Oceanic whitetip shark | |
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Female individual surrounded by pilot fish in the Red Sea | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Chondrichthyes |
Subclass: | Elasmobranchii |
Order: | Carcharhiniformes |
Family: | Carcharhinidae |
Genus: | Carcharhinus |
Species: | C. longimanus |
Binomial name | |
Carcharhinus longimanus (Poey, 1861) | |
Range of the oceanic whitetip shark | |
Synonyms [3] | |
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The oceanic whitetip shark (Carcharhinus longimanus) is a large pelagic requiem shark inhabiting tropical and warm temperate seas. It has a stocky body with long, white-tipped, rounded fins. The species is typically solitary, though they may gather in large numbers at food concentrations. Bony fish and cephalopods are the main components of its diet and females give live birth.
Though slow-moving, the shark is opportunistic and aggressive, and is reputed to be dangerous to shipwreck survivors. The IUCN Red List considers the species to be critically endangered. Recent studies show steeply declining populations as they are harvested for their fins and meat. As with other shark species, the whitetip faces mounting fishing pressure throughout its range.
The oceanic whitetip shark, or lesser white shark, was described in 1831 by naturalist René-Primevère Lesson, who named the shark Carcharhinus maou. It was next described by Cuban Felipe Poey in 1861 as Squalus longimanus. [4] The name Pterolamiops longimanus has also been used. The species epithet longimanus refers to the size of its pectoral fins (longimanus means "long hands" in Latin). The oceanic whitetip shark is called many things in English: Brown Milbert's sand bar shark, brown shark, shipwreck shark, nigano shark, oceanic white-tipped whaler, and whitetip shark. [5]
The rules of the International Commission on Zoological Nomenclature are that in general the first-published description has priority; therefore, the valid scientific name for the oceanic whitetip shark should be Carcharhinus maou. However, Lesson's name remained forgotten for so long that Carcharhinus longimanus remains widely accepted. [6]
This shark is found worldwide between 45°N and 43°S latitude. It lives in deep, open oceans, with a temperature greater than 18 °C (64 °F), [3] It prefers water temperatures above 20 °C (68 °F), and up to 28 °C (82 °F) but can also be found in waters as cool as 15 °C (59 °F) but avoids temperatures lower than this. [6] [7] It was once extremely common and widely distributed, and still inhabits a wide band around the globe; however, recent studies suggest that its numbers have drastically declined. [8]
The shark spends most of its time in the upper layer of the ocean—to a depth of 150 m (490 ft) [3] —and prefers off-shore, deep-ocean areas. According to longline capture data, increasing distance from land correlates to a greater population of sharks. [5] It is sometimes found close to land, in waters as shallow as only 37 m (120 ft) deep, mainly around oceanic islands and narrow continental shelves. [6]
C. longimanus' most distinguishing characteristics are its long, wing-like pectoral and dorsal fins. The fins are significantly larger than most other shark species, and are conspicuously rounded. The shark's snout is rounded and its eyes are circular, with nictitating membranes. [5]
The oceanic whitetip shark is a robust, large-bodied shark. The largest specimen ever caught measured at more than 4 m (13 ft) in length, though they usually grow up to 3 m (10 ft) in length and 150 kg (330 lb) in weight. [9] However, the all-tackle record listed by the International Game Fish Association (IGFA) is 167 kg (368 lb) for a 2.2-metre (7.2 ft) long individual, suggesting that weight is likely much more in larger individuals. [10] The female is typically larger than the male by 10 cm (3.9 in). [5] [6] In the Gulf of Mexico in the 1950s, the mean weight of oceanic whitetip sharks was 86.4 kg (190 lb). In the 1990s, the sharks of the species from the same area averaged only 56.1 kg (124 lb). [11]
The species is grey-bronze dorsally and white ventrally. [6] As its name suggests, most of its fins (dorsal, pectoral, pelvic and caudal) have white tips. Along with white tips, the fins may be mottled, and young specimens can have black marks. A saddle-like patch may be apparent between first and second dorsal fins. The shark has two kinds of teeth. Those in the mandible (lower jaw) are thinner with a serrated tip. Between 13 and 15 teeth are on either side of the jaw. The teeth in the upper jaw are triangular, but much larger and wider with entirely serrated edges—14 or 15 occur along each side. The denticles are nearly flat and wide, typically have between five and seven ridges. There is little overlap between them, revealing some skin. [5]
