Smooth hammerhead shark
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Smooth hammerhead shark ( Sphyrna zygaena ) |
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| Sphyrna zygaena | ||||||||||||
| ( Linnaeus , 1758) |
The smooth hammerhead shark ( Sphyrna zygaena ) belongs to the family of hammerhead sharks (Sphyrnidae). It is after the great hammerhead shark ( Sphyrna mokarran ) with a maximum length between 3.70 and 4.00 meters, the second largest shark within this family. Unlike other hammerheads, this species prefers moderate water temperatures, which means that it can be found significantly further north than its relatives. In summer, the animals migrate towards the poles in colder water areas, where they can form schools of hundreds or even thousands of animals.
The smooth hammerhead shark is an active hunter and feeds on a wide variety of bony and cartilaginous fish including small sharks and members of their own species, as well as invertebrates such as cephalopods and crustaceans . Like all other great hammerhead sharks, this species is classified as potentially dangerous to humans. However, hammerhead shark accidents are very rarely documented and due to its preference for cooler waters, this shark is likely to be responsible for very few accidents. Because of its large fins and skin, it is hunted commercially and is classified by the International Union for Conservation of Nature (IUCN) as "endangered" ( vulnerable ).
features
After the great hammerhead, the smooth hammerhead is the largest type of hammerhead. The average size is between 2.50 and 3.50 meters, but there are also larger specimens with a body length of up to 3.70 and 4.00 meters (according to other sources up to 5.00 meters) and a maximum weight of 400 kilograms. The back color is dark brown-gray to olive green and becomes lighter on the flanks. The belly is white and the pectoral fins may have black edges or tips on the underside.
It can be distinguished from other hammerheads by the shape of its widened head ( cephalofoil ), which has a rounded front without an indentation in the middle of the head. The cephalofoil has a width of 26 to 29% of the body length. The nostrils are near the ends of the cephalofoil and have long pits that reach the center of the head. There are 26 to 32 teeth in the upper jaw and 25 to 30 teeth in the lower jaw. As with other sharks, there are more rows of teeth behind these teeth. The teeth are triangular with smooth or slightly serrated cutting edges.
The body is streamlined with an interdorsal ridge between the two dorsal fins. Like all species of the family also owns the Hammerhead 5 gill slits , a suction hole missing. It has a comparatively large and sickle-shaped first dorsal fin with a rounded tip, which attaches at the level of the inner edge of the pectoral fins. The anal fin is larger than the second dorsal fin and has a long, free end. The pectoral and ventral fins are not crescent-shaped and instead have a straight fin edge, which distinguishes them from those of the great hammerhead. The skin teeth ( placoid scales ) are very close together and have 5 to 7 horizontal ridges and a W-shaped rear edge in adult specimens (3 in young animals).
distribution and habitat
In contrast to all other hammerhead sharks, the smooth hammerhead shark is relatively tolerant of cooler water in the temperate zones , which makes it more northerly than all other species. It is found in temperate and subtropical waters of the Atlantic Ocean , the Pacific Ocean and the Indian Ocean mainly near the coast of the continental shelf . It can be found in the western Atlantic from Nova Scotia , Canada , to the Virgin Islands and from Brazil to southern Argentina , in the eastern Atlantic the area extends from the British Isles to Côte d'Ivoire , including the Mediterranean . In the Indian Ocean it occurs on the coasts of South Africa , India and Sri Lanka . In the western Pacific, the distribution area extends from the Gulf of Tonkin to southern Japan and Siberia , and it has also been proven for the coastal areas of southern Australia and New Zealand . He lives in the Central and East Pacific around Hawaii and from California to Panama , the Galapagos Islands and Ecuador to Chile . It is commonly believed that the species avoids tropical waters, but there have been some sightings from tropical waters in the Gulf of Mannar off India and off southern Mozambique . These occurrences are difficult to confirm and there could be confusion with other species.
