The great hammerhead (''Sphyrna mokarran'') is the largest

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

hammerhead shark The hammerhead sharks are a group of sharks that form the family Sphyrnidae, named for the unusual and distinctive form of their heads, which are flattened and laterally extended into a Hammerhead shark#Cephalofoil, cephalofoil (a T-shape or " ...

, belonging to the family Sphyrnidae, attaining an average length of and reaching a maximum length of . It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...

. 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 dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

. A solitary, strong-swimming

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

, the great hammerhead feeds on a wide variety of prey ranging from

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s and

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s, to

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

, to smaller

shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

s. Observations of this species in the wild suggest that the cephalofoil functions to immobilize

stingray Stingrays are a group of sea Batoidea, rays, a type of cartilaginous fish. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae (deepwate ...

s, a favored prey. This species has a

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

mode of reproduction, bearing litters of up to 50 pups every two years. Although potentially dangerous, the great hammerhead rarely attacks humans and can sometimes behave inquisitively toward divers. This shark is heavily fished for its large fins, which are valuable on the Chinese market as the main ingredient of

shark fin soup Shark's fin soup is a soup or stewed dish served in parts of China, Taiwan, and Southeast Asia. The shark fins provide texture, while the taste comes from the other ingredients. It is commonly served at special occasions such as weddings and ba ...

. As a result, great hammerhead populations are declining substantially worldwide, and it has been assessed as

critically endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...

by the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

(IUCN) as of 2019.

Taxonomy and phylogeny

The great hammerhead was first described as ''Zygaena mokarran'' in 1837 by German

naturalist Natural history is a domain of inquiry involving organisms, including animals, fungi, and plants, in their natural environment, leaning more towards observational than experimental methods of study. A person who studies natural history is cal ...

Eduard Rüppell Wilhelm Peter Eduard Simon Rüppell, also spelled Rueppell (20 November 1794 – 10 December 1884) was a German Natural history, naturalist and List of explorers, explorer, best known for his collections and descriptions of plants and animals from ...

. The species name is the common name in Arabic ''مقرن'' and means ''"horned"''. The name was later changed to the current ''Sphyrna mokarran''. For many years, though, the valid scientific name for the great hammerhead was thought to be ''Sphyrna tudes'', which was coined in 1822 by

Achille Valenciennes Achille Valenciennes (9 August 1794 – 13 April 1865) was a French zoology, zoologist. Valenciennes was born in Paris, and studied under Georges Cuvier. His study of parasitic worms in humans made an important contribution to the study of parasi ...

. 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 A synonym is a word, morpheme, or phrase that means precisely or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...

, ''Sphyrna mokarran'' became the great hammerhead's valid name. The

lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...

for this species is a 2.5-m-long (8.2 ft) male from the

Red Sea The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...

. Older studies based on

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

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, but this view has been refuted by

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analyses using

nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics * Nuclear space *Nuclear ...

and

mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the D ...

, which found that the great hammerhead and the

smooth hammerhead The smooth hammerhead (''Sphyrna zygaena'') is a species of hammerhead shark, and part of the family Sphyrnidae. This species is named "smooth hammerhead" because of the distinctive shape of the head, which is flattened and laterally extended in ...

(''S. zygaena'') form a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

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

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

s of 40°N and 37°S. In the

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

, it is found from

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

Uruguay Uruguay, officially the Oriental Republic of Uruguay, is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast, while bordering the Río de la Plata to the south and the A ...

, including the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

and the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

, and from

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

Senegal Senegal, officially the Republic of Senegal, is the westernmost country in West Africa, situated on the Atlantic Ocean coastline. It borders Mauritania to Mauritania–Senegal border, the north, Mali to Mali–Senegal border, the east, Guinea t ...

