The whitetip reef shark (''Triaenodon obesus'') is a
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
requiem shark
Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas (sometimes of brackish or fresh water) and include such species as the tiger shark, bull shark, le ...
, in the
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Carcharhinidae, and the only member of its
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
. A small shark that does not usually exceed in length, this species is easily recognizable by its slender body and short but broad head, as well as tubular skin flaps beside the
nostril
A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...
s, oval eyes with vertical pupils, and white-tipped
dorsal
Dorsal (from Latin ''dorsum'' ‘back’) may refer to:
* Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism
* Dorsal, positioned on top of an aircraft's fuselage
* Dorsal c ...
and
caudal fin
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...
s. One of the most common sharks found on
Indo-Pacific coral reef
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
C ...
s, the whitetip reef shark occurs as far west as
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
and as far east as
Central America
Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
. It is typically found on or near the bottom in clear water, at a depth of .
During the day, whitetip reef sharks spend much of their time resting inside caves. Unlike other requiem sharks, which rely on ram ventilation and must constantly swim to breathe, this shark can pump water over its
gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
s and lie still on the bottom. At night, whitetip reef sharks emerge to hunt
bony fishes,
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...
s, and
octopus in groups, their elongate bodies allowing them to force their way into crevices and holes to extract hidden prey. Individuals may stay within a particular area of the reef for months or years, frequently returning to the same shelter. This species is
viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...
, in which the developing
embryos are sustained by a
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
l connection to their mother.
Whitetip reef sharks are rarely aggressive towards humans, though they may investigate swimmers closely. However,
spear fishers are at risk of being bitten by one attempting to steal their catch. This species is caught for food, though
ciguatera poisoning
Ciguatera fish poisoning (CFP), also known simply as ciguatera, is a foodborne illness caused by eating reef fish whose flesh is contaminated with certain toxins. Such individual fish are said to be ciguatoxic. Symptoms may include diarrhea, vom ...
resulting from its consumption has been reported. The
IUCN has assessed the whitetip reef shark as Vulnerable, noting its numbers are dwindling due to increasing levels of unregulated fishing activity across its range. The slow reproductive rate and limited habitat preferences of this species renders its populations vulnerable to
overfishing.
Taxonomy and phylogeny
![Triaenodon obesus drawing](https://upload.wikimedia.org/wikipedia/commons/0/0b/Triaenodon_obesus_drawing.jpg)
The whitetip reef shark was first described by the German naturalist
Eduard Rüppell as ''Carcharias obesus'', in the 1837 ''Fische des Rothen Meere'' (''Fishes of the Red Sea'').
His choice of the
specific epithet ''obesus'' was curious, given that this shark is actually quite slender. Later in 1837,
Johannes Müller and
Friedrich Henle moved this species into its own genus ''Triaenodon'', from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
''triaena'' meaning "trident", and ''odon'' meaning "tooth". As Rüppell did not originally designate a
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...
, in 1960 a 31-cm-long specimen caught off
Jeddah,
Saudi Arabia
Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in Western Asia. It covers the bulk of the Arabian Peninsula, and has a land area of about , making it the fifth-largest country in Asia, the second-largest in the A ...
, was made the species
lectotype
In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
.
Other
common names for this shark include blunthead shark, light-tip shark, reef whitetip shark, and whitetip shark.
Once placed in the family
Triakidae, the whitetip reef shark is now recognized by most authors as belonging to the family
Carcharhinidae on the basis of
morphological characters, such as a full
nictitating membrane, well-developed precaudal pit, strong lower
caudal fin
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...
lobe, and scroll-like
intestinal
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
valves.
Morphological and
molecular phylogenetic analyses suggest the whitetip reef shark is grouped with the
lemon sharks (''Negaprion'') and the
sliteye shark (''Loxodon'') in occupying an intermediate position on the carcharhinid
evolutionary tree
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...
, between most
basal genera (''
Galeocerdo'', ''
Rhizoprionodon
''Rhizoprionodon'' is a genus of requiem sharks, and part of the family Carcharhinidae, commonly known as sharpnose sharks because of their long, pointed snouts.
Species
* '' Rhizoprionodon acutus'' ( Rüppell, 1837) (milk shark)
* '' Rhizopri ...
'', and ''
Scoliodon
''Scoliodon'' is a genus of requiem sharks in the family Carcharhinidae. It was formerly thought to include only a single Indo-Pacific species, the spadenose shark (''S. laticaudus''), but recent taxonomic research has found an additional spe ...
