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Lifespan, longevity, and ageing

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Maximum longevity: 35 years (wild)
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Distribution

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Scalloped hammerheads are pelagic sharks that are found worldwide in tropical warm water regions, including the Atlantic, Indian, and Pacific oceans, between 40°N to 36°S lattitude and 80°W to 80°E longitude.

Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )

Other Geographic Terms: cosmopolitan

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Associations

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While scalloped hammerheads are one of the largest reef fishes and a top predator, they are occasionally preyed on by larger tiger sharks (Galeocerdo cuvier), great white sharks (Carcharodon carcharias), and killer whales (Orcinus orca). Humans also harvest hammerheads for their fins, which are sold in the lucrative global shark fin trade.

Scalloped hammerheads form schools that consist mainly of females, with males rarely entering these aggregations. This behavior lowers an individual’s chance of being attacked by predators. Scalloped hammerheads also exhibit countershading as a form of camouflage in open water, with a grey to bronze colored dorsum and a pale white/grey underside.

Known Predators:

  • great white sharks (Carcharodon carcharias)
  • tiger sharks (Galeocerdo cuvier)
  • killer whales (Orcinus orca)
  • humans (Homo sapiens)

Anti-predator Adaptations: cryptic

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Morphology

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Scalloped hammerheads have a small but prominent notch in the center of their characteristically-shaped head, which also bears pronounced grooves along its anterior margin, giving this species its common name. The side “wings” of the head are relatively narrow and are swept backwards. The first dorsal fin is larger than the second and is sickle-shaped, with a rounded tip, while the second dorsal fin has a concave rear edge. Both the pectoral and dorsal fins are slightly rounded. The tips of the pectoral fins are either a dark grey or black. The caudal fin is heterocercal and forked. Body coloration in this species displays typical pelagic countershading, with a grey dorsum and a white ventral surface.

Range mass: 152.4 (high) kg.

Range length: 4.3 (high) m.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Life Expectancy

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The oldest known scalloped hammerhead was 31.5 years old, and was caught in the Atlantic Ocean, off the coast of Brazil. The authors of that study estimated the maximum lifespan of this species to be 55 years. In a separate study conducted off the coast of Sinoloa, Mexico, the oldest individual sampled was approximately 10.5 years old. There is no published information available for the expected lifespan of this species in captivity.

Range lifespan
Status: wild:
10.5 to 31.5 years.

Typical lifespan
Status: wild:
55 (high) years.

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Habitat

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Although they primarily inhabit open marine waters, scalloped hammerheads can also be found near continental and island shelves and often enter bays and estuaries as well.

Scalloped hammerheads utilize different habitats daily. At dawn, they move from their offshore hunting grounds to island shelves, seamounts, and enclosed bays and estuaries. During the day they migrate to drop-off zones and reefs where females form schools for the purpose of social interaction. At dusk the sharks return to offshore pelagic areas and actively search for food.

Range depth: 5 to 525 m.

Average depth: 268 m.

Habitat Regions: temperate ; tropical ; saltwater or marine

Aquatic Biomes: pelagic ; benthic ; reef ; coastal

Other Habitat Features: estuarine

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Trophic Strategy

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Younger individuals tend to feed in coastal waters, on benthic and neritic fish. Adults live in deeper oceanic waters, feeding on neritic and epipelagic fishes and cephalopods (squid, octopus and cuttlefishes), lobsters, shrimps, and crabs, as well as various smaller sharks and rays. Hammerheads located in the Indo-West Pacific have been observed to prey on sea snakes. Scalloped hammerheads actively forage for food during the night, using a “smash and grab” feeding technique. They accelerate towards prey and either swallow it whole, or disable prey by biting it. Great hammerheads (Sphyrna lewini) have been observed using their hammer-like head to pin stingrays to the ocean floor before consuming them, and it is thought that scalloped hammerheads may use the same technique.

Animal Foods: reptiles; fish; mollusks; aquatic crustaceans; other marine invertebrates

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods, Molluscivore )

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Associations

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Scalloped hammerheads are among the largest of reef sharks, making them top predators of the animals on which they prey.

Scalloped hammerheads have mutualistic symbioses with several species of cleaner fish, allowing wrasses and blennies to remove external parasites from their skin, gills, and mouths.

This species is a host to several types of ectoparasitic invertebrates. At least one leech and over half a dozen copepod species have also been found on the underside of scalloped hammerhead snouts. In addition, this species plays host to at least two different types of platyhelminth endoparasites.

Mutualist Species:

  • wrasses (Labridae)
  • blennies (Blenniidae)
  • gobies (Gobiidae)

Commensal/Parasitic Species:

  • Stilarobdella macrotheca (Subclass Hirudinea, Phylum Annelida)
  • Alebion carchariae (Subclass Copepoda, Subphylum Crustacea)
  • Alebion elegans (Subclass Copepoda, Subphylum Crustacea)
  • Eudactylina pollex (Subclass Copepoda, Subphylum Crustacea)
  • Nesippus crypturus (Subclass Copepoda, Subphylum Crustacea)
  • Nemesis robusta (Subclass Copepoda, Subphylum Crustacea)
  • Kroyeria scotterum (Subclass Copepoda, Subphylum Crustacea)
  • Pandarus floridanus (Subclass Copepoda, Subphylum Crustacea)
  • Otobothrium kurisi (Class Cestoda, Phylum Platyhelminthes)
  • Multicalyx cristata (Class Trematoda, Phylum Platyhelminthes)
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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Benefits

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Scalloped hammerheads serve as an important resource for traditional fisheries in Mexico. They are fished both commercially and recreationally, and highly valued for their fins. While their meat has a high concentration of urea and is not typically consumed, the skin is used for leather and oil is obtained from the liver. Their jaws and teeth are also sold as marine curios.

