Smooth hammerhead
Encyclopedia
The smooth hammerhead is a species
of hammerhead shark
, family Sphyrnidae, so named because of the distinctive shape of the head, which is flattened and laterally extended into a hammer
shape (called the "cephalofoil"), without an indentation in the middle of the front margin (hence "smooth"). Unlike other hammerheads, this species prefers temperate
waters and occurs worldwide at medium latitude
s. In the summer
, these sharks migrate
towards the poles following cool water masses, sometimes forming schools
numbering in the hundreds to thousands.
The second-largest hammerhead shark, the smooth hammerhead can measure up to 5 m (16.4 ft) long. It is an active predator that takes a wide variety of bony fishes and invertebrate
s, with larger individuals also feeding on sharks and rays. As in the rest of its family, this shark is viviparous and gives birth to litters of 20–40 pups. A relatively common shark, it is captured, intentionally or otherwise, by many commercial fisheries
throughout its range; its fins are extremely valuable for use in shark fin soup
. This shark is potentially dangerous and has likely been responsible for a few attacks on humans
, though it is less likely to encounter swimmers than other large hammerhead species due to its temperate habitat
.
", originally described the smooth hammerhead as Squalus zygaena in the 1758 tenth edition
of Systema Naturae
, without designating a type specimen. The name was later changed to Sphyrna zygaena. The specific epithet zygaena comes from the Greek
word zygon, meaning "yoke
", referring to the shape of its head. Other common names for this species include common hammerhead, common smooth hammerhead, round-headed hammerhead, or simply hammerhead. Phylogenetic analyses based on morphology
, isozyme
s, and mitochondrial DNA
show that the scalloped hammerhead
(Sphyrna lewini) is the sister species of the smooth hammerhead, and that the two of them form a clade
with the great hammerhead
(S. mokarran).
s than any other species. In the Atlantic, it occurs from Nova Scotia
to the Virgin Islands
and from Brazil
to southern Argentina
in the west, and from the British Isles
to Côte d'Ivoire
, including the Mediterranean Sea
, in the east. In the Indian Ocean
, it is found off South Africa
, India
, and Sri Lanka
. In the western Pacific, it occurs from the Gulf of Tonkin
to southern Japan
and Siberia
, as well as off Australia
and New Zealand
. In the central and eastern Pacific, it occurs off the Hawaiian Islands
, California
, Panama
, the Galapagos Islands
, Ecuador
, and Chile
. This species is usually considered to be amphitemperate (absent from the tropics
) in distribution, though there are rare reports from tropical waters such as in the Gulf of Mannar
off India, and off southern Mozambique
. Its presence in the tropics is difficult to determine due to confusion with other hammerhead species.
Compared to the scalloped and great hammerheads, the smooth hammerhead stays closer to the surface, in water less than 20 m (65.6 ft) deep. However, it has been recorded diving to a depth of 200 m (656.2 ft). It prefers inshore waters such as bay
s and estuaries, but is sometimes found in the open ocean over the continental shelf
, and around oceanic islands. This shark has also been reported entering freshwater
habitats, such as the Indian River
in Florida
. In the summer, smooth hammerheads migrate poleward to stay in cooler water, heading back towards the equator
in winter.
The second-largest hammerhead next to the great hammerhead, the smooth hammerhead typically measures 2.5–3.5 m (8.2–11.5 ft) long, with a maximum recorded length and weight of 5 m (16.4 ft) and 400 kg (881.8 lb) respectively. The smooth hammerhead differs from other large hammerheads in the shape of its cephalofoil, which has a curved front margin without an indentation in the center. The cephalofoil is wide but short, measuring 26–29% of the body length across. The nostril
s are located near the ends of the cephalofoil, with long grooves running towards the center. There are 26–32 tooth rows in the upper jaw and 25–30 tooth rows in the lower jaw. Each tooth is triangular in shape, with smooth to weakly serrated edges.
The body is streamlined, without a dorsal ridge between the two dorsal fin
s. The first dorsal fin is moderately tall and falcate (sickle-like) in shape, with a rounded tip. The pectoral and pelvic fins are not falcate, rather having nearly straight rear margins. The anal fin is larger than the second dorsal fin, with long free rear tip and a strong notch in the rear margin. The dermal denticles are densely packed, each with 5–7 horizontal ridges (3 in juveniles) leading to a W-shaped rear margin. The back is dark brownish gray to olive in color, in contrast to the simple brown of most other hammerheads, becoming lighter on the flanks. The belly is white, and sometimes the pectoral fins have dark edges underneath.
