Blacktip shark
Encyclopedia
The blacktip shark is a species
of requiem shark
, family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses
have revealed substantial variation within this species, with populations from the western Atlantic Ocean
isolated and distinct from those in the rest of its range. The blacktip shark has a stout, fusiform body with a pointed snout, long gill slit
s, and no ridge between the dorsal fin
s. Most individuals have black tips or edges on the pectoral, dorsal, pelvic, and caudal fins. It usually attains a length of 1.5 m (4.9 ft).
Swift, energetic piscivore
s, blacktip sharks are known to make spinning leaps out of the water while attacking schools of small fish. Their demeanor has been described as "timid" compared to other large requiem sharks. Both juveniles and adults form groups of varying size. Like other members of its family, the blacktip shark is viviparous; females bear 1–10 pups every other year. Young blacktip sharks spend the first months of their lives in shallow nurseries, and grown females will return to the nurseries where they were born to give birth themselves. In the absence of males, females are also capable of asexual reproduction
.
Normally wary of humans, blacktip sharks can become aggressive in the presence of food and have been responsible for a number of attacks
on people. This species is of importance to both commercial
and recreational fisheries
across many parts of its range, with its meat, skin, fins, and liver oil used. It has been assessed as Near Threatened
by the International Union for Conservation of Nature (IUCN), on the basis of its low reproductive rate and high value to fishers.
as Carcharias (Prionodon) limbatus in Johannes Müller
and Friedrich Henle
's 1839 Systematische Beschreibung der Plagiostomen. The type specimens were two individuals caught off Martinique
, both of which have since been lost. Later authors moved this species to the genus Carcharhinus
. The specific epithet limbatus is Latin
for "bordered", referring to the black edges of this shark's fins. Other common names used for the blacktip shark include blackfin shark, blacktip whaler, common or small blacktip shark, grey shark, and spotfin ground shark.
(C. amblyrhynchoides) and the spinner shark
(C. brevipinna), due to similarities in morphology and behavior. However, this interpretation has not been borne out by studies of mitochondrial
and ribosomal DNA
, which instead suggest affinity with the blacknose shark
(C. acronotus). More work is required to fully resolve the relationship between the blacktip shark and other Carcharhinus species.
Analysis of mitochondrial DNA has also revealed two distinct lineages within this species, one occupying the western Atlantic and the other occupying the eastern Atlantic, Indian, and Pacific Oceans. This suggests that Indo-Pacific blacktip sharks are descended from those in the eastern Atlantic, while the western Atlantic sharks became isolated by the widening Atlantic Ocean on one side and the formation of the Isthmus of Panama
on the other. Blacktip sharks from these two regions differ in morphology, coloration, and life history characteristics, and the eastern Atlantic lineage may merit species status. Fossil teeth belonging to this species have been found in Early Miocene
(23–16 Ma) deposits in Delaware
and Florida
.
to Brazil
, including the Gulf of Mexico
and the Caribbean Sea
, and from the Mediterranean Sea
, Madeira
, and the Canary Islands
to the Democratic Republic of the Congo
. It occurs all around the periphery of the Indian Ocean, from South Africa
and Madagascar
to the Arabian Peninsula
and the Indian subcontinent
, to Southeast Asia
. In the western Pacific, it is found from southern China
to northern Australia
, including the Philippines
and Indonesia
. In the eastern Pacific, it occurs from Baja California
to Peru
. It has also been reported at a number of Pacific islands, including New Caledonia
, Tahiti
, the Marquesas, Hawaii
, Revillagigedo, and the Galápagos.
