Hammerhead shark

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

Hammerhead sharks Temporal range: Early Miocene – recent PreꞒ Ꞓ O S D C P T J K Pg N
Scalloped hammerhead
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Subdivision:	Selachimorpha
Order:	Carcharhiniformes
Family:	Sphyrnidae T. N. Gill, 1872
Genera
Eusphyra Sphyrna

The hammer-like shape of the head means that hammerhead sharks can sweep for prey more effectively.

Hammerheads are found worldwide, preferring life in warmer waters along coastlines and continental shelves. Unlike most sharks, some hammerhead species will congregate and swim in large schools during the day, becoming solitary hunters at night.

Description

The known species range from 0.9 to 6.0 m (2 ft 11 in to 19 ft 8 in) in length and weigh 3–580 kg (6.6–1,300 lb).^[1][2] One specimen caught off the Florida coast in 1906 weighed over 680 kg (1,500 lb).^[3] They are usually light gray and have a greenish tint. Their bellies are white, which allows them to blend into the background when viewed from below and sneak up to their prey.^[4] Their heads have lateral projections that give them a hammer-like shape. While overall similar, this shape differs somewhat between species; examples are: a distinct T-shape in the great hammerhead, a rounded head with a central notch in the scalloped hammerhead, and an unnotched rounded head in the smooth hammerhead.^[5]

Hammerheads have disproportionately small mouths compared to other shark species.^[6] Some species are also known to form schools.^[7] In the evening, like most other sharks, they become solitary hunters.^{[citation needed]} National Geographic explained that hammerheads can be found in warm, tropical waters, but during the summer, they participate in a mass migration to search for cooler waters.^[8]

Taxonomy and evolution

 

A hammerhead shark gliding along the sea bed

Since sharks do not have mineralized bones and rarely fossilize, only their teeth are commonly found as fossils. Their closest relatives are the requiem sharks (Carcharinidae). Based on DNA studies and fossils, the ancestor of the hammerheads probably lived in the Early Miocene epoch about 20 million years ago.^[6][9]

Using mitochondrial DNA, a phylogenetic tree of the hammerhead sharks showed the winghead shark as its most basal member. As the winghead shark has proportionately the largest "hammer" of the hammerhead sharks, this suggests that the first ancestral hammerhead sharks also had large hammers.^[10]

Cephalofoil

The hammer-like shape of the head may have evolved at least in part to enhance the animal's vision.^[11] The positioning of the eyes, mounted on the sides of the shark's distinctive hammer head, allows 360° of vision in the vertical plane, meaning the animals can see above and below them at all times.^[12][13] They also have an increased binocular vision and depth of visual field as a result of the cephalofoil.^[14][15] The shape of the head was previously thought to help the shark find food, aiding in close-quarters maneuverability, and allowing sharp turning movement without losing stability. The unusual structure of its vertebrae, though, has been found to be instrumental in making the turns correctly, more often than the shape of its head, though it would also shift and provide lift. From what is known about the winghead shark, the shape of the hammerhead apparently has to do with an evolved sensory function. Like all sharks, hammerheads have electroreceptory sensory pores called ampullae of Lorenzini. The pores on the shark's head lead to sensory tubes, which detect electric fields generated by other living creatures.^[16] By distributing the receptors over a wider area, like a larger radio antenna, hammerheads can sweep for prey more effectively.^[17]

Reproduction

Reproduction occurs only once a year for hammerhead sharks, and usually occurs with the male shark biting the female shark violently until she agrees to mate with him.^[18] The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Like other sharks, fertilization is internal, with the male transferring sperm to the female through one of two intromittent organs called claspers. The developing embryos are at first sustained by a yolk sac. When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta (called a "yolk sac placenta" or "pseudoplacenta"), through which the mother delivers sustenance until birth. Once the baby sharks are born, they are not taken care of by the parents in any way. Usually, a litter consists of 12 to 15 pups, except for the great hammerhead, which gives birth to litters of 20 to 40 pups. These baby sharks huddle together and swim toward warmer water until they are old enough and large enough to survive on their own.^[18]

In 2007, the bonnethead shark was found to be capable of asexual reproduction via automictic parthenogenesis, in which a female's ovum fuses with a polar body to form a zygote without the need for a male. This was the first shark known to do this.^[19]