'') and the most
derived (''
Carcharhinus'' and ''
Sphyrna
''Sphyrna'' (from the Greek word σφῦρα, "hammer") is a genus of hammerhead sharks with a cosmopolitan distribution in the world's oceans. Members of ''Sphyrna'' have a tendency to inhabit coastal waters along the intertidal zone rather th ...
'').
Distribution and habitat
![Triaenodon obesus malaysia](https://upload.wikimedia.org/wikipedia/commons/e/eb/Triaenodon_obesus_malaysia.jpg)
The whitetip reef shark is distributed widely across the entire
Indo-Pacific region. It was once thought to have formerly existed in the Atlantic Ocean, based on
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
teeth found in
North Carolina
North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and ...
dating to the
Miocene epoch
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...
. However, more recent research indicates that the teeth belonged to a
mackerel shark
The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of sharks commonly known as mackerel sharks (which may also refer specifically to the family Lamnidae). It includes some of the most familiar species of sharks, such as the gr ...
, and that this species has never colonized the Atlantic.
In the Indian Ocean, it occurs from northern
KwaZulu-Natal,
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
to the
Red Sea
The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...
and the
Indian subcontinent
The Indian subcontinent is a list of the physiographic regions of the world, physiographical region in United Nations geoscheme for Asia#Southern Asia, Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian O ...
, including
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
,
Mauritius
Mauritius ( ; french: Maurice, link=no ; mfe, label= Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It ...
, the
Comoros, the
Aldabra Group
The Aldabra Group are part of the Outer Islands of the Seychelles, lying in the southwest of the island nation, around from the capital, Victoria, on Mahé Island.
Population and area
The group contains four islands and atolls. The largest in ...
, the
Seychelles
Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, ...
,
Sri Lanka, and the
Chagos Archipelago
The Chagos Archipelago () or Chagos Islands (formerly the Bassas de Chagas, and later the Oil Islands) is a group of seven atolls comprising more than 60 islands in the Indian Ocean about 500 kilometres (310 mi) south of the Maldives arch ...
. In the western and central Pacific, it occurs from off southern
China,
Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
, and the
Ryukyu Islands
The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Taiwan: the Ōsumi, Tokara, Amami, Okinawa, and Sakishima Islands (further divided into the Miyako and Yaeyama Islands), with Yona ...
, to the
Philippines
The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no),
* bik, Republika kan Filipinas
* ceb, Republika sa Pilipinas
* cbk, República de Filipinas
* hil, Republ ...
,
Southeast Asia
Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainlan ...
, and
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
, to northern
Australia, and is also found around numerous islands in
Melanesia
Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from Indonesia's New Guinea in the west to Fiji in the east, and includes the Arafura Sea.
The region includes the four independent countries of Fiji, Va ...
,
Micronesia
Micronesia (, ) is a subregion of Oceania, consisting of about 2,000 small islands in the western Pacific Ocean. It has a close shared cultural history with three other island regions: the Philippines to the west, Polynesia to the east, and ...
, and
Polynesia
Polynesia () "many" and νῆσος () "island"), to, Polinisia; mi, Porinihia; haw, Polenekia; fj, Polinisia; sm, Polenisia; rar, Porinetia; ty, Pōrīnetia; tvl, Polenisia; tkl, Polenihia (, ) is a subregion of Oceania, made up of ...
, as far as
Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
to the north and the
Pitcairn Islands to the southeast. In the eastern Pacific, it occurs from
Costa Rica to
Panama
Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country spanning the southern part of North America and the northern part of South America. It is bordered by Co ...
, and off the
Galápagos Islands
The Galápagos Islands (Spanish: , , ) are an archipelago of volcanic islands. They are distributed on each side of the equator in the Pacific Ocean, surrounding the centre of the Western Hemisphere, and are part of the Republic of Ecuador ...
.
Associated almost exclusively with
coral reef
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
C ...
habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s, whitetip reef sharks are most often encountered around coral heads and ledges with high vertical relief, and additionally over sandy flats, in
lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') ...
s, and near drop-offs to deeper water.
They prefer very clear water and rarely swim far from the bottom.
This species is most common at a depth of .
On occasion, they may enter water less than 1 m deep, and there is an exceptional record of a whitetip reef shark being captured from a depth of in the Ryukyu Islands.
Description
![Triaenodon obesus moc](https://upload.wikimedia.org/wikipedia/commons/5/57/Triaenodon_obesus_moc.jpg)
A relatively small species, few whitetip reef sharks are longer than . The maximum length this species attains is often given as , though this was originally based on visual observations and may be dubious.
