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Oceanic whitetip shark

The Oceanic whitetip shark, Carcharhinus longimanus, is a large pelagic shark of tropical and warm temperate seas. It is a stocky shark, most notable for its long, white tipped rounded fins.

This aggressive but slow-moving fish dominates feeding frenzies, and has attacked more humans than all other shark species combined “” it is a notable danger to survivors of oceanic ship wrecks and downed aircraft. Recent studies have shown that its numbers are in steep decline “” its large fins are highly valued as the chief ingredient of shark-fin soup and, as with other shark species, the oceanic whitetip faces mounting pressure from fishing throughout its range.

Distribution and habitat

The oceanic whitetip is found globally in deep, open water, with a temperature greater than 64.4° F (18° C). It prefers waters between 68 and 82.4° F (20 and 28° C) and tends to withdraw from areas when temperatures fall below this. They were once extremely common and widely distributed, and still inhabit a wide band around the globe; however, recent studies suggest that their numbers have drastically declined. An analysis of the US pelagic longline logbook data between 1992″“2000 (covering the Northwest and Western Central Atlantic) estimated a decline of 70% over that period.

They are found worldwide between 45° north and 43° south latitude. In 2004, an oceanic whitetip was discovered dead on the west coast of Sweden””far beyond what was once considered the northern boundary of its range.

The shark spends most of its time in the upper layer of the ocean””to a depth of 500 ft (150 m)””and prefers off-shore, deep-ocean areas. According to longline capture data, increasing distance from land correlates to a greater population of sharks. Occasionally it is found close to land, in waters as shallow as 120 ft (37 m), mainly around mid-ocean islands such as Hawaii, or in areas where the continental shelf is narrow and there is access to deep water nearby. It is typically solitary, though gatherings have been observed where food is available. Unlike many animals, it does not have a diurnal cycle, but is active during both day and night. Its swimming style is slow, with the pectoral fins widely spread. Despite their habitual isolation from members of their own species, they may be observed with pilot fishes, dolphin fishes, and remoras. In 1988, Jeremy Stafford-Deitsch reported seeing an individual accompanied by a Shortfin pilot whale.

Anatomy and appearance

The most distinguishing characteristic of the Oceanic whitetip is its long, wing-like pectoral and dorsal fins. The fins are significantly larger than in most other shark species, and are conspicuously rounded. The shark’s nose is rounded and its eyes are circular, with nictitating membranes. It has a ‘typical’, although somewhat flattened requiem shark body, often with a mildly humpbacked aspect. It is bronze, brown, bluish or grey dorsally (the color varies by region), and white ventrally (although it may occasionally have a yellow tint). The maximum size of the oceanic whitetip shark is 13 ft (4 m), although usually it does not exceed 10 ft (3 m). Its maximum weight is 370 lb (170 kg). The female is larger than the male (although typically only by 4 in (10 cm)) with males about 71 in (1.8 m), and females about 75 in (1.9 m).

Most of the fins on its body (dorsal, pectoral, pelvic, and caudal) have a white tips (juvenile specimens and occasional adults may lack these). As well as the white tips, the fins may be mottled””and in young specimens can even have black marks. A saddle-like marking may be apparent between first and second dorsal fins. The shark has several kinds of teeth””those in the mandible (lower jaw) have a thin serrated tip and are relatively small and triangular (somewhat fang-like). There are between 13 and 15 teeth on either side of the symphysis. The teeth in the upper jaw are triangular, but much larger and broader with entirely serrated edges””there are 14 or 15 along each side of the symphysis.

Diet

C. longimanus feeds mainly on pelagic cephalopods and bony fish. However, its diet can be far more varied and less selective””it is known to eat threadfins, stingrays, sea turtles, sea birds, gastropods, crustaceans, mammalian carrion, and even rubbish dumped from ships. The bony fish it feeds on include lancetfish, oarfish, barracuda, jacks, dolphinfish, marlin, tuna, and mackerel. Its methods of predation include biting into groups of fish and swimming through schools of tuna with an open mouth. When feeding with other species, it becomes aggressive. Peter Benchley, author of Jaws, observed this shark swimming among pilot whales and eating their feces.