Diet

Hammerhead sharks eat a large range of prey such as fish (including other sharks), squid, octopus, and crustaceans. Stingrays are a particular favorite, with the positioning of their (comparatively) smaller, crescent-shaped mouths underneath their T-shaped heads allowing for skilled skate, ray, and flounder hunting, among other seafloor-dwellers. These sharks will often be found swimming above the sand along the bottom of the ocean, stalking their prey. Their unique heads are further utilized as a tool (or weapon) if hunting rays and flatfishes; the shark uses its head to pin down and briefly stun the prey, and only eats once their quarry is clearly weakened and in shock.^[18] The great hammerhead, tending to be larger and more aggressive to its own kind than other hammerheads, occasionally engages in cannibalism, eating other hammerhead sharks, including mothers consuming their own young.^[20] In addition to the typical animal prey, bonnetheads have been found to feed on seagrass, which sometimes makes up as much as half their stomach contents. They may swallow it unintentionally, but they are able to partially digest it. At the time of discovery, this was the only known case of a potentially omnivorous species of shark^[21] (since then, whale sharks were also found to be omnivorous).^[22]

Species

There are nine distinct species of Hammerhead shark in the wild:^[23]

	Species	Common names	IUCN Red List status	Population trend	References
	Eusphyra blochii	Winghead shark	Endangered	Decreasing	^[24]
	Sphyrna corona	Scalloped bonnethead	Critically Endangered	Decreasing	^[25]
	Sphyrna gilberti	Carolina hammerhead	Data Deficient	Unknown	^[26]
	Sphyrna lewini	Scalloped hammerhead	Critically Endangered	Decreasing	^[27]
	Sphyrna media	Scoophead	Critically Endangered	Decreasing	^[28]
	Sphyrna mokarran	Great hammerhead	Critically Endangered	Decreasing	^[29]
	Sphyrna tiburo	Bonnethead	Endangered	Decreasing	^[30]
	Sphyrna tudes	Smalleye hammerhead	Critically Endangered	Decreasing	^[31]
	Sphyrna zygaena	Smooth hammerhead	Vulnerable	Decreasing	^[32]

Relationship with humans

 

A hammerhead shark in shallow water

According to the International Shark Attack File, humans have been subjects of 17 documented, unprovoked attacks by hammerhead sharks within the genus Sphyrna since AD 1580. No human fatalities have been recorded.^[33] Most hammerhead shark species are too small to inflict serious damage to humans.^[8]

 

Man carrying a hammerhead shark along a street in Mogadishu, Somalia

The great and the scalloped hammerheads are listed on the World Conservation Union's (IUCN) 2008 Red List as endangered, whereas the smalleye hammerhead is listed as vulnerable. The status given to these sharks is as a result of overfishing and demand for their fins, an expensive delicacy. Among others, scientists expressed their concern about the plight of the scalloped hammerhead at the American Association for the Advancement of Science annual meeting in Boston. The young swim mostly in shallow waters along shores all over the world to avoid predators.^[34]

Shark fins are prized as a delicacy in certain countries in Asia (such as China), and overfishing is putting many hammerhead sharks at risk of extinction. Fishermen who harvest the animals typically cut off the fins and toss the remainder of the fish, which is often still alive, back into the sea.^[35] This practice, known as finning, is lethal to the shark.^[36]

Scalloped hammerhead swimming

In captivity

The relatively small bonnethead is regular at public aquariums, as it has proven easier to keep in captivity than the larger hammerhead species,^[37][38] and it has been bred at a handful of facilities.^[39] Nevertheless, at up to 1.5 m (5 ft) in length and with highly specialized requirements, very few private aquarists have the experience and resources necessary to maintain a bonnethead in captivity.^[40] The larger hammerhead species can reach more than twice that size and are considered difficult, even compared to most other similar-sized sharks (such as Carcharhinus species, lemon shark, and sand tiger shark) regularly kept by public aquariums.^[38] They are particularly vulnerable during transport between facilities, may rub on surfaces in tanks, and may collide with rocks, causing injuries to their heads, so they require very large, specially adapted tanks.^[38][41] As a consequence, relatively few public aquaria have kept them for long periods.^[38] The scalloped hammerhead is the most frequently maintained large species, and it has been kept long term at public aquaria in most continents, but primarily in North America, Europe, and Asia.^[38][42][43] In 2014, fewer than 15 public aquaria in the world kept scalloped hammerheads.^[41] Great hammerheads have been kept at a few facilities in North America, including Atlantis Paradise Island Resort (Bahamas), Adventure Aquarium (New Jersey), Georgia Aquarium (Atlanta), Mote Marine Laboratory (Florida), and the Shark Reef at Mandalay Bay (Las Vegas).^[44] Smooth hammerheads have also been kept in the past.^[38]