Adult smooth hammerheads are either solitary or form small groups. They may come together in great numbers during their annual migrations; schools of over a hundred juveniles under 1.5 m (4.9 ft) long have been observed off the eastern Cape of South Africa
, and schools thousands strong have been reported off California. During hot summer weather, they can be seen swimming just below the surface with their dorsal fins exposed. Young smooth hammerheads are preyed upon by larger sharks such as the dusky shark
(Carcharhinus obscurus); adults have been observed being consumed by killer whales (Orcinus orca) off New Zealand. Known parasites of the smooth hammerhead include the nematode
s Parascarophis sphyrnae and Contracaecum spp.
The smooth hammerhead is an active-swimming predator that feeds on bony fishes, rays, sharks (including of its own species), cephalopods, and to a lesser extent crustacean
s such as shrimp
, crab
s, and barnacle
s. They readily scavenge
from fishing lines. In some areas, stingray
s are a favored prey and comprise a majority of its diet. The venom
ous barbs of stingrays are often found lodged in and around the mouths of these sharks; one specimen examined contained 95 such spines. In northern Europe
, the smooth hammerhead feeds on herring
and seabass
, while in North America
it takes Spanish mackerel
and menhaden
. Off South Africa, smooth hammerheads feed on squid such as Loligo vulgaris
and small schooling fish such as pilchard over the deep coral reef
s at the edge of the continental shelf, with individuals over 2 m (6.6 ft) long taking increasing numbers of smaller sharks and rays. Off Australia, squid are the most important prey, followed by bony fish.
Like other hammerheads, the smooth hammerhead is viviparous: once the young exhaust their supply of yolk, the empty yolk sac
is converted into a placenta
l connection through which the mother delivers nourishment. Females bear relatively large litters of 20–50 pups after a gestation period
of 10–11 months. Birthing occurs in shallow coastal nurseries, such as Bulls Bay in North Carolina
. The pups measure 50–61 cm (19.7–24 in) long at birth; females reach maturity at 2.7 m (8.9 ft) long and males at 2.1–2.5 m (6.9–8.2 ft) long, depending upon locality. Off South Africa, newly mated females have been caught in February and females with full-term embryos in November; off the east coast of Australia, birthing takes place between January and March, with ovulation
taking place around the same time. This shark is thought to live for 20 years or more.
lists 34 attacks attributable to large hammerhead sharks, 17 of them unprovoked (1 fatal). However, due to the smooth hammerhead's occurrence in temperate regions where people are less likely to enter the water, it was likely responsible for a minority of these attacks. Off southern California, this species has been reported to steal catches from sport fishers and divers.
Smooth hammerheads are caught by commercial fisheries throughout the world, including those off the United States
(East and West Coasts), Brazil
, Spain
, Taiwan
, the Philippines
, southwestern Australia, and western Africa
, primarily using gillnet
s and longlines. Fishery catches of smooth hammerheads are difficult to quantify due to a frequent lack of distinction between them and other large hammerheads. The meat is sold fresh, dried and salted, or smoked, though in most markets it is considered undesirable and there are reports of poison
ing. Much more valuable are the fins, which have the highest rating for use in shark fin soup
and often leads to captured sharks being finned
at sea. Additionally, the liver oil
is used for vitamin
s, the skin for leather
, and the offal
for fishmeal. This shark is also used in Chinese medicine.
Many other fisheries from every ocean also take smooth hammerheads as bycatch
, and they are caught in some numbers by recreational angler
s. Smooth hammerheads are also killed by entanglement in shark net
s used to protect beaches. Fewer than 10 smooth hammerheads were caught annually in the nets off KwaZulu-Natal
, South Africa, from 1978–1990. In contrast, in the nets off New South Wales
, Australia, smooth hammerheads comprised 50% of the 4,715 sharks captured from 1972–1990. At present, this species remains relatively common and has been assessed as "Lower Risk/Near Threatened" by the World Conservation Union. Off New Zealand, it is a prohibited target species and is the most abundant shark along the northwest coast. It also does not appear to have been negatively impacted by fishing off southern Australia. Off the eastern United States, catches of this species are regulated by the National Marine Fisheries Service
(NMFS) Atlantic shark Fishery Management Plan (FMP), under which it is classified as a Large Coastal Shark (LCS).
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of hammerhead shark
Hammerhead shark
The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna while the...