Compared to the great hammerhead and the bow-forehead hammerhead, the smooth hammerhead lives closer to the water surface at depths that usually do not exceed 20 meters. However, individual animals were registered at depths of up to 200 meters. It prefers coastal waters in the area of bays and estuaries , but also occurs further in the open ocean above the continental shelf and in the area of archipelagos. The shark tolerates brackish water and has also been seen entering freshwater rivers such as the Indian River in Florida . In summer the animals migrate towards the poles in colder waters and in winter they return towards the equator .
Way of life
Sexually mature smooth hammerheads are mostly solitary animals or form small groups. During their annual migrations, they sometimes come together in very large numbers, with schools with more than a hundred individuals off the Eastern Cape of South Africa and schools with several thousand individuals off the coast of California. Especially in summer and in warm weather, they can be observed as surface swimmers with their dorsal fin sticking out of the water.
The young sharks can be captured by other, larger sharks such as the black shark ( Carcharhinus obscurus ) as well as by individuals of their own species. Great hammerheads can be prey of the great killer whale ( Orcinus orca ), as observations from New Zealand show. The nematode worms Parascarophis sphyrnae and Contracaecum spp are known parasites of the hammerhead shark .
nutrition
The smooth hammerhead shark is an active hunter who feeds on bony fish , rays , other sharks including small members of their own species, cephalopods and, to a lesser extent, crustaceans such as shrimp , crabs and barnacles . They also eat carrion and bait from fishing lines. In some regions, like the great hammerhead shark, stingrays are the preferred prey and represent a large proportion of the prey. The poisonous spines of these rays are found accordingly often in and around the mouth of the shark, a captured specimen of the great hammerhead shark had a total of 95 sting in the mouth. In Northern Europe the smooth hammerhead feeds mainly on herring and sea bass , while in North America it mainly prey on mackerel and menhaden . Off South Africa it lives mainly on cephalopods such as Loligo vulgaris and on small schooling fish such as sardines in the coral reef area on the edge of the continental shelf, with larger individuals increasingly preying on small sharks and rays. Even before Australia, cephalopods are the most important food source, followed by small bony fish.
Reproduction and development
Like all hammerhead sharks, this species is viviparous (ovoviviparous), whereby the unborn young sharks are fed via a yolk sac placenta . After the yolk supply has been used up by the young sharks , the yolk sac is transformed into a placenta that is analogous to that of mammals and ensures nutrition via the maternal bloodstream in the course of further development. After a gestation period of 10 to 11 months, the females have between 29 and 37 young animals with a size of around 50 to 61 centimeters. Birth takes place in shallow bays such as Bulls Bay in North Carolina , which serve as "maternity wards".
The females reach sexual maturity with a body length of about 2.70 meters, the males regionally different with 2.10 to 2.50 meters. Off South Africa, newly fertilized females were caught in February and females with almost fully grown embryos in November; off Australia the females get their young between January and March, at the same time ovulation takes place there. The lifespan of the sharks is more than 20 years.
Systematics
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Relationships among hammerheads according to Cavalcanti 2007
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Relationships among hammerheads according to Lim et al. 2010
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The smooth hammerhead was first described in 1758 by the Swedish naturalist Carl von Linné in his well-known 10th edition of the Systema naturae as Squalus zygaena . Linnaeus did not assign this type to any type as a reference individual. The name was later changed to the current name Sphyrna zygaena . The species name zygaena is derived from the Greek word zygon ( Greek ζυγόν ), which denotes the yoke of a draft animal and refers to the shape of the shark's head.
A total of eight species are listed in the genus Sphyrna , which together with the genus Eusphyrna formed only by the winged hammerhead shark ( Eusphyra blochii ) form the family of hammerheads (Spyrnidae). On the basis of phylogenetic studies on the basis of morphological and molecular biological characteristics ( isoenzymes and mitochondrial DNA ) it could be proven that the smooth hammerhead is the sister species of the great hammerhead ( Sphyrna mokarran ) and the bow-forehead hammerhead ( Sphyrna lewini ) and forms a taxon with them , which is compared to the other species of the genus Spyrna . The position of the large species with particularly expansive cephalofoil could also be confirmed by further investigations in 2010, whereby the results regarding the relationships between the species differ slightly from the results of 2007: Here only the great hammerhead and the smooth hammerhead form a common taxon , while the bow-fronted hammerhead shark is assigned to the group of all other hammerhead sharks as a basal species.