The oceanic whitetip is typically solitary, though gatherings have been observed where food is plentiful. [6] It swims during the day and night. The oceanic whitetip is usually solitary and slow-moving, and tends to cruise near the top of the water column, in open water. [5] During summer, when the water surface is warmer, oceanic whitetips tend to swim more quickly and at deeper depths. [12] They have been observed to breach out of the water. [13]
The species feeds mainly on pelagic cephalopods, like squid, and bony fish, [3] such as lancetfish, oarfish, barracuda, jacks, mahi-mahi, marlin, tuna, and mackerel. However, its diet can be far more varied and less selective—it is known to eat threadfins, stingrays, sea turtles, seabirds, gastropods, crustaceans, and marine mammal carcasses. Its feeding methods include swimming through schools of frenzied tuna with an open mouth, waiting for the fish to swim in before biting down; when whaling formerly took place in warm waters, oceanic whitetips were the most common scavengers of floating carcasses. Whitetips commonly compete for food with silky sharks, explaining its comparatively leisurely swimming style combined with aggressive displays. [6] They are known to trail pilot whales since they both feed on squid. [5] [14]
Pilot fish, dolphinfish, and remora may follow these sharks. [5] Evidence in the form of sucker scars on the skin of an individual filmed off Hawaii indicate that the species may also dive deep enough to battle with giant squid. [15] Until the 16th century, sharks were known to mariners as "sea dogs" [16] and the oceanic whitetip, the most common ship-following shark. Groups often form when individuals converge on a food source. They are recorded to segregate by both sex and size. They commonly get into feeding frenzies. [6] Oceanic whitetips gather in large numbers off Cat Island, Bahamas from winter to spring, due to the abundance of large bony fish. [14]
Mating and birthing seems to occur in early summer in the northwest Atlantic Ocean and southwest Indian Ocean, although females captured in the Pacific have been found with embryos year round, suggesting a longer mating season there. [6] The shark is viviparous—embryos develop in utero and are fed by a placental sac. Its gestation period lasts nine months to one year. [7] [17] In the northwest Atlantic, shark pups are born 65–75 cm (26–30 in) long while off South Africa, birth length is 60–65 cm (24–26 in) long. [7] In the Pacific Ocean, newborns average 45–55 cm (18–22 in) long, and number two to fourteen per litter. [17]
In one population off Brazil, sharks were recorded to grow an average of 25.2 cm (9.9 in) in one year, reducing to 13.6 cm (5.4 in) per year up to four years and then 9.7 cm (3.8 in) in their fifth year. Both sexes reached maturity at 180–190 cm (71–75 in) between the ages of six and seven and continued to grow at 9.10 cm (3.58 in) per year. [18] The average length of maturity for sharks averages in the greater equatorial and southwestern Atlantic is 170 cm (67 in) for females and 170–190 cm (67–75 in) for males. [19] In the Pacific, sharks appear to mature at four to five years. [17] One oceanic whitetip shark was estimated to have lived 22 years. [5] [20]
Oceanographic researcher Jacques Cousteau described the oceanic whitetip as "the most dangerous of all sharks". [21] Author and big-game fisherman Ernest Hemingway depicted them as aggressive opportunists that attacked the catch of fishermen in The Old Man and the Sea . [22] After the USS Indianapolis was torpedoed on 30 July 1945, some sailors who survived the sinking reportedly died from exposure to the elements and some may have died from shark bites. [23] According to survivor accounts published in several books about sharks and shark attacks, potentially hundreds of the Indianapolis crew were eventually killed by sharks before a plane spotted them on the fifth day after the sinking. Oceanic whitetips are believed to have been responsible for most if not all of those attacks. [24] [25] Also during World War II, the RMS Nova Scotia, a steamship carrying about 1,000 people near South Africa, was sunk by a German submarine. One hundred and ninety-two people survived; many deaths were attributed to the whitetip. [26] Subsequently, the species is recorded to have attacked 21 people between 1955 and 2020, including nine divers, eight swimmers, two fishermen, one shipwrecked person and one fallen pilot. Five of these attacks were fatal. [27]
