Whitetip reef shark

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Whitetip reef shark
Whitetip reef shark off Marsa Alam in the Red Sea

Whitetip reef shark off Marsa Alam in the Red Sea

Systematics
without rank: Sharks (selachii)
Superordinate : Galeomorphii
Order : Ground Sharks (Carcharhiniformes)
Family : Requiem sharks (Carcharhinidae)
Genre : Triaenodon
Type : Whitetip reef shark
Scientific name of the  genus
Triaenodon
Müller & Henle , 1838
Scientific name of the  species
Triaenodon obesus
( Rüppell , 1837)

The whitetip reef shark ( Triaenodon obesus ) is the only species of the genus Triaenodon within the Requiem sharks (Carcharhinidae). It is a medium-sized shark with an average body length of about 1.50 meters. The whitetip reef shark is characterized by a slender body with a broad head, distinctly developed skin flaps next to the nostrils, large oval eyes with vertical pupils and the eponymous white color of the tips of the dorsal fins and the caudal fin are characteristic . It is one of the most common sharks in the coral reefs of the Indo-Pacific , with a distribution area that extends west to South Africa and east to the coast of Central America . It lives primarily in clear water near the sea floor at depths of 8 to 40 meters.

During the day, whitetip reef sharks rest in reef caves and crevices most of the time. Unlike the requiem sharks of the genus Carcharhinus and other related species, which have to swim continuously to breathe so that the gills are washed by water, this shark can pump the breath water into the gill space and thus lie quietly on the sea floor. At night these sharks hunt in groups for bony fish , crustaceans and cephalopods . Their elongated body allows them to look for hidden prey in narrow crevices and holes.

Whitetip reef sharks are local; individual individuals can stay within a reef area for months or years or return to these areas regularly. The species is viviparous ( viviparous ). In the few matings observed so far, the male chased the fertile female and tried to grab the female's pectoral fins and maneuver her into a mating position. The females give birth to 1 to 6 young sharks after a gestation period of 10 to 13 months.

features

Whitetip reef shark
The head of a whitetip reef shark in close-up with a distinct shovel-shaped snout, oval eyes and distinct skin flaps in the area of ​​the nostrils.

The whitetip reef shark is a comparatively small requiem shark that rarely exceeds a body length of 1.60 meters. The maximum body length is usually given as 2.10 meters, although this is based on the estimation of a sighting and can be doubtful. The proven maximum weight was 18.3 kilograms. The shark has a slender body with a short and broad head, the muzzle is flattened and rounded. The back color is gray to brownish with an individual pattern of black spots, the belly is white. The tips of the first dorsal fin and the upper caudal fin lobe, sometimes those of the second dorsal fin and the lower caudal fin lobe, are bright white.

In the area of ​​the nostrils there are elongated, beard-like skin flaps. The eyes are small and oval with a vertical pupil and distinct bars over the eyes; there is often a small, distinct lump behind the eyes. The mouth is clearly bent downwards, giving the shark a "grim expression", and has short pits in the corners of the mouth. The dentition consists of 42 to 50 teeth in the upper jaw and 42 to 48 teeth in the lower jaw, with each tooth having a single narrow, imperforate, smooth central point, which is flanked on both sides by significantly smaller side points. As with other sharks, there are more rows of teeth behind these teeth.

The first of the two dorsal fins is relatively far back and therefore closer to the pelvic fins than the pectoral fins. The second dorsal fin and anal fin are large and about half to three quarters of the height of the first dorsal fin. There is no interdorsal ridge between the two dorsal fins. The broad, triangular pectoral fins begin at or just before the 5th cleft gill. The lower lobe of the caudal fin is about half the length of the upper, which has a distinct notch near the upper end. The skin teeth are small and overlap. They usually have seven horizontal scale keels, which gives the skin a velvety smooth surface.

distribution and habitat

Distribution area of ​​the whitetip reef shark
Whitetip reef shark

The distribution area of ​​the whitetip reef shark covers a large area of ​​the Indo-Pacific . It extends in the Indian Ocean from KwaZulu-Natal in South Africa over the East African coast to the Red Sea and the Indian subcontinent including the areas around Madagascar , Mauritius , the Comoros , the Aldabra group , the Seychelles , Sri Lanka , the Maldives and the Chagos -Archipelago . In the western and central Pacific, it extends from southern China , Taiwan and the Ryūkyū Islands to Southeast Asia including the Philippines , Indonesia and the north coast of Australia . He also lives in the area of ​​numerous Pacific island groups such as Melanesia , Micronesia and Polynesia to Hawaii in the north and the Pitcairn Islands in the southeast. In the eastern Pacific, it is also common in the coastal regions of Costa Rica to Panama , and a marginal population lives in the region of the Galapagos Islands.