Positive Impacts: food ; body parts are source of valuable material; source of medicine or drug ; research and education

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Benefits

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Large hammerhead sharks are considered to pose a potential danger to humans. To date, however, there have been no confirmed attacks on humans by this species.

Negative Impacts: injures humans (bites or stings)

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Life Cycle

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Fertilized eggs develop into embryos that are nourished by a yolk-sac placenta attached to either of the female's two uteruses. Scalloped hammerheads give birth to live young that are miniature versions of their parents.

In the Gulf of California, female hammerheads were discovered at a depth of 50 m, whereas males of a similar size were caught at 25 m. It has been suggested that females may grow more rapidly and mature at a larger size than do males due to differences in food availability between these habitats.

Development - Life Cycle: indeterminate growth

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Conservation Status

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Scalloped hammerheads are listed as an endangered species by the IUCN Red List, since they are vulnerable to illegal fishing and bycatch during all stages of their lives, making them susceptible to extinction in the future. In 2007, surveys in the northwest Atlantic documented a 98 percent decline from historical estimates, while a 90 percent decline in population abundance was noted in the southwest Atlantic.

As of 2012, hammerheads made up approximately 6% of the identified fins entering the Hong Kong market, translating to an estimated 1.3 million to 2.7 million hammerheads being exploited annually for the global fin trade. This level of exploitation is unlikely to be sustainable and can have substantial negative impacts on marine ecosystems worldwide.

The International Commission for the Conservation of Atlantic Tunas (ICCAT) has banned the retention of hammerhead sharks caught while tuna fishing, but this measure does not address the impact of the lucrative shark fin trade. The U.S.A. passed the Shark Conservation Act of 2010 to prevent finning with US waters.

US Federal List: no special status

CITES: appendix ii

State of Michigan List: no special status

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Behavior

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Like all sharks, scalloped hammerheads use their eyes for visual perception, and nares for detection of chemical cues. Like other elasmobranchs, they have special sensory organs called Ampullae of Lorenzini; these special electroreceptors are located on the underside of the snout and "hammer", and aid in the detection of buried prey, as well as navigation (by sensing changes in the Earth's magnetic field). Pacific scalloped hammerheads are able to follow geological fault lines along the ocean floor. Recently cooled magma forms rocks that have a strong magnetic signal, which the animals follow to the locations where they form congregations to feed, school, and mate.

Sharks are able to visually display aggression, submission, and dominance to conspecifics. When provoked or threatened, an individual will point its pectoral fins downward and arch its back. Sharks indicate submission by rapidly shaking their head side to side. Dominant sharks exhibit a “corkscrewing”, or upward swimming pattern, and will ram submissive sharks with their snout.

Communication Channels: visual

Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical ; electric ; magnetic

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Reproduction

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Mating behavior in scalloped hammerheads is not fully understood, but it has been observed that during mating season, sexually mature males migrate to deeper waters in search of females. Since schools are formed primarily of females, male sharks will enter and swim in an S shape, signaling the desire to mate. Larger and more sexually mature females tend to be located in the center of the schools, pushing smaller females to the outside. When a male locates a receptive female, he bites her pectoral fin and secures himself. During mating, he curls his tail around her body to align their genitalia and inserts one of his claspers (modified anal fins) into her urogenital opening to deposit sperm. Because scalloped hammerheads are negatively buoyant, the mating pair sinks while copulation occurs.

Mating System: polygynandrous (promiscuous)

Reproductive maturity of female sharks can sometimes be determined through morphological measurements. Depending on the location of the shark (Northern or Southern hemisphere), some female sharks can begin reproduction anywhere from 15 to 17 years old, which corresponds to a total length of over 2 meters. Male sharks reach sexual maturity at 6 years old, and around 1.5 meters in length. In Northern Australia, the breeding season occurs from February to March, although this is likely to vary according to geographic region. After a gestation period of 9 to 10 months, litters of 12 to 38 young measuring 38 to 45 cm are born live. There is no published information regarding the birth mass of pups, which is due to the fact that pregnant females are rarely caught. Immediately after birth, pups must find their own food, but they usually live in large schools until adulthood.

Breeding interval: It is thought that scalloped hammerheads breed every other year.

Breeding season: The breeding season for northern Australian scalloped hammerheads occurs from February to March.

Range number of offspring: 12 to 41.

Range gestation period: 8 to 12 months.

Range age at sexual or reproductive maturity (female): 15 to 17 years.

Range age at sexual or reproductive maturity (male): 6 (low) years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous

As in other viviparous species, female scalloped hammerheads provide nutrition and protection to their internally developing young. As in other sharks, there is no parental care after birth.

Parental Investment: female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female)

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Ruiz, E. and S. Trujillo 2012. "Sphyrna lewini" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphyrna_lewini.html
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Erick Ruiz, San Diego Mesa College
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Sierra Trujillo, San Diego Mesa College
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Paul Detwiler, San Diego Mesa College
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Jeremy Wright, University of Michigan-Ann Arbor
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Biology

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Forming impressively large schools, female scalloped hammerheads gather in the Gulf of California during the day, around underwater mountains known as seamounts, where they perform a wide range of poorly-understood behaviours (2). These aggregations are thought to be a result of many sharks, particularly younger females, seeking refuge in a safe place near a rich food supply, although many alternative theories have been put forward (5). Young scalloped hammerheads also tend to live in large schools, whereas adults usually occur singly, in pairs, or in small groups (2). These sharks feed on fish, cephalopods, lobsters, shrimps, crabs, other sharks, and rays. They are thought to be potentially dangerous to humans although few attacks have been recorded (3). The teeth of the scalloped hammerhead are best suited to seizing prey that can be swallowed whole, rather than ripping into larger prey. The hammer-shaped head is thought to be a mechanism to spread out the ampullae of Lorenzini – sensory organs that detect electric currents, chemicals in the water, and temperature changes (5). Larger shark species may attack young scalloped hammerheads, but adults have no natural enemies. Adults visit cleaning stations where fish known as cleaner wrasse remove parasites from their skin and mouths (2). During the 9 to 10 month gestation, the eggs of the scalloped hammerhead hatch inside the body of the female. After hatching, but before birth, they are nourished by a yolk sac placenta. The female moves to shallow waters during the summer where she will give birth to between 15 and 31 live young (3).
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Conservation

