grey reef shark
Agile and energetic shark of the Indo-Pacific
The Grey Reef shark (Carcharhinus amblyrhynchos, is a species of requiem shark, in the family Carcharhinidae. It is one of the most common reef sharks in the Indo-Pacific. It is an agile and energetic predator that is known to offer a threat display. There behavior is based more socially rather than territorially.
Family: Carcharhinidae – Requiem sharks
Common Name– Ground Sharks
Common Name– Requiem Sharks
Status: IUCN Red List NEAR THREATENED
Average Size and Length: Grey Reef sharks have an average length of 5 feet to 6.6 feet. Some reports as long as 7 feet long.
Average Weight: Grey Reef sharks have an average weight of 33 to 41 pounds.
Teeth and Jaw: Grey Reef shark teeth are triangular and serrated with 13-14 teeth in each jaw half. The upper teeth are narrower and more serrated, semi-erect to oblique in shape with high cusps, though the crown feet have coarser serrations. The lower teeth are erect or semi-oblique with narrowly serrated cusps.
Head: The Grey Reef shark has a long, broadly rounded snout and large eyes.
Demographic, Distribution, Habitat, Environment and Range: Grey Reef sharks prefer shallow, coastal waters at depths of 200 feet or less, but on occasion down to 3,300 feet. They can be found near the drop-offs at the outer edges of the reef, particularly near reef channels with strong currents, and less commonly within lagoons. On occasion, this shark may venture several kilometers out into the open ocean. They are found over continental and insular shelves, preferring the leeward sides of coral reefs with clear water and rugged topography.
The grey reef shark is native to the Indian and Pacific Oceans. In the Indian Ocean, it can be found from South Africa to India, including Madagascar and surrounding islands, the Red Sea, and the Maldives. In the Pacific Ocean, it is found from southern China to northern Australia and New Zealand, including the Gulf of Thailand, the Philippines, and Indonesia. The Grey Reef shark has also been reported being seen at many Pacific islands, including American Samoa, the Chagos Archipelago, Easter Island, Christmas Island, the Cook Islands, the Marquesas Islands, the Tuamotu Archipelago, Guam, Kiribati, the Marshall Islands, Micronesia, Nauru, New Caledonia, the Marianas Islands, Palau, the Pitcairn Islands, Samoa, the Solomon Islands, Tuvalu, Vanuatu and the Hawaiian Islands.
Diet: The preferred prey of Grey Reef sharks is bony fishes. They are very good at catching fish swimming in the open. Grey Reef sharks sometimes accompany hunting Whitetip Reef sharks, which are more adept at capturing fish inside caves and crevices. Secondary, they eat cephalopods such as and octopus and squid, and occasionally crustaceans like crabs and lobsters.
Grey Reef sharks hunt individually or in groups and have been known to pin schools of fish against the outer walls of coral reefs for feeding. Hunting groups of up to 700 grey reef sharks have been observed at Fakarava Atoll in French Polynesia.
Grey reef sharks are prey for larger sharks, such as the Silvertip shark. Great Hammerhead sharks in Rangiora Atoll will feed on Grey Reef sharks who have been exhausted by pursuing mates.
Aesthetic Identification: Grey Reef sharks are counter-shaded grey above, sometimes with a bronze sheen, and white below. The entire rear margin of the caudal fin has a distinctive, broad, black band. There are dusky to black tips on the pectoral, pelvic, second dorsal, and anal fins.
In the Western Indian Ocean Grey Reef sharks have a narrow, white margin at the tip of the first dorsal fin; this trait is usually absent from Pacific populations. Grey Reef sharks that spend time in shallow water eventually tan and darken in color.
The Grey Reef shark has a streamlined, moderately stout body. The first dorsal fin is medium-sized, and there is no ridge running between it and the second dorsal fin. The pectoral fins are narrow and falcate.
