo and the Galapagos.
Global Endemism: All species, TEP non-endemic, Circumtropical ( Indian + Pacific + Atlantic Oceans), "Transpacific" (East + Central &/or West Pacific), West + East Pacific (but not Central), East Pacific + Atlantic (East +/or West), Transisthmian (East Pacific + Atlantic of Central America), East Pacific + all Atlantic (East+West)
Regional Endemism: All species, Eastern Pacific non-endemic, Tropical Eastern Pacific (TEP) non-endemic, Continent + Island (s), Continent, Island (s)
Climate Zone: North Temperate (Californian Province &/or Northern Gulf of California), Northern Subtropical (Cortez Province + Sinaloan Gap), Northern Tropical (Mexican Province to Nicaragua + Revillagigedos), Equatorial (Costa Rica to Ecuador + Galapagos, Clipperton, Cocos, Malpelo), South Temperate (Peruvian Province )
Great hammerhead sharks occur in all tropical waters worldwide.
Biogeographic Regions: oceanic islands (Native ); indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )
Widespread in the south-west Indian Ocean but in South Africa is confined to the KwaZulu-Natal coast, where it co-exists with the scalloped hammerhead S. lewini, also an inhabitant of the tropic, and the smooth hammerhead S. zygaena, which favours cooler waters (Cliff 1995, Bass et al. 1975). There is a pupping and nursery ground in a coastal mangrove estuarine area of southern Belize (R.T. Graham pers. obs).
Regularity: Regularly occurring
Type of Residency: Year-round
Great hammerhead sharks posses a virtually straight anterior margin of the head with a deep central indentation. They have high second dorsal fins and the pelvic fins have curved rear margins. The teeth are triangular with extraordinarily serrated edges, becoming increasingly oblique toward the corners of the mouth. Their coloration varies from deep olive green to brownish grey above and white below. They are generally 4 to 6 m in length.
Range mass: 400 to 460 kg.
Other Physical Features: bilateral symmetry
Inshore/Offshore: Offshore, In & Offshore, Inshore
Water Column Position: Mid Water, Near Bottom, Bottom
Habitat: Reef (rock &/or coral), Corals, Reef and soft bottom, Reef associated (reef + edges-water column & soft bottom), Soft bottom (mud, sand,gravel, beach, estuary & mangrove), Water column
FishBase Habitat: Pelagic
These sharks are found in both open ocean and shallow coastal waters. During summer they may make small migrations towards more northerly areas.
Aquatic Biomes: reef ; coastal
Habitat and Ecology
The diet includes fish (mainly demersal species), other elasmobranchs, crustacea and cephalopods (Compagno in prep. b). Strong et al. (1990) observed a large (ca 4 m) great hammerhead feeding on a southern stingray Dasyatis americana (disc width 1.5 m).
Habitat Type: Marine
Water temperature and chemistry ranges based on 48 samples.
Depth range (m): 0 - 1750
Temperature range (°C): 3.860 - 27.331
Nitrate (umol/L): 0.171 - 29.210
Salinity (PPS): 34.006 - 36.580
Oxygen (ml/l): 3.107 - 6.104
Phosphate (umol/l): 0.083 - 1.926
Silicate (umol/l): 0.380 - 23.528
Depth range (m): 0 - 1750
Temperature range (°C): 3.860 - 27.331
Nitrate (umol/L): 0.171 - 29.210
Salinity (PPS): 34.006 - 36.580
Oxygen (ml/l): 3.107 - 6.104
Phosphate (umol/l): 0.083 - 1.926
Silicate (umol/l): 0.380 - 23.528
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Recorded at 80 meters.
Habitat: pelagic. Great hammerhead. (Ruppell, 1837) Vivaparous; 20 pups per litter. Attains 5 metres. May be angerous to man. In tropical waters on our east coast, extending south to Natal; ranges widely in tropical seas, both inshore and over deep water.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
The great hammerhead can be found around the world in tropical waters such as the Atlantic, Pacific and Indian Oceans, and smaller seas like the Mediterranean, the Black Sea, and the Arabian Gulf. The great hammerhead migrates poleward during the summer in search of cooler waters.
