Blacktip reef shark
Encyclopedia
The blacktip reef shark (Carcharhinus melanopterus) is a species
of requiem shark
, family
Carcharhinidae, easily identified by the prominent black tips on its fins (especially on the first dorsal fin
and the caudal fin). Among the most abundant sharks inhabiting the tropical coral reef
s of the Indian
and Pacific Ocean
s, this species prefers shallow, inshore waters and its exposed first dorsal fin is a common sight in the region. Most blacktip reef sharks are found over reef ledges and sandy flats, though they have also been known to enter brackish and freshwater
environments. This species typically attains a length of 1.6 m (5.2 ft).
Blacktip reef sharks have extremely small home ranges and exhibit strong site fidelity, remaining within same local area for up to several years at a time. They are active predators of small bony fishes, cephalopod
s, and crustacean
s, and have also been known to feed on sea snakes and seabird
s. Accounts of the blacktip reef shark's life history have been variable and sometimes contradictory, in part reflecting geographical differences within the species. Like other members of its family, this shark is viviparous
with females giving birth to 2–5 young on a biennial, annual, or possibly biannual cycle. Reports of the gestation period
range from 7–9, to 10–11, to possibly 16 months. Mating
is preceded by the male following closely behind the female, likely attracted by her chemical signals. Newborn sharks are found further inshore and in shallower water than adults, frequently roaming in large groups over areas flooded by high tide
.
Timid and skittish, the blacktip reef shark is difficult to approach and seldom poses a danger to humans unless roused by food. However, people wading through shallow water are at risk of having their legs mistakenly bitten. This shark is used for its meat, fins, and liver oil
but is not considered to be a commercially significant species. The International Union for Conservation of Nature (IUCN) has assessed the blacktip reef shark as Near Threatened
. Although the species as a whole remains widespread and relatively common, overfishing
of this slow-reproducing shark has led to its decline at a number of locales.
s Jean René Constant Quoy
and Joseph Paul Gaimard
originally described the blacktip reef shark during the 1817–1820 exploratory voyage of the corvette
Uranie. In 1824, their account was published as part of Voyage autour du monde...sur les corvettes de S.M. l'Uranie et la Physicienne, Louis de Freycinet
's 13-volume report on the voyage. The type specimen was a 59 cm (23.2 in) long juvenile male caught off the island of Waigeo
, west of New Guinea
. Quoy and Gaimard chose the name Carcharias melanopterus, from the Greek melas meaning "black" and pteron meaning "fin" or "wing", in reference to this shark's prominent fin markings.
Subsequent authors moved the blacktip reef shark to the genus
Carcharhinus; in 1965 the International Commission on Zoological Nomenclature
(ICZN) designated it as the type species
for the genus. In some earlier literature, the scientific name of this shark was mistakenly given as C. spallanzani, now recognized as a synonym
of the spottail shark
(C. sorrah). Other common name
s for this species include blackfin reef shark, black finned shark, blacktip shark, reef blacktip shark, and guliman.
, Jack Garrick proposed in 1982 that the closest relative of the blacktip reef shark is the nervous shark
(C. cautus). Leonard Compagno
's 1988 morphological analysis suggested affinity not only between this species and the nervous shark but also four other species, and could not resolve their relationships further. A 1998 allozyme
analysis by Gavin Naylor again yielded ambiguous results, finding that the blacktip reef shark forms a polytomy
(irresolvable group) with 10 other Carcharhinus species.
. In the Indian Ocean
, it occurs from South Africa
to the Red Sea
, including Madagascar
, Mauritius
, and the Seychelles
, and from there eastward along the coast of the Indian subcontinent
to Southeast Asia
, including Sri Lanka
, the Andaman Islands
, and the Maldives
. In the Pacific Ocean
, it is found from southern China
and the Philippines
to Indonesia
, northern Australia
and New Caledonia
, and also inhabits numerous oceanic islands including the Marshall
, Gilbert
, Society
, Tuamotu, and Hawaiian Islands
. Contrary to what most sources state, there are no confirmed records of this species from Japan
ese waters, and purported Japanese specimens likely came from Taiwan
. A Lessepsian migrant, this shark has colonized the eastern Mediterranean Sea
by way of the Suez Canal
.
Although it has been reported from a depth of 75 m (246.1 ft), the blacktip reef shark is usually found in water only a few meters deep, and can often be seen swimming close to shore with its dorsal fin exposed. Younger sharks prefer shallow sandy flats, while older sharks are most common around reef ledges and can also be found near reef drop-offs. This species has also been reported from brackish estuaries and lake
s in Madagascar, and freshwater
environments in Malaysia, though it is not able to tolerate low salinity
to the same degree as the bull shark
(C. leucas). At Aldabra
in the Indian Ocean, blacktip reef sharks congregate in the channels between reef flats during low tide and travel to the mangrove
s when the water rises. There is equivocal evidence that sharks from the northern and southern extremes of its distribution are migratory
.
has a flap of skin in front that is expanded into a nipple-shaped lobe. Not counting small symphysial (central) teeth, the tooth rows number 11–13 (usually 12) on either side of the upper jaw and 10–12 (usually 11) on either side of the lower jaw. The upper teeth are upright to angled and narrowly triangular in shape, bearing serrations that are more coarse on the bases; the lower teeth are similar but more finely serrated. The teeth of adult males are more abruptly curved than those of females.