Biology and Reproduction: Known parasites of the Grey Reef shark are juvenile stages of the isopods Gnathia trimaculata and G. grandilaris that attach to the gill filaments and septa, and nematode Huffmanela lata and several copepod species that attach to the sharks’ skin.
Grey Reef sharks are viviparous.
Each female has a single functional ovary (on the right side) and two functional uteruses. 1 to 4 pups (6 in Hawaii) are born every other year; the number of young increases with female size. Gestation ranges from 9 to 14 months.
Parturition is thought to take place from July to August in the Southern Hemisphere and from March to July in the Northern Hemisphere. However, females with “full-term embryos” have also been reported in the fall off Enewetak. The pups measure between 18–24 inches long.
Sexual maturation occurs at around seven years of age, when the males are 4.3–4.9 feet long and females are 3.9–4.6 feet long. Females on the Great Barrier Reef mature at 11 years of age and are larger than sharks in other locations. Grey Reef sharks live at least 25 years.
Behavioral Traits, Sensing and Intelligence: Grey Reef sharks have an extremely strong sense of smell. They are capable of detecting one-part tuna extract in 10 billion parts of sea water. When there is a large quantity of food, Grey Reef sharks may be roused into a feeding frenzy. They actively expel most other shark species from favored habitats, even species larger in size.
On the rare occasions when Grey Reef sharks venture into oceanic waters, they often associate with marine mammals or large pelagic fishes, such as sailfish. Rainbow Runners have been observed rubbing against grey reef sharks, using the sharks’ rough skin to scrape off parasites.
Grey Reef sharks are most active at night but are active at all times of the day.
In the Marshall Islands, Grey Reef sharks that are from different parts of the reef exhibit different social and ranging behaviors. Sharks on the outer ocean reefs tend to be nomadic, swimming long distances along the reef, while those around lagoon reefs and underwater pinnacles stay within defined daytime and night-time home ranges.
There is little evidence of territoriality in the Grey Reef shark; individuals will tolerate others of their species entering and feeding within their home ranges. In some locations some sharks stay around the same part of the reef for years. But in others they may shift locations. In Enewetak, Grey Reef sharks are highly aggressive in some locations, and may dominate over other sharks. They do participate in social aggregation. Aggregation behaviors change in different locations.
Grey Reef sharks were the first shark species known to perform a threat display prior to attacking. They exhibit a “hunched” posture with characteristically dropped pectoral fins, and an exaggerated, side-to-side swimming motion. Grey Reef sharks often do so if they are followed or cornered by divers to indicate they perceive a threat. Sometimes the swimming is combined with rolls or figure-8 loops. When this begins to happen, (especially if it is blocked) it is best to retreat immediately.
Grey Reef sharks have never been seen performing threat displays towards each other. This suggests the display is a response to potential threats or predators rather than competitors.
During mating, the male grey reef shark will bite at the female’s body or fins to hold onto her for copulation.
Speed: Grey Reef sharks are fast and agile swimmers.
Grey Reef Shark Future and Conservation: The Grey reef shark is fished commercially, mainly for their fins which are used in shark fin soup. The meat is also consumed and used as fishmeal. The Grey Reef shark is more valued, however, in dive tourism as it shows high site faithfulness and is a common inhabitant of coral reef dive sites.
Grey Reef Shark Recorded Attacks on Humans: The Grey Reef shark is considered one of the more aggressive sharks but will typically only show aggression towards a person when it feels threatened. According to the International Shark Attack File, the grey reef shark is responsible for 8 confirmed shark bites on humans, one of which was fatal.
The Grey Reef shark often shows curiosity and approaches divers. If cornered or threatened in some way, the grey reef shark displays explicit threat behavior. If the threat continues, the shark may immediately flee or may deliver a quick bite prior to retreating (Compagno, 2005). The Grey Reef shark is more likely to attack while solitary rather than schooling, perhaps due to an increased feeling of vulnerability (Nelson 1986).