Diet: mobile benthic crustacea (shrimps/crabs), mobile benthic gastropods/bivalves, octopus/squid/cuttlefish, bony fishes, sharks/rays
Great hammerhead sharks feed on rays, smaller sharks, and many species of bony fishes.
Known prey organisms
This list may not be complete but is based on published studies.
Life History and Behavior
Great Hammerhead sharks are viviparous. At a length of 3m, maturity is reached. Litters are made up of between 20 and 40 pups. Young are born in the summer season and are approximately 70 cm in length. Head shape of a newborn pup is more rounded than that of an adult but this changes as they grow.
Mating has not been that observed in this species, but unlike other sharks the great hammerhead is known to mate at the surface. Males use extensions of the pelvic fins called ‘claspers’ to transfer sperm to the females. The pregnancy’s last 11 months, and then the young are born live in the spring or summer.
Molecular Biology and Genetics
Barcode data: Sphyrna mokarran
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Sphyrna mokarran
Public Records: 37
Specimens with Barcodes: 49
Species With Barcodes: 1
CITES: Not listed
Great hammerhead shark populations seem to be stable.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: endangered
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2000Data Deficient
National NatureServe Conservation Status
Rounded National Status Rank: NNR - Unranked
NatureServe Conservation Status
Rounded Global Status Rank: GNR - Not Yet Ranked
The great hammerhead is desperately in need of coordinated conservation efforts involving the management of directed fisheries and those that take this species as bycatch. Fortunately, the increasing recognition of the detrimental effects of shark finning has led to the implementation of finning bans by fishing states in the U.S.A., Australia and the European Union. Nevertheless, improved enforcement of legislation is required to prevent ongoing illegal finning activities. Bycatch limits for sharks in the South African longline fishery are also helping to conserve this imperilled species
There was a directed shark fishery operated by Taiwan around the northern coast of Australia that regularly caught great hammerheads up until 1986 (Stevens and Lyle 1989). Other possible threats include sport fishing (Pepperell 1992) and capture in anti-shark measures around the beaches of Australia and South Africa (Paterson 1990, Cliff 1995). Bonfil (1994) gives an overview of global shark fisheries. This species is mentioned specifically with reference to fisheries in Brazil, East USA and Mexico, however Sphyrna spp. are mentioned in the majority of tropical fisheries cited.
Mainly taken by drift gillnets, bottom gillnets and on longlines, hook and line, pelagic and bottom trawls (Schneider 1990). This species is a bycatch in both the industrial and artisanal fisheries but a specialised artisanal fishery for charcharhinid and sphyrnid species was introduced in Sierra Leone in 1975, and since then fishing pressure has not decreased (M. Seisay pers. obs). The Subregional workshop for sustainable management of sharks and rays in West Africa, 26-28 April 2000 in St Louis, Senegal (Ducrocq 2002) noted the high threat to sharks in the west African region and a noticeable decline in the CPUE of total sharks and rays. This workshop identified S. mokkarran as particularly threatened. The subsequent sub-regional plan of action for sharks of West Africa (member states of the Sub Regional Fishing Commission) states that landings of S. mokarran have collapsed and lists this as one of the four most threatened species, deserving the greatest attention in the whole region (Ducrocq 2002).
Previously observed from Mauritania to Angola, reportedly abundant from November to January in Senegal, and in October in Mauritania (Cadenat and Blache 1981). However, recent scientific trawl surveys off Guinea-Bissau, Mauritania, Senegal, Gambia and Guinea-Conakry between 20 to 1,000 m have failed to record it, except in very low numbers off Guinea-Conakry and one record from Senegal in 1995 (FISA unpublished data). Anecdotal evidence from interviews with fishermen in Senegal, Guinea-Bissau and Guinea suggest there was a large decline in all shark species during the 1990s and that S. mokarran is almost extirpated from these areas (M. Ducrocq pers. obs.).
