Triaenodon obesus

Geographic Range

The whitetip reef shark in found in both the Indian and Pacific oceans. They exist as far west as the coasts of South Africa and Sri Lanka in the Indian Ocean and can be seen as far east as the coasts of Costa Rica and Panama in the Pacific Ocean. They are most prominent in the Indo-Pacific seas and around the southern coast of the Indian sub-continent. Fossils have been found in North Carolina from the Miocene epoch indicating that the shark existed in the Atlantic Ocean several million years ago; however they not currently found in the Atlantic Ocean.

• Biogeographic Regions
• oriental oriental
  • native native
• indian ocean
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Triaenodon obesus is a reef shark as its name would indicate and lives in or around coral reefs. These reef settings are in tropical, coastal waters. Being a nocturnal animal, it spends much of the day in caves and deep crevices in coral reefs or coral reef lagoons. Whitetip reef sharks share these habitats with other reef sharks. However each species takes on a particular location within the reef system. The blacktip reef shark takes the shallow, high-energy coastal waters. The grey reef shark takes the deeper clear waters off the reef edge. The whitetip reef shark is the shark that lives in among the coral reefs, most commonly between the depths of 8 and 40 meters.

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• benthic benthic
• reef reef
• coastal coastal

• Other Habitat Features
• caves

Physical Description

The whitetip reef shark is a medium-sized shark averaging about 1.6 meters in length and 20 kg in mass, but growing as big as 2 meters and 28 kg. It is grey in color with a white belly and characteristic white tips on its first dorsal, upper caudal and occasionally the pelvic fins. The snout is short and broad with a mouth full of smooth edged teeth on both jaws. Both the mouth and nostrils are located on the underside of the head. The skin is very tough and the lateral fins are highly flexible. Both of these characteristics allow them to exist more easily among the rough and jagged edges of a coral reef. A diagnostic feature that distinguishes Triaenodon obesus from the similar silvertip and oceanic whitetip sharks is the second dorsal fin. In the whitetip reef shark it is significantly larger in comparison to the other species.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Development

The embryos are maintained in the mother for 5 months. They are then born alive and fully functional. The new-born juveniles are a mini-version of an adult whitetip reef shark, capable of surviving on their own. They grow relatively slowly however, and reach sexual maturity five years later.

Reproduction

Male whitetip reef sharks have been known to school in groups of nearly a hundred in pursuit of a female ready to mate. Mating in this particular species happens in autumn and winter. The sharks orient themselves parallel to each other and at about a 45 degree angle to the water column during copulation. They position themselves with their snouts in the sea floor, maintaining this vertical position with occasional simultaneous undulations of their bodies. The male then bites the pectoral fin of the female and inserts his clasper into the cloaca. This ritual of biting the female’s pectoral fin to hold position is common to several species.

Once the female is pregnant, the gestation period is thought to be about 5 months, however more research is needed in this area. The female gives birth to 2 or 3 live sharks of about 60 cm each.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• viviparous viviparous

Because the whitetip reef shark is a viviparous species it gives birth to live young. While in the embryo stage, the juvenile receives all its nutrients from the mother via a yolk sac placenta. The female shark, having a litter of young sharks within her, is slower and less maneuverable making her more vulnerable to predators. All of the parental investment in this species is by the female, and it is all internal in embryo stage. Once the juveniles are born, they are completely independent and capable of fending for themselves.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

The whitetip reef shark is believed to live to a maximum of 25 years.

Behavior

The whitetip reef shark is a docile, non-aggressive shark. It has the ability to pump water across its gills without moving forward, so it can sit motionless on the sea floor. However the shark prefers the safety and seclusion of caves. They will return to the same cave day after day for several months. Whitetip reef sharks remain in a relatively small area throughout their life. The longest recorded travel over the coarse of a year by an individual is 3 km. The whitetip reef shark is non-territorial, sharing its range with conspecifics or other species of sharks.

• Key Behaviors
• natatorial natatorial
• nocturnal nocturnal
• motile motile
• sedentary sedentary

Home Range

Estimations of the home range for whitetip reef sharks are on the order of a couple square kilometers.

Communication and Perception

As with most sharks the main form of perception is visual. Sharks in general tend to have good eyesight especially in dim light. The eyes are large and oval in shape. The large eyes are particularly useful to the whitetip because it is a nocturnal animal that does most of its hunting and traveling at night.

Like other sharks, they have very strong chemosensory systems as well. This is most useful to the whitetip reef sharks in hunting and eating.

Whitetip reef sharks respond to sounds in the water. They are believed to be attracted to the sounds of spearfishing in the water.

Like other sharks, this species also has electroreceptive abilities to help them detect prey.

