Post by creature386 on May 19, 2013 22:01:22 GMT 5
Scalloped hammerhead (Sphyrna lewini)
Cladistic:
Animalia
Chordata
Chondrichthyes
Elasmobranchii
Carcharhiniformes
Sphyrnidae
Sphyrna
S. lewini (Griffith & Smith, 1834)[1]
Description:
The scalloped hammerhead (originally described as Zygaena lewini by Griffith and Smith in 1834.[1]) is a shark with a broad, narrow-bladed head, which is 24-30% (mostly above 26%) as wide, as the shark is long. So, the head may be quite wide, but it is rather short (1/3-1/5 of the head's width). It's teeth have weakly serrated edges (juveniles lack those), the anterior teeth are moderately long and the crown can be either stout or slender. The posterior teeth are mostly cuspidate. The scalloped hammerhead has a falcate first dorsal fin and a second one, who is a not as tall and more concave.
This shark can have a total vertebral centra number of 174 to 209. Its back is grey, its belly is white and it's fins have black tips.[2]
Adult males can be 2,1-2,2 m long and adult females 2,25 m+.[3] Large ones can be over 3 m long. The maximum is more than 4 m in females and ~3 m in males.[2] The maximum known weight is ~150 kg.[1] A 1,40-1,65 m long male can be called an adult a female at 2,12 m. A new born scalloped hammerhead can range in size from 42 to 55 cm.[2] In the northwestern Atlantic Ocean, males mature at 1,8 m in length and 29 kg in weight, while females do so at 2,5 m in length and 80 kg in weight. Scalloped hammerheads can live 30 years.[1]
Habitat:
Scalloped hammerheads are among the most abundant hammerhead species. They are found in warm seas, near the coasts. They are often found in the Indo-West Pacific. Prefered depths range from the surface, to 275 m below the surface.[2] Females usually dive deeper.[4] Scalloped hammerheads often migrate, in the summer, some populations migrate to areas closer to the poles, like South Africa. The populations of East China may not migrate.[2]
Diet:
The diet varies between the sexes. Females attack more pelagic prey and they are more succesful.[4] Juvenile scalloped hammerheads prey on benthic fishes and crustaceans.[5] Benthic fishes only make up 15% of the diet of adult females.[4] The diet of adults includes Food sardines and herring, anchovies, ten-pounders (Elopidae), conger eels, milkfish, sea catfish, silversides, halfbeaks, mullet, lizardfish, barracuda, bluefish, spanish mackeral, jacks, porgies, mojarras, cardinal fishes, goatfish, grunts, damselfishes, parrotfishes, wrasses, butterfly fishes, surgeonfish, gobies, flatfish, sharpnose sharks (Rhizoprionodon), blacktip reef sharks, angelsharks, stingrays, squid, octopi, cuttlefishes, sea snails, shrimp, mantis shrimp, crabs, lobsters and isopods.[2]
Social behaviour:
Scalloped hammerheads are known for their social behaviour. Juveniles live in large schools, while larger sharks are either solitary or living in pairs. They also can occur in small schools. Females in the Gulf of California have shown a wide range of behaviours.[1] These include ramming each other, shaking the head while smimming acceleratedly, corkscrew swimming, lateral tiling of the body (maybe for the field of vision), jaw opening and caspler flexion.[2]
Predators and parasites:
An adult scalloped hammerhead has no major predators, but parasites. These are external leeches (Stilarobdella macrotheca) and copepods (Alebion carchariae, A. elegans, Nesippus crypturus, Kroyerina scotterum), hence they often visit reefs ("cleaning stations") to let cleaner wrasses eat the parasites.[1]
Reproduction:
Scalloped hammerheads are viviparous, having a gestation period, which lasts 9 to ten months.[1] Litters can include 15 to 31 babys. The Kaneohe Bay (Hawaii) represents a nursey are used by scalloped hammerheads. Neonates stay close to the bay, but as they grow, they more and more start leaving it.[2]
Scalloped hammerheads and humans:
The scalloped hammerhead is seen as potentionally dangerous to humans. There exist provoked and unprovoked attacks on swimmers, divers and boats, but in most cases, it isn't sure whether it was done by a scalloped hammerhead as they are often confused with other large hammerheads.[2]
Scalloped hammerheads are very vunerable to fishing.[1] They are in the list of "globally endangered" animals.[6]
Classification:
The scalloped hammerhead belongs to the family Sphynidae, a monophyletic clade characterized by their flattened and laterally extended heads, known as cephalofoil.[7] According to a tree created in 2007, it's closest relative within the family is the smooth hammerhead. It is also closely related to the great hammerhead.