Most blacktip sharks are found in water less than 30 m (100 ft) deep over continental and insular shelves, though they may dive to 64 m (210 ft). Favored habitats are muddy bays, island lagoons, and the drop-offs near coral reefs; they are also tolerant of low salinity
and enter estuaries and mangrove swamps. Although an individual may be found some distance offshore, blacktip sharks do not inhabit oceanic waters. Seasonal migration
has been documented for the population off the east coast of the United States, moving north to North Carolina
in the summer and south to Florida
in the winter.
s are longer than those of similar requiem shark species. The jaws contain 15 tooth rows on either side, with 2 symphysial teeth (at the jaw midline) in the upper jaw and 1 symphysial tooth in the lower jaw. The teeth are broad-based with a high, narrow cusp and serrated edges. The first dorsal fin is tall and falcate (sickle-shaped) with a short free rear tip; there is no ridge running between the first and second dorsal fins. The large pectoral fins are falcate and pointed.
The coloration is gray to brown above and white below, with a conspicuous white stripe running along the sides. The pectoral fins, second dorsal fin, and the lower lobe of the caudal fin usually have black tips. The pelvic fins and rarely the anal fin may also be black-tipped. The first dorsal fin and the upper lobe of the caudal fin typically have black edges. Some larger individuals have unmarked or nearly unmarked fins. Blacktip sharks can temporarily lose almost all their colors during blooms
, or "whitings", of coccolithophores. This species attains a maximum known length of 2.8 m (9.0 ft), though 1.5 m (4.9 ft) is more typical, and a maximum known weight of 123 kg (271 lb).
s Pandarus sinuatus and P. smithii, and the flatworm
s Dermophthiris penneri and Dionchus spp., which attach the shark's skin. This species is also parasitized by nematode
s in the family Philometridae, which infest the ovaries.
launches it into the air. Observations in the Bahamas suggest that blacktip sharks may also jump out of the water to dislodge attached sharksuckers (Echeneis naucrates), which irritate the shark's skin and compromise its hydrodynamic shape. The speed attained by the shark during these jumps has been estimated to average 6.3 m/s (21 ft/s).
Blacktip sharks have a timid disposition and consistently lose out to Galapagos shark
s (C. galapagensis) and silvertip shark
s (C. albimarginatus) of equal size when competing for food. If threatened or challenged, they may perform an agonistic display
: the shark swims towards the threat and then turns away, while rolling from side to side, lowering its pectoral fins, tilting its head and tail upwards, and making sideways biting motions. The entire sequence lasts around 25 seconds. This behavior is similar to the actions of a shark attempting to move a sharksucker; it is possible that one of these behaviors is derived from the other.
s, herring
, anchovies, ladyfish, sea catfish
, cornetfish
, flatfish
, threadfin
s, mullet, mackerel
, jacks
, grouper
s, snook
, porgies
, mojarra
s, emperors
, grunts
, butterfish, tilapia
, triggerfish
, boxfish
, and porcupinefish
. They also feed on rays and skates
, as well as smaller sharks such as smoothhounds and sharpnose sharks
. Crustacean
s and cephalopod
s are occasionally taken. In the Gulf of Mexico, the most important prey of the blacktip shark is the Gulf menhaden
(Brevoortia patronus), followed by the Atlantic croaker (Micropogonias undulatus). Off South Africa, jacks and herring are the most important prey. Hunting peaks at dawn and dusk. The excitability and sociability of blacktip sharks makes them prone to feeding frenzies
when large quantities of food are suddenly available, such as when fishing vessels dump their refuse overboard.
Mating occurs from spring to early summer, and the young are born at around the same time the following year after a gestation period
of 10–12 months. Females have one functional ovary
and two functional uterus
es; each uterus is separated into compartments with a single embryo
inside each. The embryos are initially sustained by a yolk sac
; in the 10th or 11th week of gestation, when the embryo measures 18–19 cm long (7.1–7.5 in), the supply of yolk is exhausted and the yolk sac develops into a placenta
l connection that sustains the embryo until birth. The length at birth is 55–60 cm (22–24 in) off the eastern United States and 61–65 cm (24–26 in) off North Africa. The mortality rate
in the first 15 months of life is 61–91%, with major threats being predation and starvation. The young remain in the nurseries until their first fall, at which time they migrate to their wintering grounds.