The pectoral fins are large and narrowly falcate (sickle-shaped), tapering to points. The sizable first dorsal fin
is high with a curving "S"-shaped rear margin, and originates over the free rear tips of the pectoral fins. The second dorsal fin is relatively large with a short rear margin, and is placed opposite the anal fin. There is no ridge between the dorsal fins. This shark is a pale grayish brown above and white below, with an obvious white band on the sides extending forward from above the anal fin. All the fins have black tips highlighted by lighter-colored borders, which are especially striking on the first dorsal fin and lower caudal fin lobe. Most blacktip reef sharks are no more than 1.6 m (5.2 ft) long, though rarely individuals may reach 1.8 m (5.9 ft) or possibly 2 m (6.6 ft). The maximum weight on record is 13.6 kg (30 lb).
Along with the grey reef shark (C. amblyrhinchos) and the whitetip reef shark
(Triaenodon obesus), the blacktip reef shark is one of the three most common sharks inhabiting coral reefs in the Indo-Pacific. This species predominates in shallow habitats, while the other two are mostly found deeper. Fast-swimming and active, the blacktip reef shark may be encountered alone or in small groups; large "social" aggregations have also been observed. For the most part juvenile and adult sharks are not segregated by sex, save for the movements of pregnant females to give birth. Individual blacktip reef sharks exhibit strong fidelity to particular areas, where they may remain for up to several years.
A tracking study off Palmyra Atoll
in the central Pacific has found that the blacktip reef shark has a home range of around 0.55 square kilometre, among the smallest of any shark species. The size and location of the range does not change with time of day. Within this range, 3–17% of the area constitute favored hunting patches that are disproportionately occupied by the resident shark. The sharks spend most of their time swimming back and forth along reef ledges, making occasional short forays onto sandy flats. Their average swimming speed decreases when the tide rises at night, possibly because the influx of cooler water reduces their metabolism
, or the accompanying movement of prey fishes makes foraging easier. Blacktip reef sharks at Aldabra tend to be more mobile than those at Palmyra, with recorded individual movements of up to 2.5 km (1.6 mi) over 7 hours.
Blacktip reef sharks, particularly small individuals, fall prey to larger fishes including grouper
s, grey reef sharks, tiger shark
s (Galeocerdo cuvier), and members of their own species. At Palmyra Atoll, adult blacktip reef sharks avoid patrolling tiger sharks by staying out of the central, deeper lagoon. Known parasites of the blacktip reef shark include the tapeworms Anthobothrium lesteri, Nybelinia queenslandensis, Otobothrium alexanderi, and Platybothrium jondoeorum, a myxosporidian in the genus Unicapsula, and the monogenea
n Dermophthirius melanopteri. One of the few documented examples of infectious disease
in a shark was a fatal case of hemorrhagic
septicemia in a blacktip reef shark, caused by the bacterium Aeromonas salmonicida
subsp. salmonicida.
within its ecosystem
, the blacktip reef shark plays a major role in structuring inshore ecological communities
. Its diet is composed primarily of small teleost fishes, including mullet
, groupers, grunters
, jacks
, mojarra
s, wrasse
s, surgeonfish, and smelt-whitings
. Groups of blacktip reef sharks in the Indian Ocean have been observed herding schools
of mullet against the shore for easier feeding. Squid
, octopus
, cuttlefish
, shrimp
, and mantis shrimp
are also taken, as well as carrion
and smaller sharks and rays, though this is rare. Off northern Australia, this species is known to consume sea snakes, including Acrochordus granulatus
, Hydrelaps darwiniensis, Hydrophis
spp. and Lapemis hardwickii
. Sharks off Palmyra Atoll have been documented preying on seabird
chicks that have fallen out of their nest
s into the water. Miscellaneous items that have been found inside the stomach
s of this species include algae
, turtle grass, coral
, hydrozoa
, bryozoa
, rat
s, and stones.
Researchers working at Enewetak Atoll in the Marshall Islands have found that the blacktip reef shark can be readily attracted by splashing or striking metal tools against hard objects underwater, as well as by the scent of both healthy and injured fish. As with most sharks, the blacktip reef shark does not have any cone cell
s in its retina
, limiting its ability to discriminate colors and fine details. Instead, its vision is adapted for sensitivity to movement or contrast under low light conditions, which is further enhanced by the presence of a reflective tapetum lucidum
. Experiments have shown that this shark is capable of detecting small objects up to 1.5–3 m (4.9–9.8 ft) away, but is unable to clearly discern the shape of the object. Electroreception
is another means by which this shark can locate prey; its ampullae of Lorenzini
have a sensitivity of approximately 4 nV/cm and an effective range of 25 cm (10 in). Similar to the grey reef shark, this species becomes more excited and "confident" in the presence of other individuals of its species, and in extreme situations can be roused into a feeding frenzy
. Feeding activity may be greater at night than during the day.
