Oceanic whitetip shark

Oceanic whitetip shark
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Chondrichthyes
Order:Carcharhiniformes
Family:Carcharhinidae
Genus:Carcharhinus
Species: C. longimanus
Binomial name
Carcharhinus longimanus
(Poey, 1861)
Range of the oceanic whitetip shark
Synonyms[2]
  • Carcharias obtusus Garman, 1881
  • Squalus longimanus Poey, 1861
  • Carcharias longimanus (Poey, 1861)
  • Pterolamiops longimanus (Poey, 1861)
  • Carcharinus longimanus (Poey, 1861)
  • Squalus maou Lesson, 1831
  • Carcharhinus maou (Lesson, 1831)
  • Carcharias insularum Snyder, 1904
  • Pterolamiops magnipinnis Smith, 1958
  • Pterolamiops budkeri Fourmanoir, 1961

The oceanic whitetip shark (Carcharhinus longimanus), also known as Brown Milbert's sand bar shark, brown shark, lesser white shark, nigano shark, oceanic white-tipped whaler, and silvertip shark, is a large pelagic requiem shark inhabiting tropical and warm temperate seas. Its stocky body is most notable for its long, white-tipped, rounded fins.

This slow-moving but aggressive fish dominates feeding frenzies, and is a danger to shipwreck or air crash survivors.[3] Recent studies show steeply declining populations because its large fins are highly valued as the chief ingredient of shark fin soup, and as with other shark species, the whitetip faces mounting fishing pressure throughout its range.[1][4]

Taxonomy

The oceanic whitetip shark, or lesser white shark, was described in 1831 by naturalist René-Primevère Lesson, who named the shark Carcharhinus maou.[5] It was next described by Cuban Felipe Poey in 1861 as Squalus longimanus.[5] The name Pterolamiops longimanus has also been used. The species epithet longimanus refers to the size of its pectoral fins (longimanus translates from Latin as "long hands").[6] The oceanic whitetip shark has many common names in English: Brown Milbert's sand bar shark, brown shark, nigano shark, oceanic white-tipped whaler, and whitetip shark.[6]

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.[7]

Distribution and habitat

The oceanic whitetip is found globally in deep, open oceans, with a temperature greater than 18 °C (64 °F),[2] although exceptionally it occurs in water as cold as 15 °C (59 °F).[1] It prefers waters between 20 and 28 °C (68–82 °F) and tends to withdraw from areas when temperatures fall outside of these limits.[1][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.[4] An analysis of the US pelagic longline logbook data between 1992 and 2000 (covering the Northwest and Western Central Atlantic) estimated a decline of 70% over that period.[1]

It is found worldwide between 45°N and 43°S latitude.[2] In September 2004, a 2.3-metre (7.5 ft) vagrant oceanic whitetip shark was seen in the brackish waters of Gullmarsfjorden in Sweden; it died shortly after.[8][9] This is the only North European record and far north of its usual range limit.[8]

The shark spends most of its time in the upper layer of the ocean—to a depth of 150 m (490 ft)[2]—and prefers off-shore, deep-ocean areas. According to longline capture data, increasing distance from land correlates to a greater population of sharks.[6] Occasionally, it is found close to land, in waters as shallow as 37 m (120 ft), mainly around midocean islands such as Hawaii, or in areas where the continental shelf is narrow with access to nearby deep water. It is typically solitary, though gatherings have been observed where food is plentiful.[7] Unlike many animals, it does not have a diurnal cycle, and is active both day and night.[6] Its swimming style is slow, with widely spread pectoral fins. Despite its habitual isolation from members of its own species, pilot fish, dolphinfish, and remora may accompany it.[6] In 1988, Jeremy Stafford-Deitsch reported seeing an individual accompanied by a shortfin pilot whale.[10]

Description

Upper teeth
Lower teeth

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 nose is rounded and its eyes are circular, with nictitating membranes.[6]

C. longimanus has a 'typical', although somewhat flattened requiem shark body, often with a mildly humpbacked aspect. It is bronze, brown, bluish, or grey dorsally (the colour varies by region), and white ventrally (although it may occasionally have a yellow tint). The oceanic whitetip shark is a medium-sized requiem shark. The largest specimen ever caught measured 4 m (13 ft), an exceptionally large size considering few specimens are known to exceed a length of 3 m (9.8 ft). The maximum reported weight is 170 kg (370 lb). The female is typically larger than the male by 10 cm (3.9 in). Males attain sexual maturity at 1.7 to 1.9 m (5.6 to 6.2 ft) and females about 1.8 to 2.0 m (5.9 to 6.6 ft).[6][7] 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]