The maximum reported weight is .
The whitetip reef shark has a slim body and a short, broad head. The snout is flattened and blunt, with large flaps of skin in front of the
nares that are furled into tubes. The eyes are small and oval with vertical
pupil
The pupil is a black hole located in the center of the Iris (anatomy), iris of the Human eye, eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing ...
s and prominent ridges above, and are often followed by a small notch. The mouth has a distinct downward slant (imparting a disgruntled expression to the shark), with short furrows at the corners. There are 42–50 tooth rows in the upper jaw and 42–48 tooth rows in the lower jaw. Each tooth has a single narrow, smooth-edged cusp at the center, flanked by a pair of much smaller cusplets.
The first
dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...
is positioned well back on the body, closer to the
pelvic
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The p ...
than the
pectoral fin
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...
s. The second dorsal and
anal fins are large, about half to three-quarters as high as the first dorsal fin. The broad, triangular pectoral fins originate at or slightly before the level of the fifth
gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In con ...
. There is no ridge between the first and second dorsal fins. The lower lobe of the caudal fin is half the length of the upper, which has a strong notch near the tip.
The
dermal denticles are small and overlapping, usually with 7 horizontal ridges, giving the skin a smooth feel. The coloration is grayish to brownish above and white below, with a pattern of scattered small, dark spots unique to each individual. The tips of the first dorsal fin and upper caudal fin lobe, and sometimes also the second dorsal fin and lower caudal fin lobe, are bright white.
Biology and ecology
![Triaenodon obesus guam](https://upload.wikimedia.org/wikipedia/commons/4/4e/Triaenodon_obesus_guam.jpg)
The whitetip reef shark is one of the three most common sharks inhabiting the reefs of the Indo-Pacific, the other two being the
blacktip reef shark (''Carcharhinus melanopterus'') and the
grey reef shark
The grey reef shark (''Carcharhinus amblyrhynchos'', sometimes misspelled ''amblyrhynchus'' or ''amblyrhinchos'') is a species of requiem shark, in the family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as ...
(''Carcharhinus amblyrhynchos''). The habitat preferences of this species overlap those of the other two, though it does not tend to frequent very shallow water like the blacktip reef shark, nor the outer reef like the grey reef shark.
The whitetip reef shark swims with strong undulations of its body, and unlike other requiem sharks can lie motionless on the bottom and actively pump water over its gills for
respiration
Respiration may refer to:
Biology
* Cellular respiration, the process in which nutrients are converted into useful energy in a cell
** Anaerobic respiration, cellular respiration without oxygen
** Maintenance respiration, the amount of cellul ...
.
This species is most active at night or during
slack tide
Slack water is a short period in a body of tidal water when the water is completely unstressed, and there is no movement either way in the tidal stream, and which occurs before the direction of the tidal stream reverses. Slack water can be estim ...
, and spends much of the day resting inside caves singly or in small groups, arranged in parallel or stacked atop one another. Off Hawaii, these sharks may be found sheltering inside underwater
lava tubes, while off Costa Rica they are often seen lying in the open on sandy flats.
[Martin, R.A]
Coral Reefs: Whitetip Reef Shark
ReefQuest Centre for Shark Research. Retrieved on August 7, 2009.
Whitetip reef sharks generally remain within a highly localized area; only rarely do they undertake long movements, wandering for a while before settling down somewhere new. One study at
Johnston Atoll found that none of the sharks examined had moved more than away from their original capture location over periods of up to a year.
Another study at
Rangiroa Atoll in
French Polynesia found that, after more than three years, around 40% of the originally tagged sharks were still present on the same reef where they were first captured. An individual shark may rest inside the same cave for months to years. The daytime
home range
A home range is the area in which an animal lives and moves on a periodic basis. It is related to the concept of an animal's territory which is the area that is actively defended. The concept of a home range was introduced by W. H. Burt in 1943. He ...
of a whitetip reef shark is limited to approximately ; at night this range increases to .
These sharks are not
territorial
A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal.
In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
and share their home ranges with others of their species; they do not perform
threat displays
Deimatic behaviour or startle display means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey anima ...
.
