| ||? Carcharias falcipinnis Lowe, 1839; (see Garrick, 1982).|
| ||Carcharias (Prionodon) menisorrah Valenciennes, in Müller & Henle, 1839|
| ||Squalus or Prionodon tiburo Poey, 1860; (not Squalus tiburo Linnaeus, 1758 = Sphyrna tiburo).|
| ||Gymnorhinus or Gymnorrhinus pharaonis Hemprich & Ehrenberg, 1899|
| ||Aprionodon sitankaiensis Herre, 1931|
| ||Carcharhinus floridanus Bigelow, Schroeder & Springer, 1943|
| ||Eulamia malpeloensis Fowler, 1944|
| ||Carcharhinus atrodorsus Deng, Xiong & Zhan, 1981|
|En - Silky shark, Fr - Requin soyeux, Sp - Tiburón jaquetón.|
3Alpha Code: FAL Taxonomic Code: 1080201017|
|Scientific Name with Original Description|
|Carcharias (Prionodon) falciformis Bibron, in Müller & Henle, 1839, Syst. Beschr. Plagiost., (2): 47. Holotype: Museum National d'Histoire Naturelle, Paris, MNHN 1134, 528 mm female fetus. Type Locality: Cuba.|
Large, fairly slender sharks (up to about 3.3 m) with snout moderately long and rounded, internarial width 1.2 to 1.6 in preoral length. Eyes circular and moderately large, length 1.2-2.7%TL. Upper labial furrows short and inconspicuous. Hyomandibular line of pores just behind mouth corners not conspicuously enlarged.
Gill slits moderate-sized, 3rd 2.9-3.6% TL and less than 2/5 of first dorsal base.
Usually 15/15 rows of anteroposterior teeth in each jaw half but varying from 14-16/13-17; upper teeth with fairly narrow, strongly serrated, erect to moderately oblique cusps, well-delimited from crown feet, feet with heavy serrations or small cusplets; lower teeth with erect, narrow, smooth-edged cusps and transverse roots.
A narrow interdorsal ridge present. Pectoral fins large (especially in adults, shorter in young), narrowly falcate, with narrowly rounded or pointed apices, length of anterior margins about 14 to 22%TL. First dorsal fin moderate-sized and falcate, with narrowly to broadly rounded apex and posterior margin curving ventral from fin apex; origin of first dorsal fin behind pectoral free rear tips; inner margin of first dorsal long, about half dorsal base or slightly more or less. Second dorsal fin very small and low, height 1.3-2.2% TL, inner margin long and 1.6-3.0 (usually over 2.0) times height; origin of second dorsal over or slightly behind anal origin. 199-215 total vertebral centra, 98-106 precaudal centra.
Colour dark gray or gray brown above, sometimes nearly blackish, white below; tips of fins other than first dorsal dusky but not black-tipped; an inconspicuous white band on flank.
|fieldmarks: A large, dark, slim, oceanic gray shark with moderately long rounded snout, moderately large eyes, oblique-cusped serrated teeth in the upper jaw, upper teeth with basal cusplets or very strong serrations, usually 15/15 rows of anteroposterior teeth, an interdorsal ridge, long narrow pectoral fins, a moderate-sized first dorsal with its origin behind the pectoral rear tips, a low second dorsal with a greatly elongated inner margin and rear tips, and no conspicuous markings.|
|Oceanic and coastal, circumtropical.Western Atlantic: Massachusetts to southern Brazil, including Gulf of Mexico and Caribbean Sea. Central Atlantic from St. Paul's Rocks. Eastern Atlantic: Madeira, Atlantic Spain, Senegal to northern Angola. Indian Ocean: Madagascar, Mozambique, Tanzania, Comores and Aldabra Island, between Somalia and Maldive Islands, Oman, Red Sea, Sri Lanka. Western Pacific: Thailand, The Philippines, New Caledonia, New Zealand and China (including Taiwan Province). Central and eastern Pacific: Caroline, Hawaiian, Phoenix and Line Islands, westward to Cocos, Revillagigedo, Clipperton and Malpelos Islands, southern Baja California to Peru.|
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|Habitat and Biology|
|An abundant offshore, oceanic and epipelagic and littoral, tropical shark, found near the edge of continental and insular shelves but also far from land in the open sea. It occasionally occurs inshore where the water is as shallow as 18 m; in the open ocean it occurs from the surface down to at least 500 m.The silky shark is often found over deepwater reefs and near insular slopes.Water temperatures of 23 to 24°C have been recorded where it occurs.
It is an active, quick-moving, aggressive shark, but defers to the more sluggish but stubbornly persistent oceanic whitetip shark . When approached by divers individuals have been seen to perform a "hunch" display, with back arched, head raised and caudal fin lowered, possibly as a defensive threat display. Population dynamics and structure are poorly known. Longline sampling in the Eastern and Central Pacific shows this shark to be much more abundant offshore near land than in the open ocean, unlike the blue shark (Prionace glauca ) and the oceanic whitetip shark, (Carcharhinus longimanus ), which occur with it. One is tempted to speculate that this shark is perhaps less well-adapted to oceanic life than the whitetip and blue sharks, and that its greater activity is best supported in offshore areas close to land masses that have higher productivity of prey species than the open ocean. The sluggishness, opportunistic feeding habits, and long pectoral fins of the blue and whitetip sharks may be energy-saving adaptations for life in the open sea; the blue shark additionally has gillraker papillae that apparently adapt it to preying on small pelagic animals. Sketchy data shows no strong tendency for sexual segregation in the silky shark, but this may very well occur. There is size segregation, with young occurring on offshore nursery areas and adults seawards from them. This is one of the three commonest oceanic sharks, along with the blue and oceanic whitetip sharks, and one of the more abundant large marine organisms.|
Viviparous, with a yolk-sac placenta; number of young 2 to 14 per litter. There seems to be no pronounced seasonality in birth of young. The gestation period is not known. In the Western North Atlantic nursery areas for the young of this shark occur along the outer edge of the continental shelf and on oceanic banks in the Caribbean.