The scalloped hammerhead is one of the seven species belonging to the Genus Sphyrna, which is (together with Eusphyra) one of the two Geni belonging to the family Sphyrnidae.[8]
Sources:
[1] www.flmnh.ufl.edu/fish/Gallery/Descript/Schammer/ScallopedHammerhead.html
[2] Leonard J. V. Compagno (1984) Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 2. Carcharhiniformes. FAO Species Catalogue for Fishery Purposes. pp. 545–546. pdf
[3] Steven Branstetter (1987) Age, growth and reproductive biology of the silky shark, Carcharhinus falciformis, and the scalloped hammerhead, Sphyrna lewini, from the northwestern Gulf of Mexico Volume 19, Issue 3, pp. 161-173 link
[4] A. Peter Kimley (1987) The determinants of sexual segregation in the scalloped hammerhead shark, Sphyrna lewini Environmental Biology of Fishes Volume 18, Issue 1, pp 27-40 pdf
[5] Stephen M. Kajiura and Kim N. Holland Electroreception in juvenile scalloped hammerhead and sandbar sharks link
[6] www.redorbit.com/news/science/1259813/hammerhead_shark_makes_endangered_species_list/
[7] Compagno LJV. 1988. Sharks of the order Carcharhiniformes. Princeton, NJ: Princeton Univ. Press.
[8] Mauro José Cavalcanti (2007) A Phylogenetic Supertree of the Hammerhead Sharks (Carcharhiniformes: Sphyrnidae) Zoological Studies46(1): 6-11
Cladistic:
Animalia
Chordata
Chondrichthyes
Elasmobranchii
Carcharhiniformes
Sphyrnidae
Sphyrna
S. lewini (Griffith & Smith, 1834)[1]
Description:
The scalloped hammerhead (originally described as Zygaena lewini by Griffith and Smith in 1834.[1]) is a shark with a broad, narrow-bladed head, which is 24-30% (mostly above 26%) as wide, as the shark is long. So, the head may be quite wide, but it is rather short (1/3-1/5 of the head's width). It's teeth have weakly serrated edges (juveniles lack those), the anterior teeth are moderately long and the crown can be either stout or slender. The posterior teeth are mostly cuspidate. The scalloped hammerhead has a falcate first dorsal fin and a second one, who is a not as tall and more concave.