, with mating taking place from January to February, as well as off Moorea
in French Polynesia
, where mating occurs from November to March. The cycle is biennial off Aldabra, where intense competition within and between species for food may constrain females to only bearing young every other year. Earlier accounts from the Indian Ocean by Johnson (1978), Madagascar by Fourmanoir (1961), and the Red Sea by Gohar and Mazhar (1964), indicated a biannual cycle in these regions with two breeding seasons per year from June to July and December to January. If accurate, the shorter reproductive cycles of these subpopulations may be a consequence of warmer water.
When receptive to mating, a female blacktip reef shark swims slowly in a sinusoidal pattern near the bottom with her head pointed down; observations in the wild suggest that female sharks release chemical signals that allow males to track them. Once the male finds her, he closes to around 15 cm (5.9 in) and follows her with his snout oriented towards her vent. A courting male may also bite the female behind her gills or on her pectoral fins; these mating wounds heal completely after 4–6 weeks. After a period of synchronous swimming, the male pushes the female on her side and positions her so that her head is against the bottom and her tail is raised. Once the female is in position, the male inserts one of his claspers into her cloaca
. Copulation lasts for several minutes, after which the sharks separate and resume their regular behaviors. Off Moorea, individual older females mate and give birth at a consistent time every year, often to within a week's precision, whereas younger females exhibit more variability in their timing. Younger females are also more likely to fail to become pregnant after mating.
The gestation period
has been reported as 10–11 months long in the Indian Ocean and Pacific islands, and 7–9 months long off northern Australia. Earlier authors such as Melouk (1957) have estimated a gestation period as long as 16 months, though the validity of this figure has subsequently been challenged. The female has a single functional ovary
(on the right) and two functional uterus
es, divided into separate compartments for each embryo
. Newly ovulated
egg cases measure 3.9 cm (1.5 in) by 2.6 cm (1 in); after hatching the embryos are sustained by a yolk sac
during the first stage of development. After two months, the embryo measures 4 cm (1.6 in) long and has well-developed external gills. After four months, the yolk sac has begun to be converted into a placenta
l connection that attaches to the uterine wall; at this time the embryo's dark fin markings develop. By five months, the embryo measures 24 cm (9.4 in) and has resorbed its external gills; the placenta is fully formed though some yolk remains until seven months into gestation.
Parturition occurs from September to November, with females making use of shallow nursery areas interior of the reef. Newborn pups measure 40–50 cm (15.7–19.7 in) long in the Indian Ocean and off northern Australia, while free-swimming pups as small as 33 cm (13 in) long have been observed in the Pacific islands. The litter size is 2–5 (typically 4), and is not correlated with female size. Young blacktip reef sharks commonly form large groups in water barely deep enough to cover their bodies, over sand flats or in mangrove swamps close to shore. During high tide, they also move onto flooded coral platforms or seaweed
beds. Growth is initially rapid; one documented captive shark grew an average of 23 cm (9.1 in) per year in its first two years of life. The growth rate slows to around 5 cm (2 in) per year in juveniles and adults. Males and females mature sexually at lengths of 95 cm (37.4 in) and 97 cm (38.2 in) respectively off northern Australia, and 105 cm (41.3 in) and 110 cm (43.3 in) respectively off Aldabra. Males mature at 97 cm (38.2 in) long off Palmyra Atoll.
Under most circumstances, the blacktip reef shark has a timid demeanor and is easily frightened away by swimmers. However, its inshore habitat preferences bring it into frequent contact with humans, and thus it is regarded as potentially dangerous. As of early 2009, there are 11 unprovoked attacks and 21 attacks total (none fatal) listed on the International Shark Attack File
that are attributable to the blacktip reef shark. Most attacks involve sharks biting the legs or feet of waders, apparently mistaking them for their natural prey, and do not result in serious injury. In the Marshall Islands, native islanders avoid blacktip reef shark attacks by swimming rather than wading through shallow water, and a way of discouraging these sharks is to submerge one's body. The blacktip reef shark has also been known to become aggressive in the presence of bait, and may pose a threat while attempting to steal the catches of spear fishers
.
The blacktip reef shark is a regular catch of coastal fisheries such as those operating off Thailand
and India
, but is not targeted or considered commercially important. The meat (sold fresh, frozen, dried and salted, or smoked for human consumption), liver oil
, and fins
are utilized. The International Union for Conservation of Nature (IUCN) has assessed the blacktip reef shark as Near Threatened
. Though it remains widespread and common overall, substantial local declines due to overfishing
have now been documented in many areas. This species has a low reproductive rate, limiting its capacity for recovering from depletion. Blacktip reef sharks are popular subjects of public aquarium
exhibits, because of their "sharky" appearance and modest size, and are also attractions for ecotourism
divers.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Carcharhinidae, easily identified by the prominent black tips on its fins (especially on the first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
and the caudal fin). Among the most abundant sharks inhabiting the tropical coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s of the Indian
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
s, this species prefers shallow, inshore waters and its exposed first dorsal fin is a common sight in the region. Most blacktip reef sharks are found over reef ledges and sandy flats, though they have also been known to enter brackish and freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
environments. This species typically attains a length of 1.6 m (5.2 ft).