In Egypt in 2010, one oceanic whitetip was implicated in several bites on tourists in the Red Sea near Sharm El Sheikh, resulting in one death and four injuries to humans. Accumulating evidence revealed this shark to have been conditioned to being hand fed. [28] [29] In October 2019, an oceanic whitetip shark brutally attacked a female snorkeler off Mo'orea, French Polynesia, but the person survived. Based on eyewitness reports and examinations of the bites, the shark appears to have been acting like a predator attacking prey. [27]
The oceanic whitetip has been kept in captivity. Among five recorded captive oceanic whitetips, the three with time records all lived for more than a year in captivity. One of these, a female in Monterey Bay Aquarium's Outer-Bay exhibit, lived for more than three years before dying in 2003, during which it grew 0.3 m (1 ft). [30] [31] The two remaining lack a time record, but grew about 0.5 m (1.6 ft) during their time in captivity. [30]
As of 2019, the IUCN Red List list the oceanic whitetip shark as critically endangered, as their numbers appear to have decreased in every ocean region they inhabit. While their total global population is unknown, they are estimated to have declined by around 98 percent "with the highest probability of >80% reduction over three generation lengths (61.2 years)". [1]
In 1969, Lineaweaver and Backus wrote of the oceanic whitetip: "[it is] extraordinarily abundant, perhaps the most abundant large animal, large being over 100 pounds [45 kg], on the face of the earth". [32] A study focusing on the northwest Atlantic and Gulf of Mexico, using a mix of data from US pelagic longline surveys from the mid-1950s and observations from the late 1990s, estimated a decline in numbers in this location of 99.3% over this period. [8] However, changes in fishing practices and data collection methods complicate estimates. [33] According to a January 2021 study in Nature which studied 31 species of sharks and rays, the number of these species found in open oceans had dropped by 71 per cent in around 50 years. The oceanic whitetip was included in the study. [34] [35]
Oceanic whitetip sharks are mainly threatened by fisheries, sometimes intentional but usually bycatch. They are victims of longlines, hook-lines, gillnets and trawls. The sharks are used for their fins and meat. [1] [6] It is eaten fresh, smoked, dried, and salted and its skin made into leather. [6] Bycatching of oceanic whitetip sharks may be reduced by removing hooks from longliners when they are in shallow water. [36] Sharks may also be threatened by pollution. Those in the northwest Atlantic have been found to accumulate high amounts of mercury. [37]
In March 2013, the oceanic whitetip was added to Appendix II of CITES meaning the species (including parts and derivatives) require CITES permits for international trade. [38] On 30 January 2018, NOAA Fisheries published a final rule to list the oceanic whitetip shark as a threatened species under the United States Endangered Species Act (ESA) (83 FR 4153). [39] From 3 January 2013, the shark was fully protected in New Zealand territorial waters under the Wildlife Act 1953. [40] [41] The New Zealand Department of Conservation has classified the oceanic whitetip shark as "Migrant" with the qualifier "Secure Overseas" under the New Zealand Threat Classification System. [42]
Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas and include such species as the bull shark, lemon shark, blacktip shark, and whitetip reef shark.
The grey reef shark or gray reef shark is a species of requiem shark, in the family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as far east as Easter Island and as far west as South Africa. This species is most often seen in shallow water near the drop-offs of coral reefs. It has the typical "reef shark" shape, with a broad, round snout and large eyes. It can be distinguished from similar species by the plain or white-tipped first dorsal fin, the dark tips on the other fins, the broad, black rear margin on the tail fin, and the lack of a ridge between the dorsal fins. Most individuals are less than 1.88 m (6.2 ft) long.
The silky shark, also known by numerous names such as blackspot shark, gray whaler shark, olive shark, ridgeback shark, sickle shark, sickle-shaped shark and sickle silk shark, is a species of requiem shark, in the family Carcharhinidae, named for the smooth texture of its skin. It is one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge of the continental shelf down to 50 m (164 ft). The silky shark has a slender, streamlined body and typically grows to a length of 2.5 m. It can be distinguished from other large requiem sharks by its relatively small first dorsal fin with a curving rear margin, its tiny second dorsal fin with a long free rear tip, and its long, sickle-shaped pectoral fins. It is a deep, metallic bronze-gray above and white below.