Protection

 

Most, if not all, hammerhead shark species are threatened with extinction.

Humans are the number one threat to hammerhead sharks. Although they are not usually the primary target, hammerhead sharks are caught in fisheries all over the world.^[45] Tropical fisheries are the most common place for hammerheads to be caught because of their preference to reside in warm waters.^[45] The total number of hammerheads caught in fisheries is recorded in the Food and Agriculture Organization of the United Nations Global Capture Production dataset.^[45] The number steadily increased from 75 metric tons in 1990, to 6,313 metric tons by 2010.^[45]

Shark fin traders say that hammerheads have some of the best quality fin needles which makes them good to eat when prepared properly.^[45] Hong Kong is the world's largest fin trade market and accounts for about 1.5% of the total annual amount of fins traded.^[45] It is estimated that around 375,000 great hammerhead sharks alone are traded per year which is equivalent to 21,000 metric tons of biomass.^[45] However, it is important to note that most sharks that are caught are only used for their fins and then discarded.^[45] The actual meat of hammerheads is generally unwanted. Consumption of regular hammerhead meat has been recorded in countries such as Trinidad and Tobago, Venezuela, Kenya, and Japan.^[45]

In March 2013, three endangered, commercially valuable sharks, the hammerheads, the oceanic whitetip, and porbeagle, were added to Appendix II of CITES, bringing shark fishing and commerce of these species under licensing and regulation.^[46]

Cultural significance

Among Torres Strait Islanders, the hammerhead shark, known as the beizam, is a common family totem and often represented in cultural artefacts such as the elaborate headdresses worn for ceremonial dances, known as dhari (dari). They are associated with law and order.^[47] Renowned artist Ken Thaiday Snr is known for his representations of beizam in his sculptural dari and other works.^[48][49]

In native Hawaiian culture, sharks are considered to be gods of the sea, protectors of humans, and cleaners of excessive ocean life. Some of these sharks are believed to be family members who died and have been reincarnated into shark form, but others are considered man-eaters, also known as niuhi. These sharks include great white sharks, tiger sharks, and bull sharks. The hammerhead shark, also known as mano kihikihi, is not considered a man-eater or niuhi; it is considered to be one of the most respected sharks of the ocean, an aumakua. Many Hawaiian families believe that they have an aumakua watching over them and protecting them from the niuhi. The hammerhead shark is thought to be the birth animal of some children. Hawaiian children who are born with the hammerhead shark as an animal sign are believed to be warriors and are meant to sail the oceans. Hammerhead sharks rarely pass through the waters of Maui, but many Maui natives believe that their swimming by is a sign that the gods are watching over the families, and the oceans are clean and balanced.^[50]

See also

For a topical guide, see Outline of sharks.

