Small-eyed hammerhead shark
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Small-eyed hammerhead shark ( Sphyrna tudes ) |
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| ( Valenciennes , 1822) |
The small-eyed hammerhead shark ( Sphyrna tudes ) is a relatively small species from the family of hammerhead sharks (Sphyrnidae) with an average body length of 1.20 to 1.30 meters . It lives in the tropical and subtropical coastal areas and the continental shelf in the western Atlantic Ocean from Venezuela to Uruguay . Its habitat is muddy and cloudy due to the large rivers that flow into it, with limited visibility, in which the eyes are secondary as a sense organ and in this species are correspondingly receded. The adult males and juveniles form groups, while the females tend to live as solitary animals. The light yellow to orange color of the head, the flanks and the fins is striking. Like other hammerheads, this species also has a hammer-shaped enlarged head ( cephalofoil ), which is curved in this species.
The yellow-orange coloring probably comes from shrimps of the species Xiphopenaeus kroyeri , which are the main food of the young sharks, as well as the fish and fish roe, on which the adult sharks mainly feed. Because of its abundance, the small-eyed hammerhead shark is an economically important by-catch for South American coastal fishermen. In recent years the high fishing pressure has led to a sharp decline in the number of stocks. Because of this development and the shark's slow reproductive rates, the International Union for Conservation of Nature (IUCN) classified the shark as potentially endangered ("vulnerable").
features
The small-eyed hammerhead shark is one of the smaller species within the hammerhead group with a maximum body length of 122 to 150 centimeters, although it usually only reaches 120 to 130 centimeters in length and weighs nine kilograms. The body is streamlined and comparatively slim. The head or the cephalofoil is greatly broadened and hammer-shaped, it reaches a width that is between 28 and 32% of the total length of the shark. The front is broadly arched with clear notches in the middle and at both ends. In young animals, the cephalofoil is wider and more curved with more indistinct depressions than in adult sharks. The most striking feature of this hammerhead is its coloration: the back and the dorsal fins are gray to yellowish-gray while the edges of the cephalofoil, the flanks and the ventral side, the pectoral, ventral and anal fins are bright yellow to orange and have a metallic and iridescent color Have a shimmer. Newborn sharks are gray on top with a darker first dorsal fin and upper caudal fin and a whitish belly. With a body length of about 45 centimeters, they get a light yellow color on the underside, which darkens to an orange from about 50 centimeters. Sharks between 55 and 70 centimeters in length have the strongest intensity with a golden color, and this decreases again with sexual maturity. The color disappears very quickly in dead individuals.
The eyes, which are located on the two ends of the cephalofoil, are significantly smaller than those of all other hammerhead shark species and have a nictitating membrane to protect the eye. The nostrils are right in front of the eyes and have a distinct furrow that extends to the center of the cephalofoil. The mouth is strongly curved and contains 15 to 16 teeth on each side of the upper jaw and 15 to 17 teeth on each side of the lower jaw. The teeth of the upper and lower jaw are triangular with a narrow point and serrated smooth to slightly. In the upper jaw they are angled and oblique, while in the lower jaw they are straight.
Like all species of the family also owns the Hammerhead five gill slits , a suction hole missing. The first dorsal fin is large and slightly curved to sickle-shaped and attaches above the base of the pectoral fins . The second dorsal fin is significantly smaller, but relatively large compared to other species, and has a concave rear edge. The pelvic fins have an almost straight rear edge and the anal fin is larger and longer than the second dorsal fin. The asymmetrical caudal fin has a clearly developed lower lobe and a large upper lobe with a small end lobe. The skin teeth ( placoid scales ) are oval with five horizontal keels that terminate in small teeth.
distribution
The distribution area of the small-eyed hammerhead stretches along the subtropical Atlantic coast of South America from Uruguay to Venezuela , with the shark only rarely appearing west of the Orinoco Delta southeast of Trinidad . There are also unconfirmed sightings from the coastal areas of Mexico , Panama and Florida ; further sightings from other marine areas can be considered faulty and result from confusion and the complicated taxonomic history of the species allocation. It is one of the most common sharks within its range.
