Author: (Snodgrass and Heller, 1905)
Field Marks:
A large grey shark with moderately long broadly rounded snout, low anterior nasal flaps, fairly large eyes, broad, triangular, high, erect and semiobliquecusped 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, semifalcate pectoral fins, a moderately large first dorsal with a short rear tip and origin about opposite midlengths of pectoral fins and no conspicuous markings on fins.
Diagnostic Features:
A very large, fairly slender species (up to between 3 and 4 m). Snout moderately long and broadly rounded; internarial width 1 to 1.3 times in preoral length; eyes circular and moderately large, their length 1.3 to 2.4% of total length; anterior nasal flaps Inw snol nnnriv rIovPlnnorl: linnor labial furrows short and inconspicuous; hyomandibular line of pores just behind mouth corners not conspicuously enlarged; gill slits moderately long, third 2.7 to 4% of total length and less than a third of first dorsal base; usually 14/14 rows of anteroposterior teeth in each jaw half but varying from 13 to 15/13 to 15; upper teeth with broad, triangular, strongly serrated, fairly high 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 slightly arched roots. A low interdorsal ridge present. First dorsal fin moderately large and falcate, with pointed or narrowly rounded apex and posterior margin curving ventrally or anteroventrolaterally from fin apex; origin of first dorsal fin over midlengths of pectoral inner margins; inner margin of first dorsal moderately short, 2/5 of dorsal base or less; second dorsal fin moderately high, its height 2.6 to 2.8% of total length, inner margin fairly short and 1.3 to 1.7 times its height; origin of second dorsal about over anal origin; pectoral fins large and semifalcate, with narrowly rounded or pointed apices, length of anterior margins about 18 to 23% of total length; 200 to 215 total vertebral centra, 103 to 109 precaudal centra. Colour brownish-grey above, white below; tips of most fins dusky but not black or white; an inconspicuous white band on flank.
Geographical Distribution:
Circumtropical but generally associated with oceanic islands. Western North Atlantic: Bermuda, Virgin Islands. Central and eastern Atlantic: Madeira, possibly off Spain or Portugal, Cape Verde, Ascension, St. Helena and Sao Thome Islands. Southwestern Indian Ocean: Walter's Shoal, south of Madagascar. Western central Pacific: Middleton and Elizabeth Reefs (off eastern coast of Australia), Lord Howe Island, Marianas, Marshall, Kermadec, and Tubai Islands (Rapa), Tuamotu Archipelago (Pitcairn and Ducie Islands), Hawaiian group (Hawaiian and low islands, including Laysan and Pearl and Hermes Reefs). Eastern Pacific: Galapagos, Cocos, Revillagigedo, Clipperton, and Malpelo Islands, also coasts of southern Baja California, Guatemala and Colombia.
Habitat and Biology:
A common but habitat-limited tropical shark that occurs close inshore to well offshore near or on the insular or continental shelves; occurs in water 2 m deep but ranges to the open ocean adjacent to islands, from the surface to at least 180 m. Not oceanic but coastal pelagic and capable of crossing considerable distances of open ocean between islands (at least 50 km). Although occurring off the coasts of continental land masses in a few places (mostly in the tropical eastern Pacific, but possibly also Spain in the eastern Atlantic), this shark is mostly known from around islands, where it can be the most abundant of local sharks. Juveniles seem to be restricted to shallower water, in 25 m or less, which they apparently use as nursery grounds, while the adults range well offshore. This shark seems to favour clear water and rugged coral and rocky bottoms, and often swims a few metres above the substrate, but will come readily to the surface to feed or investigate disturbances. They are found in aggregations but apparently do not form coordinated schools. They are aggressive but at equal sizes defer to the silvertip shark, C. albimarginatus while being dominant to the blacktip shark, C. limbatus. Galapagos sharks perform a "hunch" display, with arched back, raised head, and lowered caudal and pectoral fins, while swimming in a conspicuous twisting, rolling motion, like the grey reef shark (C. amblyrhynchos); this is interpreted as a threat display, liable to be followed by an attack.
Viviparous, with a yolk-sac placenta; number of young 6 to 16 in Hawaiian waters.
Feeds primarily on bottom fishes, including eelss sea bass, flatfish, flatheads, and triggerfish, but also flyingfish, squid, octopi, and occasional garbage. Fresh baits presented to these sharks suggests that they definitely prefer fish to crab, mollusc and bird meat; they may be repelled by decayed shark and fish. Definitely known to be dangerous to people, as one was positively identified as the perpetrator of a fatal attack on a swimmer in the Virgin Islands, and possibly another was responsible for a nonfatal attack on a swimmer off Bermuda. In waters where they are abundant they often closely attend-divers, and may show attraction to their swimfins and hands. Off Clipperton Island in the eastern Pacific, Limbaugh (1963) found small Galapagos.sharks very abundant and aggressive, and a hindrance to diving operations. Continued diving activities tended to excite the sharks further, so that these had to be suspended. Aggressive actions by divers had a minimal deterring effect to sharks, but startled sharks would circle back and bring other excited sharks in their wake. Fish collecting by rotenone and blasting brought in numerous sharks, which went into a feeding frenzy. With many sharks, feeding stimuli, and social facilitation, the chances of an attack occurring are considerable, and the presence of large numbers of aggressive Galapagos sharks should be good reason to limit diving activity or to use passive protective gear such as shark cages, small submersibles, or anti-shark armor. Use of anti-shark weapons such as powerheads under such circumstances could further arouse uninjured sharks, and might start a feeding frenzy that could lead to attacks.
Size:
Maximum possibly 370 cm, males maturing between 170 and 236 cm, adult males up to at leat 292 cm, females maturing at about 235 cm, reaching over 300 cm; size at birth 57 to 80 cm.
Interest to Fisheries:
No information on utilization or fishing methods for this shark are available, but likely to figure in shark fisheries where it occurs because of its abundance in habitats it prefers.
Remarks:
This shark closely resembles the largely allopatric dusky shark, Carcharhinus obscurus, but differs in having usually taller dorsal fins (first dorsal height 9.1 to 12.1% of total length, versus 5.8 to 9.9% of total length in C. obscurus; second dorsal height 2.1 to 3.3% of total length, versus 1.5 to 2.3 in C. obscurus; and second dorsal inner margin 1.3 to 1.7 times second dorsal height, versus 1.6 to 2.1 in C. obscurus), less falcate pectoral fins, a slightly more anterior first dorsal fin (usually over midlengths of pectoral inner margins, versus usually over their free rear tips in C. obscurus), higher upper anterolateral teeth, and more vertebral centra (86 to 97 precaudals and 173 to 194 total centra). Bass, D'Aubrey and Kistnasamy (1973) give a "discriminant function" for separating the two species, here modified as DF = (607 D1H + 2308 D2H + 875 ANH - 353 IDS)/TOT, where DF = discriminant function, D1H = first dorsal height, D2H = second dorsal height, ANH = anal height, IDS = interdorsal space, TOT = total length. Values of this function were calculated as 80 to 110 for this species but 32 to 67 for C. obscurus.
Type material:
Holotype: Stanford University Natural History Museum, SU 12324,650 mm fetus, apparently lost. Type Locality: Galapagos Islands.