Data are lacking as there is little species specific data collection in the region, however this is a very distinctive species with a large dorsal fin which is highly valued for the shark fin trade. Increased targeting of sharks began in the 1970s, when a Ghanaian fishing community settled in the Gambia and established a commercial network throughout the region, encouraging local fishermen to target sharks for exportation to Ghana. By the 1980s many fishermen were specialising in catching sharks, resulting in a decline in overall shark populations (Walker et al. 2005). There has been rapid growth in the shark fin market in this region, for export to the Far East, and yearly production of dried fins exported from Guinea-Bissau alone is estimated at 250 t (dry weight) (Walker et al. 2005). Sphyrna species combined represented 42% of bycatch in the European industrial pelagic trawl fishery off Northwest Africa (Zeeberg 2006).
Although there are very little species specific data available, the absence of recent records and region-wide recognition of the extent of the decline, give cause to suspect that the population has decreased by least 80% in the past 25 years. Fisheries in this region remain largely unmonitored and unmanaged, leading to an assessment of Critically Endangered in the Eastern Atlantic.
Southwest Indian Ocean
This species is widely distributed in the SW Indian Ocean and is a summer migrant to KwaZulu-Natal (KZN) (east coast of South Africa), where the annual catch in the KZN shark nets is 11 sharks (1978 to 1999), consisting mainly of adolescents and adults. Over this period there has been a significant decline in annual catch (18 to 4 sharks) and catch rate (0.5 to 0.2 sharks.km-net-1.yr-1 (p = 0.000) (Dudley 2002). A continued decline in catch rate was reported for the period 1978 to 2003 (Dudley and Simpfendorfer 2006). Over this period, regression of catch and catch rate against year revealed a significant decline in annual catch from 18 to two sharks (89%) and in catch rate from 0.44 to 0.09 sharks.km-net-1.yr-1 (79%) (S. Dudley pers. obs. 2006). It is uncertain whether these declines reflect highly localized stock depletion or whether they reflect a general decline in the Southwest Indian Ocean, but large numbers of longline vessels have been reported to be operating illegally in coastal waters of the western Indian Ocean where they are targeting primarily hammerhead sharks and giant guitarfish Rhynchobatus djiddensis (IOTC 2005 in Dudley and Simpfendorfer 2006). This species is generally regarded as solitary, and is therefore unlikely to be abundant wherever it occurs. This is in contrast to other large hammerheads, such as Sphyrna lewini which forms large schools. Sphyrna mokarran, like other hammerheads, readily takes baited hooks and is sought after for its fins. Based on these characteristics, together with the decline of 79% in catch rates in the KZN shark nets, this species is assessed as Endangered in the southwest Indian Ocean.
This species is caught primarily as a bycatch in the pelagic longline, bottom longline and net fisheries along the northwest Atlantic and Gulf of Mexico. It is also caught in the recreational fishery. The species represents 0.7% of the species catch and suffers from greater than 90% at-vessel fishing mortality in the U.S. bottom longline fishery (Commercial Shark Fishery Observer Program unpubl. data). The U.S. pelagic fishery logbook data has shown a decline close to 90%, however this data-set is known for inaccurate data reporting (Beerkircher et al. 2002). There is probably a lack of reporting of the catch of great hammerheads because this species is routinely finned and discarded, which is illegal in the US Atlantic Federal Waters (Commercial Shark Fishery Observer Program unpub. data). Both the pelagic and bottom longline observer programs have recorded a 2 to 3:1 ratio for S. Lewini to S. mokarran. The meat is not valuable but the fins are high grade and bring in a good price, thus finning still occurs in the U.S. fishery. Interview with shark fishermen in Belize indicate that hammerheads (S. mokarran in particular) are a favoured target species for their large fins (R.T. Graham pers. obs.). Fin prices are rising above US$50/lb in the neighbouring countries of Guatemala, driven by Asian buyers, according to these interviews (R.T. Graham pers. obs). This species is probably caught in other fisheries but is usually placed in a combined "hammerhead" category. Species identification (S. mokarran vs. S. lewini) a large obstacle in the proper assessment of this species. The high at-vessel fishing mortality for both species of hammerhead makes the threat of fishing even greater for this species. In the Pacific Ocean off of Guatemala this species is caught as by-catch in the commercial longline fishery.