The species populates cloudy coastal areas at depths of 5 to 40 meters above muddy ground. In doing so, he forms aggregations that are separated according to gender and age; Newborns and young sharks under 40 centimeters in length occur in the shallow water zones and migrate to deeper areas with increasing age. Sexually mature females are mainly found at depths of 9 to 18 meters, while larger juveniles and sexually mature males live at depths of 27 to 36 meters. The species is also tolerant of brackish water and requires a salinity of 20 to 34 ppt.
Way of life
The distribution area of the small-eye hammerhead overlaps with that of four other hammerhead shark species: the two small species of spoon-headed and shovel-nosed hammerheads and the large species of bow-forehead and great hammerhead . Due to their different ways of life, habitats and food specializations , however, there is hardly any competition between these species. The small-eyed hammerhead shark is the dominant species in the shallow and muddy coastal areas, where the high cloudiness severely limits the field of vision and other sensory organs come to the fore; the eyes, which are significantly smaller in this shark, only play a secondary role.
Sexually mature males and young animals of both sexes form schools of animals of the same size, whereby these groups play no role in reproduction or migration. Sexually mature females are likely to be loners.
The predators of the small-eye hammerhead are mainly larger sharks such as the bull shark ( Carcharhinus leucas ), and young animals are also preyed on by larger bony fish. The yellow coloring of the sharks can serve as camouflage in the murky water. A well-known parasite of the small- eyed hammerhead shark is the Monogenea worm Erpocotyle schmitti , and the shark can also serve as a host for ectoparasitic and common Copepoda such as Echthrogaleus coleoptratus , Pandarus saturus and P. cranchii .
nutrition
Young small- eyed hammerheads with a body length of less than 67 centimeters feed mainly on flagellated shrimp (Penaeidae), in particular of the species Xiphopenaeus kroyeri . The larger sharks prey on bony fish, especially cross catfish (Ariidae) and in doing so also take in their roe , as they are mouthbrooders . The shrimp as well as the phlegm coating of the fish and the eggs of the catfish contain large amounts of carotenoids , which are probably the reason for the strong yellow to orange coloration of the sharks; It is unclear whether the color of the catfish can also be traced back to the shrimp. In 1996 it was shown that the carotenoids consist of 98% α- and β-carotenoids while xanthophylls are not included.
The small-eyed smooth shark ( Mustelus higmani ), which also lives in these habitats and also feeds on the carotenoid-rich shrimp, has a yellowish color that does not, however, reach the intensity of the hammerhead. The small-eyed hammerhead also prey on swimming crabs , cephalopods , umberfish and newborn bow-forehead hammerheads.
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. The females only have one fully developed ovary , but two uteri . Due to the fact that ovulation is also possible during the gestation period, they can bear and give birth to young animals every year.
The number of young animals and the development of the small-eyed hammerhead vary depending on the region. Before Trinidad, reproduction takes place during a fixed annual cycle, with mating between August and September and the young in the following year in late May to June. The female carries between five and twelve young animals over a period of ten months, using the prey rich shallow water areas of the bays as a birth and rearing area. The newborn sharks have a size of about 30 centimeters, the males reach sexual maturity with about 80 centimeters and the females with about 90 centimeters. In contrast, the sharks off the coast of the Brazilian state of Maranhão are significantly larger, the males reach sexual maturity with about 92 centimeters and the females with about 101 centimeters. Since the number of juvenile sharks increases with the size of the females, sharks off Maranhão have been documented with up to 19 juveniles. The seasonal cycles do not exist here either: pregnant females were found from June to October and January to April, males ready for copulation appear from May to November and in March.
Systematics
Although the small-eyed hammerhead shark is one of the easiest shark species to identify and also differs significantly from all other hammerhead sharks, its taxonomic classification has repeatedly been subject to uncertainties and revisions in the past. Its scientific name has not yet been conclusively clarified. The first scientific description of the shark was in 1822 by the French zoologist Achille Valenciennes as Zygaena tudes in the journal Memoires du Museum National d'Histoire Naturelle ; the epithet tudes comes from the Latin language and means "hammer". Valenciennes referred to three individuals in his description: a shark from Nice (France), one from Cayenne in French Guiana and one from the Coromandel Coast in India . For more than two centuries, however, taxonomists assumed that the description referred to the great hammerhead , which became known as Zygaena (later Sphyrna ) tudes , while the small-eyed hammerhead was scientifically named Sphyrna bigelowi , first described by Stewart Springer in a 1944 edition of the Journal of the Washington Academy of Sciences .