The blacktip reef shark is a species of requiem shark, in the family Carcharhinidae, which can be easily identified by the prominent black tips on its fins. Among the most abundant sharks inhabiting the tropical coral reefs of the Indian and Pacific Oceans, this species prefers shallow, inshore waters. Its exposed first dorsal fin is a common sight in the region. The blacktip reef shark is usually found over reef ledges and sandy flats, though it has also been known to enter brackish and freshwater environments. It typically attains a length of 1.6 m (5.2 ft). Like other sharks, the females are larger than the males.
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.
The whitetip reef shark is a species of requiem shark, in the family Carcharhinidae, and the only member of its genus. A small shark that does not usually exceed 1.6 m (5.2 ft) 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 eyes with vertical pupils, and white-tipped dorsal and caudal fins. One of the most common sharks found on Indo-Pacific coral reefs, the whitetip reef shark occurs as far west as South Africa and as far east as Central America. It is typically found on or near the bottom in clear water, at a depth of 8–40 m (26–131 ft).
The dusky shark is a species of requiem shark, in the family Carcharhinidae, occurring in tropical and warm-temperate continental seas worldwide. A generalist apex predator, the dusky shark can be found from the coast to the outer continental shelf and adjacent pelagic waters, and has been recorded from a depth of 400 m (1,300 ft). Populations migrate seasonally towards the poles in the summer and towards the equator in the winter, traveling hundreds to thousands of kilometers. One of the largest members of its genus, the dusky shark reaches more than 4 m (13 ft) in length and 350 kg (770 lb) in weight. It has a slender, streamlined body and can be identified by its short round snout, long sickle-shaped pectoral fins, ridge between the first and second dorsal fins, and faintly marked fins.
The silvertip shark is a large species of requiem shark, in the family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. It is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of 800 m (2,600 ft). The silvertip shark resembles a larger and bulkier grey reef shark, but can be easily identified by the prominent white margins on its fins. It attains a maximum length of 3 m (10 ft).
The longfin mako shark is a species of mackerel shark in the family Lamnidae, with a probable worldwide distribution in temperate and tropical waters. An uncommon species, it is typically lumped together under the name "mako" with its better-known relative, the shortfin mako shark. The longfin mako is a pelagic species found in moderately deep water, having been reported to a depth of 220 m (720 ft). Growing to a maximum length of 4.3 m (14 ft), the slimmer build and long, broad pectoral fins of this shark suggest that it is a slower and less active swimmer than the shortfin mako.
The blacktip shark is a species of requiem shark, and part of the 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 slits, and no ridge between the dorsal fins. 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).
The Caribbean reef shark is a species of requiem shark, belonging to the family Carcharhinidae. It is found in the tropical waters of the western Atlantic Ocean from Florida to Brazil, and is the most commonly encountered reef shark in the Caribbean Sea. With a robust, streamlined body typical of the requiem sharks, this species is difficult to tell apart from other large members of its family such as the dusky shark and the silky shark. Distinguishing characteristics include dusky-colored fins without prominent markings, a short free rear tip on the second dorsal fin, and tooth shape and number.
The Galapagos shark is a species of requiem shark, in the family Carcharhinidae, found worldwide. It favors clear reef environments around oceanic islands, where it is often the most abundant shark species. A large species that often reaches 3.0 m (9.8 ft), the Galapagos reef shark has a typical fusiform "reef shark" shape and is very difficult to distinguish from the dusky shark and the grey reef shark. An identifying character of this species is its tall first dorsal fin, which has a slightly rounded tip and originates over the rear tips of the pectoral fins.
The pelagic thresher is a species of thresher shark, family Alopiidae; this group of sharks is characterized by the greatly elongated upper lobes of their caudal fins. The pelagic thresher occurs in the tropical and subtropical waters of the Indian and Pacific Oceans, usually far from shore, but occasionally entering coastal habitats. It is often confused with the common thresher, even in professional publications, but can be distinguished by the dark, rather than white, color over the bases of its pectoral fins. The smallest of the three thresher species, the pelagic thresher typically measures 3 m (10 ft) long.