The growth rate of this species slows with age: 25–30 cm (10–12 in) in the first six months, then 20 cm (8 in) a year until the second year, then 10 cm (4 in) a year until maturation, then 5 cm (2 in) a year for adults. The size at maturity varies geographically: males and females mature at 1.4–1.5 m (4.6–4.9 ft) and 1.6 m (5.2 ft) respectively in the northeastern Atlantic, 1.3–1.4 m (4.3–4.6 ft) and 1.5–1.6 m (4.9–5.2 ft) respectively in the Gulf of Mexico, 1.5 m (4.9 ft) and 1.6 m (5.2 ft) respectively off South Africa, and 1.7 m (5.6 ft) and 1.8 m (5.9 ft) respectively off North Africa. The age at maturation is 4–5 years for males and 7–8 years for females. The lifespan is at least 12 years.
In 2007, a 9-year-old female blacktip shark at the Virginia Aquarium & Marine Science Center
was found to be pregnant with a single near-term female pup, despite having never mated with a male. Genetic analysis confirmed that her offspring was the product of automictic parthenogenesis
, a form of asexual reproduction
in which an ovum
merges with a polar body
to form a zygote
without fertilization. Along with an earlier case of parthenogenesis in the bonnethead
(Sphyrna tiburo), this event suggests that asexual reproduction may be more widespread in sharks than previously thought.
lists 28 unprovoked attacks (one fatal) and 13 provoked attacks by this species. Blacktip sharks are responsible annually for 16% of the shark attacks around Florida. Most attacks by this species result in only minor wounds.
As one of the most common large sharks in coastal waters, the blacktip shark is caught in large numbers by commercial fisheries throughout the world, using longlines, fixed bottom nets, bottom trawls, and hook-and-line. The meat is of high quality and marketed fresh, frozen, or dried and salted. In addition, the fins are used for shark fin soup
, the skin for leather
, the liver oil
for vitamin
s, and the carcasses for fishmeal. Blacktip sharks are one of the most important species to the northwestern Atlantic shark fishery, second only to the sandbar shark
(C. plumbeus). The flesh is considered superior to that of the sandbar shark, resulting in the sandbar and other requiem shark species being sold under the name "blacktip shark" in the United States. The blacktip shark is also very significant to Indian and Mexican fisheries, and is caught in varying numbers by fisheries in the Mediterranean, South China Sea, and off northern Australia.
The blacktip shark is popular with recreational anglers in Florida, the Caribbean, and South Africa. It is listed as a game fish
by the International Game Fish Association
(IGFA). Once hooked, this species is a strong, steady fighter that sometimes jumps out of the water. Since 1995, the number of blacktip sharks taken by recreational anglers in the United States has approached or surpassed the number taken by commercial fishing. The International Union for Conservation of Nature (IUCN) has assessed the blacktip shark as Near Threatened
, as its low reproductive rate renders it vulnerable to overfishing
. The United States and Australia are the only two countries that manage fisheries catching blacktip sharks. In both cases, regulation occurs under umbrella management schemes for multiple shark species, such as that for the Large Coastal Sharks (LCS) category of the US National Marine Fisheries Service
(NMFS) Atlantic shark Fisheries Management Plan (FMP). No conservation plans specifically for this species have been implemented.
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 Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
have revealed substantial variation within this species, with populations from the western Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
isolated and distinct from those in the rest of its range. The blacktip shark has a stout, fusiform body with a pointed snout, long gill slit
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, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s, and no ridge between the 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...
s. Most individuals have black tips or edges on the pectoral, dorsal, pelvic, and caudal fins. It usually attains a length of 1.5 m (4.9 ft).
Swift, energetic piscivore
Piscivore
A piscivore is a carnivorous animal which eats primarily fish. Piscivory was the diet of early tetrapods , insectivory came next, then in time reptiles added herbivory....
s, blacktip sharks are known to make spinning leaps out of the water while attacking schools of small fish. Their demeanor has been described as "timid" compared to other large requiem sharks. Both juveniles and adults form groups of varying size. Like other members of its family, the blacktip shark is viviparous; females bear 1–10 pups every other year. Young blacktip sharks spend the first months of their lives in shallow nurseries, and grown females will return to the nurseries where they were born to give birth themselves. In the absence of males, females are also capable of asexual reproduction
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
.
