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Grey reef shark

Posted on: March 10, 2010

Above the Grey reef shark

1. The Grey reef shark is native to the Indian and Pacific Oceans. In the Indian Ocean it occurs from South Africa to India including Madagascar and nearby 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. Generally a coastal shallow-water species Grey reef sharks are mostly found in depths of less than 60 m (200 ft). However they have been known to dive to 1,000 m (3,300 ft). They are frequently found near the drop-offs at the outer edges of the reef and less commonly within lagoons. On occasion this shark may travel a few kilometers out into the open ocean.

2. The Grey reef shark has 13–14 tooth rows on each side of both jaws. The teeth are larger in the upper jaw than in the lower jaw. The first dorsal fin is medium-sized and a bit more down is the second dorsal fin. The color of this shark is grey sometimes with a bronze and white below. Grey reef sharks that spend time in shallow water eventually darken in color, due to tanning. Most Grey reef sharks are less than 1.9 m (6.2 ft) long. The maximum reported length is 2.6 m (8.4 ft) and the maximum reported weight is 33.7 kg (74.3 lb).

3. Grey reef sharks feed mainly on bony fishes, squid and octopus, crabs, lobsters. Grey reef sharks hunt individually or in groups. They have been known to pin schools of fish against the outer walls of coral reefs for feeding. Their sense of smell is extremely acute being capable of detecting one part tuna in 10 billion parts of sea water. This shark has been known to go in to a  feeding frenzy. In one documented frenzy caused by an underwater explosion that killed several snappers and one of the sharks involved was attacked and consumed by the others.

5. Grey reef sharks are active all times of the day and night. A group of around 30 sharks spend the day together in a small part of their home range, dispersing at night into shallower water to forage for food. The home range of a Grey reef shark is about 0.8 km2 (0.31 sq mi). 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. Off Hawaii, individual Grey reef sharks may stay around the same part of the reef for up to three years, while at Rangiroa they regularly shift their location by up to 15 km (9.3 mi). Individual Grey reef sharks at Enewetak become highly aggressive at specific locations suggesting that they may dominant behavior over other sharks in their home areas.

6. Social aggregation is well-documented in Grey reef sharks. large numbers of pregnant adult females have been seen slowly swimming in circles in shallow water occasionally exposing their dorsal fins or backs. These groups last from 11:00 A.M. to 3:00 P.M. A female Grey reef sharks form aggregations in shallow water from March to June. The number of sharks per group differs from year to year. Each day the sharks begin arriving at the aggregation area at 9:00 A.M. reaching a peak in numbers during the hottest part of the day in the afternoon and dispersing by 7:00 P.M. Individual sharks return to the aggregation site every one to six days. Grey reef sharks different social behaviors on different parts of the reef. Sharks tend to be solitary on shallower reefs. Near reef drop-offs, loose aggregations of 5–20 sharks form in the morning and grow in number throughout the day before dispersing at night. In some areas, sharks form schools of around 30 individuals near the sea bottom, arranging themselves parallel to each other or slowly swimming in circles. Most individuals within schools are females. And pups may form schools to keep safe.

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