Latin name

Carcharhinus amblyrhynchos

Other names

Gray reef shark

Identification

The body of the fish is torpedo-shaped, the snout is round, wide, the eyes are round, rather large, their length is 1.2-2.1% of the total length. The distance between the nostrils is equal to or 1.2 times the distance from the tip of the snout to the mouth. Lip furrows are short and sparsely marked. The mouth has 13-14 rows of teeth on either side of each jaw. The upper teeth are triangular with a sloping tip, while the lower teeth are narrower with a vertical tip. The edges of the upper teeth are more serrated than those of the lower teeth. The total number of vertebrae is between 168 and 193.

Features of fish fins

The first dorsal fin is medium sized with no ridge between the dorsal fins. The base of the first dorsal fin begins behind the tips of the pectoral fins and the second dorsal fin begins above the base of the anal fin. The pectoral fins are narrow and sickle-shaped. The height of the second dorsal fin is 3.1-3.7% of the total length.  

Fish colouring

The dorsal colour of this shark species is light to dark grey, sometimes brownish, the caudal fins have a black border, and a broad dark band runs along the caudal edge of the caudal fin. In individuals from the western Indian Ocean, the tip of the first dorsal fin is white. The belly of these fish is much lighter in colour than the back.

Distribution

They are found in the Indian and Pacific Oceans off the coasts of Madagascar, the Seychelles, the Maldives, Thailand, Australia, New Zealand, Hawaii, Tahiti, the Red Sea, China, the Philippines and Indonesia. The grey reef shark is the most common shark species in the coral reef waters of Oceania, particularly off the coasts of American Samoa, Chagos Archipelago, Easter Island, Christmas Island, Cook Islands, Marquesas Islands, Tuamotu Archipelago, Guam, Kiribati, Marshall Islands, Micronesia, Nauru, New Caledonia, Mariana Islands, Palau, Pitcairn Islands, Samoa, Solomon Islands, Tuvalu, Hawaii and Vanuatu.

Habitat

They live in lagoons, channels and around reefs in tropical and subtropical seas. Sharks prefer depths of 275-280 metres and strong currents.

These sharks like to stay inshore in shallow waters no deeper than 60 metres, but they have also been found at depths of up to 1000 metres. They are found on the continental shelf and on the continental slope. They are often found on the outer edge of the reef, sometimes swimming several kilometres out into the open sea.

Often gather in schools. In the northwestern part of the Hawaiian Islands, large schools of adult pregnant females have been observed circling slowly in shallow water, sometimes with their dorsal fins above the water. 

Size

The maximum recorded length is 2.55 metres and the mass is 33.7 kg. The average size does not exceed 1.85 metres, with females being considerably smaller than males. 

Behavior

They actively displace most other sharks from their favorite sites, even if they are larger than they are. This is probably due to the similar diet and food competition between species.

Sharks occasionally swim in the open sea with marine mammals or large pelagic fish such as sailfish. 

May prey on larger predators such as white-tipped grey sharks. Dark grey sharks are parasitised by the nematode Huffmanela lataruen and some paddlefish, which attach to their skin, and the larvae of the equal-legged crustacean Gnathia trimaculata G. grandilaris, which attach to the gill stamens and septa.

At Rangiroa, pods of 30 sharks spend the day in a small area and disperse into shallow water at night to hunt. The area of their individual habitat is approximately 0.8 km².

Grey reef sharks are active around the clock, but peak activity occurs at night. At Eniwetok, Marshall Islands, sharks inhabiting different parts of the reef exhibit different social and hierarchical behaviours. Individuals from the outer edge of the ocean tend to be in constant motion, travelling long distances along the reef, while lagoon and submerged pinnacle dwellers respect individual site boundaries. Off Hawaii, some sharks remain in the same territory for up to 3 years, while at Rangiroa they regularly move up to 15 km. 

At certain locations on Eniwetok, sharks become extremely aggressive, probably due to dominant behaviour in their own habitat. In these waters, sharks show different social behaviour in different parts of the reef. On shallow areas, they form groups moving in the same direction and swim in circles near the bottom, parallel to each other. The majority of participants in such formations are females, and their formation is probably associated with mating and the birth of offspring.

Food and feeding habits

These sharks are inquisitive, active and fast swimmers. They usually hunt at night. Their diet consists mainly of bony fish, with cephalopods such as squid and octopus as a secondary source of food. Crustaceans such as crabs and lobsters can also be prey. Larger individuals have a higher proportion of cephalopods in their diet than smaller individuals. Grey reef sharks hunt both in groups and individually. They have been known to drive schools of fish away from the outer edge of the reef when hunting. They are better at catching prey while swimming in the open sea, sometimes hunting with whitetip reef sharks which are more successful in caves and crevices. Grey reef sharks have a highly developed sense of smell. In the presence of large quantities of prey, they can go into a feeding frenzy.

Reproduction

During copulation, the male bites the female to hold her down. Males and females reach sexual maturity when they reach 1.3-1.5 m and 1.2-1.4 m respectively. On the Great Barrier Reef, females become sexually mature at about 11 years of age and reach larger sizes. They are viviparous, with females giving birth to up to 4 calves (6 in Hawaii) each year, 45-60 cm long. After the yolk sac is emptied, it becomes a placental junction through which the embryo receives nutrients until birth. Adult females have one functional ovary on the right side and two functional uteri. Pregnancy lasts between 9 and 14 months. In the southern hemisphere, birth occurs in July to August, and in the northern hemisphere from March to July. The life expectancy of the dark blue shark is up to 25 years.

During the mating season, sharks protect their territory (usually about 4 km²) from their relatives. If a rival appears, the 'master' will try to force him to move away by demonstrating his displeasure - sharply waving his tail, arching his back, etc.; if this is not enough, the rival will be chased away by bites (usually non-lethal). Sharks living in the Pacific Ocean are much more aggressive than their counterparts in the Indian Ocean and the Red Sea.

Fishing

These sharks are caught as bycatch throughout their range and their meat is used for food and fishmeal.

Relationship with a person

Grey reef sharks are curious, attracted to divers and can be approached cautiously, but quickly lose interest with repeated dives. They become agitated in the presence of food and are more aggressive in the open sea than on the reefs. Several attacks on harpooners have been recorded, probably accidentally when a shark attacked a harpooned fish that was too close to a person. Dark grey sharks are capable of attacking if they are being pursued or if their escape routes are blocked. 

In 2008, the International List of Shark Attacks on Humans included 7 provoked and 6 unprovoked attacks by sharks of this species, none of which were fatal.