Normally wary of humans, blacktip sharks can become aggressive in the presence of food and have been responsible for a number of attacks
Shark attack
A shark attack is an attack on a human by a shark. Every year around 60 shark attacks are reported worldwide, although death is quite unusual. Despite the relative rarity of shark attacks, the fear of sharks is a common phenomenon, having been fueled by the occasional instances of serial attacks,...
on people. This species is of importance to both commercial
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
and recreational fisheries
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
across many parts of its range, with its meat, skin, fins, and liver oil used. It has been assessed 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...
by the International Union for Conservation of Nature (IUCN), on the basis of its low reproductive rate and high value to fishers.
Taxonomy
The blacktip shark was first described by French zoologist Achille ValenciennesAchille Valenciennes
Achille Valenciennes was a French zoologist.Valenciennes was born in Paris, and studied under Georges Cuvier. Valenciennes' study of parasitic worms in humans made an important contribution to the study of parasitology...
as Carcharias (Prionodon) limbatus in Johannes Müller
Johannes Peter Müller
Johannes Peter Müller , was a German physiologist, comparative anatomist, and ichthyologist not only known for his discoveries but also for his ability to synthesize knowledge.-Early years and education:...
and Friedrich Henle
Friedrich Gustav Jakob Henle
Friedrich Gustav Jakob Henle was a German physician, pathologist and anatomist. He is credited with the discovery of the loop of Henle in the kidney. His essay "On Miasma and Contagia" was an early argument for the germ theory of disease...
's 1839 Systematische Beschreibung der Plagiostomen. The type specimens were two individuals caught off Martinique
Martinique
Martinique is an island in the eastern Caribbean Sea, with a land area of . Like Guadeloupe, it is an overseas region of France, consisting of a single overseas department. To the northwest lies Dominica, to the south St Lucia, and to the southeast Barbados...
, both of which have since been lost. Later authors moved this species to the genus Carcharhinus
Carcharhinus
Carcharhinus is the type genus of the requiem shark family, Carcharhinidae.- Species :* Carcharhinus acarenatus * Carcharhinus acronotus...
. The specific epithet limbatus is Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "bordered", referring to the black edges of this shark's fins. Other common names used for the blacktip shark include blackfin shark, blacktip whaler, common or small blacktip shark, grey shark, and spotfin ground shark.
Phylogeny and evolution
The closest relatives of the blacktip shark were originally thought to be the graceful sharkGraceful shark
The graceful shark or Queensland shark is a species of requiem shark, family Carcharhinidae, found in the tropical Indo-Pacific from the Gulf of Aden to northern Australia. It is a midwater species that has been recorded to a depth of...
(C. amblyrhynchoides) and the spinner shark
Spinner shark
The spinner shark is a species of requiem shark, family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species occurs in tropical and warm temperate waters worldwide, except for in the eastern Pacific Ocean...
(C. brevipinna), due to similarities in morphology and behavior. However, this interpretation has not been borne out by studies of mitochondrial
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
and ribosomal DNA
Ribosomal DNA
Ribosomal DNA codes for ribosomal RNA. The ribosome is an intracellular macromolecule that produces proteins or polypeptide chains. The ribosome itself consists of a composite of proteins and RNA. As shown in the figure, rDNA consists of a tandem repeat of a unit segment, an operon, composed of...
, which instead suggest affinity with the blacknose shark
Blacknose shark
The blacknose shark is a species of requiem shark, family Carcharhinidae, common in the tropical and subtropical waters of the western Atlantic Ocean. This species generally inhabits coastal seagrass, sand, or rubble habitats, with adults preferring deeper water than juveniles...
(C. acronotus). More work is required to fully resolve the relationship between the blacktip shark and other Carcharhinus species.