Primarily a fish-eater, eating pelagic and inshore teleosts including sea catfish, mullet, mackerel, yellowfin tuna, albacore, and porcupine fish, but also squid, paper nautiluses, and pelagic crabs . Associated with schools of tuna, and earning the ire of tuna purse seiners for the damage it does to nets and catches; it is called the 'net-eater shark' in the tropical Eastern Pacific.
|Maximum about 330 cm; males maturing at about 187 to 217 cm and reaching 270 to 300 cm; females maturing at 213 to 230 cm and reaching at least 305 cm; size at birth about 70 to 87 cm. A length-weight curve for Cuban sharks is: WT = 0.8782 x 10-5 total length3.091 (Guitart, 1975).|
|Interest to Fisheries|
|This species is very commonly taken by pelagic longline fisheries but is also taken in fixed bottom nets. Important fisheries exist in the Gulf of Mexico and Caribbean Sea, but probably also elsewhere. Catch statistics for this species are reported to FAO only by Sri Lanka in area 51 (Western Indian Ocean). The catches started in 1960 with 5,000 t and since then the trend has been positive reaching a peak of 25,400 t in 1994 then slightly decreasing to 21,000 t in 1996. The total catch reported for this species to FAO for 1999 was 20 810 t. The countries with the largest catches were Sri Lanka (20 700 t) and Liberia (110 t).|
The meat of the silky shark has been utilized fresh and dried-salted for human consumption, while hides have been processed for leather, fins have figured in the oriental sharkfin trade, and its liver has been extracted for liver oil (which has a high vitamin A content in this species).
The silky shark is fished directly or as a sometimes important bycatch throughout its range. There are a few major multispecies shark fisheries that catch large numbers of silky sharks, mainly in Mexico and Sri Lanka (Bonfil 1994). It is also taken in the coastal fisheries of Taiwan and in larger numbers in the Taiwanese shark fisheries in waters of Indonesia and Papua-New Guinea (Chenet al. 1996). In addition, it is relatively common as a bycatch in tuna longline and purse seine fisheries (mostly juveniles are caught in the latter), especially when the gear is set near continental or insular shelves. Bonfil (1994) estimated that some 1 million silky sharks were caught as bycatch in tuna longline fisheries in the Central and South Pacific at the beginning of the 1990s. However, there is large uncertainty surrounding these calculations and there are no estimates of numbers discarded alive and numbers actually killed. In addition, estimates of population sizes or indices of abundance are not available for any stock of silky sharks. FAO reports catches of silky sharks in Sri Lankan fisheries starting in 1986. These figures average to about 11,000 t/y. However, only about 75% of these catches reported for Sri Lanka are actually attributable to silky sharks (Bonfil 1994). Silky sharks are thought to be overexploited as juveniles in the shelf nursery areas of the Campeche Bank (Bonfil 1990, 1996, 1997). Due to the lack of estimates of total catches and the size of the populations of this species, the status of the stocks is unknown.
Conservation Status : The silky shark has a mid-range intrinsic rebound potential (Smith et al. 1998). Its wide distribution and high abundance in most tropical shelves of the world suggests that presently there are no major concerns over the conservation of this species at the global level. However, there is a strong need to monitor the abundance of heavily fished stocks. The silky shark is preliminarily considered a species ofLower Risk/Least Concern for the IUCN Red List (Bonfil in press a). However, this classification is awaiting IUCN Shark Specialist Group consensus. According to Compagno (1984), silky sharks are among "one of the three most common oceanic sharks, along with the blue and oceanic whitetip sharks, and one of the more abundant large marine organisms". There are no published observations of trends in abundance of silky sharks anywhere in the world. Some intensive localised fisheries (e.g. Mexico, Sri Lanka) could eventually result in local depletion if not monitored and controlled, although such cases are not thought to pose a threat to the species at large given the likely enormous size of the world population. The silky shark is at present relatively free of threats in the form of habitat destruction because it does not live inshore nor does it utilise coastal lagoons as pupping or nursery areas like other shark species.
|Threat to humans: The silky shark is generally regarded as dangerous or potentially dangerous to people, particularly because of its size and abundance offshore, although no attacks have been attributed to it. Because of its lesser aggressiveness and apparently more restricted diet, it may very well be less dangerous than the more omnivorous oceanic whitetip shark.|
Bass, D'Aubrey & Kistnasamy, (1973)
Bigelow & Schroeder, (1948)
Cadenat & Blache, (1981)
Compagno & Vergara, (1978)
Garrick, (1967, 1982)
Garrick, Backus & Gibbs, (1964)
Garrick & Schultz, (1963)
Gilbert & Schlernitzauer, (1965)
Guitart & Manday, (1975)
Kato, Springer & Wagner, (1967)
Rosenblatt & Baldwin, (1958)
Springer, (1960, 1967)