Author: (Valenciennes, 1839)
Field Marks:
A large, stout grey shark with very short, bluntly rounded snout, small eyes, broadly triangular serrated teeth in upper jaw, heavy but narrower cusped teeth with arched roots in lower jaw, upper teeth without cusplets, usually 13/12 rows of anteroposterior teeth, no interdorsal ridge, large angular pectoral fins, a large triangular first dorsal with a short rear tip and a moderately large second dorsal with a short rear tip, fins with dusky tips but not strikingly marked.
Diagnostic Features:
A stocky to very heavybodied species (stoutest as adults; up to about 3.4 m). Snout very short and bluntly and broadly rounded; internarial width 0.7 to 1 times in preoral length; eyes circular and small, their length 0.8 to 1.8% of total length; anterior nasal flaps expanded or broad-based triangular lobes; upper labial furrows short and inconspicuous; hyomandibular line of pores just behind mouth corners not conspicuously enlarged; gill slits moderately long, the third 3.1 to 4.1% of total length, but less than a third of first dorsal base; usually 13/12 rows of anteroposterior teeth in each jaw half, but varying from 12 to 14/12 to 13; upper teeth with very broad, triangular, strongly serrated, erect to slightly oblique cusps, that merge smoothly with the coarsely serrated crown feet, but with no cusplets; lower teeth with erect to semioblique. broad serrated cusps and arched roots. No interdorsal ridge. First dorsal fin large and broadly triangular to somewhat falcate, with a pointed or sharply rounded apex and posterior margin curving ventrally or posteroventrally from fin apex; origin of first dorsal fin usually over or just behind pectoral insertions, but exceptionally nearer their free rear tips; inner margin of first dorsal short, less than a third of dorsal base or slightly less; second dorsal fin large and high, its height 3.2 to 4.5% of total length, its inner margin short and 0.7 to 1.1 times its height; origin of second dorsal anterior to anal origin; pectoral fins large and broad, triangular to semifalcate, with narrow, pointed apices, length of anterior margins about 18 to 21% of total length; 198 to 227 total vertebral centra, 101 to 123 precaudal centra. Fin tips dusky, especially in young, but not strikingly marked; an inconspicuous white band on flank.
Geographical Distribution:
Widespread along the continental coasts of all tropical and subtropical seas and travelling far up warm rivers and into freshwater lakes. Western Atlantic: Massachusetts to southern Brazil, including Gulf of Mexico, Caribbean Sea, and Bahamas; found in Mississippi and Atchafalaya Rivers (southern USA), Lake Nicaragua and San Juan River (Nicaragua), Lake Ysabel (Guatemala), Patula River (Honduras), Panama Canal (Panama), Amazon River (to Peru). Eastern Atlantic: Morocco, Senegal to Angola; found in Gambia River (Gambia) and Ogooue River (Gambon). Western Indian Ocean: South Africa (including Zambesi and Limpopo Rivers), Zimbabwe (Ruenwa River), Kenya, Iraq (Tigris River and Shatt-el Arab), India, including Bombay, Cochin and the Hooghly River, where it occurs along with Glyphis gangeticus; Bass, D'Aubrey and lEistnasamy (1973) give a detailed listing of freshwater localities of the species in southern and southeastern Africa. Western Pacific: Thailand (Gulf of Thailand), Viet Nam, Borneo, New Guinea (including Lake Jamser), Australia (western and northern Australia, Queensland, New South Wales; including Lake Macquarie and Swan, Brisbane, Herbert, and E. Alligator Rivers), New Caledonia, Fiji, Rangiroa Atoll (Tuamotu Archipelago), The Philippines. Eastern Pacific: Southern Baja California and Gulf of California to Ecuador and possibly Peru.
Habitat and Biology:
A coastal, estuarine, riverine and lacustrine shark usually found close inshore in marine habitats, in water less than 30 m deep and occasionally less than a metre deep, but ranging into deeper water close to shore down to at least 152 m depth. In marine habitats it commonly occurs in hyposaline and hypersaline lagoons and bays, river mouths, passages between islands, close to wharves and right off the surf line. It is ovften found in muddy areas with few other shark competitors. It is the only wide-ranging shark that penetrates far into fresh water and apparently is able to exist there at length in tropical lakes and rivers, to 3700 km from the sea in the Peruvian Amazon, although it may not be able to maintain its entire life cycle in fresh water and does not have landlocked populations there. A population of this shark in Lake Nicaragua was once thought to be landlocked (and a separate species), but members of this population have access to the sea and readily utilize it, although these sharks can and occasionally do breed in the lake (but to a minor extent compared to their use of brackish coastal waters, in estuaries and river mouths). Apparently even newborn bull sharks are euryhaline, and juveniles commonly migrate into fresh water.
In South Africa the bull shark is found in the variably hypersaline St. Lucia lake system and can tolerate salinities of up to 53°/oo, but tends to move out of the lake when salinities exceed 50 /oo; unlike bull sharks in freshwater lakes, sharks caught there are in poor condition despite adequate food and ability to feed, which suggests that hypersaline water is suboptimal for them.