Important predators of the whitetip reef shark include
tiger shark
The tiger shark (''Galeocerdo cuvier'') is a species of requiem shark and the last extant member of the family Galeocerdonidae. It is a large macropredator, capable of attaining a length over . Populations are found in many tropical and tempera ...
s (''Galeocerdo cuvier''),
Galapagos sharks (''Carcharhinus galapagensis''), and possibly also
silvertip shark
The silvertip shark (''Carcharhinus albimarginatus'') is a large species of requiem shark, in the family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. It is often encountered around offshore is ...
s (''Carcharhinus albimarginatus''), though they usually occur at depths greater than those favored by whitetip reef sharks. An long whitetip reef shark has also been found in the stomach of a
giant grouper
The giant grouper (''Epinephelus lanceolatus''), also known as the Queensland grouper, brindle grouper or mottled-brown sea bass, is a species of marine ray-finned fish, a grouper from the subfamily Epinephelinae which is part of the family Serr ...
(''Epinephelus lanceolatus''), though these groupers are unlikely to be significant predators of this species due to their rarity.
Known
parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s of the whitetip reef shark include the
copepod ''Paralebion elongatus'' and the praniza (parasitic)
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
...
e of the
isopod ''Gnathia grandilaris''.
[Bester, C]
Biological Profiles: Whitetip Reef Shark
Florida Museum of Natural History Ichthyology Department. Retrieved on August 7, 2009. While resting during the day, these sharks have been observed being cleaned by the
wrasse
The wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 81 genera, which are divided into 9 subgroups or tribes.
They are typically small, most of them le ...
''
Bodianus diplotaenia'' and the
goby
Goby is a common name for many species of small to medium sized ray-finned fish, normally with large heads and tapered bodies, which are found in marine, brackish and freshwater environments. Traditionally most of the species called gobies have b ...
''
Elacatinus puncticulatus''. Unusually, there is also a report of seven whitetip reef sharks adopting a cleaning posture (mouth agape and gills flared) in the midst of a swarm of non-cleaning
hyperiid
The Hyperiidea are a suborder of amphipods, small aquatic crustaceans. Unlike the other suborders of Amphipoda, hyperiids are exclusively marine and do not occur in fresh water. Hyperiids are distinguished by their large eyes and planktonic habi ...
amphipods; the mechanical stimulation from the moving amphipods are thought to have evoked this behavior through their similarity to actual cleaner organisms.
Feeding
![Triaenodon obesus JNC960 Lower jaw and teeth 2](https://upload.wikimedia.org/wikipedia/commons/6/62/Triaenodon_obesus_JNC960_Lower_jaw_and_teeth_2.JPG)
With its slender, lithe body, the whitetip reef shark specializes in wriggling into narrow crevices and holes in the reef and extracting prey inaccessible to other reef sharks. Alternatively, it is rather clumsy when attempting to take food suspended in open water.
This species feeds mainly on bony fishes, including
eel
Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
s,
squirrelfish
Holocentrinae is a subfamily of Holocentridae containing 40 recognized species and one proposed species. Its members are typically known as squirrelfish and all are nocturnal. All three genera in the subfamily are found in the Atlantic and ''Ho ...
es,
snappers,
damselfish
Damselfish are those within the subfamilies Abudefdufinae, Chrominae, Lepidozyginae, Pomacentrinae, and Stegastenae within the family Pomacentridae. Most species within this group are relatively small, with the largest species being about ...
es,
parrotfish
Parrotfishes are a group of about 90 fish species regarded as a family (Scaridae), or a subfamily (Scarinae) of the wrasses. With about 95 species, this group's largest species richness is in the Indo-Pacific. They are found in coral reefs, ro ...
es,
surgeonfishes,
triggerfish
Triggerfish are about 40 species of often brightly colored fish of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacifi ...
es and
goatfish
The goatfishes are perciform fish of the family Mullidae. The family is also sometimes referred to as the red mullets, which also refers more narrowly to the genus '' Mullus''.
The family name and the English common name mullet derived from La ...
es, as well as
octopuses
An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, ...
,
spiny lobster
Spiny lobsters, also known as langustas, langouste, or rock lobsters, are a family (Palinuridae) of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are also, especially in Australia, New Zealand, Ireland, So ...
s, and
crabs.
The whitetip reef shark is highly responsive to the
olfactory,
acoustic, and electrical cues given off by potential prey, while its visual system is attuned more to movement and/or contrast than to object details.
It is especially sensitive to natural and artificial low-frequency sounds in the 25–100 Hz range, which evoke struggling fish.
Whitetip reef sharks hunt primarily at night, when many fishes are asleep and easily taken. After dusk, groups of sharks methodically scour the reef, often breaking off pieces of coral in their vigorous pursuit of prey.
