Galapagos shark
| Galapagos shark | ||||||||||||
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Galapagos shark ( Carcharhinus galapagensis ) |
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| Carcharhinus galapagensis | ||||||||||||
| ( Snodgrass & Heller , 1905) |
The Galapagos shark ( Carcharhinus galapagensis ) belongs to the family of Requiem sharks (Carcharhinidae) and can be found around the world - especially in the vicinity of islands. It owes its name to the first scientific description based on a specimen from the area of the Galápagos Islands . With a maximum body length of 3.70 meters, it belongs to the large shark genera. It prefers clear water around coral reefs and is difficult to distinguish from similar species of the same genus.
Galapagos sharks are active hunters who often appear in large groups and feed primarily on bottom-dwelling bony fish and cephalopods . Larger individuals also prey on rays and other sharks, including their own conspecifics . During reproduction, 4 to 16 young sharks are born alive in shallow water, where they stay to escape larger conspecifics. The sharks are classified as dangerous to humans and are very curious. The International Union for Conservation of Nature (IUCN) puts the species on the warning list of endangered species.
features
With a length of up to 3 meters, the Galapagos shark is one of the larger species of its genus, the known maximum length is 3.70 meters and the maximum weight is 85.5 kilograms. The species has a slim and streamlined body typical of the genus. The color of the back is gray with an indistinct white stripe on the flanks, the belly is white. The edges of the fins are darker or not clearly set off.
The snout is broad and rounded and has only indistinctly developed nasal lobes. The eyes are round and medium-sized. The mouth usually has 14 rows of teeth (13–15) in both halves of the lower and upper jaw, as well as one tooth on the symphysis gland where the halves of the jaw meet. The upper jaws are large and triangular in shape, the lower teeth are narrower. Both the upper and lower teeth have serrated edges. The first dorsal fin is large and slightly sickle-shaped and begins above the rear tips of the pectoral fins . The second dorsal fin begins above the anal fin , an interdorsal ridge is formed between the two fins . The pectoral fins are large and have pointed ends.
The Galapagos shark is difficult to distinguish from other large requiem sharks. It differs from the black shark in that it has larger dorsal fins and larger teeth; compared to the gray reef shark it has a slimmer body and a less pointed first dorsal fin. The species also differ in the number of vertebrae in front of the tail. This is 58 for the Galapagos shark, 86 to 97 for the black shark and 110 to 119 for the gray reef shark.
distribution
Contrary to its name, this species can be found in tropical and subtropical regions around the world, mainly near oceanic islands. Evidence is sometimes uncertain, as this type can easily be confused with others.
Confirmed occurrences of the Galapagos shark are in the western Atlantic around Bermuda and in isolated cases around the Caribbean islands , in the eastern Atlantic around Madeira , the Cape Verde Islands , Ascension , St. Helena and São Tomé . It is found in the Indian Ocean around southern Madagascar , in the western and central Pacific around the Marshall Islands , the Marianas , the Tuamotu Archipelago , Tupai , the Kermadec Islands , the Lord Howe Island , the Elizabeth and Middleton Reefs and Hawaii . In the eastern Pacific there are deposits around Galápagos , Coconut Island , Malpelo , Clipperton , Revillagigedo Islands and off the coast of southern Baja California , Guatemala and Colombia . Individual sightings also report Galapagos sharks off the coasts of the Iberian Peninsula and eastern Australia .
They are generally found in the area of the continental shelf and on island shelves near the coast, preferring jagged coral reefs with clear water and strong currents . They also collect in the area of rocky islands or seamounts. The species is able to negotiate the high seas between the islands and has been observed in areas further than 50 kilometers from a coast. Young sharks rarely dive deeper than 25 meters, whereas adult sharks have already been documented at a depth of 180 meters. Marking tests in the area of the French Frigate Shoals ( northwestern Hawaiian Islands ) showed that the Galapagos sharks mainly use the area above 100 meters, but occasionally dive to depths of 680 meters.
Way of life
In the first scientific description, the authors Snodgrass and Heller emphasized that they had caught a few hundred individuals of the species with their schooner and that thousands more could be seen in the water. Along the isolated Sankt-Peter-und-Sankt-Pauls-Felsen on the Mid-Atlantic Ridge , the population there has been described as one of the densest shark populations in the Atlantic Ocean. In some areas, the sharks form large clusters, although these are not real schools .
When appearing together with other shark species, Galapagos sharks behave dominantly towards the lesser blacktip shark ( C. limbatus ), but reluctant towards silver tip sharks ( C. albimarginatus ) of the same size. Compared to the tiger shark ( Galeocerdo cuvieri ), which sometimes occurs in the same area and often covers great distances, the Galapagos sharks are very local.