Blacktip reef sharks have extremely small home ranges and exhibit strong site fidelity, remaining within same local area for up to several years at a time. They are active predators of small bony fishes, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, and have also been known to feed on sea snakes and seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
s. Accounts of the blacktip reef shark's life history have been variable and sometimes contradictory, in part reflecting geographical differences within the species. Like other members of its family, this shark is viviparous
Vivipary
Vivipary has two different meanings. In animals, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs...
with females giving birth to 2–5 young on a biennial, annual, or possibly biannual cycle. Reports of the gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
range from 7–9, to 10–11, to possibly 16 months. Mating
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
is preceded by the male following closely behind the female, likely attracted by her chemical signals. Newborn sharks are found further inshore and in shallower water than adults, frequently roaming in large groups over areas flooded by high tide
High Tide
High Tide was a band formed in 1969 by Tony Hill , Simon House , Peter Pavli and Roger Hadden .-History:...
.
Timid and skittish, the blacktip reef shark is difficult to approach and seldom poses a danger to humans unless roused by food. However, people wading through shallow water are at risk of having their legs mistakenly bitten. This shark is used for its meat, fins, and liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
but is not considered to be a commercially significant species. The International Union for Conservation of Nature (IUCN) has assessed the blacktip reef shark as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
. Although the species as a whole remains widespread and relatively common, overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
of this slow-reproducing shark has led to its decline at a number of locales.
Taxonomy
French naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
s Jean René Constant Quoy
Jean René Constant Quoy
Jean René Constant Quoy was a French zoologist.Along with Joseph Paul Gaimard he served as naturalist aboard La Coquille under Louis Isidore Duperrey during its circumnavigation of the globe , and the Astrolabe under the command of Jules Dumont d'Urville...
and Joseph Paul Gaimard
Joseph Paul Gaimard
Joseph Paul Gaimard was a French naval surgeon and naturalist.Along with Jean René Constant Quoy he served as naturalist on the ships L'Uranie under Louis de Freycinet 1817-1820, and L'Astrolabe under Jules Dumont d'Urville 1826-1829...
originally described the blacktip reef shark during the 1817–1820 exploratory voyage of the corvette
Corvette
A corvette is a small, maneuverable, lightly armed warship, originally smaller than a frigate and larger than a coastal patrol craft or fast attack craft , although many recent designs resemble frigates in size and role...
Uranie. In 1824, their account was published as part of Voyage autour du monde...sur les corvettes de S.M. l'Uranie et la Physicienne, Louis de Freycinet
Louis de Freycinet
Louis Claude de Saulces de Freycinet was a French navigator. He circumnavigated the earth, and was one of the first to produce a comprehensive map of the coastline of Australia.-Biography:...
's 13-volume report on the voyage. The type specimen was a 59 cm (23.2 in) long juvenile male caught off the island of Waigeo
Waigeo
Waigeo is an island in West Papua province of eastern Indonesia. The island is also known as Amberi, or Waigiu. It is the largest of the four main islands in the Raja Ampat Islands archipelago, between Halmahera and about 65 km to the northwest coast of New Guinea...
, west of New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
. Quoy and Gaimard chose the name Carcharias melanopterus, from the Greek melas meaning "black" and pteron meaning "fin" or "wing", in reference to this shark's prominent fin markings.
Subsequent authors moved the blacktip reef shark to the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Carcharhinus; in 1965 the International Commission on Zoological Nomenclature
International Commission on Zoological Nomenclature
The International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...
(ICZN) designated it as the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
for the genus. In some earlier literature, the scientific name of this shark was mistakenly given as C. spallanzani, now recognized as a synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of the spottail shark
Spottail shark
The spottail shark is a species of requiem shark, family Carcharhinidae, found in the Indo-West Pacific oceans waters between latitudes 31° N and 31° S, from the surface to 140 m. Its length is up to about 1.6 m....
(C. sorrah). Other common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s for this species include blackfin reef shark, black finned shark, blacktip shark, reef blacktip shark, and guliman.
Phylogeny
Like most other members of its genus, the phylogenetic position of the blacktip reef shark remains indeterminate. Based on morphologyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
, Jack Garrick proposed in 1982 that the closest relative of the blacktip reef shark is the nervous shark
Nervous shark
The nervous shark, Carcharhinus cautus, is a requiem shark of the family Carcharhinidae, found in the western Pacific Ocean between latitudes 5° S and 30° S. Its length is up to about 1.5 m....
(C. cautus). Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...