Very little is known about the communication of these sharks with each other. It is known that they do share caves, and occasionally hunt together, however the way in which they communicate isn’t fully understood. One case in which the communication is obvious is in mating where there is a clear tactile communication in the act of the male biting the fins of the female.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical
• electric electric

Food Habits

Despite the docile nature of this shark during the day, during feeding at night they become very aggressive. It will thrash through coral reefs looking for food. The whitetip reef shark usually hunts alone but will work with other sharks to pursue prey throughout the coral reefs. Sometimes in pursuit of a fish, the shark will wedge the front half of its body into a crack or crevice on the reef and stay there until it catches the fish. The whitetip reef shark is considered clumsy and slow in open water, however it is still considered a pelagic predator. It is capable of catching fish in coral reefs because of its maneuverability. Despite its ability to catch fish, it specializes in bottom feeding. Its ventrally located mouth is ideal for picking crab, lobster and octopi off the sea floor, but its primary source of food is several types of boney fishes including but not restricted to damselfish ( Pomacentridae ), parrotfish ( Scaridae ), surgeonfish ( Acanthuridae ), goatfish ( Mullidae ), triggerfish ( Balistidae ), squirrelfish ( Holocentridae ) and eels ( Anguilliformes ).

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Animal Foods
• fish
• aquatic crustaceans

Predation

The most dangerous predator of the whitetip reef shark is humans. However, in the ocean they can be prey for large carcharhinid sharks, such as the tiger shark ( Galeocerdo cuvier ) or the silvertip shark ( Carcharhinus albimarginatus ).

Ecosystem Roles

The whitetip reef shark uses the coral reefs as a habitat, as well as a source for food. They are important predators in reef ecosystems. The sharks’ predation of fishes may serve as a sort of population control. This is particularly important in those fishes, such as the parrotfish, that consume the coral.

However the whitetip reef shark does occasionally have a negative effect on the coral. These sharks sometimes damage corals in their aggressive pursuit of prey fish.

The whitetip reef shark also serves as host to small cleaner fish such as gobies or striped cleaner wrasses who feed on the parasites infesting the shark.

Economic Importance for Humans: Positive

Humans will consume the whitetip reef shark; in particular they use the fins in soup.

• Positive Impacts
• food food

Economic Importance for Humans: Negative

The whitetip reef shark is only a problem to humans if provoked. They are considered to be a passive, calm animal that is easily approachable by divers. A whitetip reef shark will also attack in defense if escape is not an option. Altercations with spear fisherman can occur; most commonly in dispute over possession of the speared fish. It is thought that the sound of spear fishing arouses the shark, and therefore results in their abandonment of the cave and eventual pursuit of the speared fish.

Although the flesh of these sharks is sometimes eaten for food, there are reports that the tissues, particularly the liver, may be toxic.

• Negative Impacts
• injures humans
  • bites or stings
  • poisonous poisonous

Conservation Status

There are no special conservation projects involving the whitetip reef shark. It currently has a wide tropical distribution. However, it's slow rate of reproduction would make it very vulnerable to over-fishing. The IUCN rates the species "Lower Risk/Not Threatened."

Other Comments

This species was originally described by Eduard Ruppell in 1837.

Additional Links

Encyclopedia of Life

Contributors

George Hammond (editor), Animal Diversity Web.

Andrew Feldkamp (author), University of Michigan-Ann Arbor, William Fink (editor, instructor), University of Michigan-Ann Arbor.

References

Bright, M. 2002. Sharks . Washington, D.C.: Smithsonian Institution Press.

Compagno, L. 1984. FAO species catalogue. Vol. 4. Sharks of the World. An Annotated and illustrated catalogue of shark species known to date. Part 2. Carcharhiniformes. . Grahamstown, South Africa: FAO Fish.Synop..

Perrine, D. 1995. Sharks . Stillwater, Minnesota, USA: Voyageur Press.

Randall, J. 1977. Contribution to the Biology of the Whitetip Reef Shark (Triaenodon obesus). Pacific Science , 31/2: 143-164.

Russo, R. 1984. Whitetip - the cave shark. Sea Frontiers , 30/1: 30-36.

SeaWorld Inc., 2002. "Sharks And Their Relatives" (On-line). Accessed November 19, 2004 at http://www.seaworld.org/infobooks/Sharks&Rays .

Tricas, T., E. Feuvre. 1985. Mating in the reef white-tip shark Triaenodon obesus. Marine Biology , 84/3: 233-237.

2004. Biology of Sharks and Their Relatives. Pp. 53, 74, 277, 281, 354 in Biology of Sharks and Their Relatives . Boca Raton: CRC Press.