, and the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

. It is found all along the rim of the

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

, and in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

from the

Ryukyu Islands The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Geography of Taiwan, Taiwan: the Ryukyu Islands are divided into the Satsunan Islands (Ōsumi Islands, Ōsumi, Tokara Islands, Tokara and A ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

, and

French Polynesia French Polynesia ( ; ; ) is an overseas collectivity of France and its sole #Governance, overseas country. It comprises 121 geographically dispersed islands and atolls stretching over more than in the Pacific Ocean, South Pacific Ocean. The t ...

, and from southern

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

.Bester, Cathleen
Biological Profiles: Great Hammerhead
''Florida Museum of Natural History Ichthyology Department''. Retrieved on October 18, 2008. It may occur off

Gambia The Gambia, officially the Republic of The Gambia, is a country in West Africa. Geographically, The Gambia is the List of African countries by area, smallest country in continental Africa; it is surrounded by Senegal on all sides except for ...

Guinea Guinea, officially the Republic of Guinea, is a coastal country in West Africa. It borders the Atlantic Ocean to the west, Guinea-Bissau to the northwest, Senegal to the north, Mali to the northeast, Côte d'Ivoire to the southeast, and Sier ...

Mauritania Mauritania, officially the Islamic Republic of Mauritania, is a sovereign country in Maghreb, Northwest Africa. It is bordered by the Atlantic Ocean to the west, Western Sahara to Mauritania–Western Sahara border, the north and northwest, ...

Sierra Leone Sierra Leone, officially the Republic of Sierra Leone, is a country on the southwest coast of West Africa. It is bordered to the southeast by Liberia and by Guinea to the north. Sierra Leone's land area is . It has a tropical climate and envi ...

Western Sahara Western Sahara is a territorial dispute, disputed territory in Maghreb, North-western Africa. It has a surface area of . Approximately 30% of the territory () is controlled by the Sahrawi Arab Democratic Republic (SADR); the remaining 70% is ...

, and occasionally seen near

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

but this has not been confirmed. Great hammerheads may be found from inshore waters less than deep, to a depth of offshore. They favor

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in group ...

s, but also inhabit continental shelves, island terraces,

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

s, and deep water near land. They are migratory; populations off

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

and in the

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by South China, in the west by the Indochinese Peninsula, in the east by the islands of Taiwan island, Taiwan and northwestern Philippines (mainly Luz ...

have been documented moving closer to the poles in the summer.

Description

The streamlined body of the great hammerhead with the expanded cephalofoil is typical of the

hammerhead sharks The hammerhead sharks are a group of sharks that form the family Sphyrnidae, named for the unusual and distinctive form of their heads, which are flattened and laterally extended into a cephalofoil (a T-shape or "hammer"). The shark's eyes ar ...

. Adults can be distinguished from the

scalloped hammerhead The scalloped hammerhead (''Sphyrna lewini'') is a species of hammerhead shark in the family (biology), family Hammerhead shark, Sphyrnidae. It was originally known as ''Zygaena lewini''. The Greek language, Greek word ''sphyrna'' translates into ...

and the

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 toward the corners of the mouth. Seventeen tooth rows are on either side of the upper jaw, with two or three teeth at the symphysis (the midline of the jaw), and 16–17 teeth on either side of the lower jaw and one to three at the symphysis. The first dorsal fin is distinctive, being very tall and strongly sickle-shaped, and originates over the insertions of the

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s. The second dorsal fin and

anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

are both relatively large, with deep notches in the rear margins. The

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s are sickle-shaped with concave rear margins, in contrast to the straight-margined pelvic fins of the scalloped hammerhead. The skin is covered with closely placed

dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...

s. Each denticle is diamond-shaped, with three to five horizontal ridges leading to marginal teeth in smaller individuals, and five or six 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 typical minimum great hammerhead measures long and weighs over , while the maximum measures long and weighs . A small percentage of the population, mostly or all females, are much larger. The longest great hammerhead on record was . The heaviest known great hammerhead is a female, long and in weight caught off

Boca Grande, Florida Boca Grande is a small residential community on Gasparilla Island in southwest Florida. Gasparilla Island is a part of both Charlotte County, Florida, Charlotte and Lee County, Florida, Lee counties, while the actual village of Boca Grande, wh ...