Analysis of mitochondrial DNA has also revealed two distinct lineages within this species, one occupying the western Atlantic and the other occupying the eastern Atlantic, Indian, and Pacific Oceans. This suggests that Indo-Pacific blacktip sharks are descended from those in the eastern Atlantic, while the western Atlantic sharks became isolated by the widening Atlantic Ocean on one side and the formation of the Isthmus of Panama
Isthmus of Panama
The Isthmus of Panama, also historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country of Panama and the Panama Canal...
on the other. Blacktip sharks from these two regions differ in morphology, coloration, and life history characteristics, and the eastern Atlantic lineage may merit species status. Fossil teeth belonging to this species have been found in Early Miocene
Early Miocene
The Early Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages....
(23–16 Ma) deposits in Delaware
Delaware
Delaware is a U.S. state located on the Atlantic Coast in the Mid-Atlantic region of the United States. It is bordered to the south and west by Maryland, and to the north by Pennsylvania...
and Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
.
Distribution and habitat
The blacktip shark has a worldwide distribution in tropical and subtropical waters. In the Atlantic, it is found from MassachusettsMassachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
to Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, including the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
and the Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
, and from the 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...
, Madeira
Madeira
Madeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
, and the Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
to the Democratic Republic of the Congo
Democratic Republic of the Congo
The Democratic Republic of the Congo is a state located in Central Africa. It is the second largest country in Africa by area and the eleventh largest in the world...
. It occurs all around the periphery of the Indian Ocean, 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...
and Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
to the Arabian Peninsula
Arabian Peninsula
The Arabian Peninsula is a land mass situated north-east of Africa. Also known as Arabia or the Arabian subcontinent, it is the world's largest peninsula and covers 3,237,500 km2...
and 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...
. In the western Pacific, 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...
to 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...
, including 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...
and 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...
. In the eastern Pacific, it occurs from Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
to Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
. It has also been reported at a number of Pacific islands, including 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...
, Tahiti
Tahiti
Tahiti is the largest island in the Windward group of French Polynesia, located in the archipelago of the Society Islands in the southern Pacific Ocean. It is the economic, cultural and political centre of French Polynesia. The island was formed from volcanic activity and is high and mountainous...
, the Marquesas, Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
, Revillagigedo, and the Galápagos.
Most blacktip sharks are found in water less than 30 m (100 ft) deep over continental and insular shelves, though they may dive to 64 m (210 ft). Favored habitats are muddy bays, island lagoons, and the drop-offs near coral reefs; they are also tolerant of 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...
and enter estuaries and mangrove swamps. Although an individual may be found some distance offshore, blacktip sharks do not inhabit oceanic waters. Seasonal migration
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...
has been documented for the population off the east coast of the United States, moving north to North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
in the summer and south to Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
in the winter.
Description
The blacktip shark has a robust, streamlined body with a long, pointed snout and relatively small eyes. The five pairs of gill slitGill 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, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are longer than those of similar requiem shark species. The jaws contain 15 tooth rows on either side, with 2 symphysial teeth (at the jaw midline) in the upper jaw and 1 symphysial tooth in the lower jaw. The teeth are broad-based with a high, narrow cusp and serrated edges. The first dorsal fin is tall and falcate (sickle-shaped) with a short free rear tip; there is no ridge running between the first and second dorsal fins. The large pectoral fins are falcate and pointed.
The coloration is gray to brown above and white below, with a conspicuous white stripe running along the sides. The pectoral fins, second dorsal fin, and the lower lobe of the caudal fin usually have black tips. The pelvic fins and rarely the anal fin may also be black-tipped. The first dorsal fin and the upper lobe of the caudal fin typically have black edges. Some larger individuals have unmarked or nearly unmarked fins. Blacktip sharks can temporarily lose almost all their colors during blooms
Algal bloom
An algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...
, or "whitings", of coccolithophores. This species attains a maximum known length of 2.8 m (9.0 ft), though 1.5 m (4.9 ft) is more typical, and a maximum known weight of 123 kg (271 lb).
