Author: (Nardo, 1827)
Field Marks:
A medium-sized grey shark with short rounded snout, an extremely tall triangular first dorsal fin with its origin over or anterior to the pectoral insertions, broad- and highcusped, triangular serrated upper teeth without cusplets, usually 14/13-14 rows of anterolateral teeth, an interdorsal ridge, large pectoral fins, a moderately large second dorsal with a short rear tip, and no conspicuous markings on fins.
Diagnostic Features:
A fairly stocky species (up to about 2.4 m, but mostly smaller). Snout short and broadly rounded or broadly parabolic; internarial width 0.9 to 1.3 times in preoral length; eyes circular and moderately large, their length 1.7 to 2.9% of total length; nostrils with very short, low, poorly developed anterior nasal flaps; upper labial furrows short and inconspicuous; hyomandibular line of pores iust behind mouth corners not conspicuously enlarged; gill slits short, third 2.4 to 3.6% of total length and less than a third of first dorsal base; usually 14/13 to 14 rows of anteroposterior teeth in each jaw half but varying from 14 to 15/12 to 15; upper teeth with broadly triangular, strongly serrated, semierect to slightly oblique cusps, merging smoothly into crown feet with slightly coarser serrations but no cusplets; lower teeth with erect, narrow serrated cusps and transverse roots. A narrow interdorsal ridge present. First dorsal fin very large and semifalcate, with pointed or narrowly rounded apex and posterior margin curving ventrally from fin apex; origin of first dorsal fin over or slightly anterior to pectoral insertions; inner margin of first dorsal moderately long, 2/5 of dorsal base, or slightly less; second dorsal fin moderately high, its height 2.1 to 3.5% of total length, its inner margin short and 1 to 1.6 times its height; origin of second dorsal over or slightly anterior to anal origin; pectoral fins large, semifalcate, with narrowly rounded or pointed apices, length of anterior margins about 17 to 22% of total length; 152 to 189 total vertebral centra, 82 to 97 precaudal centra. Colour grey-brown above, white below; tips and posterior edges of fins often dusky, but no conspicuous markings; an inconspicuous white band on flank.
Geographical Distribution:
Western Atlantic: Southern Massachusetts to Florida, northern and western Gulf of Mexico, Bahamas, Cuba, Nicaragua, Costa Rica, Venezuela, southern Brazil. Eastern Atlantic: Mediterranean Sea, Portugal, ? Canary Islands, ? Spain, Morocco, Senegal, Cape Verde Islands, Gulf of Guinea, Zaire. Western Indian Ocean: South Africa, Madagascar, Mozambique, Tanzania, Mauritius, Scychelles, Red Sea, the "Gulf", Gulf of Oman. Western Pacific: Viet Nam, China (including Taiwan Province), Japan, ? the Koreas, Indonesia (Aru Island), Australia (Queensland, Western Australia), New Caledonia. Central Pacific: Hawaiian Island. ? Eastern Pacific: Galapagos and Revillagigedo Islands.
Habitat and Biology:
An abundant, inshore and offshore, coastal-pelagic shark, of temperate and tropical waters, found on continental and insular shelves and in deep water adjacent to them, and oceanic banks; common at bay mouths, in harbours, inside shallow muddy or sandy bays, and at river mouths, but tends to avoid sandy beaches and the surf zone, coral reefs and rough bottom, and the surface. Depths range from the intertidal in water barely deep enough to cover it to 280 m depth. Although common in inshore environments, it does not ascend rivers into fresh water. It favours the bottom, and normally is not seen at the surface unless travelling in water so shallow that its large first dorsal fin comes out of the water.
As with several other wide-ranging carcharhinids, this species has a number of allopatric populations in different areas. In the western Atlantic Springer (1960) suggested that there are two stocks or subpopulations of sandbar sharks, a northern major one from the US Atlantic seaboard to the Gulf of Mexico and the eastern Caribbean, and a minor South American one from Trinidad eastward and southward to Brazil. Although this remains to be proven by tagging, Springer hypothesized that the separate eastern Atlantic population of this shark was capable of contributing to the South American population via migration with the equatorial current across the Atlantic.
