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Scalloped Hammerhead Sharks | SHARK ACADEMY
Scalloped Hammerhead Sharks | SHARK ACADEMY
Published: 2014/04/02
Channel: BlueWorldTV
Scalloped Hammerhead Shark Conservation in Costa Rica
Scalloped Hammerhead Shark Conservation in Costa Rica
Published: 2013/09/03
Channel: mbzFund
Deepest Scalloped Hammerhead Shark
Deepest Scalloped Hammerhead Shark
Published: 2015/06/24
Channel: serpentproject
Happy Shark Week! Scalloped Hammerhead Shark (Sphyrna lewini)
Happy Shark Week! Scalloped Hammerhead Shark (Sphyrna lewini)
Published: 2009/01/21
Channel: Wildscreen Arkive
Scalloped Hammerhead Identification
Scalloped Hammerhead Identification
Published: 2012/07/31
Channel: Capt. Mark Sampson
Hammerhead Shark Swarm
Hammerhead Shark Swarm
Published: 2014/02/11
Channel: Earth Touch
Seth Conae Scalloped Hammerhead Sharks - Epic Encounters 4
Seth Conae Scalloped Hammerhead Sharks - Epic Encounters 4
Published: 2014/10/23
Channel: Seth Conae
Reef HQ Aquarium - Scalloped Hammerhead Shark
Reef HQ Aquarium - Scalloped Hammerhead Shark
Published: 2015/06/11
Channel: Biopixel
All About Scalloped Hammerhead Sharks
All About Scalloped Hammerhead Sharks
Published: 2017/07/13
Channel: OdySea Aquarium
Baby Hammerhead sharks are adorable!
Baby Hammerhead sharks are adorable!
Published: 2014/06/18
Channel: BlueWorldTV
Hammerhead Sharks | JONATHAN BIRD
Hammerhead Sharks | JONATHAN BIRD'S BLUE WORLD
Published: 2013/03/12
Channel: BlueWorldTV
Scalloped Hammerhead Caught on Boat!
Scalloped Hammerhead Caught on Boat!
Published: 2014/02/18
Channel: Landshark Fishing
Scalloped Hammerhead Shark in very shallow water New Smyrna Beach
Scalloped Hammerhead Shark in very shallow water New Smyrna Beach
Published: 2015/04/10
Channel: Matteo Micheletti
Scalloped Hammerhead Shark
Scalloped Hammerhead Shark
Published: 2014/09/21
Channel: JM Esteban-Infantes
Scalloped Hammerhead Sharks   1080p
Scalloped Hammerhead Sharks 1080p
Published: 2015/03/10
Channel: Captain Ron's Fishing Charters
Galapagos Hammerheads: The Scalloped Hammerhead Shark on Wolf & Darwin Island
Galapagos Hammerheads: The Scalloped Hammerhead Shark on Wolf & Darwin Island
Published: 2011/01/13
Channel: Quasar Expeditions
Scalloped Hammerhead
Scalloped Hammerhead
Published: 2015/09/14
Channel: Mark D
Scalloped Hammerhead - Singer Island
Scalloped Hammerhead - Singer Island
Published: 2012/07/13
Channel: deusEXmachina1650
The Endangered Scalloped Hammerhead
The Endangered Scalloped Hammerhead
Published: 2016/02/22
Channel: Colin Koncz
Shark Diving in Florida with the Shark Addicts - Dusky, Scalloped Hammerhead, and Silky
Shark Diving in Florida with the Shark Addicts - Dusky, Scalloped Hammerhead, and Silky
Published: 2015/08/30
Channel: Bartolomeo Bove
Shark battles (quarter-final): Scalloped hammerhead shark vs Grey reef shark
Shark battles (quarter-final): Scalloped hammerhead shark vs Grey reef shark
Published: 2016/10/17
Channel: Fishing videos
Scalloped Hammerhead Shark
Scalloped Hammerhead Shark
Published: 2014/10/24
Channel: Naveh Lev
Great Hammerhead Sharks | SHARK ACADEMY
Great Hammerhead Sharks | SHARK ACADEMY
Published: 2015/02/27
Channel: BlueWorldTV
Scalloped Hammerhead (Sphyrna lewini)
Scalloped Hammerhead (Sphyrna lewini)
Published: 2013/10/15
Channel: Fasano2112
Feeding Scalloped Hammerhead Sharks
Feeding Scalloped Hammerhead Sharks