•  Sharks portal

• List of hammerhead sharks
• List of prehistoric cartilaginous fish

References

1. Hessing, S. (2000). "Sphyrna tiburo". Animal Diversity Web. University of Michigan Museum of Zoology. from the original on 29 September 2012. Retrieved 19 December 2012 – via animaldiversity.ummz.umich.edu.
2. . Discovery News. Associated Press. 1 July 2006. Archived from the original on 22 June 2011. Retrieved 18 October 2008.
3. New-York Tribune (15 April 1906). "Hammerhead Shark Captured in Florida Waters". Chronicling America. New-York Tribune. from the original on 20 September 2022. Retrieved 20 September 2022.
4. . sharks-world.com. Archived from the original on 7 July 2011. Retrieved 19 December 2012.
5. "Marine Species ID: Great Hammerhead vs. Scalloped and Smooth Hammerhead". Sport Diver. from the original on 8 August 2021. Retrieved 7 October 2020.
6. "Hammerhead shark study shows cascade of evolution affected size, head shape". ScienceDaily.com. University of Colorado at Boulder. 19 May 2010. from the original on 1 April 2019. Retrieved 9 November 2016.
7. "Hammerhead shark | Diet, Size, & Facts | Britannica". www.britannica.com. from the original on 24 July 2023. Retrieved 26 July 2023.
8. . NationalGeographic.com. 10 September 2010. Archived from the original on 10 November 2016. Retrieved 9 November 2016.
9. Mello, Waldiney; Brito, Paulo Marques Machado (September 2013). "Contributions to the tooth morphology in early embryos of three species of hammerhead sharks (Elasmobranchii: Sphyrnidae) and their evolutionary implications". Comptes Rendus Biologies. 336 (9): 466–471. doi:10.1016/j.crvi.2013.04.017. PMID 24161244. from the original on 2 June 2018. Retrieved 27 July 2022.
10. Martin, R. Aidan. "Origin and Evolution of the 'Hammer'". elasmo-research.org. from the original on 27 December 2018. Retrieved 31 January 2005.
11. McComb, D. M.; Tricas, T. C.; Kajiura, S. M. (2009). "Enhanced visual fields in hammerhead sharks". Journal of Experimental Biology. 212 (24): 4010–8. doi:10.1242/jeb.032615. PMID 19946079.
12. McComb, D. Michelle; et al. (27 November 2009). "Hammerhead shark mystery solved". BBC News. from the original on 25 February 2010. Retrieved 4 May 2010.
13. . video.nationalgeographic.com. Archived from the original on 23 April 2015. Retrieved 23 May 2015.
14. Barley, Shanta (26 February 2019). "Why the hammerhead shark@ got its hammer". New Scientist. from the original on 3 March 2021. Retrieved 3 March 2021.
15. Explained, Wildlife (5 January 2022). "Great Hammerhead Shark - Lifestyle, Diet, and More - Wildlife Explained". Wildlife Explained. Retrieved 10 August 2023.
16. Otfinoski, Steven (2000). Hammerheads and Other Sharks. World Book, Inc. pp. 16. ISBN 978-0716612100.
17. Martin, R. Aidan (August 1993). "If I Had a Hammer". Rodale's Scuba Diving. from the original on 18 February 2019. Retrieved 31 March 2006.
18. "Hammerhead Shark". AquaticCommunity.com. from the original on 30 January 2019. Retrieved 19 December 2012.
19. Chapman, DD; Shivji, MS; Louis, E; Sommer, J; Fletcher, H; Prodöhl, PA (22 August 2007). "Virgin birth in a hammerhead shark". Biology Letters. 3 (4): 425–7. doi:10.1098/rsbl.2007.0189. PMC 2390672. PMID 17519185.
20. "Great hammerhead shark". EnchantedLearning.com. Enchanted Learning Software. from the original on 30 December 2018. Retrieved 19 December 2012.
21. Hannah Lang (29 June 2017). . National Geographic. Archived from the original on 23 April 2019. Retrieved 7 December 2018.