There appear to be little data for landings and catch effort for this species in Central America and the Caribbean. Off the coast of Belize hammerheads were fished heavily by longline in the 1980s and early 1990s. Interviews with fishermen indicate that the abundance and size of Sphyrnids has declined dramatically in the past 10 years as a result of over exploitation, leading to a halt in the Belize based shark fishery (R.T. Graham pers. obs). However, the pressure is still sustained by fishers driving into Belizean waters from Guatemala (R.T. Graham pers. obs). The Cuban directed shark fishery (longline) between 1983 and 1991 recorded S. mokarran (subadults and juveniles) as one of 23 species caught. Since 1992 small increases in mean sizes were noted, indicating partial recovery of the species. In Mexico between November 1993 and December 1994 (Tamaulipas, Veracruz, Tabasco, Campeche and Yucatan) 901 vessels were monitored every day. Sphyrna mokarran represented 86% of the total catch.
The difficulty in species identification and accurate recording make an assessment of this species very difficult. However, low survival at capture makes this species very vulnerable to fishing pressure, whether directed or incidental. This species is listed as Endangered in the Northwest Atlantic under criterion A2 based on a suspected decline of at least >50% over the past 10 years. The decline is poorly documented and has not been curtailed.
There has been a large increase in the illegal, unregulated and unreported (IUU) fishing in northern Australia in the last few years (J. Stevens pers. obs.). Several initiatives are underway to identify which species are being taken and in what quantities. Hammerheads are known to feature in the catches, and are suspected targets for their large valuable fins, although no specific data are available. Some domestic boats are also suspected to be targeting species for their fins in the Northern Territory, and this likely includes hammerheads (J. Stevens pers. obs). It is not a productive species and is coming out at the "high-risk" end in recent Risk Assessments of northern Australian elasmobranchs (J. Stevens pers. obs). There is concern that this species is being increasingly targeted, and therefore an urgent need to obtain data to form an accurate assessment of the population in this region.
This species is listed on Annex I, Highly Migratory Species, of the UN Convention on the Law of the Sea, which urges States to cooperate over the management of these species. No such management yet exists. Precautionary adaptive collaborative management of target and bycatch fisheries is urgently needed for this unproductive shark. It is also essential to improve data collection and develop stock assessments for this species.
The adoption of shark finning bans by fishing states (e.g., USA, Australia), regional entities (EU) and regional fisheries organisations (ICCAT) is accelerating and should increasingly prevent the harvesting of hammerhead sharks for their fins alone.
In the U.S. this species is managed as a Large Coastal Shark on U.S. Highly Migratory Species Fishery Management Plan (National Marine Fisheries Service: Federal Fisheries Management Plan for Atlantic Tuna, Swordfish and Sharks).
In South Africa there is a shark bycatch limit in the tuna longline fishery of 10% of the weight of tuna landed, and a recreational line fishery Bag Limit of one shark per angler per day.
Relevance to Humans and Ecosystems
These sharks are potentially dangerous to humans and cases of attacks by great hammerhead sharks have been documented.
Great hammerhead sharks are classified as game fish, as are all large hammerhead sharks. Their skin is often used for leather.
