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Carcharhinus obscurus:   (click for more)

Carcharhinus obscurus:   (click for more)

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Synonyms
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  • ? Prionodon obvelatus  Valenciennes, in Webb & Berthelot, 1844
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  • ? Galeolamna greyi  Owen, 1853
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  • Carcharias macrurus  Ramsay & Ogilby, 1887
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  • Galeolamna (Galeolamnoides) eblis  Whitley, 1944
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  • Carcharhinus iranzae  Fourmanoir, 1961
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  • Carcharhinus obscurella  Deng, Xiong & Zhan, 1981
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  • Carcharhinus lamiella  , (not Carchiaras lamiella Jordan & Gilbert, 1882, equals C. brachyurus).
    FAO Names
    En - Dusky shark, Fr - Requin de sable, Sp - Tiburón arenero.
    3Alpha Code: DUS     Taxonomic Code: 1080201016
    Scientific Name with Original Description
    Squalus obscurus  LeSueur, 1818. J. Acad. Nat. Sci. Philadelphia 1(2): 223, pl. 9. Holotype: none.Type Locality: North America.
    Diagnostic Features
    fieldmarks: A large gray shark with a fairly short broadly rounded snout, low anterior nasal flaps, fairly large eyes, broad, triangular, rather low, erect and semioblique-cusped serrated anterolateral teeth without cusplets in upper jaw, lower teeth erect and narrow-cusped, usually 14/14 rows of anteroposterior teeth, a low interdorsal ridge, large, falcate pectoral fins, a moderate-sized first dorsal with a short rear tip and origin about opposite free rear tips of pectoral fins, a small, low second dorsal, and no conspicuous markings on fins.