The sharks are almost always found in coral reefs , where they live mainly in the area of ​​the reef roof and the vertical reef slopes as well as over sandbars, in lagoons and near slopes in deeper sea areas. They prefer clear, clean water and rarely swim very far above the ocean floor. This species is particularly common at depths of 8 to 40 meters. Occasionally, individual individuals move into shallow water areas with less than a meter of water. The maximum depth at which a whitetip reef shark has been caught so far was around 330 meters in the area of ​​the Ryūkyū Islands.

Way of life

Whitetip reef sharks (here in an aquarium) spend a large part of the day lying on the ocean floor.

The whitetip reef shark is one of the three most common types of coral reefs in the Indo-Pacific , along with the blacktip reef shark ( Carcharhinus melanopterus ) and the gray reef shark ( Carcharhinus amblyrhynchos ). The habitat of the three species overlap strongly, although the blacktip reef shark prefers shallow sea areas, while the gray reef shark often occurs on the edge of the coral reefs. The whitetip reef shark moves forward through strong snaking movements of its body and - unlike other requiem sharks - can lie motionless on the sea floor for a long time, actively pumping breathable water through its gills.

The species is largely nocturnal and spends a large part of the day lying dormant in caves, whereby they can lie individually or with several individuals next to each other. In the area around Hawaii they often rest in submarine volcanic vents, while in Costa Rica they can also lie open on sandbanks.

White tip reef sharks are local and individual individuals can stay within a reef area for months or years or return to these areas regularly. They rarely swim long distances and settle in other places. A study at Johnston Atoll found that within a period of up to a year, none of the tagged sharks had moved more than two miles from the location of the first catch. Another study in the Rangiroa Atoll in French Polynesia showed that after more than 3 years around 40% of the sharks caught were still living in the same reef. Individual individuals regularly rest in the same cave for months to years. The habitat of a white tip reef shark is around 0.05 km 2 during the day and around 1 km 2 at night . The sharks are not territorial and share their habitat with other species; There are no threatening gestures towards them.

nutrition

The whitetip reef shark lives and hunts mainly in coral reefs

The whitetip reef shark feeds mainly on small bony fish that live in the coral reef. These mainly include eels , soldiers and holocentrinae , snappers , damselfish , surgeonfish , parrotfish , triggerfish and red mullet . It also hunts for cephalopods and crustaceans such as lobsters and crabs . Due to its slender and agile body, the shark is able to squeeze into the crevices and caves of the reef and in this way to reach prey that are inaccessible to other reef sharks. When hunting in open water, however, they are comparatively clumsy. The shark is very sensitive to olfactory , acoustic and electrical stimuli emanating from its prey, while its visual perception is primarily used for locomotion and contrast perception. He is particularly sensitive to the perception of frequencies in the range of 25 to 100 Hertz, which can come from fighting and wriggling fish, for example.

Whitetip reef sharks primarily hunt at night when the prey fish are resting and easy to catch. After dark, groups of sharks methodically comb the reef and break off parts of the coral as they pursue prey. Several sharks hunt for the same prey and block every possible escape route from the reef crevices. Each shark hunts for itself and is in direct competition with all others for food. Unlike black tip and gray reef sharks, white tip reef sharks do not get more excited when hunting with multiple sharks and do not get a feeding frenzy. In addition to their night hunt, the sharks also hunt prey during the day, but do not hunt systematically. Before Borneo , individuals of this species stay at the edges of the reef to capture prey from the rising water currents. They chase monk seals ( Monachus schauinslandi ) off Hawaii and try to steal their prey from them.