The great hammerhead (Sphyrna mokarran) is the largest species of hammerhead shark, belonging to the family Sphyrnidae, attaining a maximum length of 6.1 m (20 ft). It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf. The great hammerhead can be distinguished from other hammerheads by the shape of its "hammer" (called the "cephalofoil"), which is wide with an almost straight front margin, and by its tall, sickle-shaped first dorsal fin. A solitary, strong-swimming apex predator, the great hammerhead feeds on a wide variety of prey ranging from crustaceans and cephalopods, to bony fishes, to smaller sharks. Observations of this species in the wild suggest that the cephalofoil functions to immobilize stingrays, a favored prey. This species has a viviparous mode of reproduction, bearing litters of up to 55 pups every two years.
Although potentially dangerous, the great hammerhead rarely attacks humans. It sometimes behaves inquisitively toward divers and should be treated with respect. This shark is heavily fished for its large fins, which are extremely valuable on the Asian market as the main ingredient of shark fin soup. As a result, great hammerhead populations are declining substantially worldwide, and it has been assessed as Endangered by the International Union for Conservation of Nature (IUCN).
Taxonomy and phylogeny
The great hammerhead was first described as Zygaena mokarran in 1837 by the German naturalist Eduard Rüppell. The name was later changed to the current Sphyrna mokarran. However, for many years the valid scientific name for the great hammerhead was thought to be Sphyrna tudes, which was coined in 1822 by Achille Valenciennes. In 1950, Enrico Tortonese determined that the specimens illustrated by Valenciennes were in fact smalleye hammerheads, to which the name S. tudes then applied. As the next most senior synonym, Sphyrna mokarran became the great hammerhead's valid name. The lectotype for this species is a 2.5 m (8.2 ft) long male from the Red Sea.
|Phylogenetic tree of hammerhead sharks.|
Older studies based on morphology have generally placed the great hammerhead as one of the more derived members of its family, reflecting the traditional view that cephalofoil size gradually increased over the course of hammerhead shark evolution. However, this view has been refuted by phylogenetic analyses using nuclear and mitochondrial DNA, which found that the great hammerhead and the smooth hammerhead (S. zygaena) form a clade that is basal to all other Sphyrna species. These results also show that the first hammerheads to evolve had large rather than small cephalofoils.
Distribution and habitat
The great hammerhead inhabits tropical waters around the world, between the latitudes of 40°N and 37°S. In the Atlantic Ocean, it is found from North Carolina to Uruguay, including the Gulf of Mexico and the Caribbean Sea, and from Morocco to Senegal, and the Mediterranean Sea. It is found all along the rim of the Indian Ocean, and in the Pacific Ocean from the Ryukyu Islands to Australia, New Caledonia, and French Polynesia, and from southern Baja California to Peru. It may occur off Gambia, Guinea, Mauritania, Sierra Leone, and Western Sahara, but this has not been confirmed. Great hammerheads may be found from inshore waters of less than 1 m (3.3 ft) deep, to a depth of 80 m (230 ft) offshore. They favor coral reefs, but also inhabit continental shelves, island terraces, lagoons, and deep water near land. They are migratory; populations off Florida and in the South China Sea have been documented moving closer to the poles in the summer.
The streamlined body of the great hammerhead with the expanded cephalofoil is typical of the hammerhead sharks. Adult great hammerheads can be distinguished from the scalloped hammerhead and the smooth hammerhead by the shape of the cephalofoil, which has a nearly straight front margin (as opposed to arched), with prominent medial and lateral indentations. The width of the cephalofoil is 23–27% of the body length. The teeth are triangular and strongly serrated, becoming more oblique towards the corners of the mouth. There are 17 tooth rows on either side of the upper jaw with 2–3 teeth at the symphysis (the midline of the jaw), and 16–17 teeth on either side of the lower jaw and 1–3 at the symphysis.