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No direct conservation action is targeted at the scalloped hammerhead.
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Description

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This large hammerhead shark can be distinguished from other hammerhead species by the 'scalloped' front edge of its hammer-shaped head, having three evenly spaced indentations between the wide-set eyes. The body of the scalloped hammerhead is relatively slim and is coloured brown-grey to bronze above and white below. The first dorsal fin is large but the second is much smaller. Juvenile scalloped hammerheads have darker fins than the adults (2).
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Habitat

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Occurring mainly over continental and insular shelves and the deeper water around them, the scalloped hammerhead also regularly enters enclosed bays and estuaries. It swims at depths of between 0 and 275 metres, and is migratory in some areas, moving poleward in summer (1).
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Range

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The scalloped hammerhead is found in the warm temperate and tropical waters of the Atlantic, Indian and Pacific Oceans (1). It may also occur in the western Mediterranean Sea (2) (4).
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Status

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The scalloped hammerhead is classified as Lower Risk – near threatened (LR/nt) on the IUCN Red List (1).
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Threats

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The scalloped hammerhead is fished in low numbers commercially and as game-fish, and is also caught as by-catch in longline fisheries. Its liver is used for vitamins, its fins for soup, its meat for human consumption and its carcasses for fishmeal (1). Pups occupying shallow coastal nursery areas are particularly exposed to fishing pressures (2).
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Conservation Status

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There has not been any drastic action in conserving the Sphyrna Lewini although the adoption of shark finning bans by fishing states (e.g., USA, Australia), regional entities (EU) and regional fisheries organizations (e.g., ICCAT, IOTC, IATTC, WCPFC) is increasing and should further prevent the capture of oceanic sharks for their fins alone.

Benefits for Humans

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The scalloped hammerhead is fished in low numbers commercially and as game-fish, and is also caught as by-catch in longline fisheries. Its liver is used for vitamins, its fins for soup, its meat for human consumption and its carcasses for fishmeal. Pups occupying shallow coastal nursery areas are particularly exposed to fishing pressures.

Benefits

provided by FAO species catalogs
This is probably the commonest hammerhead in the tropics and is readily available in abundance to inshore artisanal and small commercial fisheries as well as offshore operations; it is caught with pelagic longlines, fixed bottom longlines, fixed bottom nets, and even bottom and pelagic trawls ; the young are easily caught on light longline gear. Only 2 t of catches in 1994 and 12 t in both 1995 and 1996 have been reported to FAO for this species, all by Guinea-Bissau in Eastern Central Atlantic (area 34). The total catch reported for this species to FAO for 1999 was 10 t. The countries with the largest catches were Guinea-Bissau (10 t). The meat is utilized fresh, fresh-frozen, dried salted and smoked for human consumption; the fins are used to prepare shark-fin soup base; the hides are prepared into leather; the oil used for vitamins; and carcasses for fishmeal. Impact of fisheries Scalloped hammerhead sharks are commonly taken in coastal fisheries around the world. Because this species is known to form very large aggregations, it is easy for fishermen to occasionally take extremely large catches in a single fishing event. Purse seiners have been reported to catch as much as 35 t of scalloped hammerhead sharks in a single set (Stretta et al. 1997). Pirate fishermen are known to take advantage of the gregarious nature of scalloped hammerheads and illegally fish large quantities of this species in the Galápagos Islands Marine Reserve (Lavenberg et al. 1994, Camhi 1994). There are virtually no catch statistics for this species throughout the world, but Chen et al. (1988) report that off NE Taiwan (Province of China) where this is the most commercially important shark, at least 500 t/y were fished in the mid 1980s. Logbook data from the Atlantic US longline fisheries (Cramer 1998) shows CPUE of hammerhead sharks (3 different species, of which scalloped hammerhead sharks are likely the major part) decreasing from about 2.7 sharks/1000 hooks in 1986 to 0.35 in 1997. Brown (1998) reports non-standardised CPUE for unclassified hammerheads in the sport fishery off Virginia-Massachusetts that show wide yearly variations with an overall downward trend between 1986-97. However, scalloped hammerhead sharks are poorly represented in this sport fishery, as they tend to have a more southerly distribution. Scalloped hammerheads are also under pressure from heavy fishing in their nursery areas because these commonly occur in shallow coastal waters where heavy fishing takes place. Large quantities of newborns and juveniles of this species are taken by fisheries in nursery areas in the Gulf of México (Bonfil 1997), Mauritania (Ducroq 1998), and probably elsewhere throughout their range. Conservation Status : Smith et al. (1998) found that scalloped hammerheads have one of the lowest intrinsic rebound potentials among 26 shark species they analysed. This means that fisheries for scalloped hammerheads should be conducted under very tight management and monitoring to avoid stock collapses. The worldwide distribution and known high abundance of this shark offers a relative protection against the threat of extinction, however the occurrence of local depletion is a very real threat. Mooney-Seus and Stone (1996) consider scalloped hammerhead sharks as Reduced in US Atlantic waters and Data Deficient elsewhere. Additional information from IUCN database Additional information from CITESdatabase
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 2 - Carcharhiniformes.Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 2
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Diagnostic Description

