Carcharhinus amblyrhynchos
gray reef shark
(Also: grey reef shark)

The grey reef shark occupies a widespread range from the eastern Pacific Ocean (Costa Rica) through the western Pacific and Indian Oceans, and in the Red Sea. Grey reef sharks are most commonly encountered off the islands of Tahiti, Micronesia, Fiji, Papua New Guinea, and Malaysia. (Murphy, 1993)

This species can be found near the surface of tropical oceans and as deep as 280 m. It is common on coral reefs and areas near drop-offs into deeper water. (Compagno, 1984; Murphy, 1993)

Grey reef sharks have sleek, fusiform bodies that are unmistakable for anything but a shark. Key physical features include the anal fin, five gill slits, and a mouth positioned behind the eyes and underneath the snout. Additionally, grey reef sharks appear grey from a distance, but show a bronze tint when viewed up close. They have a white underside and are distinguished by a broad black band on the edge of the tail and black markings on the tips of the pectoral fins. The dorsal fin is either grey or tipped white. They have a long, broadly rounded snout and round eyes. They are lacking an interdorsal fin. (Murphy, 1993)

Males grow up to 255 cm in length, and are 130-145 cm long at maturity, while females are a bit smaller, maturing at 120-135 cm, with a record length of 172 cm. Males are distinguished by the elongate mating claspers on their pelvic fins. The maximum published weight for an individual of this species is 33.7 kg, but large males may be heavier. (Compagno, 1984; Fishbase, 2003; Godknecht, 2004; Murphy, 1993)

Grey reef sharks can be easily mistaken for similar species of requiem sharks. The blacktip shark (Carcharhinus limbatus) and the blacktip reef shark (Carcharhinus melanopterus) can be distinguised by a black tip on the dorsal fin, while the dorsal fin of C. amblyrhynchos is white or grey. Similarly, the silvertip shark (Carcharhinus albimarginatus) has white tips on its pectoral and caudal fins, while C. amblyrhynchos does not. (Godknecht, 2004)

The species is viviparous, meaning that its embryos are connected to a placenta-like yolk sac, and the young are born alive and free-swimming, not in an egg. Females give birth to live young, usually sized between 46 and 60 cm. Males mature at a length of 130-145 cm, and females at 122-137 cm. (Perrine, 1995)

The longest known lifespan for a wild grey reef shark is 25 years, but we don't have much information on how long this species can live. (Compagno, 1984)

Gray reef sharks are social, maintaining daytime schools, but becoming more active nocturnally. This species usually swims slowly (about 0.5 mph), seemingly inactive. However, because of its extremely sensitive perception channels, it is always constantly aware of its surroundings. When food is near or tasted, this species will speed up and become more active very quickly. Additionally, when it feels the vibrations of a fish dying it becomes highly aggressive. These sharks can be territorial. They have a very distinct agonistic display that they make to other sharks, and sometimes to human divers. A displaying shark will arch its back, point its pectoral fins completely downwards, and swing its head laterally in a slow pendulum-like motion as it swims. (Murphy, 1993; Perrine, 1995)

Home Range

No home range size has been specified. However, C. amblyrhynchos have been known to act aggressively towards other predatory sharks of similar size.

Carcharhinus amblyrhynchos perceives its environment very much through its excellent sense of smell. It can detect very low concentrations of blood by swinging its head side to side and using both nostrils to sample the water. All of its senses are acute. Its vision is sensitive to blue-green and low light because there are many rod cells in the retina. These sharks are generally thought to be far-sighted, but they can hunt by starlight. Grey reef sharks "hear" by detecting sounds through vibrations using sensory pits called the lateral line system. They have inner-ear semicircular canals used for balance, motion, and vibration. Most unique is its electromagnetic sense. This is facilitated by pores known as "ampullae of Lorenzini" that are concentrated around the snout. As sharks move through the earth's magnetic field, they create an electric field. By sensing this field, they can detect the strength and direction of it. This is the grey reef shark's navigation system.

These sharks communicate with other sharks visually (see the Behavior section for details of their territorial defense display) and by touch (see Mating Systems). (Perrine, 1995)

The primary diet of C. amblyrhynchos is bony reef fishes less than 30 cm long. It also eats squid, octopi, crabs, lobsters, and shrimp. These sharks catch their food with their jaws and sharp teeth. When hunting, grey reef sharks have been observed swimming at speeds of up to 30 mph (48 km/h). (Compagno, 1984)

The risk of predation on Carcharhinus amblyrhynchos decreases as it grows, but some are still prey to larger sharks and Orca whales. Predation has been noted in the Marshall Islands by Carcharhinus albimarginatus. (Compagno, 1984; Fishbase, 2003)

Grey reef sharks are usually the top predators on coral reefs, controlling the fish populations under them.

Although usually considered harmless, C. amblyrhynchos may occasionally bite humans. The bites are serious, but rarely fatal. Accidents most often occur during spearfishing, when the sharks become aggressive in the presence of food. Careless divers who corner the animal in a reef canyon may also be attacked in self-defense. Additionally, there are areas of eastern Micronesia, particularly the Marshall Islands, where these sharks have a reputation for being aggressive toward humans.

Since grey reef sharks are generally a harmless and inquisitive species, studies are conducted on them quite easily. Ecotourism in the form of "shark diving" has also recently blossomed into a large industry. (Murphy, 1993)

While the grey reef shark has not been identified as endangered as of yet, depletion of the species has been noticed around the Maldive Islands, and may be occurring in other parts of its range. There are several aspects of the biology and behavior of this species that make it particularly vulnerable to over-fishing. It is found relatively near shore, individuals tend to stay in one area, and they gather in predictable locations, making them easier to catch. Females matures relatively slowly, and have small litters, which means slower population growth compared to other large fish. (Fishbase, 2003; Godknecht, 2004)