Predators, parasites and cleaning organisms

The tiger shark is one of the most important predators of the white tip reef shark

The main predators of the white tip reef shark are mainly larger species of shark such as the tiger shark ( Galeocerdo cuvier ), the Galapagos shark ( Carcharhinus galapagensis ) and probably also the silver tip shark ( Carcharhinus albimarginatus ), although these are usually found in greater water depths than the white tip reef shark . An individual with a body length of about 80 centimeters was also found in the stomach of a dark giant grouper ( Epinephelus lanceolatus ); However, due to their rare occurrence, these fish are not significant enemies of the whitetip reef shark.

As parasites of the white tip reef shark were within the crustacean copepod Paralebion elongatus and the parasitic larva of the Assel gnathia grandilaris detected.

During their rest breaks, the sharks are cleaned of ectoparasites by various cleaner fish such as the fry of the wrasse Bodianus diplotaenia and the goby Elacatinus puncticulatus . In addition, there is a report of seven whitetip reef sharks, which were with open mouths and splayed gills within a school of non-cleaning amphipods from the group of Hyperiidea ; It is assumed that this posture, which is usually adopted for cleaning organisms, was stimulated by the movements of the small crustaceans.

Reproduction

Like most species of requiem sharks, the whitetip reef shark is also 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 only have one functional ovary and two pairs of outlet ducts with two uteri. The reproductive cycle runs every two years.

A whitetip reef shark in a reef cave

When mating, up to five males chase a single female and bite her fins and body to hold her in place. The males are probably attracted by a pheromone , which signals that they are ready to mate. Each male tries to grab the female's pectoral fins with his mouth and maneuver her into a mating position. It happens that a female is held by two males at the same time by one fin. As soon as a male has grabbed the female, the pair sinks to the seabed and the male (or s) turns one of its clusters , the male mating organs, forward. It fills the adjoining water sac with seawater so that the sperm can be flushed into the female genital opening. The male now tries to come into abdominal contact with the female; this is often prevented by the female pressing against the seabed, which could be a form of partner choice by the female. The male has a limited amount of time to mate because he is unable to breathe during the time he is holding the female's fin in its mouth. When the female agrees to mate, the partners lie next to each other with their heads on the sea floor and press their bodies against each other with the back half of the body facing up.

The females give birth to 1 to 6 young sharks after a gestation period of 10 to 13 months. The number of juveniles is independent of the size of the female, and each female gives birth to an average of 12 juvenile sharks in the course of her life. Young sharks are born in French Polynesia from May to August (autumn to winter), at Eniwetok in July (summer) and around Australia in October (summer). The birth takes place swimming, whereby the female bends strongly and turns. According to aquarium observations, every young animal takes less than an hour to give birth. The juvenile sharks are 52 to 60 centimeters long and have relatively longer tail fins compared to the adult animals.

Compared to other requiem sharks, this species grows very slowly. The newborns grow about 16 centimeters per year, while the sexually mature animals have a growth rate of 2 to 4 centimeters per year. The animals become sexually mature after about 8 to 9 years at about 1.1 meters; regional differences can occur, and sexually mature males with a body length of 0.85 meters have already been documented from the Maldives . In the Great Barrier Reef near Australia the males can live up to 14 years and the females up to 19 years old; the maximum age is estimated to be around 25 years. In 2008, a case of potential asexual reproduction was reported from the Nyiregyhaza Center in Hungary ; Older reports of potential asexual reproduction in sharks refer to the paddle-nosed hammerhead shark ( Sphyrna tiburo ), the lesser blacktip shark ( Carcharhinus limbatus ) and the white-spotted bamboo shark ( Chiloscyllium plagiosum ).

Evolution and systematics

The first scientific description of the whitetip reef shark was in 1837 as Carcharias obsess by the German naturalist Eduard Rüppell in his book "Fish of the Red Sea". In the same year, the species was transferred by Johannes Müller and Jakob Henle as the only species in the genus Triaenodon described by them , the name of which is derived from the trident -like tooth shape of the shark (from Greek τρίαινα , tríaina for "trident" and ὀδούς , odoús for "Tooth"). Since Rüppell did not specify a holotype , a 31 centimeter long specimen that was caught off Jeddah in Saudi Arabia was determined to be the lectotype in 1960 .