, in 2006. The weight of the female was due to her being pregnant with 55 neonatal pups. Exceptionally large individuals may possibly reach in weight, though this has not been verified. File:Sphyrna mokarran jaws.jpg, Jaws File:Sphyrna mokarran upper teeth.jpg, Upper teeth File:Sphyrna mokarran lower teeth.jpg, Lower teeth

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, it may respond with an agonistic display, dropping its pectoral fins and swimming in a stiff or jerky fashion. Juveniles are preyed upon by larger sharks such as

bull shark The bull shark (''Carcharhinus leucas''), also known as the Zambezi shark (informally zambi) in Africa and Lake Nicaragua shark in Nicaragua, is a species of requiem shark commonly found worldwide in warm, shallow waters along coasts and in riv ...

s (''Carcharhinus leucas''), while adults have no major predators except for

killer whale The orca (''Orcinus orca''), or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. The only extant species in the genus '' Orcinus'', it is recognizable by its black-and-white-patterned body. A cosmopolit ...

s, which hunt hammerheads of any age.

Yellow jack The yellow jack (''Carangoides bartholomaei''), also known as coolihoo, is a species of marine (ocean), marine fish in the jack family, Carangidae. It is one of only two representatives of its genus present in the Atlantic Ocean, inhabiting wate ...

s (''Carangoides bartholomaei'') have been seen rubbing themselves against the hammerhead's flanks, possibly to rid themselves of

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

s. Schools of

pilot fish The pilot fish (''Naucrates ductor'') is a carnivorous fish of the trevally, or jackfish family, Carangidae. It is widely distributed and lives in warm or tropical open seas. Description The pilot fish congregates around sharks, rays, and ...

(''Naucrates ductor'') sometimes accompany the great hammerhead. The great hammerhead is parasitized by several species of

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

s, including ''Alebion carchariae'', ''A. elegans'', ''Nesippus orientalis'', ''N. crypturus'', ''Eudactylina pollex'', ''Kroyeria gemursa'', and ''Nemesis atlantica''.

Feeding

The great hammerhead shark is an active predator with a varied diet, known prey of the great hammerhead include

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s such as crabs, lobsters, squid, and octopus;

es such as

tarpon Tarpon are fish of the genus ''Megalops''. They are the only members of the family Megalopidae. Of the two species, one (''M. atlanticus'') is native to the Atlantic, and the other (''M. cyprinoides'') to the Indo-Pacific Oceans. Species and ...

sardines Sardine and pilchard are common names for various species of small, oily forage fish in the herring suborder Clupeoidei. The term "sardine" was first used in English during the early 15th century; a somewhat dubious etymology says it come ...

sea catfish The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones. The family includes about 143 species. Fossil ...

es,

toadfish {{short description, Common name used for fish Toadfish is the common name for a variety of species from several different families of fish, usually because of their toad-like appearance or calls using their swimbladder. File:OysterToadfish.jpeg, ...

, porgies,

grunt Grunt, grunts or grunting may refer to: Sound and music * Grunting (tennis), in tennis refers to the loud noise, sometimes described as "shrieking" or "screaming", made by some players during their strokes * Death grunt, the death metal singi ...

s, jacks, croakers,

grouper Groupers are a diverse group of marine ray-finned fish in the family Epinephelidae, in the order Perciformes. Groupers were long considered a subfamily of the seabasses in Serranidae, but are now treated as distinct. Not all members of this f ...

flatfish A flatfish is a member of the Ray-finned fish, ray-finned demersal fish Order (biology), suborder Pleuronectoidei, also called the Heterosomata. In many species, both eyes lie on one side of the head, one or the other migrating through or around ...

es,

boxfish Ostraciidae or Ostraciontidae is a family of squared, Actinopterygii, bony fish belonging to the order Tetraodontiformes, closely related to the pufferfishes and filefishes. Fish in the family are known variously as boxfishes, cofferfishes, cowfi ...

es, and porcupine fishes; and smaller sharks such as smoothhounds. At Rangiroa Atoll, great hammerheads prey opportunistically on

grey reef shark The grey reef shark or gray reef shark (''Carcharhinus amblyrhynchos'', sometimes misspelled ''amblyrhynchus'' or ''amblyrhinchos'') is a species of requiem shark, in the family (biology), family Requiem shark, Carcharhinidae. One of the most com ...

s (''Carcharhinus amblyrhynchos'') that have exhausted themselves pursuing mates. The species is known to be cannibalistic. In the Gatun Formation of

Panama Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...