    Very large, fairly slender sharks (up to at least 3.7 m) with snout short to moderately long and broadly rounded internarial width 1.0 to 1.4 in preoral length. Eyes circular and moderately large, length 1.0-2.1%TL. Anterior nasal flaps low and poorly developed. Upper labial furrows short and inconspicuous. Hyomandibular line of pores just behind mouth corners not conspicuously enlarged.  Gill slits moderately long, 3rd 2.7-4.0% TL and less than a third of first dorsal base.  Usually 14/14 rows of anteroposterior teeth in each jaw half but varying from 14-15/13-15; upper teeth with broad, triangular, strongly serrated, rather low erect to slightly oblique cusps that smoothly merge into crown feet, which have slightly coarser serrations but no cusplets; lower teeth with erect, moderately broad, serrated cusps and transverse or sometimes arched roots.  A low interdorsal ridge present. Pectoral fins large and falcate, with narrowly rounded or pointed apices, length of anterior margins about 17 to 22%TL. First dorsal fin moderate-sized and semifalcate, with pointed or narrowly rounded apex and posterior margin curving ventrally from fin apex; origin of first dorsal fin usually over or slightly anterior to the pectoral free rear tips; inner margin of first dorsal moderately short, a third dorsal base or less. Second dorsal fin small and low, height 1.5 to 2.3% TL, inner margin fairly long and 1.6 to 2.1 times height; origin of second dorsal about over anal origin.  173-194 total vertebral centra, 86-97 precaudal centra.  Tips of most fins dusky but not black or white. An inconspicuous white band on flank. 
    Geographical Distribution
    Distribution Map
    Western Atlantic: Southern Massachusetts and Georges Bank to Florida, Bahamas, Cuba, northern Gulf of Mexico, and Nicaragua; southern Brazil. Eastern North Atlantic: ? Portugal, ? Spain, ? Morocco, ? Madeira, ? western Mediterranean, Canary and Cape Verde Islands, Senegal, Sierra Leone. Western Indian Ocean: South Africa, Mozambique, Madagascar, ? Red Sea. Western Pacific: Japan, China, VietNam, Australia (New South Wales, Queensland, Western Australia), New Caledonia. Eastern Pacific: Southern California to Gulf of California, Revillagigedo Islands, possibly Chile.
    related Launch the Aquatic Species Distribution map viewer
    Habitat and Biology
    A common, coastal-pelagic, inshore and offshore warm-temperate and tropical shark of the continental and insular shelves and oceanic waters adjacent to them, that ranges from close inshore in the surf zone to well out to sea and from the surface to 400 m depth.It does not prefer areas with reduced salinities and tends to avoid estuaries.  Adults of the species occupy an overlapping intermediate offshore coastal habitat between other similar species of Carcharhinus such as more strictly inshore coastal species such as C. plumbeus, the offshore deep-benthic C. altimus, oceanic species such as C. falciformis and C. longimanus, and island species such as C. albimarginatus and C. galapagensis . Adult dusky sharks are often seen offshore and commonly follow ships.This shark is strongly migratory in temperate and subtropical areas in the Eastern North Pacific and Western North Atlantic, moving north during the warmer months of summer and retreating south when the water cools. Off the southern coast of Natal, South Africa a nursery area occurs, where newborn sharks of 80-90 cm are resident; larger immature sharks over 90 cm move out of this area, with females tending to move north and males south, but there is some overlap in this partial sexual segregation.This pattern is complicated by seasonal, temperature-related migrations as elsewhere in the range of these sharks, going southwards in spring and summer and northwards in winter, and also a tendency for the sharks to move into deeper water during cooler months. Additionally, there may be other factors affecting the distribution of these young sharks, as may be true off Durban, South Africa, where they move into the surf zone in spring and summer and move offshore in autumn and winter, although inshore water temperatures are about the same. Still larger immature sharks up to 220 cm long may move south to southern Natal, but when they become adolescent at up to 280 m, they tend to move north of Natal along with adults into waters of southern Mozambique.The young form large feeding schools or aggregations.
    Viviparous, with a yolk-sac placenta; number of young per litter 3 to 14, with South African sharks averaging more young (about 10) than those from Florida; sex ratio approximately 1:1 in the fetuses of South African and Floridian sharks, and the same for adults in Florida. There may be no correlation between maternal size and litter size in this shark, unlike some other species of Carcharhinus. Birth may occur over a long time span of several months in a given region, and has been reported as occurring from late winter to summer. In South African waters birth may occur year-round with an increase in fall. In pregnant female sharks caught off Florida in the winter there are two size-classes of young, those 43 to 70 cm and full or near full-term fetuses of 85 to 100 cm. These classes may indicate either biannual staggered birth seasons with a gestation period of 8 or 9 months or a long gestation period of about 16 months. Whatever the case females apparently mate in alternate years; mating in the Western Atlantic occurs in the spring. Females move inshore to drop their young, then depart the nursery area.  Adults may mature at an age of about 6 years and live to at least 18 years. The young are readily kept in aquaria.Dusky sharks eat a wide variety of reef, bottom, and pelagic bony fishes,  [more...]
    Unlike the bull (C. leucas) and tiger (Galeocerdo cuvier) sharks mammalian carrion, oddities and garbage are apparently uncommon items in the diet of this species.Young dusky sharks are readily preyed on by other big sharks, including sandtiger (Carcharias), great white (Carcharodon), bull (Carcharhinus leucas), and tiger (Galeocerdo) sharks, which help to regulate the population size of this species. Reduction of these species off Natal, South Africa through an efficient shark gillnetting program to protect bathing beaches has apparently resulted in an increase in juvenile dusky sharks there.
    Size
    Maximum size possibly over 400 cm; males maturing at about 280 cm and reaching at least 340 cm; females maturing between 257 and 300 cm and reaching at least 365 cm; size at birth 69 to 100 cm.
    Interest to Fisheries
    A common offshore shark regularly caught with longlines, also hooks and-lines and set bottom nets . Catches of this species have been reported to FAO only by the USA in area 21 (Northwest Atlantic) during the years 1988-94 but they have never exceeded 100 t. The total catch reported for this species to FAO for 1997 was 7 t. The countries with the largest catches were South Africa. No catch reported for this species to FAO for 1999.
    It is utilized fresh, dried salted, frozen and smoked for human consumption; hides used for leather; fins for shark-fin soup base; and liver oil extracted for vitamins.