22. Meekan, M. G.; Virtue, P.; Marcus, L.; Clements, K. D.; Nichols, P. D.; Revill, A. T. (2022). "The world's largest omnivore is a fish". Ecology. 103 (12): e3818. Bibcode:2022Ecol..103E3818M. doi:10.1002/ecy.3818. ISSN 0012-9658. PMID 35852891. S2CID 250642078.
23. "Hammerhead Shark - an overview | ScienceDirect Topics". sciencedirect.com. Retrieved 10 August 2023.
24. Smart, J.J.; Simpfendorfer, C. (2016). "Eusphyra blochii". IUCN Red List of Threatened Species. 2016: e.T41810A68623209. doi:10.2305/IUCN.UK.2016-1.RLTS.T41810A68623209.en. Retrieved 19 May 2023.
25. Pollom, R.; Pérez Jiménez, J.C.; Bizzarro, J.; Burgos-Vázquez, M.I.; Cevallos, A.; Espinoza, M.; Herman, K.; Mejía-Falla, P.A.; Navia, A.F.; Sosa-Nishizaki, O.; Velez-Zuazo, X. (2020). "Sphyrna corona". IUCN Red List of Threatened Species. 2020: e.T44591A124434064. doi:10.2305/IUCN.UK.2020-3.RLTS.T44591A124434064.en. Retrieved 19 May 2023.
26. VanderWright, W.J.; Carlson, J.; Pollom, R.; Dulvy, N.K. (2020). "Sphyrna gilberti". IUCN Red List of Threatened Species. 2020: e.T152783714A172115852. doi:10.2305/IUCN.UK.2020-3.RLTS.T152783714A172115852.en. Retrieved 19 May 2023.
27. 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 19 May 2023.
28. Pollom, R.; Avalos, C.; Bizzarro, J.; Burgos-Vázquez, M.I.; Cevallos, A.; Charvet, P.; Espinoza, M.; Faria, V.; Herman, K.; Mejía-Falla, P.A.; Navia, A.F.; Pérez-Jiménez, J.C.; Rincon, G.; Sosa-Nishizaki, O. (2020). "Sphyrna media". IUCN Red List of Threatened Species. 2020: e.T60201A3091753. doi:10.2305/IUCN.UK.2020-3.RLTS.T60201A3091753.en. Retrieved 19 May 2023.
29. Rigby, C.L.; 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 mokarran". IUCN Red List of Threatened Species. 2019: e.T39386A2920499. doi:10.2305/IUCN.UK.2019-3.RLTS.T39386A2920499.en. Retrieved 19 May 2023.
30. Pollom, R.; Carlson, J.; Charvet, P.; Avalos, C.; Bizzarro, J.; Blanco-Parra, M.P.; Briones Bell-Iloch, A.; Burgos-Vázquez, M.I.; Cardenosa, D.; Cevallos, A.; Derrick, D.; Espinoza, E.; Espinoza, M.; Mejía-Falla, P.A.; Morales-Saldaña, J.M.; Navia, A.F.; Pacoureau, N.; Pérez Jiménez, J.C.; Sosa-Nishizaki, O. (2021) [amended version of 2020 assessment]. "Sphyrna tiburo". IUCN Red List of Threatened Species. 2021: e.T39387A205765567. doi:10.2305/IUCN.UK.2021-3.RLTS.T39387A205765567.en. Retrieved 19 May 2023.
31. Pollom, R.; Barreto, R.; Charvet, P.; Chiaramonte, G.E.; Cuevas, J.M.; Faria, V.; Herman, K.; Lasso-Alcalá, O.; Marcante, F.; Mejía-Falla, P.A.; Montealegre-Quijano, S.; Motta, F.; Navia, A.F.; Nunes, J.; Paesch, L.; Rincon, G. (2020). "Sphyrna tudes". IUCN Red List of Threatened Species. 2020: e.T60202A3091946. doi:10.2305/IUCN.UK.2020-3.RLTS.T60202A3091946.en. Retrieved 19 May 2023.
32. Rigby, C.L.; Barreto, R.; Carlson, J.; Fernando, D.; Fordham, S.; Herman, K.; Jabado, R.W.; Liu, K.M.; Marshall, A.; Pacoureau, N.; Romanov, E.; Sherley, R.B.; Winker, H. (2019). "Sphyrna zygaena". IUCN Red List of Threatened Species. 2019: e.T39388A2921825. doi:10.2305/IUCN.UK.2019-3.RLTS.T39388A2921825.en. Retrieved 19 May 2023.
33. "Statistics on Attacking Species of Shark". Florida Museum of Natural History. from the original on 15 December 2017. Retrieved 27 December 2017.
34. Royer, Mark; Meyer, Carl; Royer, John; Maloney, Kelsey; Cardona, Edward; Blandino, Chloé; Fernandes Da Silva, Guilherme; Whittingham, Kate; Holland, Kim N. (2023). ""Breath holding" as a thermoregulation strategy in the deep-diving scalloped hammerhead shark". Science. 380 (6645): 651–655. Bibcode:2023Sci...380..651R. doi:10.1126/science.add4445. PMID 37167384. S2CID 258618434. Retrieved 10 August 2023.