Biology and ecology
The blacktip shark is an extremely fast, energetic predator that is usually found in groups of varying size. There is segregation by sex and age; adult males and non-pregnant females are found apart from pregnant females, and both are separated from juveniles. In Terra Ceia Bay, Florida, a nursery area for this species, juvenile blacktips form aggregations during the day and disperse at night. They aggregate most strongly in the early summer when the sharks are youngest, suggesting that they are seeking refuge from predators (mostly larger sharks) in numbers. Predator avoidance may also be the reason why juvenile blacktips do not congregate in the areas of highest prey density in the bay. Adults have no known predators. Known parasites of the blacktip shark include the copepodCopepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s Pandarus sinuatus and P. smithii, and the flatworm
Flatworm
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
s Dermophthiris penneri and Dionchus spp., which attach the shark's skin. This species is also parasitized by nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s in the family Philometridae, which infest the ovaries.
Behavior
Like the spinner shark, the blacktip shark is known to leap out of the water and spin three to four times about its axis before landing. Some of these jumps are the end product of feeding runs, in which the shark corkscrews vertically through schools of small fish and its momentumMomentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
launches it into the air. Observations in the Bahamas suggest that blacktip sharks may also jump out of the water to dislodge attached sharksuckers (Echeneis naucrates), which irritate the shark's skin and compromise its hydrodynamic shape. The speed attained by the shark during these jumps has been estimated to average 6.3 m/s (21 ft/s).
Blacktip sharks have a timid disposition and consistently lose out to Galapagos shark
Galapagos shark
The Galapagos shark is a species of requiem shark, family Carcharhinidae, found worldwide. This species favors clear reef environments around oceanic islands, where it is often the most abundant shark species...
s (C. galapagensis) and silvertip shark
Silvertip shark
The silvertip shark is a large species of requiem shark, family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. This species is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of 800 m...
s (C. albimarginatus) of equal size when competing for food. If threatened or challenged, they may perform an agonistic display
Shark threat display
Shark threat display, a type of agonistic display, is a behaviour observed in some sharks when they feel threatened or protective. It consists of a contorting of the body into a series of "ritualized" postures coupled with an exaggerated swimming style...
: the shark swims towards the threat and then turns away, while rolling from side to side, lowering its pectoral fins, tilting its head and tail upwards, and making sideways biting motions. The entire sequence lasts around 25 seconds. This behavior is similar to the actions of a shark attempting to move a sharksucker; it is possible that one of these behaviors is derived from the other.
Feeding
Fish make up some 90% of the blacktip shark's diet. A wide variety of fishes have been recorded as prey for this species: sardineSardine
Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
s, herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, anchovies, ladyfish, sea catfish
Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...
, cornetfish
Cornetfish
The cornetfishes are a small family Fistulariidae of extremely elongated fishes in the order Syngnathiformes. The family consists of just a single genus Fistularia with four species, found worldwide in tropical and subtropical marine environments.Ranging up to in length, cornetfishes are as thin...
, flatfish
Flatfish
The flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development...
, threadfin
Threadfin
Threadfins are silvery grey perciform marine fish of the family Polynemidae. Found in tropical to subtropical waters throughout the world, the threadfin family contains nine genera and 33 species...
s, mullet, mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
, 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...
, 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, snook
Centropomidae
The Centropomidae are a single genus family of freshwater and marine fishes in Order Perciformes, including the common snook or róbalo, Centropomus undecimalis...
, porgies
Sparidae
The Sparidae is a family of fish, included in the order Perciformes. The fish of the family are commonly called sea breams and porgies . The sheepshead, scup, and red sea bream are species in this family. They are found in shallow temperate and tropical waters and are bottom-dwelling carnivores....
, 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, emperors
Lethrinidae
The emperor breams or simply emperors also known as pigface breams are a family, Lethrinidae, of fishes in the order Perciformes....
, grunts
Sciaenidae
Sciaenidae is a family of fish commonly called drums, croakers, or hardheads for the repetitive throbbing or drumming sounds they make...
, butterfish, tilapia
Tilapia
Tilapia , is the common name for nearly a hundred species of cichlid fish from the tilapiine cichlid tribe. Tilapia inhabit a variety of fresh water habitats, including shallow streams, ponds, rivers and lakes. Historically, they have been of major importance in artisan fishing in Africa and the...
