Scalloped hammerhead

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Scalloped hammerhead
Scalloped Hammerhead Shark Sphyrna Lewini (226845659).jpeg
Off Cocos Island, Costa Rica
Sphyrna lewini Gervais.jpg
CITES Appendix II (CITES) [2]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Subdivision: Selachimorpha
Order: Carcharhiniformes
Family: Sphyrnidae
Genus: Sphyrna
Species:
S. lewini
Binomial name
Sphyrna lewini
Sphyrna lewini distribution map.svg
Range of the scalloped hammerhead
Synonyms

Sphyrna couardiCadenat, 1951

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.

Contents

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 more easily proliferate the species. [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 Sphyrna lewini school.jpg
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 more easily 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.[ citation needed ]

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

Related Research Articles

<span class="mw-page-title-main">Hammerhead shark</span> Family of sharks

The hammerhead sharks are a group of sharks that form the family Sphyrnidae, named for the unusual and distinctive form of their heads, which are flattened and laterally extended into a cephalofoil. The shark's eyes are placed one on either end of this T-shaped structure, with their small mouths directly centered and underneath. Most hammerhead species are placed in the genus Sphyrna, while the winghead shark is placed in its own genus, Eusphyra. Many different— but not necessarily mutually exclusive—functions have been postulated for the cephalofoil, including sensory reception, manoeuvering, and prey manipulation. The cephalofoil gives the shark superior binocular vision and depth perception.

<span class="mw-page-title-main">Silky shark</span> Species of fish

The silky shark, also known by numerous names such as blackspot shark, gray whaler shark, olive shark, ridgeback shark, sickle shark, sickle-shaped shark and sickle silk shark, is a species of requiem shark, in the family Carcharhinidae, named for the smooth texture of its skin. It is one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge of the continental shelf down to 50 m (164 ft). The silky shark has a slender, streamlined body and typically grows to a length of 2.5 m. It can be distinguished from other large requiem sharks by its relatively small first dorsal fin with a curving rear margin, its tiny second dorsal fin with a long free rear tip, and its long, sickle-shaped pectoral fins. It is a deep, metallic bronze-gray above and white below.

<i>Sphyrna</i> Genus of sharks

Sphyrna is a genus of hammerhead sharks with a cosmopolitan distribution in the world's oceans. Members of Sphyrna have a tendency to inhabit coastal waters along the intertidal zone rather than the open ocean, as their prey such as invertebrates, fish, rays, small crustaceans, and other benthic organisms hide in the sands and sediment along these zones. Members of Sphyrna are also known by synonyms such as Zygaena, Cestracion, and Sphyrichthys. The earliest species described of this genus was Sphyrna zygaena by Carl Linnaeus in 1758, while the latest described member, Sphyrna gilberti, was discovered and described in 2013.

<span class="mw-page-title-main">Dusky smooth-hound</span> Species of shark

The dusky smooth-hound, also called the smooth dogfish or the dog shark, is a species of houndshark in the family Triakidae. This shark is an olive grey or brown in color, and may have shades of yellow or grayish white. Females live to 16 years and males have a lifespan of 10 years. M. canis was the first shark recognised to have viral infections.

<span class="mw-page-title-main">Lemon shark</span> Species of shark

The lemon shark is a species of shark from the family Carcharhinidae and is classified as a Vulnerable species by the International Union for the Conservation of Nature. Lemon sharks can grow to 3.4 metres (11 ft) in length. They are often found in shallow subtropical waters and are known to inhabit and return to specific nursery sites for breeding. Often feeding at night, these sharks use electroreceptors to find their main source of prey, fish. Lemon sharks enjoy the many benefits of group living such as enhanced communication, courtship, predatory behavior, and protection. This species of shark gives birth to live young, and the females are polyandrous and have a biennial reproductive cycle. Lemon sharks are not thought to be a large threat to humans; there have been 10 recorded bites, none of which were life-threatening. The lemon shark's life span is unknown, but the average shark is 25 to 30 years old.

<span class="mw-page-title-main">Great hammerhead</span> Species of shark

The great hammerhead is the largest species of hammerhead shark, belonging to the family Sphyrnidae, attaining an average length of 4.6 m (15 ft) and reaching a maximum length of 6.2 m (20 ft). It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf. The great hammerhead can be distinguished from other hammerheads by the shape of its "hammer", which is wide with an almost straight front margin, and by its tall, sickle-shaped first dorsal fin. A solitary, strong-swimming apex predator, the great hammerhead feeds on a wide variety of prey ranging from crustaceans and cephalopods, to bony fish, to smaller sharks. Observations of this species in the wild suggest that the cephalofoil functions to immobilize stingrays, a favored prey. This species has a viviparous mode of reproduction, bearing litters of up to 50 pups every two years.