    The dusky shark is taken in coastal shark fisheries in several parts of the world and sometimes as bycatch in swordfish/tuna fisheries when these take place close inshore. With two exceptions, for most fisheries there are no statistics on catches of this species. In the US Atlantic shark fishery, statistics began to be recorded by species since 1992; some 80 t of dusky sharks are taken there yearly (Rose 1998). There are several indications that commercial and sport shark catches have caused local depletion of the dusky sharks stock in the US East Coast. The CPUE decreased in the Chesapeake Bight region of the U.S. mid-Atlantic coast from 1.73 sharks/100 hooks in the 1974-79 period to 0.0011 sharks/100 hooks in 1991 (Musick et al. 1993). A similar decrease in CPUE was reported by Russell (1993) for Gulf of Mexico tuna longline sets, from 0.09 sharks/100 hooks in 1989 to 0.0037 in 1991. Cramer (1998) found a similar decline in her analysis of logbooks from the longliners from 1992 to 1997. Since 1993, a US management plan keeps reduced catch quotas for large coastal sharks with the aim of helping the recovery of this and other shark species. Standardised CPUEs for dusky sharks in the Virginia-Massachusetts (U.S.) area for the rod and reel fishery show a decrease from 1986-1994 but a moderate increase in 1995-1997 (Brown 1998), possibly signalling the positive outcome of management actions. The Western Australia shark fishery which started in the 1940s, has taken on average some 450 t/y of dusky sharks since the early 1980s (Simpfendorfer et al. 1998). This fishery is centred on the harvesting of newborns and very young sharks from inshore nursery areas. The catch rate of dusky sharks in W Australia fell steadily in the late 1970s and early 1980s to stabilise thereafter; presently the stock is thought to be exploited in a sustainable fashion (Simpfendorfer et al. 1998). It is estimated that the effects of this fishing strategy will become evident in the population in 5-10 years from now.

    Conservation Status : The dusky shark has one of the lowest intrinsic rebound potentials among shark according to Smith et al. (1998). Therefore, its exploitation should be conducted with extreme caution and under close monitoring. The IUCN Red List classifies dusky sharks as Lower Risk/Near Threatened at the world level, asVulnerable in the NW Atlantic, and as Lower Risk/Near Threatened in Australia (Camhi et al. 1998; Camhiet al. in press). Mooney-Seus and Stone (1996) consider the dusky shark as Reduced to Severely Reduced in the US Atlantic waters and Data Deficient in the rest of its range. Current management regulations in the US may help rebuild the impacted US Atlantic stock, although the problem of human impact on inshore nursery/pupping areas remains to be addressed. The Western Australia stock is considered to be currently out of concern. Furthermore, a no-take Marine Protected Area extending from Shark Bay to North-West Cape in WA is designed to protect the breeding stock that sustains this fishery.
    related Additional information from IUCN database
    related Additional information from CITESdatabase
    Remarks
    Some records of this species from Madeira and the Mediterranean Sea may be based on C. galapagensis, according to Garrick (1982).
    Threat to humans: The dusky shark is apparently dangerous to people, although very few attacks by it have been recorded, and very little is known of its behaviour in relation to divers, swimmers or surfers. Because of its large size when adult, it should be considered a potential hazard where it occurs. Some attacks on people off islands such as Bermuda that were attributed to this species were probably caused by the closely similar Galapagos shark (Carcharhinus galapagensis).
    Source of Information
    FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 2 - Carcharhiniformes. Compagno, L.J.V. 1984.  FAO Fish. Synop., (125) Vol.4, Part 2
    Bibliography
    Bass, D'Aubrey & Kistnasamy, (1973)
    Bigelow & Schroeder, (1948)
    Cadenat & Blache, (1981)
    Clark & von Schmidt, (1965)
    Compagno, (1981)
    Compagno & Vergara, (1978)
    Garrick, (1967, 1982)
    Garrick & Schultz, (1963)
    Randall, (1963)
    Springer, (1960, 1963)
    van der Elst, (1981)
     
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