Hammerhead shark
Hammerhead sharks Temporal range:
| |
---|---|
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 | |
The hammerhead sharks are a group of
Hammerheads are found worldwide, preferring life in warmer waters along coastlines and
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.
Taxonomy and evolution
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.
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.
In 2007, the
Diet
Hammerhead sharks eat a large range of prey such as
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
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]
The great and the scalloped hammerheads are listed on the World Conservation Union's (
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]
In captivity
The relatively small bonnethead is regular at
Protection
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
Cultural significance
Among
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
- List of hammerhead sharks
- List of prehistoric cartilaginous fish
References
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- ^ "Record Hammerhead Pregnant With 55 Pups". Discovery News. Associated Press. 1 July 2006. Archived from the original on 22 June 2011. Retrieved 18 October 2008.
- ^ New-York Tribune (15 April 1906). "Hammerhead Shark Captured in Florida Waters". Chronicling America. New-York Tribune. Archived from the original on 20 September 2022. Retrieved 20 September 2022.
- ^ "Hammerhead Shark". sharks-world.com. Archived from the original on 7 July 2011. Retrieved 19 December 2012.
- ^ "Marine Species ID: Great Hammerhead vs. Scalloped and Smooth Hammerhead". Sport Diver. Archived from the original on 8 August 2021. Retrieved 7 October 2020.
- ^ University of Colorado at Boulder. 19 May 2010. Archivedfrom the original on 1 April 2019. Retrieved 9 November 2016.
- ^ "Hammerhead shark | Diet, Size, & Facts | Britannica". www.britannica.com. Archived from the original on 24 July 2023. Retrieved 26 July 2023.
- ^ a b "Hammerhead Shark". NationalGeographic.com. 10 September 2010. Archived from the original on 10 November 2016. Retrieved 9 November 2016.
- from the original on 2 June 2018. Retrieved 27 July 2022.
- ^ Martin, R. Aidan. "Origin and Evolution of the 'Hammer'". elasmo-research.org. Archived from the original on 27 December 2018. Retrieved 31 January 2005.
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- ^ McComb, D. Michelle; et al. (27 November 2009). "Hammerhead shark mystery solved". BBC News. Archived from the original on 25 February 2010. Retrieved 4 May 2010.
- ^ "World's Deadliest: Hammerhead Sharks". video.nationalgeographic.com. Archived from the original on 23 April 2015. Retrieved 23 May 2015.
- ^ Barley, Shanta (26 February 2019). "Why the hammerhead shark@ got its hammer". New Scientist. Archived from the original on 3 March 2021. Retrieved 3 March 2021.
- ^ Explained, Wildlife (5 January 2022). "Great Hammerhead Shark - Lifestyle, Diet, and More - Wildlife Explained". Wildlife Explained. Retrieved 10 August 2023.
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- ^ Martin, R. Aidan (August 1993). "If I Had a Hammer". Rodale's Scuba Diving. Archived from the original on 18 February 2019. Retrieved 31 March 2006.
- ^ a b c "Hammerhead Shark". AquaticCommunity.com. Archived from the original on 30 January 2019. Retrieved 19 December 2012.
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- ^ "Great hammerhead shark". EnchantedLearning.com. Enchanted Learning Software. Archived from the original on 30 December 2018. Retrieved 19 December 2012.
- ^ Hannah Lang (29 June 2017). "This Shark Eats Grass, and No One Knows Why". National Geographic. Archived from the original on 23 April 2019. Retrieved 7 December 2018.
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- ^ "Hammerhead Shark - an overview | ScienceDirect Topics". sciencedirect.com. Retrieved 10 August 2023.
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- ^ 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.
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- ^ "Statistics on Attacking Species of Shark". Florida Museum of Natural History. Archived from the original on 15 December 2017. Retrieved 27 December 2017.
- S2CID 258618434. Retrieved 10 August 2023.
- ^ "Panamanian officials find half ton of shark fins". WashingtonPost.com. Associated Press. 25 February 2011. Archived from the original on 12 June 2018. Retrieved 7 December 2018.
- ^ Giam Choo Hoo (1 December 2006). "Shark's fin soup – eat without guilt" (PDF). The Straits Times. Archived from the original (PDF) on 21 February 2007. Retrieved 6 January 2007.
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- ^ "Babies Of The S.E.A. – Bonnethead Shark". SEA Aquarium. November 2013. Archived from the original on 14 September 2017. Retrieved 13 September 2017.
- ^ "The Bonnethead Shark Sphyrna tiburo: Is it Suitable for Home Aquariums?". TFH MAagazine. September 2007. Archived from the original on 14 September 2017. Retrieved 13 September 2017.
- ^ (PDF) from the original on 7 August 2020. Retrieved 7 December 2018.
- ^ "Scalloped Hammerhead, Sphyrna lewini (Griffith & Smith)". elasmollet.org. Archived from the original on 27 June 2015. Retrieved 13 September 2017.
- ^ "Scalloped hammerhead shark". Zootierliste. Archived from the original on 14 September 2017. Retrieved 13 September 2017.
- ^ "Great Hammerheads, Sphyrna mokarran (Rueppell, 1837) in Captivity". elasmollet.org. Archived from the original on 22 December 2015. Retrieved 17 December 2015.
- ^ a b c d e f g h i 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. Archived from the original on 5 February 2023. Retrieved 25 June 2023 – via National Oceanic and Atmospheric Administration.
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External links
- 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 Archived 1 October 2022 at the Wayback Machine on Check123 - Video Encyclopedia