<span class="mw-page-title-main">Winghead shark</span> Species of shark

The winghead shark is a species of hammerhead shark, and part of the family Sphyrnidae. Reaching a length of 1.9 m (6.2 ft), this small brown to gray shark has a slender body with a tall, sickle-shaped first dorsal fin. Its name comes from its exceptionally large "hammer", or cephalofoil, which can be as wide as half of the shark's total length. The function of this structure is unclear, but may relate to the shark's senses. The wide spacing of its eyes grants superb binocular vision, while the extremely long nostrils on the leading margin of the cephalofoil may allow for better detection and tracking of odor trails in the water. The cephalofoil also provides a large surface area for its ampullae of Lorenzini and lateral line, with potential benefits for electroreception and mechanoreception, respectively.

<span class="mw-page-title-main">School shark</span> Species of shark

The school shark is a houndshark of the family Triakidae, and the only member of the genus Galeorhinus. Common names also include tope, tope shark, snapper shark, and soupfin shark. It is found worldwide in temperate seas at depths down to about 800 m (2,600 ft). It can grow to nearly 2 m long. It feeds both in midwater and near the seabed, and its reproduction is ovoviviparous. This shark is caught in fisheries for its flesh, its fins, and its liver, which has a very high vitamin A content. The IUCN has classified this species as critically endangered in its Red List of Threatened Species.

<span class="mw-page-title-main">Smooth hammerhead</span> Species of shark

The smooth hammerhead is a species of hammerhead shark, and part of the family Sphyrnidae. This species is named "smooth hammerhead" because of the distinctive shape of the head, which is flattened and laterally extended into a hammer shape, without an indentation in the middle of the front margin. Unlike other hammerheads, this species prefers temperate waters and occurs worldwide at medium latitudes. In the summer, these sharks migrate towards the poles following cool water masses, sometimes forming schools numbering in the hundreds to thousands.

<span class="mw-page-title-main">Smalleye hammerhead</span> Species of fish

The smalleye hammerhead, also called the golden hammerhead or curry shark, is a small species of hammerhead shark in the family Sphyrnidae. This species was historically common in the shallow coastal waters of the western Atlantic Ocean, from Venezuela to Uruguay. It favors muddy habitats with poor visibility, reflected by its relatively small eyes. Adult males and juveniles are schooling and generally found apart from the solitary adult females. Typically reaching 1.2–1.3 m (3.9–4.3 ft) in length, this shark has a unique, bright golden color on its head, sides, and fins, which was only scientifically documented in the 1980s. As in all hammerheads, its head is flattened and laterally expanded into a hammer-shaped structure called the cephalofoil, which in this species is wide and long with an arched front margin bearing central and lateral indentations.

<span class="mw-page-title-main">Bonnethead</span> Species of shark

The bonnethead, also called a bonnet shark or shovelhead, is a small member of the hammerhead shark genus Sphyrna, and part of the family Sphyrnidae. It is an abundant species in the littoral zone of the North Atlantic and the Gulf of Mexico, is the only shark species known to display sexual dimorphism in the morphology of the head, and is the only shark species known to be omnivorous.

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<span class="mw-page-title-main">Blacktip shark</span> Species of shark

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<span class="mw-page-title-main">Daggernose shark</span> Species of shark

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<span class="mw-page-title-main">Scalloped bonnethead</span> Species of shark

The scalloped bonnethead is a rare, little-known species of hammerhead shark in the family Sphyrnidae. Its other common names include the mallethead shark and the crown shark. It is found in tropical and subtropical waters in the eastern Pacific Ocean, from Mexico to Peru, and possibly as far north as the Gulf of California. It frequents inshore habitats over soft bottoms to a depth of 100 m, and also enters mangroves and estuaries.

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<span class="mw-page-title-main">Carolina hammerhead</span> Species of shark

The Carolina hammerhead is a species of hammerhead shark, and part of the family Sphyrnidae, found in the western Atlantic Ocean. Their pupping grounds are in nearshore waters off the southeastern U.S. with the highest concentrations found in Bulls Bay, South Carolina. The Carolina hammerhead has also been found in nearshore waters off of Brazil. It was formally described in 2013. It is currently classified as Vulnerable (VU) on the IUCN Red List due to overfishing and habitat degradation.

Ornithoteuthis volatilis, the shiny bird squid, is a squid from the subfamily Ommastrephinae, the flying squids, of the family Ommastrephidae part of the pelagic squid order Oegopsida. It is a tropical and sub-tropical species which is widely distributed in the Indo-Pacific oceans. It is slightly larger than the closely related species Ornithoteuthis antillarum of the Atlantic Ocean.

Misión Tiburón is a non profit organisation established in 2009, based on the Pacific coast of Costa Rica. Founded by marine biologists and conservationists Ilena Zanella and Andres Lopez, the organisation focuses on marine research concerning sharks, sea turtles and rays as well as education programs targeted at local coastal communities.