, fossil teeth belonging to great hammerheads suggest the shark once preyed on juvenile ''

Otodus megalodon ''Otodus megalodon'' ( ; meaning "big tooth"), Common name, commonly known as megalodon, is an extinction, extinct species of giant mackerel shark that lived approximately 23 to 3.6 million years ago (Mya), from the Early Miocene to the Earl ...

'', alongside the extinct snaggletooth shark '' Hemipristis serra'', with which it was once contemporary. Great hammerheads are apex predators among sharks, and are specialists at feeding on other sharks,

rays Ray or RAY may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), the bony or horny spine on ray-finned fish Science and mathematics * Half-line (geometry) or ray, half of a line split at an ...

, and

skate Skate or Skates may refer to: Fish *Skate (fish), several genera of fish belonging to the family Rajidae * Pygmy skates, several genera of fish belonging to the family Gurgesiellidae * Smooth skates or leg skates, several genera of fish belongin ...

s, especially

s. 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 electroreceptory organs located on the underside of the cephalofoil. The cephalofoil also serves as a

hydrofoil A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains sp ...

that allows the shark to quickly turn around and strike at a ray once detected.Hammerschlag, Rick
Sandy Plains: Great Hammerhead Shark
''ReefQuest Centre for Shark Research''. Retrieved on October 18, 2008. 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 The southern stingray (''Hypanus americanus'') is a whiptail stingray found in tropical and subtropical waters of the Western Atlantic Ocean from New Jersey to southern Brazil. It has a flat, diamond-shaped disc, with a mud brown, olive, and gre ...

(''Dasyatis americana'') in the

Bahamas The Bahamas, officially the Commonwealth of The Bahamas, is an archipelagic and island country within the Lucayan Archipelago of the Atlantic Ocean. It contains 97 per cent of the archipelago's land area and 88 per cent of its population. ...

; 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 The spotted eagle ray (''Aetobatus narinari'') is a cartilaginous fish of the eagle ray family, Aetobatidae. As traditionally recognized, it is found globally in tropical regions, including the Atlantic, Pacific and Indian Oceans. Recent author ...

(''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 The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocea ...

(''Carcharodon carcharias''), and that its cephalofoil is an

adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the p ...

for prey handling. Adult great hammerheads have been observed hunting in coral reef flats as shallow as ~.

Rolled swimming and energy conservation

A 2016 study of specimens logged with accelerometers showed that great hammerhead sharks reduce drag and lessen energy expenditure by swimming on their side in a posture termed "rolled swimming". The shark uses its very large dorsal fin to help achieve lift, a habit that had previously been noted in captive specimens, and may spend up to 90% of its time in this swimming orientation. The technique is thought to save about 10% in drag and consequently movement costs.

Life history

As with other hammerhead sharks, great hammerheads are

; once the developing young use up their supply of

yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...

, the

yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...

is transformed into a structure analogous to a mammalian

placenta The placenta (: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas, and waste exchange between ...

. 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 In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once i ...

is 11 months. The litter size ranges from six to 55 pups, with 20–40 being typical. The young measure at birth; males reach maturity at long and and the females at and . 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.