's 1988 morphological analysis suggested affinity not only between this species and the nervous shark but also four other species, and could not resolve their relationships further. A 1998 allozyme
Allozyme
Variant forms of an enzyme that are coded by different alleles at the same locus are called allozymes. These are opposed to isozymes, which are enzymes that perform the same function, but which are coded by genes located at different loci....
analysis by Gavin Naylor again yielded ambiguous results, finding that the blacktip reef shark forms a polytomy
Polytomy
A polytomy , meaning many temporal based branches, is a section of a phylogeny in which the evolutionary relationships can not be fully resolved to dichotomies. In a phylogenetic tree, a polytomy is represented as a node which has more than two immediate descending branches...
(irresolvable group) with 10 other Carcharhinus species.
Distribution and habitat
The blacktip reef shark is found throughout nearshore waters of the tropical and subtropical Indo-PacificIndo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
. In the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, it occurs from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
to the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
, including Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
, Mauritius
Mauritius
Mauritius , officially the Republic of Mauritius is an island nation off the southeast coast of the African continent in the southwest Indian Ocean, about east of Madagascar...
, and the Seychelles
Seychelles
Seychelles , officially the Republic of Seychelles , is an island country spanning an archipelago of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar....
, and from there eastward along the coast of the Indian subcontinent
Indian subcontinent
The Indian subcontinent, also Indian Subcontinent, Indo-Pak Subcontinent or South Asian Subcontinent is a region of the Asian continent on the Indian tectonic plate from the Hindu Kush or Hindu Koh, Himalayas and including the Kuen Lun and Karakoram ranges, forming a land mass which extends...
to Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
, including Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, the Andaman Islands
Andaman Islands
The Andaman Islands are a group of Indian Ocean archipelagic islands in the Bay of Bengal between India to the west, and Burma , to the north and east...
, and the Maldives
Maldives
The Maldives , , officially Republic of Maldives , also referred to as the Maldive Islands, is an island nation in the Indian Ocean formed by a double chain of twenty-six atolls oriented north-south off India's Lakshadweep islands, between Minicoy Island and...
. In the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, it is found from southern China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
to Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
, and also inhabits numerous oceanic islands including the Marshall
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
, Gilbert
Gilbert Islands
The Gilbert Islands are a chain of sixteen atolls and coral islands in the Pacific Ocean. They are the main part of Republic of Kiribati and include Tarawa, the site of the country's capital and residence of almost half of the population.-Geography:The atolls and islands of the Gilbert Islands...
, Society
Society Islands
The Society Islands are a group of islands in the South Pacific Ocean. They are politically part of French Polynesia. The archipelago is generally believed to have been named by Captain James Cook in honor of the Royal Society, the sponsor of the first British scientific survey of the islands;...
, Tuamotu, and Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
. Contrary to what most sources state, there are no confirmed records of this species from Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese waters, and purported Japanese specimens likely came from Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
. A Lessepsian migrant, this shark has colonized the eastern Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
by way of the Suez Canal
Suez Canal
The Suez Canal , also known by the nickname "The Highway to India", is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea and the Red Sea. Opened in November 1869 after 10 years of construction work, it allows water transportation between Europe and Asia without navigation...
.
Although it has been reported from a depth of 75 m (246.1 ft), the blacktip reef shark is usually found in water only a few meters deep, and can often be seen swimming close to shore with its dorsal fin exposed. Younger sharks prefer shallow sandy flats, while older sharks are most common around reef ledges and can also be found near reef drop-offs. This species has also been reported from brackish estuaries and lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
s in Madagascar, and freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
environments in Malaysia, though it is not able to tolerate low salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
to the same degree as the bull shark
Bull shark
The bull shark, Carcharhinus leucas, also known as Zambezi shark or unofficially known as Zambi in Africa and Nicaragua shark in Nicaragua, is a shark common worldwide in warm, shallow waters along coasts and in rivers...
(C. leucas). At Aldabra
Aldabra
Aldabra, the world's second largest coral atoll, is in the Aldabra Group of islands in the Indian Ocean that form part of the Seychelles. Uninhabited and extremely isolated, Aldabra is virtually untouched by humans, has distinctive island fauna including the Aldabra Giant Tortoise, and is...
in the Indian Ocean, blacktip reef sharks congregate in the channels between reef flats during low tide and travel to the mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
s when the water rises. There is equivocal evidence that sharks from the northern and southern extremes of its distribution are migratory
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
.
Description
A robustly built species with a streamlined "typical shark" form, the blacktip reef shark has a short, wide, rounded snout and moderately large, oval eyes. Each nostrilNostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
has a flap of skin in front that is expanded into a nipple-shaped lobe. Not counting small symphysial (central) teeth, the tooth rows number 11–13 (usually 12) on either side of the upper jaw and 10–12 (usually 11) on either side of the lower jaw. The upper teeth are upright to angled and narrowly triangular in shape, bearing serrations that are more coarse on the bases; the lower teeth are similar but more finely serrated. The teeth of adult males are more abruptly curved than those of females.
