Along with blacktip reef sharks and whitetip reef sharks, grey reef sharks make up one of the three most common reef shark species in the Indo-Pacific region. Found from South Africa to India in the Indian Ocean and from China to New Zealand and the Pacific Islands in the Pacific Ocean, it’s no wonder I got to encounter them on Mermaid Week Maldives with Mermaid Kat. In fact, the Maldives are a leading conservation partner for Grey Reef Sharks as they use shark watching ventures and shark dive sights to promote ecotourism.
Carcharhinus amblyrhynchos are most closely related to the silvertip shark. Their broad, round snout and large eyes easily mark them as a reef shark, but their lack of a ridge between dorsal fins and their coloration help distinguish them from other reef sharks. Their first dorsal fin is plain, or in the Indian Ocean might have a white tip, while the other fins have dark tips, and the tail fin has a broad black rear margin. While they can grow to 2.6 meters (8.5 ft), they normally stay smaller than 1.9 meters (6.2 ft), or around 33.7 kilograms (74 pounds). They can live to be 25 years old.
One to four pups are born every other year after a 9-14 month gestation period. Pups are about 45-60 centimeters (18-24 inches), and reach maturity at 1.3-1.5 meters (4.3-5 ft) for males and 1.2-1.4 meters (3.9-4.6 ft) for females.
Grey reef sharks are active throughout the day, but their activity levels peak at night. On shallow reefs and pinnacles, they tend to be more solitary while deeper they have been known to aggregate, especially during peak daylight hours. Grey reef sharks prefer the leeward side of coral reefs, meaning they like the side away from the direction of the current. While they have been known to dive to 1000 meters (3300 ft), they tend to stay shallower than 60 meters (200 ft). They have a very acute sense of smell, which helps with feeding. They’ve been known to pin fish against reef walls and have been seen hunting in groups of 700 sharks as well as alone. In order of preference, their diets consist of bony fish, cephalopods (octopus and squid), and crustaceans (crabs and lobsters).
The International Union for Conservation of Nature Red List lists grey reef sharks as endangered. Their tendency to stay in the same area, need for a specific habitat, and slow reproductive rate make it hard to bounce back with depleting numbers. The main threats to grey reef sharks include the degradation of coral reefs for human development, as well as multispecies fisheries which take the sharks to use in shark fin soup and as fish meat. Grey reef sharks are also prey to silvertip sharks and hammerhead sharks, and can host a number of parasites, from copepods on their skin to juvenile isopods on their gills.
The International Shark Attack File has a few attacks listed for them as well. As of 2008, there have been 7 unprovoked and 6 provoked attacks from grey reef sharks, but none of them were fatal. Grey reef sharks are curious about divers, but generally lose interest after seeing them a few times. When food is involved, or if flash photography goes off, it can entice the shark. If it feels cornered or is pursued, it can attack. Should that happen, the divers should immediately retreat slowly and always face the shark.
Grey reef sharks have the most well-known threat display of any shark, called the “hunch” threat display. They’ll raise their snout, drop their pectoral fins, arch their backs, and laterally curve their body. Keeping this body shape, they’ll swim with stiff, exaggerated side to side motions, sometimes even rolling or looping in a figure 8 style motion. This will continue until the shark retreats or attacks rapidly with their mouth open and upper teeth slashing. If the shark is approached even closer by the threat when displaying their hunch display, or if their escape route is blocked, the intensity of the display will increase.
Sharks are not something you should be afraid of, but you should respect their boundaries and personal space. If you leave the shark alone, it will leave you alone as well.