In 1950 Enrico Tortonese determined that neither the Nice nor the Cayenne individual were great hammerheads, but rather belonged to the species now known as S. bigelow ; the specimen from India had been lost in the meantime, so that no species identification could be carried out for it. Carter Gilbert joined the Tortoneses position in his revision of the hammerheads in 1967 and pointed out that the lost shark from India was probably a great hammerhead while none of the existing individuals belonged to this species. Sphyrna tudes thereby became the official scientific name of the small-eyed hammerhead, while S. bigelowi was postponed as a synonym described later; the great hammerhead was given the scientific name Sphyrna mokarran instead . Gilbert named the specimen from Nice as the lectotype by which S. tudes should be identified, giving it priority over the individual from Cayenne.
In 1981 the two type specimens were examined again by Jean Cadenat and Jacques Blache. They found that the Nice specimen was not a small-eyed hammerhead, but a juvenile of the white-fin hammerhead ( S. couardi , now a synonym for the bow-forehead hammerhead ( S. lewini )) , which was recognized as a species at the time . This explains the unusual location of the shark off the French coast, as according to current knowledge, the shark can only be found on the American coasts. Due to the rules of binomial nomenclature would have to based on this finding Sphyra tudes rather than S. couardi the official name for the white-fin hammerhead be during smalleye hammerhead again as Sphyrna bigelowi be called would. Due to the history of taxonomy, however, the taxonomists have so far not changed their names again and kept S. tudes as their name. This solution would require an official decision of the International Commission for Zoological Nomenclature (ICZN), which would have to reject the position of the Nice specimen as a lectotype and transfer it to the Cayenne specimen; a corresponding petition has not yet been received.
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Relationships among hammerheads
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Relationships among hammerheads according to Lim et al. 2010
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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). Due phylogenetic studies on the basis of morphological and molecular biological characteristics ( isoenzymes and mitochondrial DNA ) could be demonstrated that the smalleye hammerhead the sister species one from the corona hammerhead ( Sphyrna corona ) and the scoophead ( Sphyrna media ) formed taxon represents . This taxon stands opposite the shovel-nosed hammerhead shark ( Sphyrna tiburo ) and all together form a taxon that is compared to the three large species of the genus Spyrna . Another phylogenetic work by Lim et al. 2010 confirms the basic tendency, even if it differs slightly in detail: Here the small-eyed hammerhead shark is identified as a sister species of the spoon-head hammerhead, compared to a taxon made up of corona and shovel-nosed hammerheads.
It becomes clear that the smaller species with the narrower cephalofoil compared to the hammer-headed species represent the derived state and that within the hammerheads a large cephalofoil, like the small-eyed hammerhead, represents the original state. 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 in the free-swimming species of the pelagic and mainly acts as a hydrofoil, the smaller species live with smaller cephalofoil, including the small eyes - Hammerhead sharks, especially near the ground and in muddy coastal areas and use the equipment of the sensory organs, especially the Lorenzini ampoules, to localize prey.
Relationship with people
The small sharks are shy when encountering humans and are harmless due to their small size. They are caught as by-catch in inshore fisheries and marketed as food throughout their range . In the coastal area of Trinidad, Guyana and Brazil they are among the most common sharks caught in this way, with sharks of all ages being found in the fishing nets due to the shape of the head; other individuals are caught on lines or with ground nets.
The International Union for Conservation of Nature (IUCN) classifies this shark as potentially endangered ("vulnerable") because it is under intense fishing pressure and, due to its low reproduction rate, is very susceptible to a population decline. There are individual indications that the catch numbers of the small-eyed hammerhead shark off Trinidad and northern Brazil have already decreased significantly and this can be interpreted as an indication of a population decline in its entire area of distribution. There are currently no protective measures aimed at preserving this species.
Individual evidence
- ^ 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 Sphyrna tudes on Fishbase.org (English)
- ^ A b Ferrari, A. and A. Ferrari: Sharks . Firefly Books, 2002, ISBN 1-55209-629-7 , p. 192.
- ↑ Martin, RA (Aug. 4, 1998). In Search of the Golden Hammerhead . ReefQuest Center for Shark Research. Retrieved on October 17, 2008.