The pectoral fins are large and narrowly falcate (sickle-shaped), tapering to points. The sizable first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is high with a curving "S"-shaped rear margin, and originates over the free rear tips of the pectoral fins. The second dorsal fin is relatively large with a short rear margin, and is placed opposite the anal fin. There is no ridge between the dorsal fins. This shark is a pale grayish brown above and white below, with an obvious white band on the sides extending forward from above the anal fin. All the fins have black tips highlighted by lighter-colored borders, which are especially striking on the first dorsal fin and lower caudal fin lobe. Most blacktip reef sharks are no more than 1.6 m (5.2 ft) long, though rarely individuals may reach 1.8 m (5.9 ft) or possibly 2 m (6.6 ft). The maximum weight on record is 13.6 kg (30 lb).
Biology and ecology
Whitetip reef shark
The whitetip reef shark is a species of requiem shark, family Carcharhinidae, and the only member of its genus. A small shark usually not exceeding in length, this species is easily recognizable by its slender body and short but broad head, as well as tubular skin flaps beside the nostrils, oval...
(Triaenodon obesus), the blacktip reef shark is one of the three most common sharks inhabiting coral reefs in the Indo-Pacific. This species predominates in shallow habitats, while the other two are mostly found deeper. Fast-swimming and active, the blacktip reef shark may be encountered alone or in small groups; large "social" aggregations have also been observed. For the most part juvenile and adult sharks are not segregated by sex, save for the movements of pregnant females to give birth. Individual blacktip reef sharks exhibit strong fidelity to particular areas, where they may remain for up to several years.
A tracking study off Palmyra Atoll
Palmyra Atoll
Palmyra Atoll is an essentially unoccupied equatorial Northern Pacific atoll administered as an unorganized incorporated territory by the United States federal government...
in the central Pacific has found that the blacktip reef shark has a home range of around 0.55 square kilometre, among the smallest of any shark species. The size and location of the range does not change with time of day. Within this range, 3–17% of the area constitute favored hunting patches that are disproportionately occupied by the resident shark. The sharks spend most of their time swimming back and forth along reef ledges, making occasional short forays onto sandy flats. Their average swimming speed decreases when the tide rises at night, possibly because the influx of cooler water reduces their metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
, or the accompanying movement of prey fishes makes foraging easier. Blacktip reef sharks at Aldabra tend to be more mobile than those at Palmyra, with recorded individual movements of up to 2.5 km (1.6 mi) over 7 hours.
Blacktip reef sharks, particularly small individuals, fall prey to larger fishes including grouper
Grouper
Groupers are fish of any of a number of genera in the subfamily Epinephelinae of the family Serranidae, in the order Perciformes.Not all serranids are called groupers; the family also includes the sea basses. The common name grouper is usually given to fish in one of two large genera: Epinephelus...
s, grey reef sharks, tiger shark
Tiger shark
The tiger sharks, Galeocerdo cuvier, is a species of requiem shark and the only member of the genus Galeocerdo. Commonly known as sea tigers, tiger sharks are relatively large macropredators, capable of attaining a length of over . It is found in many tropical and temperate waters, and is...
s (Galeocerdo cuvier), and members of their own species. At Palmyra Atoll, adult blacktip reef sharks avoid patrolling tiger sharks by staying out of the central, deeper lagoon. Known parasites of the blacktip reef shark include the tapeworms Anthobothrium lesteri, Nybelinia queenslandensis, Otobothrium alexanderi, and Platybothrium jondoeorum, a myxosporidian in the genus Unicapsula, and the monogenea
Monogenea
Monogenea are a group of largely ectoparasitic members of the flatworm phylum Platyhelminthes, class Monogenea.-Characteristics:Monogenea are very small parasitic flatworms mainly found on skin or gills of fish....
n Dermophthirius melanopteri. One of the few documented examples of infectious disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
in a shark was a fatal case of hemorrhagic
Bleeding
Bleeding, technically known as hemorrhaging or haemorrhaging is the loss of blood or blood escape from the circulatory system...
septicemia in a blacktip reef shark, caused by the bacterium Aeromonas salmonicida
Aeromonas salmonicida
Aeromonas salmonicida is a species of Gram-negative bacteria, from the genus Aeromonas, which causes the disease furunculosis in marine and freshwater fish.-Cell structure and metabolism:...
subsp. salmonicida.
Feeding
As often the most abundant apex predatorApex predator
Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
within its ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
, the blacktip reef shark plays a major role in structuring inshore ecological communities
Community (ecology)
In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. The term community has a variety of uses...
. Its diet is composed primarily of small teleost fishes, including mullet
Mullet (fish)
The mullets or grey mullets are a family and order of ray-finned fish found worldwide in coastal temperate and tropical waters, and in some species in fresh water. Mullets have served as an important source of food in Mediterranean Europe since Roman times...