Most of its fins (dorsal, pectoral, pelvic, and caudal) have white tips (juvenile specimens and some adults may lack these). Along with white tips, the fins may be mottled, and young specimens can have black marks. A saddle-like marking may be apparent between first and second dorsal fins.[6] 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). Between 13 and 15 teeth are on either side of the symphysis. The teeth in the upper jaw are triangular, but much larger and broader with entirely serrated edges— 14 or 15 occur along each side of the symphysis.[6] The denticles lie flat and typically have between five and seven ridges.[6]

Diet

C. longimanus feeds mainly on pelagic cephalopods and bony fish.[2] However, its diet can be far more varied and less selective—it is known to eat threadfins, stingrays, sea turtles, birds, gastropods, crustaceans, and mammalian carrion. The bony fish it feeds on include lancetfish, oarfish, barracuda, jacks, dolphinfish, marlin, tuna, and mackerel. Its feeding methods include biting into groups of fish and swimming through schools of tuna with an open mouth. When feeding with other species, it becomes aggressive.[7] Peter Benchley, author of Jaws, observed this shark swimming among pilot whales and eating their faeces.[12]

Behaviour

Shark accompanied by group of fish with black and white vertical stripes and split tail fin
Oceanic whitetip photographed at the Elphinstone reef, Red Sea, Egypt, accompanied by pilot fish

The oceanic whitetip is usually 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.[6] Until the 16th century,[13] sharks were known to mariners as "sea dogs"[14] and the oceanic whitetip, the most common ship-following shark,[7] exhibits dog-like behaviour when its interest is piqued: when attracted to something that appears to be food, its movements become more avid and it approaches cautiously but stubbornly, retreating and maintaining a safe distance if driven off, but ready to rush in if the opportunity presents itself. Oceanic whitetips are not fast swimmers, but they are capable of surprising bursts of speed. Whitetips commonly compete for food with silky sharks, making up for its comparatively leisurely swimming style with aggressive displays.[7]

Groups often form when individuals converge on a food source, whereupon a feeding frenzy may occur. This seems to be triggered not by blood in the water 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 that exploits the resource at hand, rather than avoiding trouble in favour of a possibly easier future meal.[7]

Segregation by sex and size does not seem to occur. Whitetips follow schools of tuna or squid, and trail groups of cetaceans such as dolphins and pilot whales, scavenging their prey. Their instinct is to follow baitfish migrations that accompany ocean-going ships. When whaling took place in warm waters, oceanic whitetips were often responsible for much of the damage to floating carcasses.[7]

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 there.[7] The shark is viviparous—embryos develop in utero and are fed by a placental sac. Its gestation period is one year. Litter sizes vary from one to 15 with the young born at a length around 0.6 m (24 in).[1] Sexual maturity is reached around 1.75 m (69 in) for males and 2 m (80 in) for females.[1]

Relationship with humans

Oceanic whitetip with a rusty fish hook in its mouth
Photo of shark with black and white-striped fish
Oceanic whitetip shark with a small school of pilot fish

The oceanic whitetip is a commercially important species for its fins, meat, and oil. It is eaten fresh, smoked, dried, and salted and its hide is used for leather.[7] It is subject to fishing pressure throughout virtually its whole range,[1]although it is more often taken as bycatch than by design, since it is drawn to longline bait that is intended for other species.[7]

Oceanographic researcher Jacques Cousteau described the oceanic whitetip as "the most dangerous of all sharks".[15] Despite the greater notoriety of the great white shark and other sharks habitually found nearer the shore, the oceanic whitetip is suspected to be responsible for many fatal shark bites on humans, as a result of predation on survivors of shipwrecks or downed aircraft.[3][16] Such incidents are not included in common shark-bite indices for the 20th and 21st centuries, and as a result, the oceanic whitetip does not have the highest number of recorded incidents; only five bites had been recorded as of 2009.[17][18]

After the USS Indianapolis was torpedoed on 30 July 1945, most sailors who survived the sinking reportedly died from exposure to the elements rather than from shark bites.[19] Some sailors, however, are believed to have died from shark bites, and oceanic whitetips are believed to have been responsible in those cases.[16] 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. 192 people survived; many deaths were attributed to the whitetip.[3]

In Egypt in 2010, one oceanic whitetip was implicated in several bites on tourists in the Red Sea near Sharm El Sheikh. The shark was recognized individually by the bite mark taken out of its upper tail lobe. Accumulating evidence revealed this shark to have been conditioned to being hand fed. Upon associating the divers with an easy supply of food, it bit the divers and snorkelers on the areas of the body where it had seen the fish being kept, namely, in the fanny packs the divers carried. This caused the shark to target the divers' buttock and thigh regions in the hope of obtaining a meal. The 2010 Sharm El Sheikh bites resulted in one death and four injuries to humans. The attacks might have been instigated by the overfishing in that area of the Red Sea, effectively forcing the shark closer to shore where the bites took place.[20][21]