provided by FAO species catalogs
fieldmarks: A large hammerhead with a broad, narrow-bladed head, anterior margin of head very broadly arched in adults and with a prominent median indentation, teeth with moderately broad cusps and smooth to weakly serrated edges, moderately falcate first dorsal fin with origin over or behind pectoral insertions and free rear tip in front of pelvic origins, low second dorsal fin with weakly concave posterior margin, long posterior margin about twice fin height, and free rear tip nearly or quite reaching upper caudal origin, non-falcate pelvic fins, a deeply notched posterior anal margin, and dusky or black-tipped pectoral fins. Expanded prebranchial head hammer- or axe-shaped and very wide but longitudinally narrow, its width 24 to 30% of total length (mostly above 26%), distance from tip of snout to rear insertions of posterior margins of expanded blades less than half width of head; anterior margin of head very broadly arched, with prominent medial and lateral indentations; posterior margins of head long, angled posterolaterally, and generally broader than mouth width. Well-developed prenarial grooves present anteromedial to nostrils. Preoral snout about 1/5 to 1/3 of head width. Rear of eyes slightly anterior to upper symphysis of mouth. Mouth rather broadly arched. Anterior teeth with moderately long stout to slender cusps, smooth or weakly serrated, posterior teeth mostly cuspidate and not keeled and molariform. Pelvic fins not falcate, with straight or slightly concave posterior margins. First dorsal moderately falcate, origin above or slightly behind pectoral insertions, free rear tip well anterior to pelvic origins. Second dorsal fin low, less than anal height, with a shallowly concave posterior margin; inner margin long, about twice fin height, and ending almost opposite upper caudal origin. Anal fin larger than second dorsal fin and rather long, base 4.3 to 6.4% of total length, origin well ahead of second dorsal origin, posterior margin shallowly concave to nearly straight. Total vertebral centra 174 to 209. A large hammerhead, to over 3 m. Colour gray-brown above, white below, with dusky to black pectoral fin tips.

References

  • Clarke, (1971)
  • Compagno, (l979, 1982)
  • Gilbert, (1967a,b)
  • Klimley, (1981)
  • Klimley & Nelson, (1981)
  • Nelson, (1981)
  • Sadowsky, (1965, 1967)
  • Taniuchi, (1974)

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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 2 - Carcharhiniformes.Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 2
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Size

provided by FAO species catalogs
Maximum total length about 370 to 420 cm, males maturing at 140 to 165 cm and reaching at least 295 cm, females maturing at about 212 cm and reaching at least 309 cm; size at birth 42 to 55 cm.
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 2 - Carcharhiniformes.Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 2
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Brief Summary

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Probably the most abundant hammerhead, a coastal-pelagic,semioceanic warm-temperate and tropicalspecies occurring over continental and insular shelves and in deep water adjacent to them, often approaching close inshore and entering enclosed bays and estuaries. Ranges from the intertidal and surface down to at least 275 m depth. Young sharks primarily occur close inshore.Forms large true polarized schools at different stages of its life-history, though solitary individuals of both young and adults also occur. This species is apparently highly mobile and in part migratory, and forms huge schools of small migrating individuals that move polewards in the summer in certain areas such as off Natal, South Africa. Elsewhere, as in the East China Sea, it may not migrate and is thought to form large resident populations. Adult males and females may segregate during certain phases of their life-cycle. Off southern Baja California, in the Gulf of California, polarized schools of scalloped hammerheads of mixed sexes with females predominating and sizes from immatures of slightly less than a meter to adults over 3 m have been intensely observed underwater by A. Peter Klimley and Donald R. Nelson. These congregate offshore over seamounts and near islands, and show a considerable range of behaviours including lateral tilting of the body (possibly to enhance the shark's view of divers when approached from above and behind them); accelerated swimming variants with headshaking, thrusting the midsection while swimming rightside up or upside down, and corkscrew swimming with rotation around their longitudinal axes; hitting other hammerheads with their snouts; jaw opening; and clasper flexion. Some of these displays may involve aggression or courtship. Many females bear apparent courtship scars, but a smaller proportion of males have them too. The function of these schools is uncertain: reproduction is thought unlikely because of the presence of juveniles in the schools; defence unlikely because of the absence of possible predators on the hammerheads; and grouping for attaining a swimming advantage in the strong currents that are common in these places unlikely because the sharks school when currents are absent. Feeding advantages may occur for the sharks to cluster near food resources or even for social feeding, but so far this is hypothetical because the sharks have never been seen to feed in the daytime when observations can be made though they may do so at night. Sharks have been tracked and may wander off from the schooling area. Viviparous, with a yolk-sac placenta; number of young in a litter 15 to 31. Off Hawaii adults move inshore in Kaneohne Bay, Oahu to drop young and mate. The smallest young are found close inshore in the bay but these move into deeper water as they grow, to eventually depart for open water. The scalloped hammerhead takes a wide variety of fish prey, but also invertebrates (especially cephalopods ). Food items include sardines and herring, anchovies, ten-pounders (Elopidae), conger eels, milkfish, sea catfish, silversides, halfbeaks, mullet, lizardfish, barracuda, bluefish, spanish mackerel, jacks, porgies, mojarras, cardinal fishes, goatfish, grunts, damselfishes, parrotfishes, wrasses, butterfly fishes, surgeonfish, gobies, flatfish, sharpnose sharks (Rhizoprionodon ), blacktip reef sharks, angel sharks, stingrays, squid, octopus, cuttlefishes, sea snails, shrimp, mantis shrimp, crabs, lobsters and isopods .
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 2 - Carcharhiniformes.Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 2
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Trophic Strategy

provided by Fishbase
It occurs in all tropical and warm-temperate seas. They sometimes congregate over sea mounts or around offshore islands (Ref. 54301). A coastal-pelagic, semi-oceanic shark occurring over continental and insular shelves and adjacent deep water, often approaching close inshore and entering enclosed bays and estuaries (Ref. 244, 11230, 58302). Found in inshore and offshore waters to about 275 m depth (Ref. 26938, 11230, 58302); has been filmed at a baited camera in 512 m depth (Lis Maclaren, pers. Comm. 2005). Huge schools of small migrating individuals move pole ward in the summer in certain areas (Ref. 244). Permanent resident populations also exist (Ref. 244). Feeds mainly on teleost fishes, cephalopods and zooplankton (Ref. 568, 6871); also lobsters, shrimps, crabs (Ref. 30573), including other sharks and rays (Ref. 37816).
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Recorder
Susan M. Luna
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Diseases and Parasites