The phylogenetic position of the large species between the wingtip hammerhead ( Eusphyrna blochii ) and the smaller hammerheads with a significantly narrower head suggests that within the hammerheads a large cephalofoil represents the original condition and the narrower head is derived from this. Associated with this is a change in the function of the cephalofoil, which is reflected in the way of life of hammerhead sharks: While a wide cephalofoil occurs mainly in free-swimming species of the pelagic and here primarily acts as a hydrofoil, the smaller species with smaller cephalofoil live mainly near the ground as well as in muddy coastal areas and use the equipment of the sensory organs, in particular the Lorenzini ampoules, to localize prey. Regarding height, Lim et al. 2010 due to their kinship hypothesis and the distribution of the species that the most original hammerheads were large species, from which both the small wingtip hammerhead and the smaller Sphyrna species are derived.
Relationship with people
Because of its size, the smooth hammerhead shark - like all other large hammerhead sharks, especially the great and the bow-forehead hammerhead - is classified as potentially dangerous to humans. As of 2009, the International Shark Attack File recorded 34 attacks by hammerheads of the Sphyrna genus on humans, 17 of which were unprovoked, one of which was fatal. Due to the difficulty of differentiating between the sharks, it is unclear how many of these attacks were carried out by smooth hammerheads; the only reliable assignment was in the case of an unprovoked accident. However, since the hammerhead shark lives mainly in the waters of the temperate zones, where people are less frequent in the sea, only a few attacks are likely to be attributed to it. Off the southern coast of California, the shark has been documented to steal catches from sport fishermen and divers.
Like the great hammerhead, the smooth hammerhead is fished worldwide, especially off the coasts of the United States (east and west coasts), Brazil , Spain , Taiwan , the Philippines , southwestern Australia and west Africa. Mainly fishing nets and longlines are used. The catch quotas are difficult to determine because there is usually no distinction between the individual hammerhead species. The meat is freshly dried and salted as well as smoked, but is generally not very popular and is therefore rarely used. The fins in particular are of great value for the Asian market, where they are processed into shark fin soup together with those of other large sharks ; This means that the caught sharks are often only cut off the fins and the injured animals are then thrown back into the sea ( shark finning ). In addition, their skin is processed into shark leather , the liver oil obtained from their liver is used to obtain vitamins and their carcasses are used for fish meal production. The shark is also used in traditional Chinese medicine .
Like other sharks, the smooth hammerhead shark is also unintentionally caught as bycatch and killed. Another man-made cause of death is shark nets , which are put up to protect beaches and in which many sharks become entangled. Between 1978 and 1990, fewer than 10 smooth hammerhead sharks were caught in the nets off KwaZulu-Natal , South Africa, while in the nets off New South Wales , Australia, they made up 50% of the 4,715 sharks caught between 1972 and 1990 . The shark is currently classified globally as "vulnerable" by the International Union for Conservation of Nature and Natural Resources (IUCN). In New Zealand's waters, the species is a prohibited fishing target and is the most common shark on the northwest coast. In addition, fishing off the coast of South Australia does not appear to have had a negative impact on stocks. Catches off the east coast of the United States are regulated by the Atlantic shark Fishery Management Plan (FMP) of the National Marine Fisheries Service (NMFS), where this species is classified as a "Large Coastal Shark" (LCS).
In March 2013, at the CITES Species Conservation Conference in Bangkok , it was decided to regulate the trade in hammerhead sharks; the regulation came into force on September 14, 2014.
Individual evidence
- ↑ a b c d Sphyrna zygaena in the Red List of Threatened Species of the IUCN 2010. Posted by: BM Caspar u. a., 2005. Retrieved September 15, 2010.
- ^ A b c d Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton University Press, Princeton 2005; Pp. 324-325. ISBN 0-691-12072-2 .
- ↑ a b c d e f g h i j k l m Bester, C. Biological Profiles: Smooth Hammerhead . Florida Museum of Natural History Ichthyology Department. Retrieved on October 19, 2008.
