This week’s Featured Species is one of the most commonly found sharks on coral reefs and atolls in the Pacific and Indian Oceans: the Grey Reef Shark (Carcharhinus amblyrhynchos).
The grey reef shark is a beautiful shark and a tall dorsal fin that can sometimes present with a white tip in younger individuals. Their caudal fin is lined with a stark black ridge (Parker, 2008; Skomal, 2016). The grey reef shark resembles another species that is common on corals and atolls in the Indo-Pacific, the silvertip shark (Carcharhinus albimarginatus); however the grey reef shark is usually smaller than the silvertip.
The grey reed shark’s jaw is full of small, triangular, serrated teeth. The teeth in the upper jaw have a wider base and broader cusp than the teeth of the lower jaw. These two different morphologies of teeth allow for the grey reef shark to have a widely varying diet from tropical bony reef fishes to invertebrates (Skomal, 2016).
During the day, grey reef sharks are often observed in large social groups. They choose to return to the same home site time and again, typically in lagoons or channels between coral reefs (Skomal, 2016). At night, the group breaks apart as the sharks individually hunt.
Perhaps due to social living, the grey reef shark is one of a handful species known to show a prominent threat display. Whether threatened by potential predators or competition, the grey reef shark exaggerates its swimming, moving its head and tail is wide, broad sweeps. The shark will dramatically arch its back, lifting its head high while depressing its pectoral fins. Occasionally the shark will also swim in a corkscrew-like pattern (Parker, 2008; Skomal, 2016). If the shark perceives the threat is increasing, despite the warning posture, the grey reef shark will either flee the area or turn and attack with shockingly fast speed (Skomal, 2016).
If you ever have the pleasure of diving with these incredible sharks, be sure to watch their body language. They will let you know when they have had enough of your presence. Like an predator, these sharks demand and deserve our respect.
Mimi Armstrong deGruy. (2011 September 15). Posturing Grey Reef [Video Clip]. Retrieved from https://www.youtube.com/
Authority: Bleeker, 1856
Family: Carcharhinidae, 59+ species
Length: Maximum of 8.4 feet (2.5 m)
Weight: Average of 74.3 lbs (33.7 kg)
Habitat: Shallow coastal waters, shelves, atolls, coral reefs, lagoons, adjacent oceanic waters
Depth: Usually found in less than 200 ft (60 m); occasionally have been documented in 3000 ft (1000 m)
Reproduction: Placental Viviparity
Gestation: 12 months
Litter Range: 1 – 6 pups
Home Range: Warm tropical waters of Indian and Pacific Oceans
Diet: Tropical fishes and invertebrates
IUCN Status: Near Threatened; taken by commercial fisheries
(Smale, 2009; Parker, 2008; Skomal, 2016)
If you missed that week’s Featured Species post on the Sand Tiger shark, be sure to check it out!
The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!
Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.
Featured Image Source
Alamy. (Archive). (n.d.). Grey Reef Sharks [Digital Image]. Retrieved from https://www.smithsonianmag.com/
Compagno, J. V. L. (1984). FAO species catalogue Vol. 4, part 2 sharks of the world: An annotated and illustrated catalogue of shark species known to date. Food and Agriculture Organization of the United Nations.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.
Smale, M.J. 2009. Carcharhinus amblyrhynchos. The IUCN Red List of Threatened Species 2009: e.T39365A10216946.
Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.