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Loimosina Infestation. Parasitic infestations (protozoa, worms, etc.)
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Allan Palacio
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Morphology

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Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0
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Cristina V. Garilao
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Migration

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Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.
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Kent E. Carpenter
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Life Cycle

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Viviparous, placental (Ref. 50449), with 13-23 in a litter (Ref. 6871); 12-41 pups after a gestation period of 9-10 months (Ref.58048). Size at birth 45-50 cm TL (Ref. 13562); 39-57 cm TL (Ref.58048).
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Armi G. Torres
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Diagnostic Description

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This hammerhead shark is distinguished by having the following characters: large, moderately slender body; broad, narrow bladed head, arched anterior margin with prominent median indentation and lateral indentation; nostrils with strong prenarial grooves; hind margins of eyes slightly posterior to or nearly opposite front of mouth; teeth triangular, deeply notched posteriorly, with smooth or finely serrated edges; first dorsal fin moderately high, second dorsal and pectoral fins low; upper precaudal pit transverse crescentric. Colour of body light grey or greyish brown above, shading to white below, pectoral fin tips dusky and a dark blotch on lower caudal fin lobe (Ref. 13562, 114967).
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Biology

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A coastal-pelagic, semi-oceanic shark occurring over continental and insular shelves and adjacent deep water, often approaching close inshore and entering enclosed bays and estuaries (Ref. 244, 11230, 58302). Found in inshore and offshore waters to about 275 m depth (Ref. 26938, 11230, 58302); has been filmed at a baited camera in 512 m depth (Lis Maclaren, pers. comm. 2005). Huge schools of small migrating individuals move pole ward in the summer in certain areas (Ref. 244). Permanent resident populations also exist (Ref. 244). Juveniles occur in coastal areas (Ref. 58784). Adults solitary, in pairs, or schools; young in large schools (Ref. 13562). Feed mainly on teleost fishes and cephalopods (Ref. 6871), also lobsters, shrimps, crabs (Ref. 30573), including other sharks and rays (Ref. 37816). Viviparous (Ref. 50449). Mature females produce 15-31, of 43-55 cm young in a litter (Ref. 26938, 1602). Considered potentially dangerous to people but often not aggressive when approached by divers (Ref. 13562). Readily available to inshore artisanal and small commercial fisheries as well as to offshore operations (Ref. 13562). Sold fresh, dried-salted, smoked and frozen; also sought for its fins and hides (Ref. 9987). Oil used for vitamins and carcasses for fishmeal (Ref. 13562).
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Importance

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fisheries: commercial; gamefish: yes
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分布

provided by The Fish Database of Taiwan
廣泛分布於世界溫、熱帶水域。臺灣沿岸海域可發現其蹤跡。
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利用

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主要以底拖網、流刺網及延繩釣捕獲,經濟價值高。肉質佳,魚肉紅燒或加工成各種肉製品;鰭可做魚翅;皮厚可加工成皮革;肝可加工製成維他命及油;剩餘物製成魚粉。
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描述

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體延長,側扁而粗壯。頭前部平扁,兩側特別擴展,形成很寬的鎚狀突出,狀似廣闊之丫髻狀。吻部短而寬,前緣呈波浪狀,中央區顯然凹入。眼小,圓形,瞬膜發達。前鼻溝發育完全,位於鼻孔前方內側。口裂大,弧形;上下頜齒同型,側扁三角形,齒頭傾斜,邊緣平滑,不具小齒尖。噴水孔缺如。第一背鰭高大而直立,鐮刀形,起點在胸鰭基部中部上方;第二背鰭小而低,起點於臀鰭起點後方;腹鰭後緣平直或稍凹入;臀鰭略大於第二背鰭;胸鰭中大,後緣略凹入;尾鰭寬長,尾椎軸上揚,下葉前部顯著大三角形突出,中部低平延長,與後部間有一深缺刻,後部小三角形突出,尾端尖突。體背棕色,腹部白色。胸鰭、尾鰭下葉前部、尾鰭上部尖端具黑斑;背鰭上部具黑緣。
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棲地

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棲息於沿岸至外洋性之中表層魚類,亦常出現於大陸棚或島棚較深的水域,偶也見於內灣或河口區。幼時常成一大群活動,成魚則獨游或成對巡行。胎生,每胎15-31尾幼鯊。肉食性,以其他軟、硬骨魚類及頭足類、甲殼類等底棲生物為食。具攻擊性,對人類具有潛在性危險。胎生,一胎可產下15-31尾幼鯊,剛出生之幼鯊體長可達42-55公分。
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Scalloped hammerhead

provided by wikipedia EN

The scalloped hammerhead (Sphyrna lewini) is a species of hammerhead shark in the family Sphyrnidae. It was originally known as Zygaena lewini. The Greek word sphyrna translates into "hammer" in English, referring to the shape of this shark's head, which is its most distinguishing characteristic. The shark's eyes and nostrils are at the tips of the extensions. It is a fairly large hammerhead, but is still smaller than both the great and smooth hammerheads.

This shark is also known as the bronze, kinky-headed, or southern hammerhead. It primarily lives in warm, temperate, and tropical coastal waters all around the globe between latitudes 46°N and 36°S, down to a depth of 500 m (1,600 ft). It is the most common of all hammerheads.