- ↑ a b c d e f g Compagno, LJV: Sharks of the World: An Annotated and Illustrated Catalog of Shark Species Known to Date . Food and Agricultural Organization, Rome 1984, ISBN 92-5101384-5 , pp. 548-549.
- ↑ Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean. Franckh-Kosmos, Stuttgart 2005; Pp. 216-218. ISBN 3-440-10458-3 .
- ↑ a b c Ebert, DA: Sharks, Rays, and Chimaeras of California . University of California Press, 2003, ISBN 0-520-23484-7 , pp. 178-179.
- ↑ Visser, IN: First Observations of Feeding on Thresher ( Alopias vulpinus ) and Hammerhead ( Sphyrna zygaena ) Sharks by Killer Whales ( Orcinus orca ) Specializing on Elasmobranch Prey . In: Aquatic Mammals . 31, No. 1, January 2005, pp. 83-88. doi : 10.1578 / AM.31.1.2005.83 .
- ↑ Strong, WR, Snelson, Jr., FF, and Gruber, SH: Hammerhead Shark Predation on Stingrays: An Observation of Prey Handling by Sphyrna mokarran . In: American Society of Ichthyologists and Herpetologists (Eds.): Copeia . 1990, No. 3, September 19, 1990, pp. 836-840. doi : 10.2307 / 1446449 .
- ↑ a b c d e Fowler, SL, Cavanagh, RD, Camhi, M., Burgess, GH, Cailliet, GM, Fordham, SV, Simpfendorfer, CA and Musick, JA: Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes . International Union for Conservation of Nature and Natural Resources, 2005, ISBN 2-8317-0700-5 , pp. 106-109, 318-320.
- ↑ Smale, MJ: Occurrence and feeding of three shark species, Carcharhinus brachyurus , C. obscurus and Sphyrna zygaena , on the Eastern Cape coast of South Africa . In: South African Journal of Marine Science . 11, No. 1, December 1991, pp. 31-42.
- ↑ Sumich, JL and Morrissey, JF: Introduction to the Biology of Marine Life , eighth. Edition, Jones & Bartlett Publishers, 2004, ISBN 0-7637-3313-X , p. 197.
- ↑ a b c Mauro José Cavalcanti: A Phylogenetic Supertree of the Hammerhead Sharks (Carcharhiniformes: Sphyrnidae) . In: Zoological Studies . tape 46 , no. 1 , 2007, p. 6–11 ( digitized version [PDF; 175 kB ]).
- ↑ a b c Douglas D. Lim, Philip Motta, Kyle Mara, Andrew P. Martin: Phylogeny of hammerhead sharks (Family Sphyrnidae) inferred from mitochondrial and nuclear genes . In: Molecular Phylogenetics and Evolution . tape 55 , no. 2 , 2010, ISSN 1055-7903 , p. 572-579 , doi : 10.1016 / j.ympev.2010.01.037 .
- ^ Ellis, R .: The Book of Sharks . Alfred A. Knopf Inc, New York 1989, ISBN 0-679-72210-6 .
- ^ ISAF Statistics on Attacking Species of Shark . International Shark Attack File, Florida Museum of Natural History, University of Florida. Retrieved on April 24, 2009.
- ↑ Smooth hammerhead on Fishbase.org (English)
- ↑ Cites resolution: Endangered shark and manta ray species should be protected Spiegel Online from March 11, 2013
- ↑ Species protection: These sharks must now be better protected by humans. 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. FAO Species Catalog for Fishery Purposes. Volume 4, FAO, Rome 1984; Pp. 545-554 ISBN 92-5-101383-7 . ( Family Sphyrnidae Gill, 1872 , species portrait )
- Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton University Press , Princeton 2005; P. 326. ISBN 0-691-12072-2 .
- Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean. Franckh-Kosmos, Stuttgart 2005; Pp. 221-223. ISBN 3-440-10458-3 .
Web links
- Sphyrna zygaena on Fishbase.org (English)
- Sphyrna zygaena. In: Shark Foundation.