This shark is deceptively heavy and slow-swimming when cruising about, usually near the bottom but rarely near the surface except when lured there by offal. When attacking prey it is surprisingly agile and quick in its movements, and readily runs down small sharks and bony fishes. Young individuals are often seen spinning out of the water, possibly to dislodge parasites or for feeding, but larger ones are apparently not prone to jump out of the water.
In the western Atlantic, there is a northward movement of individuals along the US Atlantic coast during the summer from its tropical stronghold, and a southward retreat when the water cools. Off Florida, young and juveniles are found inshore in coastal lagoons, but subadults and adults more to deeper coastal waters; adult females return to lagoons to drop their young.
Viviparous, with a yolk-sac placenta; number of young per litter 1 to 13. Estuaries and river mouths are normally used for pupping grounds; some females may give birth to young in freshwater lakes such as Lake Nicaragua, but this is probably exceptional. In the western North Atlantic off Florida and the Gulf of Mexico, and off South Africa, young are born in late spring or early summer; off Nicaragua females may have young throughout the year, with a peak in spring and early summer. Off South Africa, sexual maturity is attained at an age of about 6 years and 250 cm, with a maximum age of at least 14 years in the wild. In Lake Nicaragua, females may attain a greater age than males as a result of the greater size they attain, 16 years versus 12 years for males. In the western Atlantic mating occurs in the late spring and summer (June and July). An estimated gestation period is 10 to 11 months. Females are often with courtship scars, but males rarely have fighting scars.
The bull shark is hardy and lives readily in captivity, and has been kept in aquaria for over 15 years.
This shark is a versatile and opportunistic feeder, with a very broad food spectrum; its diet was thought by Bigelow and Schroeder (1948) to be "perhaps no less varied than that of the tiger shark". Favoured food includes bony fishes and elasmobranchs, with adults taking more elasmobranch prey than young, probably because of their size and habitat. In Lake Nicaragua, the young eat a more strictly fish diet than the adults, which also take tougher prey such as turtles and mammals. In South Africa, bull sharks from lakes and rivers are almost all immatures and have relatively few prey species available to them, but the more wide-ranging adults can utilize a broader prey spectrum. Bony fishes that are eaten include garfish (Lepisosteus), tarpon, ten-pounders, ffeshwater eels, snake eels, shad, menhaden and sardines, anchovies, lizardfish, milkfish, gonorhynchids, characins, sea catfish, needlefish, mullet, mackerel and spanish mackerel, tuna, sea bass, perch and striped bass, cichlids, snappers, bluefish, jacks, snook, grunts, snappers, porgies, croakers, spadefish, eleotrid gobies, parrotfish, soles and flounders, gurnards, flatheads, toadfish, and boxfish. This shark is an important predator on other elasmobranchs, particularly on young sharks in inshore nursery grounds and stingrays, and takes bramble sharks, spiny dogfish (Squalus), grey sharks (Carcharhinus, mostly other species, but occasionally cannibalizing young bull sharks), sharpnosed sharks (Rhizoprionodin), hammerheads, guitarfish, sawfish, skates, stingrays, butterfly rays, eagle rays, and devil rays (Mobula). Sea turtles, birds, dolphins, whale offal, and terrestrial mammals in whole and part such as antelope, cattle, people, tree sloths, dogs and rats have also been recorded. Invertebrate prey includes marine crabs and freshwater land crabs, shrimp, hermit crabs, mantis shrimp, squid, sea snails, and sea urchins. Slaughterhouse offal and fish and other animals scavaged from fishing gear is readily taken; however, this shark, is far less prone to swallow inedible garbage than the tigre shark, although such things are occasionally eaten. In estuarine, riverine and lacustrine situations the bull shark may habitually have to rely on other senses than sight to find its prey because of local turbidity; the eyes of this shark are very small and may be of lesser importance than in some other members of its genus with large eyes. Pregnant females about to give birth have been thought to be inhibited in their feeding, but this may not be the case.
This may be the most dangerous species of tropical shark, and is certainly one of the three most dangerous sharks by numbers of attacks recorded on people (the other two being the great white and tiger sharks). As it is less distinctive than either of the other species, and as its genus, Carcharhinus, was until recently a taxonomic disaster, its contribution to the roster of shark attacks may be underemphasized in comparison to the great white and tiger sharks. It would not surprise the writer if this species turned out to be the most dangerous living shark, because of its large size, massive jaws and proportionately very large teeth, abundance in the tropics (off Natal, South Africa, it is caught four times as often as either the great white or tiger sharks in anti-shark nets that protect the bathing beaches), indiscriminate appetite and propensity to take largish prey, and close proximity to human activities in both fresh and salt water. It is well known for its attacks on people (and dogs) in Lake Nicaragua, although the extent of its depredations there are apparently exaggerated.