Taxonomy

The scalloped hammerhead was first named Zygaena lewini and then renamed Sphyrna lewini by Edward Griffith and Hamilton Smith in 1834. It has also been named Cestracion leeuwenii by Day in 1865, Zygaena erythraea by Klunzinger in 1871, Cestracion oceanica by Garman in 1913, and Sphyrna diplana by Springer in 1941. Sphyrna comes from the Greek and translates to hammer.[3]

It is a sister species to Sphyrna gilberti, differing by the number of vertebrae.[4] Though once considered a distinct species, McEachran and Serret synonymized Sphyrna couardi with Sphyrna lewini in 1986.[5] These sharks are classified as ground sharks in the order Carcharhiniformes.[6]

Description

The scalloped hammerhead is easily distinguished from other hammerhead sharks by the central indentation on the anterior margin of the head.[6] There are also two indentations on either side of the central indentation, which gives the "scalloped" look.[6] They have a very large first dorsal fin that is slightly hooked and a smaller second dorsal fin.[6] Scalloped hammerhead sharks are typically uniform grey, grayish brown, bronze, or olive with a white underside for countershading.[6]

Typically, males measure 1.5 to 1.8 m (4.9 to 5.9 ft) and weigh about 29 kg (64 lb) when they attain sexual maturity, whereas the larger females measure 2.5 m (8.2 ft) and weigh about 36.2 kg (80 lb) at sexual maturity.[7] The maximum length of the scalloped hammerhead is 4.3 m (14 ft) and the maximum weight is 152.4 kg (336 lb), per FishBase.[8] A female caught off of Miami was found to have measured 3.26 m (10.7 ft) and reportedly weighed 200 kg (440 lb), though was in a gravid state then.[9]

These sharks have a very high metabolic rate, which governs behavior in acquiring food. They occupy tertiary trophic levels.[10] The scalloped hammerhead shark, like many other species, uses the shore as a breeding ground.[10] Due to high metabolic rates, young scalloped hammerhead sharks need a lot of food, or they will starve.

S. lewini is also noted for its large and complex brain, with high levels of cognitive capabilities, social intelligence, sensorimotor functions, intricate migrations, complex habitat relationships, and athletic capture of prey. Their social intelligence is especially important for their aggregative behavior, allowing the species to reproduce with the fittest members and proliferate the species easier.[11]

The dentition of these sharks consists of small, narrow, triangular teeth that have smooth edges, except in larger fish, which may have somewhat serrated teeth.[6] The teeth in the front of the mouth have erect cusps, and the teeth in the bottom jaw have cusps that are more erect than those of the upper jaw.[6]

Distribution and habitat

Scalloped hammerhead swimming (video)

The scalloped hammerhead is a coastal pelagic species; it occurs over continental and insular shelves and in nearby deeper water. It is found in warm temperate and tropical waters,[12] worldwide from 46°N to 36°S. It can be found down to depths over 500 m (1,600 ft), but is most often found above 25 m (82 ft).[13] During the day, they are more often found close to shore, and at night, they hunt further offshore. Adults are found alone, in pairs, or in small schools, while young sharks occur in larger schools.[3]

Juveniles and pups thrive in shallow coastal waters, such as bays and mangroves, which provide shelter from predators and waters high in nutrients from deposited sediments. Research carried out by the nongovernmental organization Misión Tiburón, using conventional and acoustic shark tagging methods, found that adult scalloped hammerheads migrate from the pelagic waters surrounding Cocos Island to the mangroves in the tropical fjord of Golfo Dulce - a tropical fjord on the Pacific Coast of Costa Rica.[14] Here, female sharks give birth to live young; juveniles remain in the shallow root system of the mangroves for around three years. After this time they leave Golfo Dulce and migrate back to Cocos Island, to feed in pelagic waters.

Behavior

Schooling

School of scalloped hammerheads

These sharks are often seen during the night, day, and morning in big schools, sometimes numbering hundreds, most likely because large groups can obtain food easier than singles or small groups, especially larger and trickier prey, as commonly seen. The younger the sharks, the closer to the surface they tend to be, while the adults are found much deeper in the ocean. They are not considered dangerous and are normally not aggressive towards humans.

Sexual dimorphism

The female scalloped hammerheads migrate offshore at a smaller size than males[15] because the larger classes of the hammerhead, such as those from 100 to 140 centimetres (39 to 55 in) long, travel deeper down.[15] Males and females differ in that males are observed to stay deeper than female sharks in general.

Sexual maturity generally occurs once the scalloped hammerhead attains 240 centimetres (7.9 ft) in total or longer. Physically, the mature females have considerably wider uteri than their maturing counterparts. A lack of mating scars has been found on mature females.[16] Unlike females, males reach sexual maturity at a much smaller size.

The male-to-female ratio of the scalloped hammerhead is 1:1.29.[16] Females probably are capable of giving birth annually,[16] usually in the summer.

Navigating behavior

Scalloped hammerhead sharks have a homing behavior to navigate in the ocean.[17] They move in the night and use the environment as a map, similar to a human reading a topographical map.[17] By experimentation in tagging these sharks, one could test for any guidance in a shark's movement.[17] These sharks use a point-to-point type of school swimming, and do not favor going too deep, where temperature changes hitchhike with current speed and directional change.