- ^ A b McEachran, JD and Fechhelm, JD: Fishes of the Gulf of Mexico: Myxiniformes to Gasterosteiformes . University of Texas Press, 1998, ISBN 0-292-75206-7 , p. 96.
- ↑ a b c d e f g h i j k Castro, JI: The biology of the golden hammerhead, Sphyrna tudes , off Trinidad . In: Environmental Biology of Fishes . 24, No. 1, 1989, pp. 3-11. doi : 10.1007 / BF00001605 .
- ^ R. Aidan Martin: In Search for the Golden Hammerhead. ReefQuest Center for Shark Research.
- ↑ a b c d e f g h i Compagno, LJV: Sharks of the World: An Annotated and Illustrated Catalog of Shark Species Known to Date . Food and Agricultural Organization of the United Nations, 1984, ISBN 92-5101384-5 , pp. 551-553.
- ↑ Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean. Franckh-Kosmos, Stuttgart 2005; Pp. 219-220. ISBN 3-440-10458-3 .
- ^ A b c d Gallagher, E. Biological Profiles: Smalleye Hammerhead . Florida Museum of Natural History Ichthyology Department. Retrieved on April 23, 2010.
- ↑ a b c d e Sphyrna tudes in the endangered Red List species the IUCN 2010. Posted by: Mycock, SG, Lessa, R. & Almeida, Z., 2006. Retrieved on 5 September, 2010.
- ↑ a b Lessa, R., Menni, RC and Lucena, F .: Biological observations on Sphyrna lewini and S. tudes (Chondrichthyes, Sphyrnidae) from northern Brazil . In: Vie et Milieu / Life & Environment . 48, No. 3, September 1998, pp. 203-213.
- ↑ a b Léopold, M .: Poissons de mer de Guyane . Editions Quae, 2004, ISBN 2-84433-135-1 , pp. 32-33.
- ^ Belleville, B .: Sunken Cities, Sacred Cenotes & Golden Sharks: Travels of a Water-Bound Adventurer . University of Georgia Press, 2004, ISBN 0-8203-2592-9 , pp. 168-176.
- ↑ Suriano, DM and Labriola, JB: Erpocotyle VanBeneden et Hesse, 1863 (Monogenea, Hexabothriidae), parasite of carcharhiniform fishes from the southwestern Atlantic Ocean, with the description of E. schmitti sp. n . In: Acta Parasitologica . 43, No. 1, January 1998, pp. 4-10.
- ↑ Cross catfish on Fishbase.org (English)
- ↑ AB Bodine, JI Castro, JT Wyffels, GJ Shafer, RS Rodgers: Isolation, and characterization of carotenoid pigments from the Golden hammerhead, Sphyrna tudes American Elasmobranch Society 12th Annual Meeting, June 13-19, 1996 in New Orleans, Louisiana ( Abstract ( Memento of the original from July 26, 2011 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. ).
- ^ Valenciennes, A .: Sur le sous-genre Marteau, Zygaena . . In: Memoires du Museum National d'Histoire Naturelle . 9, 1822, pp. 222-228.
- ↑ Springer, S .: . Sphyrna bigelowi , a new hammerhead shark from off the Atlantic coast of South America, with notes on Sphyrna mokarran from New South Wales . In: Journal of the Washington Academy of Sciences . 34, No. 8, 1944, pp. 274-276.
- ↑ Tortonese, E .: A note on the hammerhead shark, Sphyrna tudes Val. After a study of the types . In: Annals and Magazine of Natural History 12th Series . 3, No. 36, 1950, pp. 1030-1033.
- ^ Gilbert, CR: A revision of the hammerhead sharks (family Sphyrnidae) . In: Of the United States National Museum . 119, No. 3539, 1967, pp. 1-88.
- ^ Cadenat, J. and Blache, J .: Requins de Méditerranée et d'Atlantique . Editions de l'Office de la recherche scientifique et technique outre-mer, 1981, ISBN 2-7099-0576-0 , pp. 298-300.
- ↑ a b c d 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; 175 kB ]).
- ^ A b 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, p. 572-579 .
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. 92-5-101383-7. ( Family Sphyrnidae Gill (PDF), 1872, species portrait (PDF))
- Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton University Press , Princeton 2005; Pp. 325-326. ISBN 0-691-12072-2 .
Web links
- Sphyrna tudes on Fishbase.org (English)
- Sphyrna tudes. In: Shark Foundation.