, groupers, grunters
Terapontidae
Grunters or tigerperches are fishes in the family Terapontidae . They are found in shallow coastal waters in the Indian Ocean and western Pacific, where they live in saltwater, brackish and freshwater habitats...
, jacks
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
, mojarra
Mojarra
The mojarras are a family, Gerreidae, of fishes in the order Perciformes. It has seven genera.Mojarras are a common prey and bait fish in many parts of the Caribbean including the South American Coast and Caribbean islands. These species tend to be difficult to identify in the field and often...
s, wrasse
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 82 genera, which are divided into nine subgroups or tribes....
s, surgeonfish, and smelt-whitings
Sillaginidae
The Sillaginidae, commonly known as the smelt-whitings, whitings, sillaginids, sand borers and sand-smelts, are a family of benthic coastal marine fishes in the order Perciformes. The smelt-whitings inhabit a wide region covering much of the Indo-Pacific, from the west coast of Africa east to Japan...
. Groups of blacktip reef sharks in the Indian Ocean have been observed herding schools
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
of mullet against the shore for easier feeding. Squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
, cuttlefish
Cuttlefish
Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda . Despite their name, cuttlefish are not fish but molluscs....
, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, and mantis shrimp
Mantis shrimp
Mantis shrimp or stomatopods are marine crustaceans, the members of the order Stomatopoda. They are neither shrimp nor mantids, but receive their name purely from the physical resemblance to both the terrestrial praying mantis and the shrimp. They may reach in length, although exceptional cases of...
are also taken, as well as carrion
Carrion
Carrion refers to the carcass of a dead animal. Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters include vultures, hawks, eagles, hyenas, Virginia Opossum, Tasmanian Devils, coyotes, Komodo dragons, and burying beetles...
and smaller sharks and rays, though this is rare. Off northern Australia, this species is known to consume sea snakes, including Acrochordus granulatus
Acrochordus granulatus
Acrochordus granulatus is a snake species found from India through Southeast Asia to the Solomon Islands. It is completely aquatic and almost helpless on land. No subspecies are currently recognized.-Description:...
, Hydrelaps darwiniensis, Hydrophis
Hydrophis
Hydrophis is a genus of sea snakes. They are typically found in Indoaustralian and Southeast Asian waters. Currently, 34 species are recognized.-Systematics and classification:There are 34 recognized species in the genus Hydrophis....
spp. and Lapemis hardwickii
Lapemis hardwickii
The Spine-bellied Sea snake, or Hardwicke's Spine-bellied Sea snake, is a species of sea snake.-Description:*Body short, stout, neck region not less than half as thick at midbody;...
. Sharks off Palmyra Atoll have been documented preying on seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
chicks that have fallen out of their nest
Bird nest
A bird nest is the spot in which a bird lays and incubates its eggs and raises its young. Although the term popularly refers to a specific structure made by the bird itself—such as the grassy cup nest of the American Robin or Eurasian Blackbird, or the elaborately woven hanging nest of the...
s into the water. Miscellaneous items that have been found inside the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
s of this species include algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, turtle grass, coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
, hydrozoa
Hydrozoa
Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...
, bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
, rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s, and stones.
Researchers working at Enewetak Atoll in the Marshall Islands have found that the blacktip reef shark can be readily attracted by splashing or striking metal tools against hard objects underwater, as well as by the scent of both healthy and injured fish. As with most sharks, the blacktip reef shark does not have any cone cell
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
s in its retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, limiting its ability to discriminate colors and fine details. Instead, its vision is adapted for sensitivity to movement or contrast under low light conditions, which is further enhanced by the presence of a reflective tapetum lucidum
Tapetum lucidum
The tapetum lucidum is a layer of tissue in the eye of many vertebrate animals....
. Experiments have shown that this shark is capable of detecting small objects up to 1.5–3 m (4.9–9.8 ft) away, but is unable to clearly discern the shape of the object. Electroreception
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...
is another means by which this shark can locate prey; its ampullae of Lorenzini
Ampullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
have a sensitivity of approximately 4 nV/cm and an effective range of 25 cm (10 in). Similar to the grey reef shark, this species becomes more excited and "confident" in the presence of other individuals of its species, and in extreme situations can be roused into a feeding frenzy
Feeding frenzy
In ecology, a feeding frenzy is a situation where oversaturation of a supply of food leads to rapid feeding by predatory animals. For example, a large school of fish can cause nearby sharks to enter a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each...
. Feeding activity may be greater at night than during the day.
Life history
Like the other members of its family, the blacktip reef shark is viviparous, though the details of its life history vary across its range. Its reproductive cycle is annual off northern AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, with mating taking place from January to February, as well as off Moorea
Moorea
Moʻorea is a high island in French Polynesia, part of the Society Islands, 17 km northwest of Tahiti. Its position is . Moʻorea means "yellow lizard" in Tahitian...
in French Polynesia
French Polynesia
French Polynesia is an overseas country of the French Republic . It is made up of several groups of Polynesian islands, the most famous island being Tahiti in the Society Islands group, which is also the most populous island and the seat of the capital of the territory...