If Galapagos sharks are threatened or cornered, they show threatening gestures that are similar to those of gray reef sharks and consist of a deliberately rolling swim with bent back, lowered pectoral fins, protruding gills and open mouth. He also moves his head from right to left as if to keep an eye on the threat.
nutrition
The Galapagos shark's preferred diet is bottom-dwelling bony fish , including sea eels , flatfish , flatheads and triggerfish, and octopus . In addition, they occasionally prey on squids , mackerels and flying fish , which occur in open water or near the surface. With increasing size, they are among the main predators within their range and also hunt rays and smaller sharks, including smaller representatives of their own species and crustaceans. They also swallow indigestible objects such as coral sticks, stones, leaves and rubbish. In the area of the Galapagos Islands Galapagos sharks were observed Galapagos fur seals ( Arctocephalus galapagoensis ) and Galapagos sea lions ( Zalophus wollebaeki ) and sea lizards ( Amblyrhynchus cristatus ) attacks. Off Hawaii they also hunt the Hawaiian monk seal ( Monachus schauinslandi ), albatrosses and the green turtle ( Chelonia mydas ), where they compete with the tiger shark, which also lives in this area.
Parasites
Among the few known parasites of Galapagoshais belonging flatworm Dermophthirius carcharhini , that settles on the skin of the shark. There is an observation in which a horse mackerel the type Caranax melampygus is documented that rubbed against the rough skin of a Galapagos Shark to get rid of their own ectoparasites.
Reproduction and development
Like other requiem sharks, the Galapagos sharks are viviparous, with the embryo forming a yolk sac placenta to the mother animal after the yolk has been consumed in the uterus . In this way, the mother animal continues to supply the embryo with food until the end of the gestation period. The females give birth to young animals about every 2 to 3 years. The pairings take place from January to March, during which time scars appear from the attempts by the males to hold onto the fins of the females. The gestation period is probably one year.
For the birth of the young sharks, the females go to shallower sea areas, where they give birth to 4 to 16 young sharks. The size of the juvenile sharks at birth is usually 61 to 80 centimeters and is probably regionally different, as suggested by catches of free-swimming juveniles that are only 57 centimeters long in the eastern Pacific. The juveniles stay in the shallow water to avoid the feeding pressure of larger sharks.
Males reach sexual maturity with a length of 2.1 to 2.5 meters and an age of 6 to 8 years, the females with 2.2 to 2.5 meters and an age of 7 to 9 years. However, sexual reproduction is unlikely to occur before the age of 10. The lifespan of the species is at least 24 years.
Evolution and systematics
The Galapagos shark was first identified in 1905 by Robert Evans Snodgrass and Edmund Heller as Carcharias galapagensis together with a number of other fish from the Galápagos Islands in their publication Papers from the Hopkins-Stanford Galapagos Expedition, 1898–1899. XVII. Shore fishes of the Revillagigedo, Clipperton, Cocos and Galapagos Islands in the Proceedings of the Washington Academy of Science . A 65 cm long fetus from the Galápagos Islands served as the holotype for the description . Subsequent editors classified the shark in the genus Carcharhinus , in which it is still today.
Garrick (1982) placed the Galapagos Shark together with the bignose shark ( C. Altimus ), the Caribbean reef shark ( C. perezi ), the sandbar shark ( C. plumbeus ), the dusky ( C. obscurus ) and the oceanic whitetip ( C. longimanus ) into the obscurus group as one of the two large groups within the genus. All of these sharks are large requiem sharks with triangular teeth and an interdorsal crest. According to a molecular biological study on the basis of allozymes , the group was confirmed as a taxon by Naylor in 1992 , including the silky shark ( C. falciformis ) and the blue shark ( Prionace glauca ) added. According to this study, the closest relatives of the Galapagos shark are the black shark, the whitetip deep sea shark and the blue shark.
Relationship to people
As a very curious and persistent shark, the Galapagos Shark is classified as dangerous to humans and divers are advised not to dive unprotected in areas where it occurs. They swim close to swimmers and show particular interest in flippers and hands used for swimming. The sharks are attracted in large numbers by fishing boats. Limbaugh (1963) reported from Clipperton Island that the sharks first swim around interesting objects such as divers at great distances and then come closer and closer and become more aggressive; at the same time, numerous methods of defense against sharks against this species are unsuccessful. The situation can escalate if a diver has to get out of the water. Excited Galapagos Sharks are not easily deterred. If individual sharks are pushed back, others follow suit, and the use of a weapon against individual sharks can trigger a feeding frenzy in the others. Since 2008, two serious attacks by Galapagos sharks have been documented: one fatal attack in the Virgin Islands area and another with no fatal outcome off the Bermuda Islands.