, family Sphyrnidae, so named because of the distinctive shape of the head, which is flattened and laterally extended into a hammer
Hammer
A hammer is a tool meant to deliver an impact to an object. The most common uses are for driving nails, fitting parts, forging metal and breaking up objects. Hammers are often designed for a specific purpose, and vary widely in their shape and structure. The usual features are a handle and a head,...
shape (called the "cephalofoil"), without an indentation in the middle of the front margin (hence "smooth"). Unlike other hammerheads, this species prefers temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
waters and occurs worldwide at medium latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s. In the summer
Summer
Summer is the warmest of the four temperate seasons, between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, with day-length decreasing as the season progresses after the solstice...
, these sharks migrate
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
towards the poles following cool water masses, sometimes forming schools
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
numbering in the hundreds to thousands.
The second-largest hammerhead shark, the smooth hammerhead can measure up to 5 m (16.4 ft) long. It is an active predator that takes a wide variety of bony fishes and invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, with larger individuals also feeding on sharks and rays. As in the rest of its family, this shark is viviparous and gives birth to litters of 20–40 pups. A relatively common shark, it is captured, intentionally or otherwise, by many commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
throughout its range; its fins are extremely valuable for use in shark fin soup
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
. This shark is potentially dangerous and has likely been responsible for a few attacks on humans
Shark attack
A shark attack is an attack on a human by a shark. Every year around 60 shark attacks are reported worldwide, although death is quite unusual. Despite the relative rarity of shark attacks, the fear of sharks is a common phenomenon, having been fueled by the occasional instances of serial attacks,...
, though it is less likely to encounter swimmers than other large hammerhead species due to its temperate habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
.
Taxonomy and phylogeny
The Swedish natural historian Carl Linnaeus, known as the "father of taxonomyTaxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
", originally described the smooth hammerhead as Squalus zygaena in the 1758 tenth edition
10th edition of Systema Naturae
The 10th edition of Systema Naturae was a book written by Carl Linnaeus and published in two volumes in 1758 and 1759, which marks the starting point of zoological nomenclature...
of Systema Naturae
Systema Naturae
The book was one of the major works of the Swedish botanist, zoologist and physician Carolus Linnaeus. The first edition was published in 1735...
, without designating a type specimen. The name was later changed to Sphyrna zygaena. The specific epithet zygaena comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word zygon, meaning "yoke
Yoke
A yoke is a wooden beam, normally used between a pair of oxen or other animals to enable them to pull together on a load when working in pairs, as oxen usually do; some yokes are fitted to individual animals. There are several types of yoke, used in different cultures, and for different types of oxen...
", referring to the shape of its head. Other common names for this species include common hammerhead, common smooth hammerhead, round-headed hammerhead, or simply hammerhead. Phylogenetic analyses based on morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
, isozyme
Isozyme
Isozymes are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. These enzymes usually display different kinetic parameters Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. These enzymes...
s, and mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
show that the scalloped hammerhead
Scalloped hammerhead
The scalloped hammerhead is a species of hammerhead shark, family Sphyrnidae. Originally Zygaena lewini, it was later moved to its current name. The Greek word sphyrna translates into "hammer" in English, referring to the shape of this shark's head.This shark is also known as the bronze,...
(Sphyrna lewini) is the sister species of the smooth hammerhead, and that the two of them form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
with the great hammerhead
Great hammerhead
The great hammerhead is the largest species of hammerhead shark, family Sphyrnidae, attaining a maximum length of 6.1 m . It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf...
(S. mokarran).
Distribution and habitat
Of the hammerhead sharks, the smooth hammerhead is the species most tolerant of temperate water, and occurs worldwide to higher latitudeLatitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s than any other species. In the Atlantic, it occurs from Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
to the Virgin Islands
Virgin Islands
The Virgin Islands are the western island group of the Leeward Islands, which are the northern part of the Lesser Antilles, which form the border between the Caribbean Sea and the Atlantic Ocean...
and from Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
to southern Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
in the west, and from the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
to Côte d'Ivoire
Côte d'Ivoire
The Republic of Côte d'Ivoire or Ivory Coast is a country in West Africa. It has an area of , and borders the countries Liberia, Guinea, Mali, Burkina Faso and Ghana; its southern boundary is along the Gulf of Guinea. The country's population was 15,366,672 in 1998 and was estimated to be...
, including the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, in the east. In the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, it is found off South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, and Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
. In the western Pacific, it occurs from the Gulf of Tonkin
Gulf of Tonkin
The Gulf of Tonkin is an arm of the South China Sea, lying off the coast of northeastern Vietnam.-Etymology:The name Tonkin, written "東京" in Hán tự and Đông Kinh in romanised Vietnamese, means "Eastern Capital", and is the former toponym for Hanoi, the capital of Vietnam...
to southern Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
, as well as off Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. In the central and eastern Pacific, it occurs off the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
, the Galapagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
, Ecuador
Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...