The whitetip reef shark, which was formerly part of the Triakidae family, is today assigned to the Requiem shark family (Carcharhinidae) by the majority of authors due to its anatomical features . The characteristic features include the fully developed nictitating membrane , the very well-developed pit in front of the caudal fin, the significantly smaller lower caudal fin lobe and the structure of the intestine. On the basis of morphological and molecular features of the white reef shark probably forms a taxon with the lemon sharks ( negation ) and the slit eyes sharks ( Loxodon ) disposed within the Requiem sharks between the basal taxa of the tiger shark ( Galeocerdo ), the rhizoprionodon ( Rhizoprionodon ) and the Spade-nosed sharks ( Scoliodon ) and the further derived species of the genus Carcharhinus and hammerhead sharks ( Sphyrna ).

Relationship to people

Whitetip reef sharks are often found in groups, here five individuals.
The sharks are curious about divers and get close to the camera

Whitetip reef sharks rarely behave aggressively towards humans, although there are frequent occurrences of them approaching swimmers and watching them. Danger most likely spear fishermen ; Bite attacks sometimes occur when sharks try to steal their prey from them. In some areas, local shark populations have learned to associate the sound of a harpoon or a lowered anchor with food and react to it in seconds. In 2008 the International Shark Attack File listed two provoked and three unprovoked shark accidents involving this species.

Whitetip reef sharks are very suitable for tourist purposes due to their local loyalty and their ability to learn to be fed by divers . In Hawaiian mythology , the sharks' loyalty to their place led to the belief in the nā ʻaumākua, the spirits of the ancestors who take on animal form and protect their offspring.

The commercial shark catch of the whitetip reef shark is mainly carried out in Pakistan , India , Sri Lanka and Madagascar , using both long lines and trawls. The species is caught for meat and liver consumption, but there have been reports of fish poisoning from Ciguatera specifically from the liver, which can contain high levels of the toxins.

In the Red List of the International Union for Conservation of Nature (IUCN), the whitetip reef shark is classified as a species on the early warning list (Near Threatened), as the population has been declining in recent decades due to the unregulated fishing in its range. Due to its relatively low reproduction and limited habitats, the species is classified as sensitive to overfishing . In the Great Barrier Reef, the white tip reef shark populations decreased by 80% compared to the protected areas in areas with high fishing pressure. In addition, in areas where boats are allowed but fishing is prohibited, declines of comparable magnitudes from poaching have been found. Without improved protection, populations will decline by a further 6.6 to 8.3% over the next few years, according to demographic models.