This species has an annual migration cycle along the western North Atlantic seaboard of the United States, heading south for the winter and north for the summer. Seasonal temperature changes apparently are a prime cause of these migrations, but they are strongly influenced by the pattern of currents and locally by upwelling. Although young on nursery grounds form mixed-sex schools, adults are usually segregated. When engaged in southward migrations, males migrate earlier and deeper than females. Southward-migrating sharks often travel in large schools. Off South Africa a similar southward migration in spring and summer and northward movement in winter appears to occur. Off the Hawaiian Islands these sharks are apparently year-round residents. Preferred temperatures in shallow water off Madagascar are 23 to 24 C; off the Hawaiian Islands these sharks occur in waters 24° to 27°C. Viviparous, with a yolk-sac placenta; number of young 1 to 14 per litter, with 5 to 12 common. Litter size varies directly with size of the mother, and in populations with smaller adults the litter size averages smaller. The size of young at birth varies considerably among different allopatric populations of this shark, including adjacent ones in the western Atlantic, as does the size attained by adults. In this shark as in many other carcharhinids, the size range of adults is relatively narrow, indicating virtually determinate growth after maturity. The gestation period is estimated as 8 to 12 months, commonly 9 months off Florida, and 11 to 12 months off South Africa and in the South China Sea. Females may give birth every other year at most. Young are born at a ratio of 1:1, but in the western Atlantic off the US southeastern seaboard adult females far outnumber males by 5 or 6:1. However, only about 17 to 27% of adult females are gravid, which may be a reflection of the apparent scarcity of males but might be due to some other factor. Off the Hawaiian Islands such inbalances in sexes apparently do not occur, and about 42% of adult females are gravid. In the western North Atlantic pupping grounds are found in temperate waters, in shallow bays and estuaries of the east-central USA, into which gravid females come to drop their young in summer (June to August). Off Senegal in the eastern Atlantic young are born in April. Females are thought to be inhibited from feeding when they give birth and shortly afterwards, and leave the pupping grounds soon after giving birth. The young inhabit shallow coastal nursery grounds during the summer and move offshore into deeper, - warmer water in winter. These nursery grounds are separate from the ordinary ranges of adults, except for females arriving to drop their young and shortly departing after doing so, which probably protects the young from cannibalism. Mating occurs in the spring and summer in various populations. The males apparently follow and bite the female in the back until they swim upside down, then mate with both claspers. Mating wounds are apparent on females during the mating season. In captivity these sharks show growth rates that suggest maturation in as little as three years, but other estimates based on tooth replacement suggests 10 years for males and 13 for females. Springer (1960) suspected that sandbar sharks may mature in only two years, but on little real evidence. Presumably maturation time is somewhere between 3 and 10 years. The sandbar shark is primarily a predator on relatively small bottom fishes, with some molluscs and crustaceans taken. Its diet includes sardines, shad, menhaden, anchovies, sea catfishes, moray and snake eels, pipefish, barracuda, mullets, goatfishes, hairtails, spanish mackeral, bonito, mackeral, jacks, groupers, croakers, grunts, porgies, flounders and soles, sea robins, toadfish, cusk eels, porcupine fish, sharpnose sharks (Rhizoprionodon), spiny dogfish (Squalus), bonnethead sharks, guitarfish, skates, stingrays, cow-nosed rays, squid, cuttlefish, octopi, bivalves and conchs, amphipods, shrimp and crabs. It does not consume garbage and mammalian carrion as a rule, unlike some other members of its genus. Evidence from fisheries indicates that very fresh fish bait is greatly preferred by these sharks to stale or even fresh-frozen fish, and fish greatly preferred to mammalian meat. These sharks feed by day and night, more actively at night. It is thought that this shark is far more successful in obtaining a regular supply of food than larger carcharhinids such as Galeocerdo cuvier, Carcharhinus leucas and Carcharhinus obscurus; this is reflected in greater number of sandbar sharks with full or nearly full stomachs, and liver weight, which shows much less fluctuation in sandbar sharks than in the three larger species. Data from captive individuals suggests that digestion is relatively rapid, and prey is largely digested after two days. Although relatively large and common, and with large, triangular teeth, this species has never been indicted in attacks on people, and is thought to be not particularly dangerous because of its strong preference for live fish and invertebrate prey. It is thought that adult sandbar sharks are rarely eaten by other larger sharks and may be difficult prey for them (with the likely exception of the great white shark, which is known to eat adults of this species), but that the young are readily taken by other sharks, particularly the bull and tiger sharks, which feed on them in inshore areas.
Size:
Maximum possibly to 3 m but otherwise to 239 cm or less for adults; males maturing at 131 to 178 cm and reaching 224 cm; females maturing at 144 to 183 cm and reaching 234 cm; size at birth 56 to 75 cm.
Interest to Fisheries:
This is an abundant inshore and offshore species where it occurs, and forms an important object of fisheries especially in the western North Atlantic, eastern North Atlantic, and South China Sea. It is caught with longlines, hook-and-line, and set bottom nets and is also fished with rod and reel by sports anglers as a game fish. It is utilized fresh, fresh-frozen, smoked and dried salted for human consumption; the hides are prized for leather and other products; the fins are prepared as the base for shark-fin soup; and the liver is extracted for oil (rich in vitamins).:
Type material:
Holotype: No type material. Type Locality: Adriatic Sea.