Bow-forehead hammerhead
| Bow-forehead hammerhead | ||||||||||||
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Bow-fronted hammerhead shark ( Sphyrna lewini ) |
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| Sphyrna Lewini | ||||||||||||
| ( Griffith & Smith , 1834) |
The bow- fronted hammerhead shark or notched hammerhead shark ( Sphyrna lewini ) belongs to the family of hammerhead sharks (Sphyrnidae) and reaches maximum sizes between 3.7 and 4.3 meters and a weight of more than 150 kilograms . It is probably the most common hammerhead shark near the coast and is distributed almost worldwide in tropical, subtropical and temperate regions. Unlike many other sharks, it forms large groups and some populations show marked migratory behavior.
Like all other large hammerhead sharks, this species is classified as potentially dangerous to humans, but shark accidents with hammerhead sharks are very rarely documented. Because of its fins and his skin, he is hunted commercially and is known as "high risk" (endangered) classified.
features
The bow-forehead hammerhead reaches maximum sizes between 3.7 and 4.3 meters and a weight of more than 150 kilograms. The front edge of the very broad, flattened and hammer-shaped head of this species is arched (hence the name) and has an indentation or notch in the middle, the rear edge is concave. The width of the head corresponds to between 24 and 30 percent of the total length of the shark. It forms a hammer head ( cephalofoil ) that is very noticeable compared to other hammerheads . The mouth on the underside of the head is wide and parabolic in shape with short lip folds (labial folds). The eyes at the ends of the extended head are small, the nasal pits in front of them are noticeably large. The teeth have serrated edges, which are still missing in young sharks, and only have one point. There are 15 to 16 teeth on each side in both the lower and upper jaw and flank one or two frontal teeth.
The first dorsal fin of the bow-forehead hammerhead is very large and high. It starts at the level of the free rear ends of the pectoral fins and is slightly sickle-shaped. The second dorsal fin is very small in relation to the first and has an extended rear end that extends almost to the caudal fin. The anal fin is significantly larger than the second dorsal fin. The pectoral fins are set on broad and relatively short. The caudal fin has a relatively short lower lobe and a very large upper lobe that ends in a separate end lobe. There are no injection holes in hammerhead sharks; like other ground sharks, they have five gill slits , the fourth and fifth gill slits in this species being above the pectoral fin.
The upper side of the body is colored olive, bronze or dark gray-brown, the abdominal region is whitish and the undersides of the pectoral fins have dark ends on a white background. At the tip of the pectoral fin, these spots merge into a blurred, black fin tip. In very rare cases, albinotic animals can occur.
Upper row of teeth
Lower row of teeth
Cub
distribution and habitat
The bow-forehead hammerhead is found almost worldwide in coastal regions of tropical, subtropical and temperate regions. It is probably the most common hammerhead shark in coastal regions. The distribution area includes the western Atlantic (New Jersey to Brazil, Gulf of Mexico and the Caribbean), the eastern Atlantic (Senegal to Zaire), the Red Sea , the Indian Ocean (South Africa, Pakistan, India, Maldives, Thailand), the western Pacific (Indonesia, China, Japan, Australia), the Central Pacific (Hawaii and Tahiti) and the Eastern Pacific (Southern California to Ecuador). In the Mediterranean these sharks rarely occur and hike probably the Suez Canal and the Strait of Gibraltar , a, a reproduction does not take place here.
The sharks move between the water surface and depths of at least 275 meters, whereby they mainly occur in the area of the continental shelf . They can be found both in open water near the coast and in open water ( pelagic ). However, the sharks can also appear in very shallow bank zones and swim in estuaries and bays. On coral reefs they can be found on the outer reef slope. Young animals usually spend their first years of life due to better protection from larger predatory fish in shallower waters where they are also born.
Way of life
behavior
Adult animals either live in pairs or as solitary animals and are predominantly nocturnal. The young live in schools of up to several hundred animals, as they are regularly observed in the Gulf of California and in the area of several archipelagos such as the Galapagos Islands . Larger schools can also be set up seasonally or regionally. Some populations are tied to a specific location, as in the area of the East China Sea , while others migrate over long distances in the direction of the South Pole, such as the population off Natal , South Africa .