Scalloped hammerhead cocos.jpg

The scalloped hammerhead uses deep water to survive as safety and feeding.[18] Although they have high metabolic rates, they have a tendency to be sedentary and allow currents to carry them as they swim. As a result, this causes scalloped hammerheads to be selective where they swim and the depth at which they tend to stay. They also make use of earth's magnetic field.[19]

Predation

The scalloped hammerhead has several advantages to capture its prey. The shape of its head allows it to bury into the seafloor and pin stingrays down. The wide head and special sensory cells allow the scalloped hammerhead to successfully detect fish.[20]

Reproduction

The gestation period is reported to be around 12 months.[21] Scalloped hammerheads give live birth. Compared to other species, the scalloped hammerhead produces large litters (12–41 pups),[21] and this is most likely due to high infant mortality. Like most sharks, parental care is not seen.[22] Nursery grounds for this species are predictable and repeated over the years, and they are faithful to their natal sites.[22] Their natal sites still cause high infant mortality; a lack of resources prevents all the young from surviving. As a result, only the fittest grow to maturity. Also, should a population get depleted, it recovers through reproduction and not immigration.[22] This species does not seem to attack each other even in periods of starvation. In addition, scalloped hammerheads have migratory behaviors. As a result, deprivation results from migration and young growth. While the Taiwan scalloped hammerhead seems to have an earlier maturity rate, it is still reported to be slow to mature.[23]

Diet

Scalloped hammerheads are generalists and opportunistic predators, eating whatever is available and abundant in their area. There is no difference in what male and female sharks eat, but larger sharks are noted to eat larger prey than smaller, juvenile hammerheads. Juveniles typically feed on inshore fish, while adults feed on inshore fish as well as larger organisms that live in deeper waters.[24]

Specifically, this shark feeds primarily on fish such as sardines, mackerel, and herring, and occasionally they feed on cephalopods such as squid and octopus. Larger specimens may also feed on smaller species of shark such as the blacktip reef shark, Carcharhinus melanopterus.

Conservation

The scalloped hammerhead was the first shark species to be protected under the U.S. Endangered Species Act.[25] As of 2021, the scalloped hammerhead has been categorized as Critically Endangered by the IUCN Red List.[26] The IUCN cites overfishing as the main cause for the drop in population numbers.[26] These sharks are slow growing, mature late, and low fecundity, which makes them very vulnerable to fishing.[27] Scalloped hammerheads are over harvested for their large sizes and fins that have 'high fin needle content;' their fins are sold for US $100–120 per kilogram.[28] Many conservation efforts have been taken to protect this species, such as using genetic information from fins purchased from a Hong Kong market to pinpoint where scalloped hammerheads are being caught and track their exploitation levels.[28] Another important effort has been protecting Sphyrna lewini nurseries. Scalloped hammerheads return to their birthplace to have their own pups; the pups will then spend their first years of life in these coastal nursery areas where they are safe from predators and have less competition for feeding before they venture into the open ocean.[29] Fishing bans have been placed on some of these areas, such as in the Western Yucatan Peninsula, during breeding seasons to protect the young and juvenile scalloped hammerheads.[30]

In many areas, officials have implemented management regulations on fishing vessels. They have made a regulation that prohibits taking the sharks onboard to transship, sell, or store for future selling. [27] This not only protects the scalloped hammerhead shark, but also the entire order of Carcharhiniformes. Hammerhead sharks are not only being intentionally caught, but also being caught non-intentionally on longlines and nets. Bycatch has also greatly reduced these species because they often migrate in large groups. [27] This allows the fisheries to catch many sharks at once. The mortality rate of the sharks that are caught is almost always 90% of the individuals. [25] Even though it is hard to prevent these sharks from biting the bait or getting in the net, there has been devices put in place for bycatch reduction. Along the Eastern Atlantic, regulations have been implemented to control the over exploitation of the scalloped hammerhead.[6] The team in this area has concluded this species is at high risk of extinction now and for the future.[6] It is essential to understand the movement patterns of these sharks to be able to place effective conservation and management efforts. [25]

Marine reserves have been implemented in many areas to allow the sharks to recover. It is very important to place these reserves over areas that sharks use as breeding grounds and nurseries, so they have somewhere to raise their pups. It is also beneficial to place the marine reserves in areas where they are prized as a non consumptive resource through shark diving tourism. [31]

In parts of the Atlantic Ocean, their populations had declined by over 95% in the past 30 years. Among the reasons for this drop are overfishing and the rise in demand for shark fins. Researchers attribute this growth in demand to the increase in shark fins as an expensive delicacy (such as in shark fin soup) and in 2008 called for a ban on shark finning, a practice in which the shark's fins are cut off and the rest of the animal is thrown back in the water to die. Hammerheads are among the most commonly caught sharks for finning.[32] "This species tendency to aggregate in large groups making capture in large numbers on long lines, bottom nets and trawls even easier."[33]

Hammerhead sharks are overfished all around the world for their fins and liver oil. As of 2020 an estimated 1.3 to 2.7 million fins are collected each year from smooth and scalloped hammerhead sharks for the shark-fin trade.[34] DNA barcoding can assist in the identification of scalloped hammerhead remains to aid conservation efforts.[35]

According to a January 2021 study in Nature which studied 31 species of sharks and rays, the number of these species found in open oceans had dropped by 71 per cent in around 50 years. The scalloped hammerhead was included in the study.[36][37]