Dr. Christopher Neff, a policy analyst at the University of Sydney, argues that terms like "attack" are laden with cultural stigmatization.[22] Instead of the word "attack", he proposes labeling human-shark interactions, on a scale of extremity, as encounters, minor bites, moderate bites and fatal bites. The term "attack" is only appropriate in specific instances where specialists can confirm the predatory nature of the shark-human encounter, which is extremely difficult to do. While many encounters with oceanic whitetip sharks appear predatory in nature, without the verification of a scientific community in each instance, Neff argues that it is best to assume the accidental or nonpredatory intent of the encounters.[23][24]

Captivity

The oceanic whitetip has fared better in captivity than other large sharks of the open ocean, such as the mako and blue shark. 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 during which it grew 0.3 m (1 ft).[25] The two remaining lack a time record, but grew about 0.5 m (1.6 ft) during their time in captivity.[25]

Conservation status

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".[26] Little further population study occurred until 2003, when the numbers were estimated to have dropped by as much as 70% in the Northwest and Western Central Atlantic between 1992 and 2000.[1] Another study focusing on the 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.[4] However, changes in fishing practices and data collection methods complicate estimates.[27]

As a result of these findings, its status on the IUCN Red List was moved to "Vulnerable" globally (from "Lower Risk/Near Threatened") and "Critically Endangered" in the Northwest and Western Central Atlantic areas.[1]

Under the 1995 UN Agreement on the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks, coastal and fishing states are specifically required to adopt measures to conserve listed species, but little progress is visible on the oceanic whitetip.[1]

From 3 January 2013, the shark was fully protected in New Zealand territorial waters under the Wildlife Act 1953.[28][29]

In March 2013, three endangered commercially valuable sharks, the hammerheads, the oceanic whitetip, and porbeagle were added to Appendix II of CITES, bringing shark fishing and commerce of these species under licensing and regulation.[30]

On January 30, 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).[31]