35. "Panamanian officials find half ton of shark fins". WashingtonPost.com. Associated Press. 25 February 2011. from the original on 12 June 2018. Retrieved 7 December 2018.
36. Giam Choo Hoo (1 December 2006). (PDF). The Straits Times. Archived from the original (PDF) on 21 February 2007. Retrieved 6 January 2007.
37. Compagno, L.; M. Dando & S. Fowler (2004). Sharks of the World. HarperCollins. p. 325. ISBN 978-0-00-713610-0.
38. Smith, M.; D. Warmolts; D. Thoney; R. Hueter, eds. (2004). Elasmobranch Husbandry Manual: Captive Care of Sharks, Rays, and their Relatives. Ohio Biological Survey. ISBN 9780867271522.
39. "Babies Of The S.E.A. – Bonnethead Shark". SEA Aquarium. November 2013. from the original on 14 September 2017. Retrieved 13 September 2017.
40. "The Bonnethead Shark Sphyrna tiburo: Is it Suitable for Home Aquariums?". TFH MAagazine. September 2007. from the original on 14 September 2017. Retrieved 13 September 2017.
41. Tristram, H.; S. Thomas; L. Squire-Junior (2014). "Husbandry of scalloped hammerhead sharks Sphyrna lewini (Griffith & Smith, 1834) at Reef HQ Aquarium, Townsville, Australia" (PDF). Der Zoologische Garten. 83 (4–6): 93–113. Bibcode:2014DZGar..83...93T. doi:10.1016/j.zoolgart.2014.08.002. (PDF) from the original on 7 August 2020. Retrieved 7 December 2018.
42. "Scalloped Hammerhead, Sphyrna lewini (Griffith & Smith)". elasmollet.org. from the original on 27 June 2015. Retrieved 13 September 2017.
43. "Scalloped hammerhead shark". Zootierliste. from the original on 14 September 2017. Retrieved 13 September 2017.
44. "Great Hammerheads, Sphyrna mokarran (Rueppell, 1837) in Captivity". elasmollet.org. from the original on 22 December 2015. Retrieved 17 December 2015.
45. Miller, Margaret H.; Carlson, J.; Hogan, L.; Kobayashi, D. (2014). Status review report : great hammerhead shark (Sphyrna mokarran) (Report). National Marine Fisheries Service, Office of Protected Resources. from the original on 5 February 2023. Retrieved 25 June 2023 – via National Oceanic and Atmospheric Administration.
46. McGrath, Matt (11 March 2013). "'Historic' day for shark protection". BBC News. from the original on 10 June 2013. Retrieved 27 July 2013.
47. Gerhardt, Katrin (30 November 2018). "Indigenous knowledge and cultural values of hammerhead sharks in Northern Australia" (PDF). Marine Diversity Hub. (PDF) from the original on 16 November 2020. Retrieved 14 November 2020.
48. "Dr Ken Thaiday Senior". Australia Council. 15 May 2019. from the original on 12 April 2020. Retrieved 14 April 2020.
49. "Ken Thaiday". Art Gallery NSW. from the original on 1 August 2020. Retrieved 15 April 2020.
50. Hurley, Timothy (28 September 2004). "Shark highly respected in Hawaiian culture". The Honolulu Advertiser. from the original on 5 September 2015. Retrieved 19 December 2012 – via Moolelo.com.

External links

 

Wikimedia Commons has media related to Sphyrnidae.

• Froese, Rainer, and Daniel Pauly, eds. (2011). "Sphyrnidae" in FishBase. February 2011 version.
• Animal Diversity Web Genus Sphyrna with species sub-pages
• "Electroreception in juvenile scalloped hammerhead and sandbar sharks" by Stephen M. Kajiura and Kim N. Holland, The Journal of Experimental Biology (2002). Attempts to explain the "hammer" shape.
• Great hammerhead shark, Sphyrna mokarran, MarineBio.org
• "New shark discovered in US waters". BBC News. 10 June 2006. Retrieved 9 November 2016.
• Hammerhead Sharks, Australian Marine Conservation Society
• Hammerhead Shark - Video 1 October 2022 at the Wayback Machine on Check123 - Video Encyclopedia