Web links

Commons : Whitetip Reef Shark  - Album containing pictures, videos and audio files
Wiktionary: Whitetip reef shark  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ a b c d e f g h i j k l m n Randall, JE: Contribution to the Biology of the Whitetip Reef Shark ( Triaenodon obesus ) . In: Pacific Science . 31, No. 2, 1977, pp. 143-164.
  2. ↑ Whitetip Reef Shark on Fishbase.org (English)
  3. ↑ a b c d e f g h i j k l m Compagno, LJV: Sharks of the World: An Annotated and Illustrated Catalog of Shark Species Known to Date . Food and Agricultural Organization, Rome 1984, ISBN 9251013845 , pp. 535-538.
  4. ^ A b c d e Hobson, ES: Feeding Behavior in Three Species of Sharks . In: Pacific Science . 17, 1963, pp. 171-194.
  5. ↑ a b c d Martin, RA Coral Reefs: Whitetip Reef Shark . ReefQuest Center for Shark Research. Retrieved on August 7, 2009.
  6. ↑ Alberto Siliotti and others, Memofish Book - The Fish of the Red Sea , Geodia Verlag Verona, 2002, ISBN 88-87177-43-0
  7. ^ Nelson, DR and RH Johnson. (1970). Acoustic studies on sharks: Rangiroa Atoll, July 1969. ONR Technical Report 2, No. N00014-68-C-0138.
  8. ↑ Yano, K., H. Mori, K. Minamikawa, S. Ueno, S. Uchida, K. Nagai, M. Toda and M. Masuda: Behavioral response of sharks to electric stimulation . In: Bulletin of Seikai National Fisheries Research Institute . 78, June 2000, pp. 13-30.
  9. ^ Ferrari, A. and A. Ferrari: Sharks . Firefly Books, 2002, ISBN 1552096297 , pp. 186-187.
  10. ^ Bight, M .: The Private Life of Sharks: The Truth Behind the Myth . Stackpole Books, 2000, ISBN 0811728757 , pp. 123-124.
  11. ↑ Bester, C. Biological Profiles: Whitetip Reef Shark . Florida Museum of Natural History Ichthyology Department. Retrieved on August 7, 2009.
  12. ^ Coetzee, M., NJ Smit, AS Grutter and AJ Davies: A new gnathiid (Crustacea: Isopoda) parasitizing two species of requiem sharks from Lizard Island, Great Barrier Reef, Australia . In: The Journal of Parasitology . 94, No. 3, June 2008, pp. 608-615.
  13. ^ Whitney, NM and PJ Motta: Cleaner host posing behavior of whitetip reef sharks ( Triaenodon obesus ) in a swarm of hyperiid amphipods . In: Coral Reefs . 27, No. 2, June 2008, p. 363.
  14. ↑ a b c d e Robbins, WD (2006). Abundance, demography and population structure of the gray reef shark ( Carcharhinus amblyrhynchos ) and the white tip reef shark ( Triaenodon obesus ) (Fam. Charcharhinidae). PhD thesis, James Cook University.
  15. ^ Johnson, RH, Nelson: Copulation and possible olfaction-mediated pair formation in two species of carcharhinid sharks . In: Copeia . 1978, No. 3, 1978, pp. 539-542. doi : 10.2307 / 1443626 .
  16. ^ Whitney, NM, HL Pratt (Jr.) and JC Carrier: Group courtship, mating behavior and siphon sac function in the whitetip reef shark, Triaenodon obesus . In: Animal Behavior . 68, 2004, pp. 1435-1442. doi : 10.1016 / j.anbehav.2004.02.018 .
  17. ↑ Tricas, TC and EM Le Feuvre: Mating in the reef white-tip shark Triaenodon obesus . In: Marine Biology . 84, 1985, pp. 233-237. doi : 10.1007 / BF00392492 .
  18. ^ Schaller, P .: Husbandry and reproduction of Whitetip reef sharks Triaenodon obesus at Steinhart Aquarium, San Francisco . In: International Zoo Yearbook . 40, No. 1, 2006, pp. 232-240. doi : 10.1111 / j.1748-1090.2006.00232.x .
  19. ^ A b Fowler, SL, RD Cavanagh, M. Camhi, GH Burgess, GM Cailliet, SV Fordham, CA Simpfendorfer, and JA Musick: Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes . International Union for Conservation of Nature and Natural Resources, 2005, ISBN 2831707005 , p. 314.
  20. ↑ Holtcamp, W .: Lone Parents: Parthenogenesis in Sharks . In: BioScience . 59, No. 7, July / August 2009, pp. 546-550. doi : 10.1525 / bio.2009.59.7.3 .
  21. ↑ Kevin A. Feldheim, Demian D. Chapman, Doug Sweet, Seán Fitzpatrick, Paulo A. Prodöhl, Mahmood S. Shivji, Bob Snowden: Shark Virgin Birth Produces Multiple, Viable Offspring . In: Journal of Heredity . 101, No. 3, 2010, pp. 374-377. doi : 10.1093 / jhered / esp129 .
  22. ^ Carrier, JC, JA Musick and MR Heithaus: Biology of Sharks and Their Relatives . CRC Press, 2004, ISBN 084931514X , pp. 52, 502.
  23. ↑ Taylor, LR: Sharks of Hawaii: Their Biology and Cultural Significance . University of Hawaii Press, 1993, ISBN 0824815629 , pp. 20-21.
  24. ↑ a b Triaenodon obesus in the endangered Red List species the IUCN 2006. Posted by: Smale, 2000. Retrieved on 11 May, 2006.
This article was added to the list of excellent articles on July 26, 2010 in this version .