The blacknose shark is a species of requiem shark, belonging to the 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. A small shark typically measuring 1.3 m (4.3 ft) long, the blacknose has a typical streamlined "requiem shark" shape with a long, rounded snout, large eyes, and a small first dorsal fin. Its common name comes from a characteristic black blotch on the tip of its snout, though this may be indistinct in older individuals.
The bignose shark is a species of requiem shark, in the family Carcharhinidae. Distributed worldwide in tropical and subtropical waters, this migratory shark frequents deep waters around the edges of the continental shelf. It is typically found at depths of 90–430 m (300–1,410 ft), though at night it may move towards the surface or into shallower water. The bignose shark is plain-colored and grows to at least 2.7–2.8 m (8.9–9.2 ft) in length. It has a long, broad snout with prominent nasal skin flaps, and tall, triangular upper teeth. Its pectoral fins are long and almost straight, and there is a ridge on its back between the two dorsal fins.
The spinner shark is a type of requiem shark, in the 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. It is found from coastal to offshore habitats to a depth of 100 m (330 ft), though it prefers shallow water. The spinner shark resembles a larger version of the blacktip shark, with a slender body, long snout, and black-marked fins. This species can be distinguished from the blacktip shark by the first dorsal fin, which has a different shape and is placed further back, and by the black tip on the anal fin. It attains a maximum length of 3 m (9.8 ft).
The finetooth shark is a species of requiem shark, in the family Carcharhinidae, found in the western Atlantic Ocean, from North Carolina to Brazil. It forms large schools in shallow, coastal waters, and migrates seasonally following warm water. A relatively small, slender-bodied shark, the finetooth shark can be identified by its needle-like teeth, dark blue-gray dorsal coloration, and long gill slits. It attains a maximum length of 1.9 m (6.2 ft). The diet of this species consists primarily of small bony fishes, in particular menhaden. Like other members of its family, it is viviparous with females giving birth to two to six pups in estuarine nursery areas every other year.
The night shark is a species of requiem shark, in the family Carcharhinidae, found in the temperate and tropical waters of the Atlantic Ocean. An inhabitant of the outer continental shelf and upper continental slope, this shark most commonly occurs at depths of 50–600 m (160–1,970 ft) and conducts a diel vertical migration, spending the day in deeper water and moving into shallower waters at night. Off northeastern Brazil, large numbers congregate around seamounts of varying depths. A slender, streamlined species, the night shark typically reaches a length of 2 m (6.6 ft). It can be identified by its long, pointed snout and large, green eyes, and is dark grayish blue or brown above and white below.
The pelagic stingray is a species of stingray in the family Dasyatidae, and the sole member of its genus. It is characterized by the wedge-like shape of its pectoral fin disc, which is much wider than long, as well as by the pointed teeth in both sexes, whip-like tail with extremely long tail spine, and uniform violet to blue-green coloration. It generally reaches 59 cm (23 in) in width. The pelagic stingray has a worldwide distribution in waters warmer than 19 °C (66 °F), and migrates seasonally to spend the summer closer to the continental shelf and at higher latitudes. The only stingray that almost exclusively inhabits the open ocean, this species is typically found in surface waters down to a depth of 100 m (330 ft). As a consequence of its midwater habits, its swimming style has evolved to feature more of a flapping motion of the pectoral fins, as opposed to the disc margin undulations used by other, bottom-dwelling stingrays.
The Republic of the Marshall Islands has a commercial fishery that targets bigeye and yellowfin tuna using pelagic longline fishing gear. There were 55 longline vessels licensed to fish in the Republic of the Marshall Islands Exclusive Economic Zone (EEZ) in 2011, of which 4 were Marshall Islands-flagged and 51 were foreign-licensed vessels, including 22 Chinese-flagged, 16 Japanese-flagged, 11 Federated States of Micronesia-flagged, and 2 Taiwan-flagged. The Japanese-flagged longliners land their catch in Japan; the other 39 vessels were domestically-based. In 2011, the Marshall Islands longline fleet had reported landings of principal market species of 259 mt of bigeye tuna, 99 mt of yellowfin tuna, 37 mt of blue marlin, 7 mt of black marlin, 4 mt of albacore tuna, and 3 mt of broadbill swordfish. Fresh chilled bigeye and yellowfin tuna is exported primarily to markets in the U.S., China and Canada, and frozen tuna and incidental market species are exported to China and marketed locally.