Size:
Maximum about 340 cm, males maturing at 157 to 226 cm and reaching at least 299 cm; females maturing between 180 and 230 cm and reaching at least 324 cm; size at birth between 56 and 81 cm.
Interest to Fisheries:
An important fisheries species, because of its abundance and ready availability to inshore artisanal and commercial fisheries (including those in some freshwater lakes such as Lake Nicaragua). It is caught mainly with longlines and hook-and-line gear and utilized fresh, fresh-frozen or smoked for human consumption; its hide is used for leather, its fins for shark-fin soup, and its liver for oil, which is extracted for vitamins (liver oil of this species is high in vitamin content); carcasses are also rendered for fishmeal.
This species is a popular game fish in certain areas, particularly the southeastern Atlantic and Gulf of Mexico coasts of the USA, and off South Africa. It is caught with rod and reel from shore near river mouths, or from breakwaters and piers, and huge individuals, over 200 kg weight, have been subdued after much trevail and scrambling. It is, however, not recognized as a big-game fish by the International Game Fishing Association.
Remarks:
This species has been often confused with two other less wide-ranging sympatric species, the pigeye or Java shark, Carcharhinus amboinensis, and the rare, elusive Ganges shark, Glyphis gangeticus. All of these species combine short, rounded preoral snouts with triangular, serrated upper teeth and no interdorsal ridges. From the former, the bull shark differs in its higher, more erect second dorsal fin (ratio of first:second dorsal heights 3:1 or less, but over 3:1 in amboinensis), with a more concave posterior margin, broader angle of the notched posterior anal margin (nearly a right angle, but more acute in amboinensis), higher precaudal vertebral counts (101 to 123, versus 89 to 95), narrower lower tooth cusps, and slightly greater lower anteroposterior tooth counts (usually 12 to 13, versus usually 11).
Most Indo-Pacific records of the Ganges shark in which specimens or adequate descriptive information is available have proved to be based on the bull shark (Boeseman, 1964; Bass, D'Aubrey and Kistnasamy, 1973; Garrick, 1982). Some writers have gone so far as to consider the Ganges shark a synonym of this species (Lineaweaver and Backus, 1970; Ellis, 1975,1983), although Garrick (1967, 1982) and Garrick and Schultz (1963) have recognized the species. In 1982 the writer was able to independently confirm the validity of the Ganges shark and directly compare it to C. leucas, which occurs in Indian waters. The writer saw specimens of leucas at Cochin, in Kerala, and examined a specimen of this species (Zoological Survey of India, ZSI 2234, 445 mm fetal male) from Bombay, which Day (1878, pl. 187, fig. 1) had described and illustrated as "Carcharias gangeticus". More interesting is a specimen of C. leucas (ZSI 10250, 650 mm term fetus or newborn male) collected in the Hooghly River (part of the Ganges system, and the type locality of Glyphis gangeticus) in West Bengal on 4 April 1867 by Dr J. Anderson and misidentified as 'Squalus gangeticus'. This specimen was collected on the same day and possibly the same place in the Hooghly as a true Ganges shark (see the account of Glyphis gangeticus below), which was misidentified as 'Carcharhinus temmincki'. By comparison of these specimens and the original account of gangeticus (Müller and Henle, 1839) with various accounts of the bull shark this species can be distinguished from the Ganges shark by its shorter preorbital snout (about 6% of total length in young leucas but decreasing in adults, versus 7.2% in young gangeticus), lower second dorsal fin (up to 2/4 of first dorsal height, versus 1/2 or more in gangeticus), a more abruptly vertical posterior margin on the first dorsal fin (sloping more gradually posteroventrally in the Ganges shark), a different type of upper precaudal pit (transverse and crescentic, versus longitudinal and fossate in the Ganges shark), a larger eye (about 1.8% of total length in young leucas, but 1% in young gangeticus), a different eye position (lateral in the bull shark, dorsolateral and tilted upward in the Ganges shark), slightly different gill arrangement (increasing in size from first to third slits and then decreasing to the fifth in the bull shark, but decreasing from first to fifth in the Ganges shark), less numerous anteroposterior teeth, (usually 13 upper rows versus at least 15 rows in the larger shark) much lower and more obtusely triangular upper teeth, and strikingly different lower anterior teeth (low and with broad, thick, straight cusps, no lateral cusplets, and coarse serrations in the bull shark versus high and with long, slender, hooked cusps, low lateral cusplets, and smooth edges in the Ganges shark) that do not protrude when the mouth is closed. The presence of two species of 'Ganges' sharks in fresh water in the Hooghly, and by implication the Ganges, suggests that the horrific reputation accorded the true Ganges shark may be at least a collective effect of it and the bull shark, or mainly due to the more powerfully armed, omnivorous bull shark.
Type material:
Syntypes: Of four syntypes in the Museum National d'Histoire Naturelle, Paris, two stuffed specimens are still in existence: MNHN A9650, 1600 mm adult male, and MNHN A9652, 1860 mm female. Type Locality: Antilles.