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. 1 2 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. 1 2 3 4 5 6 7 8 9 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. ↑ "Scalloped Hammerhead Sharks - Facts and Conservation | Endangered".
  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. 1 2 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. 1 2 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. 1 2 3 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. 1 2 3 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. 1 2 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.
  22. 1 2 3 Duncan, K. M.; Martin, A. P.; Bowen, B. W.; De Couet, H. G. (2006). "Global phylogeography of the scalloped hammerhead shark (Sphyrna lewini)". Molecular Ecology. 15 (8): 2239–2251. doi:10.1111/j.1365-294X.2006.02933.x. PMID   16780437. S2CID   25219770.
  23. ↑ Chen, CT; Leu, TC; Joung, SJ; Lo, NCH (1990). "Age and growth of the scalloped hammerhead, Sphyrna lewini, in northeastern Taiwan waters". Pacific Science . 44 (2): 156–170. hdl:10125/1267.
  24. ↑ Torres-Rojas, Yassir; Hernandez-Herrera, Agustin; Galvan-Magaña, Felipe. "Feeding habits of the scalloped hammerhead shark, Sphyrna lewini, in Mazatlán waters, southern Gulf of California, Mexico". Cybium. 30: 85–90.
  25. 1 2 3 Wells, R. J. David; TinHan, Thomas C.; Dance, Michael A.; Drymon, J. Marcus; Falterman, Brett; Ajemian, Matthew J.; Stunz, Gregory W.; Mohan, John A.; Hoffmayer, Eric R.; Driggers, William B.; McKinney, Jennifer A. (2018). "Movement, Behavior, and Habitat Use of a Marine Apex Predator, the Scalloped Hammerhead" (PDF). Frontiers in Marine Science. 5. doi: 10.3389/fmars.2018.00321 . ISSN   2296-7745.
  26. 1 2 "The IUCN Red List of Threatened Species". IUCN Red List of Threatened Species. Retrieved 2021-04-30.
  27. 1 2 3 Santos, Catarina C.; Coelho, Rui (2018-06-06). Tserpes, George (ed.). "Migrations and habitat use of the smooth hammerhead shark (Sphyrna zygaena) in the Atlantic Ocean". PLOS ONE. 13 (6): e0198664. Bibcode:2018PLoSO..1398664S. doi: 10.1371/journal.pone.0198664 . ISSN   1932-6203. PMC   5991395 . PMID   29874297.
  28. 1 2 Chapman, Demian D.; Pinhal, Danillo; Shivji, Mahmood S. (2009-12-01). "Tracking the fin trade: genetic stock identification in western Atlantic scalloped hammerhead sharks Sphyrna lewini". Endangered Species Research. 9 (3): 221–228. doi: 10.3354/esr00241 . hdl: 11449/71350 . ISSN   1863-5407.
  29. ↑ Kinney, Michael John; Simpfendorfer, Colin Ashley (2009). "Reassessing the value of nursery areas to shark conservation and management". Conservation Letters. 2 (2): 53–60. doi: 10.1111/j.1755-263X.2008.00046.x . ISSN   1755-263X.
  30. ↑ Cuevas‐Gómez, Gabriela Alejandra; Pérez‐Jiménez, Juan Carlos; Méndez‐Loeza, Iván; Carrera‐Fernández, Maribel; Castillo‐Géniz, José Leonardo (2020). "Identification of a nursery area for the critically endangered hammerhead shark (Sphyrna lewini) amid intense fisheries in the southern Gulf of Mexico" . Journal of Fish Biology. 97 (4): 1087–1096. doi:10.1111/jfb.14471. ISSN   1095-8649. PMID   32691418. S2CID   220671717.
  31. ↑ Gallagher, Austin J.; Klimley, A. Peter (2018-07-21). "The biology and conservation status of the large hammerhead shark complex: the great, scalloped, and smooth hammerheads". Reviews in Fish Biology and Fisheries. 28 (4): 777–794. doi:10.1007/s11160-018-9530-5. ISSN   0960-3166. S2CID   254982548.
  32. ↑ Savage, Sam (19 February 2008). "Hammerhead Shark Makes Endangered Species List". redorbit.com.
  33. ↑ "Sphyrna lewini". Florida Museum. 12 May 2017. Retrieved 25 April 2020.
  34. ↑ "Smooth Hammerhead Shark". Oceana. Retrieved 2 March 2020.
  35. ↑ Phillips, Jarrett; French, Steven H.; Hanner, Robert H.; Gillis, Daniel J. (2020). "HACSim: an R package to estimate intraspecific sample sizes for genetic diversity assessment using haplotype accumulation curves". PeerJ Computer Science. 6: e243. doi: 10.7717/peerj-cs.243 . PMC   7924493 . PMID   33816897. e243.
  36. ↑ Briggs, Helen (28 January 2021). "Extinction: 'Time is running out' to save sharks and rays". BBC News . Retrieved 29 January 2021.
  37. ↑ Richardson, Holly (27 January 2021). "Shark, ray populations have declined by 'alarming' 70 per cent since 1970s, study finds". ABC News. Australian Broadcasting Corporation . Retrieved 29 January 2021.
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