The International Union for Conservation of Nature (IUCN) puts the Galapagos shark as a species on the warning list ("Near Threatened"), as its very slow reproductive rate limits the possibility of compensating for a decline in populations. Usage data for this species are not available, although they are commercially caught in large parts of their range due to the high meat quality. While the shark is still very common in many areas like Hawaii, it has likely been wiped out in others like off the coasts of Central America. Due to its highly fragmented distribution areas, this risk also exists locally in other areas. The populations around the Kermadec and Galápagos Islands are protected by marine reserves.
supporting documents
- ↑ Galapagos Shark on Fishbase.org (English)
- ↑ a b c d e f g h i j Compagno, LJV: Sharks of the World: An Annotated and Illustrated Catalog of Shark Species Known to Date . Food and Agricultural Organization, 1984, ISBN 9251013845 , pp. 473-475. ( Complete PDF , species portrait ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. )
- ↑ a b c d e f g C. Best: Biological Profiles: Galapagos Shark . Florida Museum of Natural History Ichthyology Department . Retrieved on April 26, 2009.
- ↑ a b c Carcharhinus galapagensis in the endangered Red List species the IUCN 2006. Posted by: Bennett, MB, Gordon, I. & Kyne, PM, 2000. Accessed on 2 the Aug 2006.
- ^ A b c Carl G. Meyer, Yannis P. Papastamatiou, Kim N. Holland: A multiple instrument approach to quantifying the movement patterns and habitat use of tiger ( Galeocerdo cuvier ) and Galapagos sharks ( Carcharhinus galapagensis ) at French Frigate Shoals, Hawaii . Marine Biology, published online on May 5, 2010, doi : 10.1007 / s00227-010-1457-x .
- ↑ a b Snodgrass, RE and Heller, E .: Papers from the Hopkins-Stanford Galapagos Expedition, 1898–1899. XVII. Shore fishes of the Revillagigedo, Clipperton, Cocos and Galapagos Islands. . In: Proceedings of the Washington Academy of Science . 6, Jan 31, 1905, pp. 333-427.
- ^ Edwards, AJ and Lubbock, HR: The Shark Population of Saint Paul's Rocks . In: American Society of Ichthyologists and Herpetologists (Eds.): Copeia . 1982, No. 1, February 23, 1982, pp. 223-225. doi : 10.2307 / 1444304 .
- ↑ Martin, RA: A review of shark agonistic displays: comparison of display features and implications for shark – human interactions . In: Marine and Freshwater Behavior and Physiology . 40, No. 1, March 2007, pp. 3-34. doi : 10.1080 / 10236240601154872 .
- ↑ a b c Wetherbee, BM, Crow, GL and Lowe, CG: Biology of the Galapagos shark, Carcharhinus galapagensis , in Hawai'i . In: Environmental Biology of Fishes . 45, 1996, pp. 299-310. doi : 10.1007 / BF00003099 .
- ↑ Rand, TG, Wiles, M. and Odense, P .: Attachment of Dermophthirius carcharhini (Monogenea: Microbothriidae) to the Galapagos Shark Carcharhinus galapagensis . In: American Microscopical Society (Ed.): Transactions of the American Microscopical Society . 105, No. 2, April 1986, pp. 158-169. doi : 10.2307 / 3226388 .
- ↑ Papastamatiou, YP, Meyer, CG and Maragos, JE: Sharks as cleaners for reef fish . In: Coral Reefs . 26, No. 2, June 2007, p. 277. doi : 10.1007 / s00338-007-0197-y .
- ↑ JAF Garrick: Sharks of the genus Carcharhinus . NOAA Technical Report, NMFS CIRC-445, 1982.
- ^ Mine Dosay-Akbulut: The phylogenetic relationship within the genus Carcharhinus. Comptes Rendus Biologies 331 (7), 2008; Pages 500-509, doi : 10.1016 / j.crvi.2008.04.001 .
- ↑ Naylor, GJP: The phylogenetic relationships among requiem and hammerhead sharks: inferring phylogeny When Thousands of Equally most parsimonious trees result . In: Cladistics . 8, 1992, pp. 295-318. doi : 10.1111 / j.1096-0031.1992.tb00073.x .
- ↑ Limbaugh, C .: Field notes on sharks . In: Gilbert, PW (Ed.): Sharks and Survival . DC Heath Canada, Ltd, 1963, ISBN 0-669-24646-8 , pp. 63-94.
- ↑ Types of sharks involved in confirmed unprovoked attacks around the world. In: floridamuseum.ufl.edu. Retrieved June 8, 2018 .
literature
- LJV 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 Vol. 4. FAO Rome 1984, pages 484–86, 555–61, 588. ISBN 92-5-101383-7 ( complete PDF , species portrait )
- Leonard Compagno , Marc Dando, Sarah Fowler: Sharks of the World. Princeton Field Guides, Princeton University Press, Princeton and Oxford 2005, page 296, ISBN 978-0-691-12072-0