As a rule, the sharks swim in a normal body position, but with this species the impressive "corkscrew swimming", in which the shark rotates around its axis in a forward movement, as well as the movement in a lateral or supine position can be observed. Together with other behaviors such as shaking the head, opening the mouth, splaying the clasps or lightly ramming each other with the head, this occurs mainly in shark groups and is probably used for communication with each other and expresses aggression and threats or territorial behavior. Many females and some males have scars given by other females defending their territory.
nutrition
The food of the bow-forehead hammerhead consists mainly of various bony fish such as sardines, herrings and mackerel, but barracudas and other larger fish are also accepted as prey. The sharks also feed on invertebrates , especially cephalopods such as octopuses and squids, as well as crustaceans. In addition, he also hunts small sharks such as sharp -nosed sharks , nurse sharks or blacktip reef sharks as well as rays , including stingrays .
Predators and parasites
Young hammerhead sharks can represent prey for larger shark species, but adult animals have hardly any predators. As with most larger marine animals, they are attacked by a number of parasites, including, in particular, leeches such as Stilarobdella macrotheca or crustaceans such as Alebion carchariae , Alebion elegans , Nesippus crypturus and Kroyerina scotterum .
Reproduction
Like all hammerhead sharks, this species is viviparous (ovoviviparous), whereby the unborn young sharks are fed via a yolk sac placenta . After being consumed by the young sharks, the yolk sac is transformed into a placenta, which is analogous to that of mammals and ensures nutrition via the maternal bloodstream in the course of further development.
After a gestation period of 9 to 10 months, the females give birth to 13 to 38 young animals; to do this, they usually go to shallower sea regions, where the young sharks also spend their first years of life. The young animals are between 40 and 55 centimeters tall at birth. The animals grow relatively slowly and reach sexual maturity with a body length of 140 to 210 centimeters for the males and 200 to 230 centimeters for the females. The maximum service life is estimated at over 30 years.
Systematics
External system
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Relationships among hammerheads
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The bow-forehead hammerhead was first described in 1834 by Edward Griffith and Charles Hamilton Smith as Zygaena lewini , but later assigned to the genus Sphyrna described by Constantine S. Rafinesque-Schmaltz , to which it still belongs today. A total of eight species are listed in this genus, which together with the genus Eusphyrna, which is only formed by the winged hammerhead shark ( Eusphyra blochii ), form the family of hammerheads (Spyrnidae).
On the basis of phylogenetic studies of morphological and molecular biological characteristics ( isoenzymes and mitochondrial DNA ) it could be proven that the bow-forehead hammerhead is the sister species of the smooth hammerhead ( Sphyrna zygaena ) and that both form a taxon together with the great hammerhead ( Sphyrna mokarran ) , which is contrasted with the other species of the genus Spyrna .
Internal system
In 2006, the research group led by Joseph M. Quattro determined using molecular biological methods that there is a comparatively large genetic difference in the mitochondrial DNA between bow-forehead hammerheads from different regions within the species. Using their data, the authors identified a population in the north-western Atlantic, which they assessed as a potentially unique, cryptic species . In the same year, another working group identified the very close connection of female bow-forehead hammerheads to specific regions that serve as the birthplaces of the young sharks, as well as the associated genetic isolation of individual populations.
The white-finned hammerhead shark ( Sphyrna couardi ) listed in older literature as an independent species was synonymous with the bow-forehead hammerhead shark.
Relationship with people
Bow-forehead hammerheads are generally not aggressive towards humans and are usually rather shy. Aggressive behavior towards divers has also been observed.
The bow-forehead hammerhead, like all other great hammerhead sharks, is classified as potentially dangerous to humans. Encounters with divers and swimmers are comparatively frequent due to its coastal lifestyle. The number of unprovoked attacks is very low, however, altogether only 21 shark accidents have been documented for all hammerhead shark species of the genus Sphyrna , two of which were fatal. A precise assignment to certain species is usually not made, especially between the bow-forehead hammerhead and the great hammerhead shark ( Sphyrna mokarran ).