, triggerfish
Triggerfish
Triggerfishes are about 40 species of often brightly colored fishes 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-Pacific...
, boxfish
Boxfish
Ostraciidae is a family of squared, bony fish belonging to the order Tetraodontiformes, closely related to the pufferfishes and filefishes. Fish in the family are known variously as boxfishes, cofferfishes, cowfishes and trunkfishes...
, and porcupinefish
Porcupinefish
Porcupinefish are fish of the family Diodontidae, , also commonly called blowfish ....
. They also feed on rays and skates
Batoidea
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
, as well as smaller sharks such as smoothhounds and sharpnose sharks
Rhizoprionodon
Rhizoprionodon is a genus of requiem sharks, family Carcharhinidae, commonly known as sharpnose sharks because of their long, pointed snouts.-Species:* Rhizoprionodon acutus...
. 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 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 are occasionally taken. In the Gulf of Mexico, the most important prey of the blacktip shark is the Gulf menhaden
Gulf menhaden
The Gulf menhaden is a small marine filter feeding fish belonging to the family Clupeidae. The range of Gulf menhaden encompasses the entirety of the Gulf of Mexico nearshore waters, with the exception of the extreme eastern Yucatan and western Cuba...
(Brevoortia patronus), followed by the Atlantic croaker (Micropogonias undulatus). Off South Africa, jacks and herring are the most important prey. Hunting peaks at dawn and dusk. The excitability and sociability of blacktip sharks makes them prone to feeding frenzies
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...
when large quantities of food are suddenly available, such as when fishing vessels dump their refuse overboard.
Life history
As with other requiem sharks, the blacktip shark exhibits viviparity. Females typically give birth to 4–7 (range 1–10) pups every other year, making use of shallow coastal nurseries that offer plentiful food and fewer predators. Known nurseries include Pine Island Sound, Terra Ceia Bay, and Yankeetown along the Gulf coast of Florida, Bulls Bay on the coast of South Carolina, and Pontal do Paraná on the coast of Brazil. Although adult blacktip sharks are highly mobile and disperse over long distances, they are philopatric and return to their original nursery areas to give birth. This results in a series of genetically distinct breeding stocks that overlap in geographic range.Mating occurs from spring to early summer, and the young are born at around the same time the following year after a 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:...
of 10–12 months. Females have one 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...
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; each uterus is separated into compartments with a single 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...
inside each. The embryos are initially 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...
; in the 10th or 11th week of gestation, when the embryo measures 18–19 cm long (7.1–7.5 in), the supply of yolk is exhausted and the yolk sac develops 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 sustains the embryo until birth. The length at birth is 55–60 cm (22–24 in) off the eastern United States and 61–65 cm (24–26 in) off North Africa. The mortality rate
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...
in the first 15 months of life is 61–91%, with major threats being predation and starvation. The young remain in the nurseries until their first fall, at which time they migrate to their wintering grounds.
The growth rate of this species slows with age: 25–30 cm (10–12 in) in the first six months, then 20 cm (8 in) a year until the second year, then 10 cm (4 in) a year until maturation, then 5 cm (2 in) a year for adults. The size at maturity varies geographically: males and females mature at 1.4–1.5 m (4.6–4.9 ft) and 1.6 m (5.2 ft) respectively in the northeastern Atlantic, 1.3–1.4 m (4.3–4.6 ft) and 1.5–1.6 m (4.9–5.2 ft) respectively in the Gulf of Mexico, 1.5 m (4.9 ft) and 1.6 m (5.2 ft) respectively off South Africa, and 1.7 m (5.6 ft) and 1.8 m (5.9 ft) respectively off North Africa. The age at maturation is 4–5 years for males and 7–8 years for females. The lifespan is at least 12 years.