Published: 2015/02/19
Channel: George Glen
Close encounter with two Scalloped hammerhead sharks
Close encounter with two Scalloped hammerhead sharks
Published: 2015/07/11
Channel: Matt Noble
Scalloped hammerhead sharks HD
Scalloped hammerhead sharks HD
Published: 2012/10/23
Channel: Denis Zorzin
Scalloped Hammerheads with KoroSun Dive
Scalloped Hammerheads with KoroSun Dive
Published: 2014/09/17
Channel: SKYPRINTS
Scalloped Hammerhead Shark
Scalloped Hammerhead Shark
Published: 2013/06/18
Channel: Arh Chun Ngai
Scalloped Hammerhead Sharks @ Layang Layang Island
Scalloped Hammerhead Sharks @ Layang Layang Island
Published: 2012/05/29
Channel: Desmond Leong
Shark Fishing, 50-60lb Scalloped Hammerhead Shark
Shark Fishing, 50-60lb Scalloped Hammerhead Shark
Published: 2014/08/11
Channel: Alexander Bronsky
Scalloped Hammerhead
Scalloped Hammerhead
Published: 2014/04/24
Channel: John McGregor
Schooling Scalloped Hammerheads at Daedalus Reef, Egypt
Schooling Scalloped Hammerheads at Daedalus Reef, Egypt
Published: 2016/09/08
Channel: Whitley Schamber
scalloped hammerheads
scalloped hammerheads
Published: 2013/06/22
Channel: Mike Milligan
Scalloped Hammerhead Sharks, Molokai, 6/9/17
Scalloped Hammerhead Sharks, Molokai, 6/9/17
Published: 2017/06/10
Channel: Richard Anderson
Schooling Scalloped Hammerheads
Schooling Scalloped Hammerheads
Published: 2016/09/08
Channel: Whitley Schamber
3672 How to draw Scalloped Hammerhead Shark step by step kids drawing
3672 How to draw Scalloped Hammerhead Shark step by step kids drawing
Published: 2016/05/28
Channel: Fourpencil.com
Scalloped Hammer Head Shark
Scalloped Hammer Head Shark
Published: 2014/11/30
Channel: Edward Rivas
Scalloped hammerhead and oceanic white tip sharks are denied conservation measures ca
Scalloped hammerhead and oceanic white tip sharks are denied conservation measures ca
Published: 2013/02/27
Channel: trans2020ccc
Scalloped Hammerheads
Scalloped Hammerheads
Published: 2012/11/02
Channel: Carl Shepard
Scalloped Hammerhead and Atlantic Sharpnose shark tagging and fishing
Scalloped Hammerhead and Atlantic Sharpnose shark tagging and fishing
Published: 2016/07/14
Channel: worlwideshark conservation
Scalloped Hammerhead sharks underwater stock video footage 3
Scalloped Hammerhead sharks underwater stock video footage 3
Published: 2013/11/28
Channel: Jonathan Bird Productions
Molokai, Hawaii. Scalloped Hammerhead Shark
Molokai, Hawaii. Scalloped Hammerhead Shark
Published: 2011/11/26
Channel: R10ESY
25kg Scalloped hammerhead
25kg Scalloped hammerhead
Published: 2013/10/30
Channel: Brett Marlin
New MD State Record Shark -
New MD State Record Shark - 'Scalloped Hammerhead' August 2012 WMO
Published: 2012/08/14
Channel: UnscenePro/HookedOnOC
Scalloped Hammerhead
Scalloped Hammerhead
Published: 2010/11/19
Channel: Fasano2112
Sharks Scalloped Hammerheads
Sharks Scalloped Hammerheads
Published: 2010/02/18
Channel: Tim Powell
Mike Hughes  - 15kg Scalloped Hammerhead
Mike Hughes - 15kg Scalloped Hammerhead
Published: 2013/10/30
Channel: Brett Marlin
Scalloped Hammerheads.mov
Scalloped Hammerheads.mov
Published: 2011/05/01
Channel: Mike Ruel
Schooling Scalloped Hammerheads on Daedalus reef
Schooling Scalloped Hammerheads on Daedalus reef
Published: 2015/07/11
Channel: Matt Noble
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WIKIPEDIA ARTICLE