Multiple sharks may target the same prey item, covering every exit route from a particular coral head. Each shark hunts for itself and in competition with the others in its group.
Unlike blacktip reef sharks and grey reef sharks, whitetip reef sharks do not become more excited when feeding in groups and are unlikely to be stirred into a
feeding frenzy
In ecology, a feeding frenzy occurs when predators are overwhelmed by the amount of prey available. The term is also used as an idiom in the English language.
Examples in nature
For example, a large school of fish can cause nearby sharks, such a ...
.
Despite their nocturnal habits, whitetip reef sharks will hunt opportunistically in daytime.
Off
Borneo
Borneo (; id, Kalimantan) is the third-largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java, west of Sulawesi, and ea ...
, this species gathers around reef drop-offs to feed on food brought up by the rising current. Off
Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
, they follow
Hawaiian monk seal
The Hawaiian monk seal (''Neomonachus schauinslandi'') is an endangered species of earless seal in the family Phocidae that is endemic to the Hawaiian Islands.
The Hawaiian monk seal is one of two extant monk seal species; the other is the ...
s (''Monachus schauinslandi'') and attempt to steal their catches.
A whitetip reef shark can survive for six weeks without food.
Life history
![Triaenodon obesus group](https://upload.wikimedia.org/wikipedia/commons/b/b7/Triaenodon_obesus_group.jpg)
Like other members of its family, the whitetip reef shark is
viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...
; once the developing
embryos exhaust their supply of
yolk
Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example ...
, the
yolk sac
The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac'' is ...
is converted into a
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
l connection through which the mother delivers nourishment for the remainder of
gestation. Mature females have a single functional
ovary, on the left side, and two functional
uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
es. The reproductive cycle is biennial.
Mating
Mating is initiated when up to five males follow closely behind a female and bite at her fins and body, possibly cued by
pheromone
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s indicating the female's readiness. Each male attempts to seize the female by engulfing one of her pectoral fins; at times two males might grasp a female on both sides simultaneously. Once engaged, the sharks sink to the bottom, whereupon the male (or males) rotates one of his
clasper
In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating.
Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's c ...
s forward, inflates the associated siphon sac (a subcutaneous abdominal organ that takes in seawater that is used to flush
sperm into the female), and attempts to make contact with the female's vent. In many cases, the female resists by pressing her belly against the bottom and arching her tail; this may reflect
mate choice on her part. The male has a limited time in which to achieve
copulation
Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...
, as while he is holding the female's pectoral fin in his mouth he is being deprived of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
. On the other hand, if the female is willing, the pair settles side-by-side with their heads pressed against the bottom and their bodies at an upward angle.
After a
gestation period of 10–13 months, females give birth to litters of 1–6 (usually 2–3) pups. The number of offspring is not correlated with female size; each female produces an estimated average of 12 pups over her entire lifetime.
Parturition occurs from May to August (autumn and winter) in French Polynesia, in July (summer) off
Enewetak Atoll, and in October (summer) off Australia.
Females give birth while swimming, making violent twists and turns of their bodies; each pup takes under an hour to fully emerge. The newborns measure long and have relatively longer caudal fins than adults. This shark develops slowly compared to other requiem sharks; newborns grow at a rate of per year while adults grow as a rate of per year.
Sexual maturity
Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definit ...
is reached at a length of around and an age of 8–9 years, though mature males as small as long have been recorded from the
Maldives
Maldives (, ; dv, ދިވެހިރާއްޖެ, translit=Dhivehi Raajje, ), officially the Republic of Maldives ( dv, ދިވެހިރާއްޖޭގެ ޖުމްހޫރިއްޔާ, translit=Dhivehi Raajjeyge Jumhooriyyaa, label=none, ), is an archipelag ...
, suggesting regional variation in maturation size.
On the
Great Barrier Reef
The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, ...
, males live to 14 years and females to 19 years; the maximum lifespan of this shark may be upwards of 25 years.
In 2008, a whitetip reef shark produced a single pup through possibly
asexual means at the Nyiregyhaza Centre in
Hungary
Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Pannonian Basin, Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the ...
; previous instances of asexual reproduction in sharks have been reported in the
bonnethead
The bonnethead (''Sphyrna tiburo''), also called a bonnet shark or shovelhead, is a small member of the hammerhead shark genus ''Sphyrna'', and part of the family Sphyrnidae. It is an abundant species in the littoral zone of the North Atlantic ...
(''Sphyrna tiburo'') and the
blacktip shark (''Carcharhinus limbatus'').