The first dorsal fin is distinctive, being very tall and strongly falcate (sickle-shaped), and originates over the insertions of the pectoral fins. The second dorsal fin and anal fin are both relatively large, with deep notches in the rear margins. The pelvic fins are falcate with concave rear margins, in contrast to the straight-margined pelvic fins of the scalloped hammerhead. The skin is covered with closely placed dermal denticles. Each denticle is diamond-shaped, with 3–5 horizontal ridges leading to marginal teeth in smaller individuals, and 5–6 in larger ones. The great hammerhead is dark brown to light gray to olive above, fading to white on the underside. The fins are unmarked in adults, while the tip of the second dorsal fin may be dark in juveniles.
The average great hammerhead measures up to 3.5 m (11.5 ft) long and weighs over 230 kg (500 lb). A small percentage of the population, mostly or all females, are much larger. The longest great hammerhead on record was 6.1 m (20 ft). The heaviest known great hammerhead is a 4.4 m (14.4 ft) long, 580 kg (1,280 lb) female caught off Boca Grande, Florida in 2006. The weight of the female was due to her being pregnant with 55 near-natal pups.
Biology and ecology
The great hammerhead is a solitary, nomadic predator that tends to be given a wide berth by other reef sharks. If confronted, they may respond with an agonistic display: dropping their pectoral fins and swimming in a stiff or jerky fashion. Juveniles are preyed upon by larger sharks such as bull sharks (Carcharhinus leucas), while adults have no major predators. Yellow jacks (Carangoides bartholomaei) have been seen rubbing themselves against the hammerhead's flanks, possibly to rid themselves of parasites. Schools of pilot fish (Naucrates ductor) sometimes accompany the great hammerhead. The great hammerhead is parasitized by several species of copepods, including Alebion carchariae, A. elegans, Nesippus orientalis, N. crypturus, Eudactylina pollex, Kroyeria gemursa, and Nemesis atlantica.
An active predator with a varied diet, known prey of the great hammerhead include invertebrates such as crabs, lobsters, squid, and octopus, bony fishes such as tarpon, sardines, sea catfishes, toadfish, porgies, grunts, jacks, croakers, groupers, flatfishes, boxfishes, and porcupine fishes, and smaller sharks such as smoothhounds. At Rangiroa Atoll, great hammerheads prey opportunistically on grey reef sharks (Carcharhinus amblyrhynchos) that have exhausted themselves pursuing mates. The species is known to be cannibalistic.
The favorite prey of the great hammerhead are rays and skates, especially stingrays. The venomous spines of stingrays are frequently found lodged inside its mouth and do not seem to bother the shark as one specimen caught off Florida had 96 spines in and around its mouth. Great hammerheads primarily hunt at dawn or dusk, swinging their heads in broad angles over the sea floor so as to pick up the electrical signatures of stingrays buried in the sand, via numerous ampullae of Lorenzini located on the underside of the cephalofoil. The cephalofoil also serves as a hydrofoil that allows the shark to quickly turn around and strike at a ray once detected. Off Florida, large hammerheads are often the first to reach newly baited sharklines, suggesting a particularly keen sense of smell.
Another function of the cephalofoil is suggested by an observation of a great hammerhead attacking a southern stingray (Dasyatis americana) in the Bahamas: the shark first knocked the ray to the sea bottom with a powerful blow from above, and then pinned it with its head while pivoting to take a large bite from each side of the ray's pectoral fin disc. This effectively crippled the stingray, which was then picked up in the jaws and sawed apart with rapid shakes of the head. A great hammerhead has also been seen attacking a spotted eagle ray (Aetobatus narinari) in open water by taking a massive bite out of one of its pectoral fins. The ray thus incapacitated, the shark once again used its head to pin it to the bottom and pivoted to take the ray in its jaws head-first. These observations suggest that the great hammerhead seeks to disable rays with the first bite, a strategy similar to that of the great white shark (Carcharodon carcharias), and that its cephalofoil is an adaptation for prey handling.