The shark is fished both commercially and in recreational fishing . It can be caught both in the coastal area and in the high seas, using long lines as well as bottom and trawl nets. As with other large sharks, the large fins are particularly popular in Asia as the basis of the well-known shark fin soup , the mostly still living torso is very often thrown back into the sea after removal ( shark finning ) , where it dies. However, the meat of the animals and, above all, the skin ( shark leather ) are also regularly used, the remains are used to make fish meal and obtain vitamins.
In addition, there are regularly high numbers of bycatches in regions where hammerhead sharks are not hunted themselves , as the animals near the coast are usually associated with commercially highly sought-after and heavily fished species. Due to the very imprecise data on deep-sea fishing, however, there are no specific catch figures or information on population sizes and changes.
The bow-fronted hammerhead shark is widely considered to be one of the most common hammerhead species. He is still in its entire distribution area as a "high risk" (endangered) in the Red List of Threatened Species of IUCN classified. In March 2013, at the CITES Species Conservation Conference in Bangkok , it was decided to regulate the trade in bow-forehead hammerheads; the regulation came into force on September 14, 2014.
Individual evidence
- ↑ a b c d e f g h i j k l Leonard J. V. Compagno: Sharks of the world. An annotated and illustrated catalog of shark species known to date. Part 2. Carcharhiniformes. In: FAO Species Catalog for Fishery Purposes. tape 4 . FAO, Rome 1984, ISBN 92-5101383-7 , Family Sphyrnidae Gill, 1872, p. 545-547 ( fao.org [PDF]).
- ^ A b Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton University Press, Princeton 2005, ISBN 0-691-12072-2 , pp. 323-324.
- ↑ a b c d e Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean. Franckh-Kosmos, Stuttgart 2005, ISBN 3-440-10458-3 , pp. 213-215.
- ↑ a b c d e f g h i j k Cathleen Bester: Scalloped Hammerhead. In: Florida Museum of Natural History. Retrieved September 1, 2010 (English).
- ↑ a b K. M. Duncan et al. a .: Global phylogeography of the scalloped hammerhead shark ( Sphyrna lewini ). In: Molecular Ecology. 15, No. 8, 2009, pp. 2239-2251, doi: 10.1111 / j.1365-294X.2006.02933.x .
- ↑ a b Mauro José Cavalcanti: A Phylogenetic Supertree of the Hammerhead Sharks (Carcharhiniformes: Sphyrnidae) . In: Zoological Studies . tape 46 , no. 1 , 2007, p. 6–11 ( zoolstud.sinica.edu.tw [PDF; 171 kB ]).
- ↑ JM Quattro u. a .: Genetic evidence of cryptic speciation within hammerhead sharks (Genus Sphyrna). In: Marine Biology. 148, No. 5, 2006, pp. 1143-1155, doi: 10.1007 / s00227-005-0151-x .
- ^ R. Aidan Martin: Recent Changes in Hammerhead Taxonomy. In: ReefQuest Center for Shark Research. February 24, 1998, accessed October 18, 2008 .
- ↑ a b c Sphyrna lewini in the Red List of Threatened Species of the IUCN 2010. Posted by: J. Baum u. a., 2007. Retrieved July 18, 2010.
- ^ Cites resolution: Endangered shark and manta ray species should be protected . Spiegel Online from March 11, 2013.
- ↑ Protection of species: Humans now have to protect these sharks better . The time of September 12, 2014.
literature
- Leonard J. V. Compagno : Sharks of the world. An annotated and illustrated catalog of shark species known to date. Part 2. Carcharhiniformes. In: FAO Species Catalog for Fishery Purposes. Volume 4, FAO Rome 1984, ISBN 92-5-101383-7 , pp. 545-554 ( fao.org , Family Sphyrnidae Gill, 1872 ).
- Leonard J. V. Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton University Press , Princeton 2005, ISBN 0-691-12072-2 , pp. 323-324.
- Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean. Franckh-Kosmos, Stuttgart 2005, ISBN 3-440-10458-3 , pp. 213-215.
Web links
- Bow-fronted hammerhead on Fishbase.org (English)
- Bow-forehead hammerhead. In: Shark Foundation.
- Cathleen Bester: Scalloped Hammerhead. In: Florida Museum of Natural History. Retrieved December 9, 2008.