, where mating occurs from November to March. The cycle is biennial off Aldabra, where intense competition within and between species for food may constrain females to only bearing young every other year. Earlier accounts from the Indian Ocean by Johnson (1978), Madagascar by Fourmanoir (1961), and the Red Sea by Gohar and Mazhar (1964), indicated a biannual cycle in these regions with two breeding seasons per year from June to July and December to January. If accurate, the shorter reproductive cycles of these subpopulations may be a consequence of warmer water.
When receptive to mating, a female blacktip reef shark swims slowly in a sinusoidal pattern near the bottom with her head pointed down; observations in the wild suggest that female sharks release chemical signals that allow males to track them. Once the male finds her, he closes to around 15 cm (5.9 in) and follows her with his snout oriented towards her vent. A courting male may also bite the female behind her gills or on her pectoral fins; these mating wounds heal completely after 4–6 weeks. After a period of synchronous swimming, the male pushes the female on her side and positions her so that her head is against the bottom and her tail is raised. Once the female is in position, the male inserts one of his claspers into her cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
. Copulation lasts for several minutes, after which the sharks separate and resume their regular behaviors. Off Moorea, individual older females mate and give birth at a consistent time every year, often to within a week's precision, whereas younger females exhibit more variability in their timing. Younger females are also more likely to fail to become pregnant after mating.
The gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
has been reported as 10–11 months long in the Indian Ocean and Pacific islands, and 7–9 months long off northern Australia. Earlier authors such as Melouk (1957) have estimated a gestation period as long as 16 months, though the validity of this figure has subsequently been challenged. The female has a single functional ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
(on the right) and two functional uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
es, divided into separate compartments for each embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
. Newly ovulated
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
egg cases measure 3.9 cm (1.5 in) by 2.6 cm (1 in); after hatching the embryos are sustained by a yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
during the first stage of development. After two months, the embryo measures 4 cm (1.6 in) long and has well-developed external gills. After four months, the yolk sac has begun to be converted into a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection that attaches to the uterine wall; at this time the embryo's dark fin markings develop. By five months, the embryo measures 24 cm (9.4 in) and has resorbed its external gills; the placenta is fully formed though some yolk remains until seven months into gestation.
Parturition occurs from September to November, with females making use of shallow nursery areas interior of the reef. Newborn pups measure 40–50 cm (15.7–19.7 in) long in the Indian Ocean and off northern Australia, while free-swimming pups as small as 33 cm (13 in) long have been observed in the Pacific islands. The litter size is 2–5 (typically 4), and is not correlated with female size. Young blacktip reef sharks commonly form large groups in water barely deep enough to cover their bodies, over sand flats or in mangrove swamps close to shore. During high tide, they also move onto flooded coral platforms or seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
beds. Growth is initially rapid; one documented captive shark grew an average of 23 cm (9.1 in) per year in its first two years of life. The growth rate slows to around 5 cm (2 in) per year in juveniles and adults. Males and females mature sexually at lengths of 95 cm (37.4 in) and 97 cm (38.2 in) respectively off northern Australia, and 105 cm (41.3 in) and 110 cm (43.3 in) respectively off Aldabra. Males mature at 97 cm (38.2 in) long off Palmyra Atoll.
Human interactions
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 panel of shark experts developed a standard system for...
that are attributable to the blacktip reef shark. Most attacks involve sharks biting the legs or feet of waders, apparently mistaking them for their natural prey, and do not result in serious injury. In the Marshall Islands, native islanders avoid blacktip reef shark attacks by swimming rather than wading through shallow water, and a way of discouraging these sharks is to submerge one's body. The blacktip reef shark has also been known to become aggressive in the presence of bait, and may pose a threat while attempting to steal the catches of spear fishers
Spearfishing
Spearfishing is an ancient method of fishing that has been used throughout the world for millennia. Early civilizations were familiar with the custom of spearing fish from rivers and streams using sharpened sticks....
.
The blacktip reef shark is a regular catch of coastal fisheries such as those operating off Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
and India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, but is not targeted or considered commercially important. The meat (sold fresh, frozen, dried and salted, or smoked for human consumption), liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
, and fins
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
are utilized. The International Union for Conservation of Nature (IUCN) has assessed the blacktip reef shark as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
. Though it remains widespread and common overall, substantial local declines due to overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
have now been documented in many areas. This species has a low reproductive rate, limiting its capacity for recovering from depletion. Blacktip reef sharks are popular subjects of public aquarium
Public aquarium
A public aquarium is the aquatic counterpart of a zoo, housing living aquatic species for viewing. Most public aquariums feature tanks larger than those kept by home aquarists, as well as smaller tanks. Since the first public aquariums were built in the mid-19th century, they have become popular...
exhibits, because of their "sharky" appearance and modest size, and are also attractions for ecotourism
Ecotourism
Ecotourism is a form of tourism visiting fragile, pristine, and usually protected areas, intended as a low impact and often small scale alternative to standard commercial tourism...
divers.