In 2007, a 9-year-old female blacktip shark at the Virginia Aquarium & Marine Science Center
Virginia Aquarium
The Virginia Aquarium & Marine Science Center, formerly known as the Virginia Marine Science Museum, is an aquarium and marine science museum located in Virginia Beach, Virginia, just south of Rudee Inlet...
was found to be pregnant with a single near-term female pup, despite having never mated with a male. Genetic analysis confirmed that her offspring was the product of automictic parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
, a form of asexual reproduction
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
in which an ovum
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
merges with a polar body
Polar body
A polar body is a cell structure found inside an ovum. Both animal and plant ova possess it. It is also known as a polar cell.Asymmetrical cell division leads to the production of polar bodies during oogenesis. To conserve nutrients, the majority of cytoplasm is segregated into the secondary...
to form a zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
without fertilization. Along with an earlier case of parthenogenesis in the bonnethead
Bonnethead
The bonnethead shark or shovelhead, Sphyrna tiburo, is a member of the hammerhead shark genus Sphyrna. The Greek word sphyrna translates as hammer, referring to the shape of this shark's head - tiburo is the Taino word for shark....
(Sphyrna tiburo), this event suggests that asexual reproduction may be more widespread in sharks than previously thought.
Human interactions
There are reports of blacktip sharks showing curiosity towards divers, but remaining at a safe distance. Under most circumstances, this timid shark is not regarded as highly dangerous to humans. However, they may become aggressive in the presence of food, and their size and speed invite respect. As of 2008, the International Shark Attack FileInternational 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...
lists 28 unprovoked attacks (one fatal) and 13 provoked attacks by this species. Blacktip sharks are responsible annually for 16% of the shark attacks around Florida. Most attacks by this species result in only minor wounds.
As one of the most common large sharks in coastal waters, the blacktip shark is caught in large numbers by commercial fisheries throughout the world, using longlines, fixed bottom nets, bottom trawls, and hook-and-line. The meat is of high quality and marketed fresh, frozen, or dried and salted. In addition, the fins are used for shark fin soup
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...
, the skin for leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
, the 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...
for vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
s, and the carcasses for fishmeal. Blacktip sharks are one of the most important species to the northwestern Atlantic shark fishery, second only to the sandbar shark
Sandbar shark
The sandbar shark, Carcharhinus plumbeus, is a species of requiem shark, family Carcharhinidae, native to the Atlantic Ocean and the Indo-Pacific. It is distinguishable by its very high first dorsal fin and inter-dorsal ridge....
(C. plumbeus). The flesh is considered superior to that of the sandbar shark, resulting in the sandbar and other requiem shark species being sold under the name "blacktip shark" in the United States. The blacktip shark is also very significant to Indian and Mexican fisheries, and is caught in varying numbers by fisheries in the Mediterranean, South China Sea, and off northern Australia.
The blacktip shark is popular with recreational anglers in Florida, the Caribbean, and South Africa. It is listed as a game fish
Game fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
by the International Game Fish Association
International Game Fish Association
The International Game Fish Association is the leading authority on angling pursuits and the keeper of the most current World Record fishing catches by fish categories. Fishermen who are sport fishers are careful to follow their stringent rules for fair play and line requirements in order to...
(IGFA). Once hooked, this species is a strong, steady fighter that sometimes jumps out of the water. Since 1995, the number of blacktip sharks taken by recreational anglers in the United States has approached or surpassed the number taken by commercial fishing. The International Union for Conservation of Nature (IUCN) has assessed the blacktip 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...
, as its low reproductive rate renders it vulnerable 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....
. The United States and Australia are the only two countries that manage fisheries catching blacktip sharks. In both cases, regulation occurs under umbrella management schemes for multiple shark species, such as that for the Large Coastal Sharks (LCS) category of the US National Marine Fisheries Service
National Marine Fisheries Service
The National Marine Fisheries Service is a United States federal agency. A division of the National Oceanic and Atmospheric Administration and the Department of Commerce, NMFS is responsible for the stewardship and management of the nation's living marine resources and their habitat within the...
(NMFS) Atlantic shark Fisheries Management Plan (FMP). No conservation plans specifically for this species have been implemented.