This shark can have a total vertebral centra number of 174 to 209. Its back is grey, its belly is white and it's fins have black tips.[2]
Adult males can be 2,1-2,2 m long and adult females 2,25 m+.[3] Large ones can be over 3 m long. The maximum is more than 4 m in females and ~3 m in males.[2] The maximum known weight is ~150 kg.[1] A 1,40-1,65 m long male can be called an adult a female at 2,12 m. A new born scalloped hammerhead can range in size from 42 to 55 cm.[2] In the northwestern Atlantic Ocean, males mature at 1,8 m in length and 29 kg in weight, while females do so at 2,5 m in length and 80 kg in weight. Scalloped hammerheads can live 30 years.[1]
Habitat:
Scalloped hammerheads are among the most abundant hammerhead species. They are found in warm seas, near the coasts. They are often found in the Indo-West Pacific. Prefered depths range from the surface, to 275 m below the surface.[2] Females usually dive deeper.[4] Scalloped hammerheads often migrate, in the summer, some populations migrate to areas closer to the poles, like South Africa. The populations of East China may not migrate.[2]
Diet:
The diet varies between the sexes. Females attack more pelagic prey and they are more succesful.[4] Juvenile scalloped hammerheads prey on benthic fishes and crustaceans.[5] Benthic fishes only make up 15% of the diet of adult females.[4] The diet of adults includes Food sardines and herring, anchovies, ten-pounders (Elopidae), conger eels, milkfish, sea catfish, silversides, halfbeaks, mullet, lizardfish, barracuda, bluefish, spanish mackeral, jacks, porgies, mojarras, cardinal fishes, goatfish, grunts, damselfishes, parrotfishes, wrasses, butterfly fishes, surgeonfish, gobies, flatfish, sharpnose sharks (Rhizoprionodon), blacktip reef sharks, angelsharks, stingrays, squid, octopi, cuttlefishes, sea snails, shrimp, mantis shrimp, crabs, lobsters and isopods.[2]
Social behaviour:
Scalloped hammerheads are known for their social behaviour. Juveniles live in large schools, while larger sharks are either solitary or living in pairs. They also can occur in small schools. Females in the Gulf of California have shown a wide range of behaviours.[1] These include ramming each other, shaking the head while smimming acceleratedly, corkscrew swimming, lateral tiling of the body (maybe for the field of vision), jaw opening and caspler flexion.[2]
Predators and parasites:
An adult scalloped hammerhead has no major predators, but parasites. These are external leeches (Stilarobdella macrotheca) and copepods (Alebion carchariae, A. elegans, Nesippus crypturus, Kroyerina scotterum), hence they often visit reefs ("cleaning stations") to let cleaner wrasses eat the parasites.[1]
Reproduction:
Scalloped hammerheads are viviparous, having a gestation period, which lasts 9 to ten months.[1] Litters can include 15 to 31 babys. The Kaneohe Bay (Hawaii) represents a nursey are used by scalloped hammerheads. Neonates stay close to the bay, but as they grow, they more and more start leaving it.[2]
Scalloped hammerheads and humans:
The scalloped hammerhead is seen as potentionally dangerous to humans. There exist provoked and unprovoked attacks on swimmers, divers and boats, but in most cases, it isn't sure whether it was done by a scalloped hammerhead as they are often confused with other large hammerheads.[2]
Scalloped hammerheads are very vunerable to fishing.[1] They are in the list of "globally endangered" animals.[6]
Classification:
The scalloped hammerhead belongs to the family Sphynidae, a monophyletic clade characterized by their flattened and laterally extended heads, known as cephalofoil.[7] According to a tree created in 2007, it's closest relative within the family is the smooth hammerhead. It is also closely related to the great hammerhead.
The scalloped hammerhead is one of the seven species belonging to the Genus Sphyrna, which is (together with Eusphyra) one of the two Geni belonging to the family Sphyrnidae.[8]
Sources:
[1] www.flmnh.ufl.edu/fish/Gallery/Descript/Schammer/ScallopedHammerhead.html
[2] Leonard J. V. Compagno (1984) Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 2. Carcharhiniformes. FAO Species Catalogue for Fishery Purposes. pp. 545–546. pdf
[3] Steven Branstetter (1987) Age, growth and reproductive biology of the silky shark, Carcharhinus falciformis, and the scalloped hammerhead, Sphyrna lewini, from the northwestern Gulf of Mexico Volume 19, Issue 3, pp. 161-173 link
[4] A. Peter Kimley (1987) The determinants of sexual segregation in the scalloped hammerhead shark, Sphyrna lewini Environmental Biology of Fishes Volume 18, Issue 1, pp 27-40 pdf
[5] Stephen M. Kajiura and Kim N. Holland Electroreception in juvenile scalloped hammerhead and sandbar sharks link
[6] www.redorbit.com/news/science/1259813/hammerhead_shark_makes_endangered_species_list/
[7] Compagno LJV. 1988. Sharks of the order Carcharhiniformes. Princeton, NJ: Princeton Univ. Press.
[8] Mauro José Cavalcanti (2007) A Phylogenetic Supertree of the Hammerhead Sharks (Carcharhiniformes: Sphyrnidae) Zoological Studies46(1): 6-11
