Author: Jordan and Evermann, 1896
Field Marks:
Small to large sharks with round eyes, internal nictitating eyelids, no nasoral grooves or barbels, usually no spiracles, a long, arched mouth that reaches past anterior ends of eyes, moderately long labial furrows, small to large, more or less bladelike teeth in both jaws, often broader in the upper jaw, two dorsal fins and an anal fin, the first dorsal fin moderate-sized to large and with its base well ahead of pelvic bases, the second dorsal fin usually much smaller than the first, precaudal pits present, caudal fin with a strong ventral lobe and lateral undulations on its dorsal margin, intestine with a scroll valve, and usually no colour pattern.
Diagnostic Features:
Head without laterally expanded blades; eyes circular, vertically oval, or horizontally oval, their lengths 1.5 times their height or less; nictitating eyelids internal; spiracles usually absent (except for Galeocerdo; occasionally present in Loxodon, Negaprion and Triaenodon); anterior nasal flaps varying from lobular and tube-shaped (Triaenodon) to vestigial, not barbel-like; internarial width usually about 3 to 6 times the nostril width (exceptionally 1.5 times in Nasolamia); labial furrows varying from moderately long and conspicuous, to short and hidden when mouth is closed; teeth small to large, with acute and narrow to moderately broad cusps, sometimes lateral cusplets, but with basal ledges and grooves low or absent; teeth variably differentiated in upper and lower jaws, uppers often more compressed and bladelike, lowers often more cuspidate and not compressed; posterior teeth not comblike; tooth rows 18 to 60/18 to 56. Precaudal pits present. First dorsal fin moderate-sized to very large but not keel-like, much shorter than caudal fin; first dorsal base ahead of pelvic bases, varying from closer to pectoral bases to closer to pelvics; midpoint of first dorsal base always in front of pelvic origins; second dorsal fin usually much smaller than first (Lamiopsis and Negaprion are exceptions); pectoral fins with radials extending into distal web of fins; ventral caudal lobe strong, undulations or ripples present in dorsal caudal margin. Neurocranium without supraorbital crests. Vertebral centra with strong, wedge-shaped intermedial calcifications. Valvular intestine with a scroll valve. Colour variable, usually no colour pattern. Development usually viviparous.
Habitat, Distribution and Biology:
This is one of the largest and most important families of sharks, with many common and wide-ranging species found in all warm and temperate seas. These are the dominant sharks in tropical waters, often both in variety and in abundance and biomass. Most species inhabit tropical continental coastal and offshore waters; several species prefer coral reefs and oceanic islands while a few, including the blue, silky and oceanic whitetip sharks, are truely oceanic and range far into the great ocean basins. A minority of species range into temperate waters; one of these, the blue shark (Prionace glauca), has the greatest geographic range of any elasmobranch and one of the largest ranges of any marine vertebrate. Most requiem sharks are marine, ranging from close inshore to the outermost shelf edges near the bottom and the epipelagic zone, but none are truly specialized deepwater sharks, unlike many species of Squalidae and Scyliorhinidae. Although species in other families may enter river mouths and ascend rivers for a short distance, a few members of this family, particularly the bull shark (Carcharhinus leucas) but possibly also the little-known river sharks (Glyphis), apparently are the only living sharks that can live in fresh water for extended periods; the bull shark has a wide range in tropical and temperate rivers and lakes of the world. Requiem sharks are active, strong swimmers, occurring singly or in small to large schools. Some species are continually active, while others are capable of resting motionless for extended periods on the bottom. Many are more active at night or dawn and dusk than the daytime. At least some of the species have been shown to give specialized displays when confronted by divers or other sharks, which may be indicative of aggressive or defensive threat. Some species are relatively small, reaching about a metre long, but most requiem sharks are medium to large-sized, between 1 and 3 m long, and one species, the tiger shark, is one of the biggest sharks and may reach a length of 7.4 m. Except for the ovoviviparous tiger shark, all species are viviparous, with a yolk sac placenta, and have litters of young from 1 or 2 to 135. All are voracious predators, feeding heavily on bony fishes, other sharks, rays, squid, octopi, cuttlefishes, crabs, lobsters, and shrimp, but also sea birds, turtles, sea snakes, marine mammals, gastropods, bivalves, carrion, and garbage. Smaller species tend to select for a narrow range of prey, but certain very large species, especially the tiger shark (Galeocerdo) are virtually omnivorous. This family contains more dangerous species than any other; several of the larger requiem sharks have attacked people and boats while a few species (particularly the bull and tiger sharks) are among the most dangerous living sharks.
Interest to Fisheries:
This is by far the most important shark family for fisheries in the tropics, and various species figure prominently in artisanal, commercial and sports fisheries. Most are utilized for human food, but also for the preparation of various subproducts, including oil and vitamin A from the liver, fishmeal, fins for the oriental soupfin market, and leather. Several species are the subjects of sports fisheries, and two species, the blue and tiger sharks, are listed as International Game Fish Association record species.
Remarks:
The arrangement of this family follows Compagno (1979).