, and Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. This species is usually considered to be amphitemperate (absent from the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
) in distribution, though there are rare reports from tropical waters such as in the Gulf of Mannar
Gulf of Mannar
The Gulf of Mannar is a large shallow bay forming part of the Laccadive Sea in the Indian Ocean. It lies between the southeastern tip of India and the west coast of Sri Lanka. A chain of low islands and reefs known as Adam's Bridge, also called Ramsethu, which includes Mannar Island, separates the...
off India, and off southern Mozambique
Mozambique
Mozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest...
. Its presence in the tropics is difficult to determine due to confusion with other hammerhead species.
Compared to the scalloped and great hammerheads, the smooth hammerhead stays closer to the surface, in water less than 20 m (65.6 ft) deep. However, it has been recorded diving to a depth of 200 m (656.2 ft). It prefers inshore waters such as bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s and estuaries, but is sometimes found in the open ocean over the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
, and around oceanic islands. This shark has also been reported entering freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
habitats, such as the Indian River
Indian River (Florida)
The Indian River is a waterway in Florida, a part of the Indian River Lagoon system which forms the Atlantic Intracoastal Waterway. It extends southward from the Ponce de Leon inlet in New Smyrna Beach, Florida [Volusia County] southward and across the "Haulover Canal" and along the western shore...
in Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
. In the summer, smooth hammerheads migrate poleward to stay in cooler water, heading back towards the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
in winter.
Description
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s are located near the ends of the cephalofoil, with long grooves running towards the center. There are 26–32 tooth rows in the upper jaw and 25–30 tooth rows in the lower jaw. Each tooth is triangular in shape, with smooth to weakly serrated edges.
The body is streamlined, without a dorsal ridge between the two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s. The first dorsal fin is moderately tall and falcate (sickle-like) in shape, with a rounded tip. The pectoral and pelvic fins are not falcate, rather having nearly straight rear margins. The anal fin is larger than the second dorsal fin, with long free rear tip and a strong notch in the rear margin. The dermal denticles are densely packed, each with 5–7 horizontal ridges (3 in juveniles) leading to a W-shaped rear margin. The back is dark brownish gray to olive in color, in contrast to the simple brown of most other hammerheads, becoming lighter on the flanks. The belly is white, and sometimes the pectoral fins have dark edges underneath.
Biology and ecology
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, and schools thousands strong have been reported off California. During hot summer weather, they can be seen swimming just below the surface with their dorsal fins exposed. Young smooth hammerheads are preyed upon by larger sharks such as the dusky shark
Dusky shark
The dusky shark is a species of requiem shark, family Carcharhinidae, occurring in tropical and warm-temperate continental seas worldwide. A generalist apex predator, the dusky shark can be found from the coast to the outer continental shelf and adjacent pelagic waters, and has been recorded from...
(Carcharhinus obscurus); adults have been observed being consumed by killer whales (Orcinus orca) off New Zealand. Known parasites of the smooth hammerhead include the nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s Parascarophis sphyrnae and Contracaecum spp.
The smooth hammerhead is an active-swimming predator that feeds on bony fishes, rays, sharks (including of its own species), cephalopods, and to a lesser extent crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s such as shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, and barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
s. They readily scavenge
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
from fishing lines. In some areas, stingray
Stingray
The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...
s are a favored prey and comprise a majority of its diet. The venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
ous barbs of stingrays are often found lodged in and around the mouths of these sharks; one specimen examined contained 95 such spines. In northern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, the smooth hammerhead feeds on herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
and seabass
European seabass
The European seabass, Dicentrarchus labrax, also known as Morone labrax, is a primarily ocean-going fish that sometimes enters brackish and fresh waters. It is also known as the sea dace...
, while in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
it takes Spanish mackerel
Atlantic Spanish mackerel
The Atlantic Spanish mackerel, Scomberomorus maculatus, is a migratory species of mackerel that swimsto the northern Gulf of Mexico in spring, returns to south Florida in the eastern gulf, and to Mexico in the western gulf in the fall.-Description:...
and menhaden
Menhaden
Menhaden, also known as mossbunker, bunker and pogy, are forage fish of the genera Brevoortia and Ethmidium, two genera of marine fish in the family Clupeidae.-Description:...