As with other hammerhead sharks, great hammerheads are viviparous: once the developing young use up their supply of yolk, the yolk sac is transformed into a structure analogous to a mammalian placenta. Unlike most other sharks, which mate on or near the sea bottom, great hammerheads have been observed mating near the surface. In one account from the Bahamas, a mating pair ascended while swimming around each other, mating when they reached the surface. Females breed once every two years, giving birth from late spring to summer in the Northern Hemisphere and from December to January in Australian waters. The gestation period is 11 months. The litter size ranges from 6–55 pups, with 20–40 being typical. The young measure 50–70 cm (20–28 in) at birth; males reach maturity at 2.3–2.8 m (7.5–8.9 ft) long and 51 kg (113 lbs) and the females at 2.5–3.0 m (8.2–9.8 ft) and 41 kg (90 lbs). The young differ from the adults in having a rounded frontal margin on the head. The typical lifespan of this species is 20–30 years; the record Boca Grande female was estimated to be 40–50 years old.
With its large size and cutting teeth, the great hammerhead is certainly capable of inflicting fatal injuries to a human and caution should be exercised around them. This species has a (possibly undeserved) reputation for aggression and being the most dangerous of the hammerhead sharks. Divers underwater have reported that great hammerheads tend to be shy or unreactive toward humans. However, there have been reports of great hammerheads approaching divers closely and even charging them when they first enter the water. As of 2011, the International Shark Attack File lists 34 attacks, 17 of them unprovoked and none fatal, attributable to hammerhead sharks of the genus Sphyrna. Due to the difficulty in identifying the species involved, it is uncertain how many were caused by great hammerheads. This shark has been confirmed to be responsible for only one (provoked) attack.
The great hammerhead is regularly caught both commercially and recreationally in the tropics, using longlines, fixed bottom nets, hook-and-line, and trawls. Though the meat is rarely consumed, their fins are becoming increasing valuable due to the Asian demand for shark fin soup. In addition, their skin used for leather, their liver oil for vitamins, and their carcasses for fishmeal. The great hammerhead is also taken unintentionally as bycatch and suffers very high mortality, over 90% for fisheries in the northwest Atlantic and the Gulf of Mexico. Entanglement in shark nets around Australian and South African beaches is another source of mortality.
The great hammerhead is extremely vulnerable to overfishing due to its low overall abundance and long generation time. Assessment of its conservation status is difficult as few fisheries separate the great hammerhead from other hammerheads in their reported catches. This species is listed as globally Endangered on the IUCN Red List. It is Endangered in the northwestern Atlantic and the Gulf of Mexico, where though it is a non-targeted species, populations have dropped 50% since the 1990s due to bycatch. It is also Endangered in the southwestern Indian Ocean, where large numbers of longline vessels operate illegally along the coasts for hammerheads and the giant guitarfish (Rhynchobatus djiddensis). The great hammerhead catch rate in Indian Ocean has declined 73% from 1978 to 2003, though it is yet undetermined whether these represent localized or widespread depletion. The great hammerhead is Critically Endangered along the western coast of Africa, where stocks have collapsed with an estimated 80% decline in the past 25 years. The West African Sub-Regional Fishing Commission (SRFC) has recognized the great hammerhead as one of the four most threatened species in the region, though fishing continues unmonitored and unregulated. Off northern Australia, this species was assessed as Data Deficient but at "high risk". Concern has arisen there over a substantial increase in illegal, unreported, and unregulated (IUU) fishing, reflecting the raising value of this shark's fins.
No conservation measures specifically protecting the great hammerhead have been enacted. It is listed on Annex I, Highly Migratory Species, of the UN Convention on the Law of the Sea, though no management schemes have yet been implemented under this agreement. The banning of shark finning by countries and supranational entities such as United States, Australia, and the European Union, and international regulatory bodies such as the International Commission for the Conservation of Atlantic Tunas (ICCAT), should reduce fishing pressure on the great hammerhead.
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