Behavior

The oceanic whitetip is solitary and slow-moving, and tends to cruise near the top of the water column, covering vast stretches of empty water scanning for possible food sources. Until the 16th century, sharks were known to mariners as ‘sea dogs’ and the oceanic whitetip, the most common ship-following shark, exhibits dog-like behavior when its interest is piqued: when attracted to something that appears to be food, its movements become more avid and it will approach cautiously but stubbornly, retreating and maintaining the minimum safe distance if driven off, but ready for a rush of boldness if the opportunity presents itself. Oceanic whitetips are not fast sharks, but they are capable of surprising bursts of speed. It is commonly found competing for food with silky sharks, making up for its comparatively leisurely swimming style with an aggressive attitude.

Groups are often formed when nearby individuals converge on a food source, whereupon the fabled “feeding frenzy” may occur. This seems to be triggered not by blood in the water per se, or by bloodlust, but by the species’ highly strung and goal-directed nature (conserving energy between infrequent feeding opportunities when it is not slowly plying the open ocean). The oceanic whitetip is a competitive, opportunistic predator with great incentive to exploit the resource at hand, rather than avoiding trouble in favor of a possibly easier meal in the future.

There does not seem to be segregation by sex and size as with some other species. Whitetips will follow schools of tuna or squid, and will trail groups of cetaceans such as dolphins and pilot whales as scavengers of their prey. Their instinct to follow is so strongly imprinted, as the result of countless millennia of baitfish migrations, that they will accompany ocean-going ships. When whaling took place in warm waters, oceanic whitetips were often responsible for much of the damage to floating carcasses.

Reproduction

Mating season is 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 in this region. The shark is viviparous. It has a gestation period of one year. Litter sizes vary from one to 15 with the young born at a length of about 24 in (0.6 m). Sexual maturity is reached at close to 70 in (1.75 m) for males and 80 in (2 m) for females.

Relationship to humans

It is a commercially important species to the extent that its fins are prized for soup and its meat and oil frequently utilized. It is used fresh, smoked, dried and salted for human consumption and its hide utilized for leather. It is subject to fishing pressure throughout virtually its whole range – although it is more often taken as bycatch than by design, since it takes bait from longlines intended for other species.

The oceanic whitetip poses a minimal threat to bathers or inshore sportsman, but a high risk for humans caught in the open ocean in conditions in which they might be seen as prey.

Famed oceanographic researcher Jacques Cousteau described the oceanic whitetip as “the most dangerous of all sharks”. Despite the greater notoriety of the great white shark and other sharks habitually found nearer the shore, the oceanic whitetip is considered responsible for more fatal attacks on humans than all other species combined, as a result of predation on those shipwrecked or from aircraft downed in the open ocean. These incidents are not included in common shark-attack indices for the 20th and 21st centuries, but would appear to total in the thousands worldwide, with one incident alone, the torpedoing of USS Indianapolis on July 30, 1945, giving a minimum figure of between 60 and 80 sailors killed by sharks. Also during World War II, the Nova Scotia, a steamship carrying approximately 1,000 people near South Africa was torpedoed and sunk by a German submarine. There were only 192 survivors, and many deaths were attributed to the oceanic whitetip shark.

Even though the oceanic whitetip is highly opportunistic and aggressive and has been known to attack humans for food, divers have swum with this shark repeatedly without being harmed (it is a popular draw for dive tourism because of its size and the perceived danger). However, divers are advised to approach the shark only with extreme caution, not spear fish near this shark and if the shark comes too close or gets too inquisitive to get out of the water as soon as possible. It is generally suggested that if a shark starts to push the diver, then to hit it on the snout, gills or eyes, but anecdotal evidence suggests that this may be less effective in deterring whitetips than with other species of sharks.

Oceanic whitetip shark


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