See also

References

  1. ^ Rigby, C.L.; Dulvy, N.K.; Barreto, R.; Carlson, J.; Fernando, D.; Fordham, S.; Francis, M.P.; Herman, K.; Jabado, R.W.; Liu, K.M.; Marshall, A.; Pacoureau, N.; Romanov, E.; Sherley, R.B.; Winker, H. (2019). "Sphyrna lewini". IUCN Red List of Threatened Species. 2019: e.T39385A2918526. Retrieved 20 May 2023.
  2. ^ "Appendices | CITES". cites.org. Retrieved 2022-01-14.
  3. ^ a b Bester, Cathleen. "Greek Translation". Florida Museum of Natural History.
  4. ^ Quattro, J. M.; Driggers, W. B. I. I.; Grady, J. M.; Ulrich, G. F.; Roberts, M. A. (2013). "Sphyrna gilberti sp. Nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the western Atlantic Ocean". Zootaxa. 3702 (2): 159–78. doi:10.11646/zootaxa.3702.2.5. PMID 26146715.
  5. ^ Martin, R. Aidan. (February 24, 1998). Recent Changes in Hammerhead Taxonomy. ReefQuest Centre for Shark Research. Retrieved on October 18, 2008.
  6. ^ a b c d e f g h i Miller, Margaret H.; Carlson, John; Cooper, Peter; Kobayashi, Donald; Nammack, Marta; Wilson, Jackie (March 2013). Status Review Report: Scalloped Hammerhead Shark (Sphyrna lewini) (PDF) (Report). National Marine Fisheries Service, Office of Protected Resources. Retrieved 20 May 2023.
  7. ^ https://marinesanctuary.org/blog/scalloped-hammerhead-shark/#:~:text=Male%20scalloped%20hammerhead%20sharks%20can,to%2014%20feet%20in%20length.
  8. ^ Sphyrna lewini, Scalloped hammerhead : fisheries, gamefish. Fishbase.org (2012-07-03). Retrieved on 2013-05-23.
  9. ^ Castro, José I. (2011) The Sharks of North America. Oxford University Press. ISBN 978-0-19-539294-4
  10. ^ a b Duncan, Kanesa May (1 August 2006). "Estimation of daily energetic requirements in young scalloped hammerhead sharks, Sphyrna lewini". Environmental Biology of Fishes. 76 (2–4): 139–149. doi:10.1007/s10641-006-9016-5. S2CID 10155904.
  11. ^ Gallagher, Austin J.; Hammerschlag, Neil; Shiffman, David S.; Giery, Sean T. (2014-05-27). "Evolved for Extinction: The Cost and Conservation Implications of Specialization in Hammerhead Sharks". BioScience. 64 (7): 619–624. doi:10.1093/biosci/biu071. ISSN 0006-3568.
  12. ^ "Scalloped Hammerhead Sharks- Facts and Conservation". National Marine Sanctuary Foundation. Retrieved 21 March 2023.
  13. ^ Froese, Ranier; Pauly, Daniel (eds.). Sphyrna lewini. FishBase. Retrieved 10 December 2008.
  14. ^ "Hammerhead Shark – Mision Tiburon". misiontiburon.org. Archived from the original on 2016-07-03.
  15. ^ a b Klimley, A. Pete (1 January 1987). "The determinants of sexual segregation in the scalloped hammerhead shark, Sphyrna lewini". Environmental Biology of Fishes. 18: 27–40. doi:10.1007/BF00002325. S2CID 29448517.
  16. ^ a b c Hazin, Fabio; Fischer, Alessandra; Broadhurst, Matt (1 June 2001). "Aspects of Reproductive Biology of the Scalloped Hammerhead Shark, Sphyrna lewini, off Northeastern Brazil". Environmental Biology of Fishes. 61 (2): 151–159. doi:10.1023/A:1011040716421. S2CID 44367667.
  17. ^ a b c Klimley, A. P. (1993). "Highly directional swimming by scalloped hammerhead sharks, Sphyrna lewini, and subsurface irradiance, temperature, bathymetry, and geomagnetic field". Marine Biology. 117: 1–22. doi:10.1007/BF00346421. S2CID 86223091.
  18. ^ Jorgensen, S. J.; Klimley, A. P.; Muhlia-Melo, A. F. (2009). "Scalloped hammerhead shark Sphyrna lewini, uses deep-water, hypoxic zone in the Gulf of California". Journal of Fish Biology. 74 (7): 1682–1687. doi:10.1111/j.1095-8649.2009.02230.x. PMID 20735666.
  19. ^ "Fact Sheet: Scalloped Hammerhead Shark". www.sharkinfo.ch. Retrieved 30 March 2020.
  20. ^ "Smooth Hammerhead Shark". Oceana. Retrieved 18 February 2020.
  21. ^ a b Branstetter, Steven (1 July 1987). "Age, growth and reproductive biology of the silky shark, Carcharhinus falciformis, and the scalloped hammerhead, Sphyrna lewini, from the northwestern Gulf of Mexico". Environmental Biology of Fishes. 19 (3): 161–173. doi:10.1007/BF00005346. S2CID 41048341.
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Scalloped hammerhead: Brief Summary

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The scalloped hammerhead (Sphyrna lewini) is a species of hammerhead shark in the family Sphyrnidae. It was originally known as Zygaena lewini. The Greek word sphyrna translates into "hammer" in English, referring to the shape of this shark's head, which is its most distinguishing characteristic. The shark's eyes and nostrils are at the tips of the extensions. It is a fairly large hammerhead, but is still smaller than both the great and smooth hammerheads.

This shark is also known as the bronze, kinky-headed, or southern hammerhead. It primarily lives in warm, temperate, and tropical coastal waters all around the globe between latitudes 46°N and 36°S, down to a depth of 500 m (1,600 ft). It is the most common of all hammerheads.

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Description

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A coastal-pelagic, semi-oceanic shark occurring over the continental and insular shelves. Young form schools and forage near the bottom, migrating to deeper outer reef waters as they grow. Adults solitary or in pairs. Feeds on fishes, including other sharks and rays (Ref. 1602), cephalopods, and crustaceans; also on turtles (Ref. 2334). Non-aggressive unless stimulated by fish blood. Utilized: fresh, dried-salted, smoked and frozen; also sought for fins and hides (Ref. 9987). Game fish record weighed almost 450 kg (Ref. 9987).

Reference

Froese, R. & D. Pauly (Editors). (2023). FishBase. World Wide Web electronic publication. version (02/2023).

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Distribution

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New Jersey to Florida and the Gulf of Mexico

Reference

North-West Atlantic Ocean species (NWARMS)

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Habitat

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nektonic

Reference

North-West Atlantic Ocean species (NWARMS)

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Kennedy, Mary [email]