. Off South Africa, smooth hammerheads feed on squid such as Loligo vulgaris
Loligo vulgaris
The European squid is a large squid belonging to the family Loliginidae. It occurs abundantly in coastal waters from the North Sea to at least the west coast of Africa. This species lives from sea level to depths of . Its mantle is up to long...
and small schooling fish such as pilchard over the deep coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s at the edge of the continental shelf, with individuals over 2 m (6.6 ft) long taking increasing numbers of smaller sharks and rays. Off Australia, squid are the most important prey, followed by bony fish.
Like other hammerheads, the smooth hammerhead is viviparous: once the young exhaust their supply of yolk, the empty yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
is converted into a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection through which the mother delivers nourishment. Females bear relatively large litters of 20–50 pups after a gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
of 10–11 months. Birthing occurs in shallow coastal nurseries, such as Bulls Bay in North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
. The pups measure 50–61 cm (19.7–24 in) long at birth; females reach maturity at 2.7 m (8.9 ft) long and males at 2.1–2.5 m (6.9–8.2 ft) long, depending upon locality. Off South Africa, newly mated females have been caught in February and females with full-term embryos in November; off the east coast of Australia, birthing takes place between January and March, with ovulation
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
taking place around the same time. This shark is thought to live for 20 years or more.
Human interactions
The smooth hammerhead is potentially dangerous to humans. As of 2008, the International Shark Attack FileInternational Shark Attack File
The International Shark Attack File is a global database of shark attacks. It began as an attempt to catalogue shark attacks on servicemen during World War II. The Office of Naval Research funded it from 1958 until 1968. During that time a panel of shark experts developed a standard system for...
lists 34 attacks attributable to large hammerhead sharks, 17 of them unprovoked (1 fatal). However, due to the smooth hammerhead's occurrence in temperate regions where people are less likely to enter the water, it was likely responsible for a minority of these attacks. Off southern California, this species has been reported to steal catches from sport fishers and divers.
Smooth hammerheads are caught by commercial fisheries throughout the world, including those off the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
(East and West Coasts), Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
, the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, southwestern Australia, and western Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, primarily using gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
s and longlines. Fishery catches of smooth hammerheads are difficult to quantify due to a frequent lack of distinction between them and other large hammerheads. The meat is sold fresh, dried and salted, or smoked, though in most markets it is considered undesirable and there are reports of poison
Poison
In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....
ing. Much more valuable are the fins, which have the highest rating for use in shark fin soup
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
and often leads to captured sharks being finned
Shark finning
Shark finning refers to the removal and retention of shark fins and the discarding of the rest of the fish. Shark finning takes place at sea so the fishers only have to transport the fins.Shark finning is widespread, and largely unmanaged and unmonitored...
at sea. Additionally, the liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
is used for vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
s, the skin for leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
, and the offal
Offal
Offal , also called, especially in the United States, variety meats or organ meats, refers to the internal organs and entrails of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but includes most internal organs other than...
for fishmeal. This shark is also used in Chinese medicine.
Many other fisheries from every ocean also take smooth hammerheads as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
, and they are caught in some numbers by recreational angler
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
s. Smooth hammerheads are also killed by entanglement in shark net
Shark net
A shark net is a submerged net placed around beaches to reduce shark attacks on swimmers.Shark nets do not offer complete protection but work on the principle of "fewer sharks, fewer attacks". They reduce occurrence via shark mortality. Reducing the local shark populations is believed to reduce the...
s used to protect beaches. Fewer than 10 smooth hammerheads were caught annually in the nets off KwaZulu-Natal
KwaZulu-Natal
KwaZulu-Natal is a province of South Africa. Prior to 1994, the territory now known as KwaZulu-Natal was made up of the province of Natal and the homeland of KwaZulu....
, South Africa, from 1978–1990. In contrast, in the nets off New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
, Australia, smooth hammerheads comprised 50% of the 4,715 sharks captured from 1972–1990. At present, this species remains relatively common and has been assessed as "Lower Risk/Near Threatened" by the World Conservation Union. Off New Zealand, it is a prohibited target species and is the most abundant shark along the northwest coast. It also does not appear to have been negatively impacted by fishing off southern Australia. Off the eastern United States, catches of this species are regulated by the National Marine Fisheries Service
National Marine Fisheries Service
The National Marine Fisheries Service is a United States federal agency. A division of the National Oceanic and Atmospheric Administration and the Department of Commerce, NMFS is responsible for the stewardship and management of the nation's living marine resources and their habitat within the...
(NMFS) Atlantic shark Fishery Management Plan (FMP), under which it is classified as a Large Coastal Shark (LCS).