Human interactions
Unlike its Oceanic cousin, the white tip reef shark is more harmless and is seldom aggressive unless provoked. They are also fearless and curious, as the whitetip reef sharks may approach swimmers closely to investigate. However, these sharks readily attempt, and quite boldly, to steal catches from
spear fishers, which has resulted in several people being bitten in the process.
In some places, local whitetip reef sharks have learned to associate the sound of a
speargun
A speargun is a ranged underwater fishing device designed to launch a tethered spear or harpoon to impale fish or other marine animals and targets. Spearguns are used in sport fishing and underwater target shooting. The two basic types are ''pn ...
discharge or a boat dropping anchor with food and respond within seconds.
As of 2008, the
International Shark Attack File
The International Shark Attack File' is a global database of shark attacks. It began as an attempt to catalogue shark attacks on servicemen during World War II. The Office of Naval Research funded it from 1958 until 1968. During that time, a p ...
lists two provoked and three unprovoked attacks to this species. Whitetip reef sharks are well-suited to
ecotourism
Ecotourism is a form of tourism involving responsible travel (using sustainable transport) to natural areas, conserving the environment, and improving the well-being of the local people. Its purpose may be to educate the traveler, to provide fund ...
diving, and with conditioning they can be hand-fed by divers.
In
Hawaiian mythology
Hawaiian religion refers to the indigenous religious beliefs and practices of native Hawaiians, also known as the kapu system. Hawaiian religion is based largely on the tapu religion common in Polynesia and likely originated among the Tahitian ...
, the fidelity (i.e. "loyalty") of whitetip reef sharks to certain areas of the reef for years at a time may have inspired belief in ''
ʻaumākua'', the spirits of family ancestors that take animal form and protect their descendants.
The whitetip reef shark is taken by
fisheries operating off
Pakistan
Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-lar ...
,
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
,
Sri Lanka,
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
, and likely elsewhere, using
longlines,
gillnets, and
trawl
Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different speci ...
s. The meat and
liver
The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
are eaten, though sharks from certain areas present a substantial risk of
ciguatera poisoning
Ciguatera fish poisoning (CFP), also known simply as ciguatera, is a foodborne illness caused by eating reef fish whose flesh is contaminated with certain toxins. Such individual fish are said to be ciguatoxic. Symptoms may include diarrhea, vom ...
(especially the liver, which contains a much higher concentration of the toxin than the meat).
The
International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...
(IUCN) has assessed this species as Vulnerable, as its numbers have dropped in recent decades due to increasing, and thus far unregulated, fishing pressure in the tropics.
Its restricted habitat, low dispersal, and slow reproduction are factors that limit this shark's capacity for recovering from
overfishing.
On the Great Barrier Reef, populations of whitetip reef sharks in fishing zones have been reduced by 80% relative to no-entry zones. Furthermore, populations in no-take zones, where boats are allowed but fishing prohibited, exhibit levels of depletion comparable to fishing zones due to
poaching
Poaching has been defined as the illegal hunting or capturing of wild animals, usually associated with land use rights.
Poaching was once performed by impoverished peasants for subsistence purposes and to supplement meager diets. It was set a ...
. Demographic models indicate that these depleted populations will continue to decline by 6.6–8.3% per year without additional conservation measures.
[Robbins, W.D. (2006). Abundance, demography and population structure of the grey reef shark (''Carcharhinus amblyrhynchos'') and the white tip reef shark (''Triaenodon obesus'') (Fam. Charcharhinidae). PhD thesis, James Cook University.] In June 2018 the New Zealand
Department of Conservation
An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as Ministry of the Environment ...
classified the whitetip reef shark as "Vagrant" under the
New Zealand Threat Classification System.
See also
*
List of sharks
Shark is the naming term of all members of Selachimorpha suborder in the subclass Elasmobranchii, in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. The first shark-like chon ...
References
External links
Whitetip reef shark (''Triaenodon obesus'')a
FishBasea
Florida Museum of Natural History Ichthyology Department*
{{DEFAULTSORT:shark, reef, whitetip
whitetip reef shark
The whitetip reef shark (''Triaenodon obesus'') is a species of requiem shark, in the family Carcharhinidae, and the only member of its genus. A small shark that does not usually exceed in length, this species is easily recognizable by its slen ...
whitetip reef shark
The whitetip reef shark (''Triaenodon obesus'') is a species of requiem shark, in the family Carcharhinidae, and the only member of its genus. A small shark that does not usually exceed in length, this species is easily recognizable by its slen ...