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Scalloped hammerhead
Scalloped hammerhead cocos.jpg
Sphyrna lewini Gervais.jpg
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Carcharhiniformes
Family: Sphyrnidae
Genus: Sphyrna
Species: S. lewini
Binomial name
Sphyrna lewini
(E. Griffith & C. H. Smith, 1834)
Sphyrna lewini distribution map.svg
Range of the scalloped hammerhead
Synonyms

Sphyrna couardi Cadenat, 1951

The scalloped hammerhead (Sphyrna lewini) is a species of hammerhead shark, and part of the family Sphyrnidae. Originally known as Zygaena lewini, its genus name was later changed to its current name. The Greek word sphyrna translates into "hammer" in English, referring to the shape of this shark's head. The most distinguishing characteristic of this shark, as in all hammerheads, is the 'hammer' on its head. The shark's eyes and nostrils are at the tips of the extensions. This is a fairly large hammerhead, though is smaller than both the great and smooth hammerheads.

This shark is also known as the bronze, kidney-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[edit]

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 into 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]

Description[edit]

On average, 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 80 kg (180 lb) on average at sexual maturity.[6] The maximum length of the scalloped hammerhead is 4.3 m (14 ft) and the maximum weight 152.4 kg (336 lb), per FishBase.[7] 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 at that point.[8]

These sharks have a very high metabolic rate, governing behavior in acquiring food. These sharks occupy tertiary trophic levels.[9] The scalloped hammerhead shark, like many other species, uses the shore as a breeding ground.[9] Due to high metabolic rates, young scalloped hammerhead sharks need a lot of food, or they will starve.

Distribution and habitat[edit]

A school of scalloped hammerheads.

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, 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).[10] 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]

Behavior[edit]

Schooling[edit]

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[edit]

The female scalloped hammerheads undergo migration offshore at a smaller size than males[11] because the larger classes of the hammerhead, such as those from 100 to 140 cm long, travel deeper down.[11] 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 cm 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.[12] Unlike females, males reach sexual maturity at a much smaller size.

The male-to-female ratio of the scalloped hammerhead is 1:1.29.[12] Females probably are capable of giving birth annually.[12] usually in the summer.

Navigating behavior[edit]

Scalloped hammerhead sharks have a homing behavior to navigate in the ocean.[13] They move in the night and use the environment as a map, similar to a human reading a topographical map.[13] By experimentation in tagging these sharks, one could test for any guidance in a shark’s movement.[13] 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.

The scalloped hammerhead uses deep water to survive as safety and feeding.[14] 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 the scalloped hammerhead to be selective where they swim and the depth at which they tend to stay. The scalloped hammerhead has a tendency to eat cephalopods.[15]

Reproduction[edit]

The gestation period is reported to be around 12 months.[16] Compared to other species, the scalloped hammerhead produces large litters,[16] and this is most likely due to high infant mortality. Like most sharks, parental care is not seen.[17] Nursery grounds for this species are predictable and repeated over the years, and they are faithful to their natal sites.[17] 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.[17] 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.[18]

Diet[edit]

This shark feeds primarily on fish such as sardines, mackerel, and herring, and occasionally 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.

Human interaction[edit]

As of 2008, the scalloped hammerhead is on the "globally endangered" species list. In parts of the Atlantic Ocean, their populations have declined by over 95% in the past 30 years. Among the reasons for this drop off 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 are calling 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.[19]

See also[edit]

References[edit]

  1. ^ Baum, J., Clarke, S., Domingo, A., Ducrocq, M., Lamónaca, A.F., Gaibor, N., Graham, R., Jorgensen, S., Kotas, J.E., Medina, E., Martinez-Ortiz, J., Monzini Taccone di Sitizano, J., Morales, M.R., Navarro, S.S., Pérez-Jiménez, J.C., Ruiz, C., Smith, W., Valenti, S.V. & Vooren, C.M. (2007). Sphyrna lewini. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2.
  2. ^ "More oceanic sharks added to the IUCN Red List" (Press release). IUCN. 2007-02-22. Archived from the original on 2008-07-06. Retrieved 2007-02-25. The status of scalloped hammerhead shark was heightened from Near Threatened to Endangered. 
  3. ^ a b "Scalloped Hammerhead". 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. doi:10.11646/zootaxa.3702.2.5. 
  5. ^ Martin, R. Aidan. (February 24, 1998). Recent Changes in Hammerhead Taxonomy. ReefQuest Centre for Shark Research. Retrieved on October 18, 2008.
  6. ^ FLMNH Ichthyology Department: Scalloped Hammerhead. Flmnh.ufl.edu. Retrieved on 2013-05-23.
  7. ^ Sphyrna lewini, Scalloped hammerhead : fisheries, gamefish. Fishbase.org (2012-07-03). Retrieved on 2013-05-23.
  8. ^ Castro, José I. (2011) The Sharks of North America. Oxford University Press. ISBN 978-0-19-539294-4
  9. ^ a b Duncan, Kanesa May (2006-08-01). "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. 
  10. ^ Froese, Ranier and Pauly, Daniel (ed.). Sphyrna lewini. FishBase. Retrieved 10 December 2008. 
  11. ^ a b Klimley, A. Pete (1987-01-01). "The determinants of sexual segregation in the scalloped hammerhead shark, Sphyrna lewini". Environmental Biology of Fishes. 18: 27–40. doi:10.1007/BF00002325. 
  12. ^ a b c Hazin, Fabio; Fischer, Alessandra; Broadhurst, Matt (2001-06-01). "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. 
  13. ^ 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. 
  14. ^ 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. 
  15. ^ Smale, M. J.; Cliff, G. (1998). "Cephalopods in the diets of four shark species (Galeocerdo cuvier, Sphyrna lewini, S. Zygaena and S. Mokarran) from Kwa Zulu-Natal, South Africa". South African Journal of Marine Science. 20: 241. doi:10.2989/025776198784126610. 
  16. ^ a b Branstetter, Steven (1987-07-01). "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. 
  17. ^ a b c 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. 
  18. ^ 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. 
  19. ^ Savage, Sam (February 19, 2008). "Hammerhead Shark Makes Endangered Species List". redorbit.com. 

External links[edit]

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