See also

References

  1. 1 2 3 4 5 6 7 8 9 10 11 Baum, J.; Medina, E.; Musick, J. A. & Smale, M. (2005). "Carcharhinus longimanus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 17 June 2012.
  2. 1 2 3 4 5 Froese, Rainer and Pauly, Daniel, eds. (2013). "Carcharhinus longimanus" in FishBase. February 2013 version.
  3. 1 2 3 Bass, A.J. & JD'Aubrey, J.D. & Kistnasamy, N. (1973). "Sharks of the east coast of southern Africa. 1. The genus Carcharhinus (Carcharhinidae)." Archived 2013-09-06 at the Wayback Machine. Invest. Rep. Oceanogr. Res. Inst., Durban, no. 33.
  4. 1 2 3 Baum, J.K. & Myers, R.A. (2004). "Shifting baselines and the decline of pelagic sharks in the Gulf of Mexico" (PDF). Ecology Letters. 7 (3): 135–45. doi:10.1111/j.1461-0248.2003.00564.x. Archived from the original (PDF) on 2012-01-24.
  5. 1 2 "Carcharhinus longimanus (Poey, 1861)". Integrated Taxonomic Information System. Retrieved 18 August 2008.
  6. 1 2 3 4 5 6 7 8 9 10 11 Bester, Cathleen. "Oceanic Whitetip Shark". Florida Museum of Natural history. Retrieved 22 July 2006.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 Compagno, Leonard J. V. (1984). Sharks of the World: An annotated and illustrated catalogue of shark species known to date. Vol. 4, Part 2. Carcharhiniformes. Food and Agriculture Organization of the United Nations. pp. 484–86, 555–61, 588. ISBN 92-5-101383-7.
  8. 1 2 "Marine Life News". British Marine Life Study Society. Summer 2004. Retrieved 3 September 2017.
  9. ↑ Eli. "Fishwatcher". Fishwatcher. Archived from the original on 8 December 2005. Retrieved 6 February 2006.
  10. ↑ Stafford-Deitsch, Jeremy (1988). Shark: A Photographer's Story. Sierra Club Books. ISBN 0871567334.
  11. ↑ "Consideration of Proposals for Amendment of Appendices I and II (CoP15 Prop. 16)" (PDF). Convention on International Trade in Endangered Species (CITES). March 2010. Archived from the original (PDF) on 2013-05-12.
  12. ↑ Benchley, Peter (2002). Shark Trouble. Random House. ISBN 0812966333.
  13. ↑ "Online Etymology Dictionary". Retrieved 2006-08-08.
  14. ↑ Marx R.F. (1990). The History of Underwater Exploration. Courier Dover Publications. p. 3. ISBN 0-486-26487-4.
  15. ↑ Cousteau, Jacques-Yves & Cousteau, Philippe (1970). The Shark: Splendid Savage of the Sea. Doubleday & Company, Inc.
  16. 1 2 Martin, R. Aidan. "Elasmo Research". ReefQuest. Retrieved 6 February 2006.
  17. ↑ "ISAF Statistics on Attacking Species of Shark". Flmnh.ufl.edu. 2009-05-20. Retrieved 2010-07-05.
  18. ↑ "Oceanic Whitetip". howstuffworks.com.
  19. ↑ Stanton, Doug (2003). In Harm's Way: The Sinking of the USS Indianapolis and the Extraordinary Story of Its Survivors (1st Owl Books ed.). New York: H. Holt. ISBN 978-0-8050-7366-9.
  20. ↑ Egypt: German tourist killed in fourth Sharm el-Sheikh shark attack in a week. telegraph.co.uk (5 December 2010)
  21. ↑ US Experts Head to Egypt to Probe Shark Attacks. CBS News (7 December 2010)
  22. ↑ Neff, Christopher (January 2, 2015). "The Jaws Effect: How movie narratives are used to influence policy responses to shark bites in Western Australia". Australian Journal of Political Science. 50 (1): 114–127. doi:10.1080/10361146.2014.989385.
  23. ↑ Neff, Christopher; Hueter, Robert (2013). "Science, policy, and the public discourse of shark "attack": A proposal for reclassifying human–shark interactions". Journal of Environmental Studies and Sciences. 3: 65. doi:10.1007/s13412-013-0107-2.
  24. ↑ Shiffman, David (2013). "World's largest group of shark scientists calls on AP and Reuters to resist using the phrase "shark attacks"". Southern Fried Science. Retrieved 2015-06-19.
  25. 1 2 "Oceanic Whitetip Shark Carcharhinus longimanus (Poey, 1861) in Captivity". H. F. Mollet. Retrieved 15 May 2014.
  26. ↑ Lineaweaver, Thomas H. III & Backus, Richard H. (1969). The Natural History of Sharks. Lippincott.
  27. ↑ Baum, J.K.; Kehler, D. & Myers, R.A. (2005). "Robust estimates of decline for pelagic shark populations in the northwest Atlantic and Gulf of Mexico" (PDF). Fisheries. 30: 27–30. Archived from the original on 2009-10-07.
  28. ↑ "Endangered whitetip sharks to be protected". New Zealand Government. 27 September 2012. Archived from the original on 15 September 2016. Retrieved 27 September 2012.
  29. ↑ "Wildlife (Oceanic Whitetip Shark) Order 2012". New Zealand government gazette. 6 December 2012.
  30. ↑ MCGrath, Matt (11 March 2013). "'Historic' day for shark protection". BBC News. Retrieved 27 July 2013.
  31. ↑ http://www.fpir.noaa.gov/PRD/prd_oceanic_whitetip_shark.html

Further reading

  • Backus, Richard H. & Springer, Stewart & Arnold Jr., Edgar L. (1956). "A contribution to the natural history of the white-tip shark, Pterolamiops longimanus (Poey)". Deep-Sea Research. 3.
  • Compagno, Leonard J.V. (1984). "Sharks of the World". FAO Species Catalogue. Rome. 4, Parts 1 and 2.
  • Compagno, Leonard J.V. (1988). Sharks of the Order Carcharhiniformes. Princeton University Press. ISBN 0-691-08453-X.
  • Ellis, Richard (1976). The Book of Sharks. New York: Grosset & Dunlap.
  • Eschmeyer, William N. (1998). Special Publication of the Center for Biodiversity Research and Information. 1–3. California Academy of Sciences. ISBN 0-940228-47-5.
  • Froese, Rainer and Pauly, Daniel, eds. (2005). "Carcharhinus longimanus" in FishBase. 09 2005 version.
  • "Sharks: Silent Hunters of the Deep". Reader's Digest. Sydney. 1989.
  • "Introducing an ongoing study of the Oceanic Whitetip Shark in the Red Sea". longimanus.info.
  • Oceanic Whitetip shark Carcharhinus longimanus at marinebio.org
  • "Whitetip Oceanic Shark profile". Florida Museum of Natural History.

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