Human interactions

With its large size and cutting teeth, the great hammerhead could seriously injure a human, so 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 nonreactive toward humans.Great Hammerhead
''Elasmodiver.com''. Retrieved on October 18, 2008. Reports have been made 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 bites, with 17 of them unprovoked and none fatal, attributable to hammerhead sharks of the genus ''Sphyrna''. Due to the difficulty in identifying the species involved, how many were caused by great hammerheads is uncertain. This shark has been confirmed to be responsible for only one (provoked) bite. The great hammerhead is regularly caught both commercially and recreationally in the tropics, using longlines, fixed bottom nets, hook-and-line, and

trawl Trawling is an industrial method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch di ...

s. Though the meat is rarely consumed, their fins are becoming increasing valuable due to the Asian demand for

. In addition, their skin used for

leather Leather is a strong, flexible and durable material obtained from the tanning (leather), tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffal ...

, their liver oil for

vitamin Vitamins are Organic compound, organic molecules (or a set of closely related molecules called vitamer, vitamers) that are essential to an organism in small quantities for proper metabolism, metabolic function. Nutrient#Essential nutrients, ...

s, and their carcasses for

fishmeal Fish meal (sometimes spelled fishmeal) is a commercial product made from whole wild-caught fish, bycatch, and fish by-products to feed farm animals, such as pigs, poultry, and farmed fish.R. D. Miles and F. A. Chapman.FA122: The Benefits of Fish ...

. The great hammerhead is also taken unintentionally as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

and suffers very high mortality, over 90% for fisheries in the northwest Atlantic and the Gulf of Mexico. Entanglement in

shark net A shark net is a submerged section of gillnets placed at beaches designed to intercept large marine animals including sharks, with the aim to reduce the likelihood of shark attacks on swimmers. The gillnets form a wall of netting that hangs in t ...

s around Australian and South African beaches is another source of mortality. In

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

, Australia recreational fishers are prohibited from taking any hammerhead species. In Australia's other northern jurisdictions (the

Northern Territory The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an states and territories of Australia, Australian internal territory in the central and central-northern regi ...

and

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

) recreational targeting and catching of great hammerheads is allowed.

Conservation status

The great hammerhead is extremely vulnerable to

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing Fish stocks, fish stock), resu ...

due to its low overall abundance and long

generation time In population biology and demography Demography () is the statistical study of human populations: their size, composition (e.g., ethnic group, age), and how they change through the interplay of fertility (births), mortality (deaths), and mi ...

. 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

on the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...

. It is endangered in the north-western Atlantic and the Gulf of Mexico, where though it is not a 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 whether these represent localized or widespread depletions is uncertain. 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

, this species was assessed as

data deficient A data deficient (DD) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as offering insufficient information for a proper assessment of conservation status to be made. This does not necessaril ...

, but at "high risk". Concern has arisen there over a substantial increase in illegal, unreported, and unregulated fishing, reflecting the rising 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 The United Nations Convention on the Law of the Sea (UNCLOS), also called the Law of the Sea Convention or the Law of the Sea Treaty, is an international treaty that establishes a legal framework for all marine and maritime activities. , 169 sov ...

, though no management schemes have yet been implemented under this agreement. The banning of

shark finning Shark finning is the act of removing fins from sharks and discarding the rest of the shark back into the ocean. This act is prohibited in many countries. The sharks are often still alive when discarded, but without their fins.Spiegel, J. (200 ...

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 The International Commission for the Conservation of Atlantic Tunas (ICCAT) is a tuna regional fishery management organisation, responsible for the management and conservation of tuna and tuna-like species in the Atlantic Ocean and adjacent seas. ...

, should reduce fishing pressure on the great hammerhead. According to a January 2021 study in ''

Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...

'', which studied 31 species of sharks and

, the number of these species found in open oceans had dropped by 71% in around 50 years. The great hammerhead was included in the study.

References

External links

Species Description of Sphyrna mokarran at www.shark-references.com
*
A 3D model of a Great hammerhead
{{Good article

great hammerhead The great hammerhead (''Sphyrna mokarran'') is the largest species of hammerhead shark, belonging to the family Sphyrnidae, attaining an average length of and reaching a maximum length of . It is found in tropical and warm temperate waters world ...

Pantropical fish Apex predators Extant Burdigalian first appearances

Critically endangered fauna of the United States