Blowhole Cliffed coast Coastal biogeomorphology Coastal erosion Concordant coastline Current Cuspate foreland Discordant coastline Emergent coastline Feeder bluff Fetch Flat coast Graded shoreline Headlands and bays Ingression coast Large-scale coastal behaviour Longshore drift Marine regression Marine transgression Raised shoreline Rip current Rocky shore Sea cave Sea foam Shoal Steep coast Submergent coastline Surf break Surf zone Surge channel Swash Undertow Volcanic arc Wave-cut platform Wave shoaling Wind wave Wrack zone
Grey reef sharks feed mainly on bony fishes, with cephalopods such as squid and octopus being the second-most important food group, and crustaceans such as crabs and lobsters making up the remainder. The larger sharks take a greater proportion of cephalopods.[20] These sharks hunt individually or in groups, and have been known to pin schools of fish against the outer walls of coral reefs for feeding.[14] Hunting groups of up to 700 grey reef sharks have been observed at Fakarava atoll in French Polynesia.[21][22] They excel at capturing fish swimming in the open, and they complement hunting whitetip reef sharks, which are more adept at capturing fish inside caves and crevices.[4] Their sense of smell is extremely acute, being capable of detecting one part tuna extract in 10 billion parts of sea water.[13] In the presence of a large quantity of food, grey reef sharks may be roused into a feeding frenzy; in one documented frenzy caused by an underwater explosion that killed several snappers, one of the sharks involved was attacked and consumed by the others.[23]
Despite its abundance in certain areas, the Caribbean reef shark is one of the least-studied large requiem sharks. They are believed to play a major role in shaping Caribbean reef communities. These sharks are more active at night, with no evidence of seasonal changes in activity or migration. Juveniles tend to remain in a localized area throughout the year, while adults range over a wider area.[7]
Grey reef sharks were the first shark species known to perform a threat display, a stereotypical behavior warning that it is prepared to attack.[3] The display involves 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. This species has been responsible for a number of attacks on humans, so should be treated with caution, especially if they begin to display. They are caught in many fisheries and are susceptible to local population depletion due to their low reproduction rate and limited dispersal. As a result, the International Union for Conservation of Nature has assessed this species as Near Threatened.
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The coloration is 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.[9] Individuals from the western Indian Ocean have a narrow, white margin at the tip of the first dorsal fin; this trait is usually absent from Pacific populations.[5] Grey reef sharks that spend time in shallow water eventually darken in color, due to tanning.[10] Most grey reef sharks are less than 1.9 m (6.2 ft) long.[4] The maximum reported length is 2.6 m (8.5 ft) and the maximum reported weight is 33.7 kg (74 lb).[9]
But another potential cause is that these sharks are skittish around people. So when too many people move into the area, the reef sharks flee to other coral reefs. Indeed, the researchers found far more sharks at small, isolated reefs than they expected. But this in itself is a danger to the reef sharks. With so many sharks concentrated in a small area, “if you really wanted to, you could fish out a few hundred sharks very easily,” said Friedlander.
They are also found in mangrove areas, moving in and out with the tide and even in fresh water near the sea. They occur singly or in small groups. Adults often aggregate in reef channels at low tide. This is one of the three most common reef sharks in the Indo-Pacific, the two others are the grey reef shark, Carcharhinus amblyrhynchos and whitetip reef shark, Triaenodon obesus.

My home in the coral reefs is being damaged by ocean acidification—which occurs when the ocean absorbs carbon and becomes acidified. I love living among thriving reefs, but increasing acidification degrades the physical structure of these reefs, putting my habitat and food supply at risk. This affects all the creatures living among the reef—not just my team of fellow blacktip reef sharks.
The coloration is 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.[9] Individuals from the western Indian Ocean have a narrow, white margin at the tip of the first dorsal fin; this trait is usually absent from Pacific populations.[5] Grey reef sharks that spend time in shallow water eventually darken in color, due to tanning.[10] Most grey reef sharks are less than 1.9 m (6.2 ft) long.[4] The maximum reported length is 2.6 m (8.5 ft) and the maximum reported weight is 33.7 kg (74 lb).[9]
They are also found in mangrove areas, moving in and out with the tide and even in fresh water near the sea. They occur singly or in small groups. Adults often aggregate in reef channels at low tide. This is one of the three most common reef sharks in the Indo-Pacific, the two others are the grey reef shark, Carcharhinus amblyrhynchos and whitetip reef shark, Triaenodon obesus.
Blacktip reef sharks are fast, pursuit predators that prefer reef fishes, but also feeds on stingrays, crabs, mantis shrimps and other crustaceans, cephalopods, and other mollusks. In the Maldives, this species has been documented feeding cooperatively on small schooling fishes, herding them against the shore and feeding en masse. Feeds heavily on sea snakes in northern Australia. A large individual (1.6 m) was observed attacking a green sea turtle, Chelonia mydas, in North Male’ Atoll, Maldives.
In California, Reef Check helps ensure the long-term sustainability and health of the nearshore rocky reefs and kelp forests. Reef Check California volunteers are divers, fishermen, kayakers, surfers, boaters, and a wide range of Californians who take a proactive role in making sure that our nearshore ecosystems are healthy and well managed. We monitor rocky reefs inside and outside of California's marine protected areas (MPAs). We work with marine managers, researchers and the public to provide the scientific data needed to make informed, science-based decisions for the sustainable management and conservation of California's ocean environment. We would love your support, volunteer today!

Are there so few reef sharks because of human activities such as fishing and finning, or were there never very many to start with? To answer this question, a team of marine biologists (which did not include Friedlander) decided to count reef sharks at coral reefs close and far to human settlements to better understand how humans impact their populations.
The International Union for Conservation of Nature (IUCN) has assessed the Caribbean reef shark as Near Threatened; its population has declined off Belize and Cuba from overfishing and exploitation continues in other regions. They are also threatened by the degradation and destruction of their coral reef habitat.[1] Commercial fishing for this species is prohibited in United States waters.[4] They are protected in the Bahamas due to their significance to ecotourism, as well as in a number of Marine Protected Areas (MPAs) off Brazil and elsewhere. However, enforcement against illegal fishing is lacking in some of these reserves, and many areas in which this species is abundant are not protected.[1]
A profitable ecotourism industry has arisen around this species involving organized "shark feeds", in which groups of reef sharks are attracted to divers using bait. Some US$6,000,000 is spent annually on shark viewing in the Bahamas, where at some sites a single living Caribbean reef shark has a value between US$13,000 and US$40,000 (compared to a one-time value of US$50–60 for a dead shark).[14] This practice has drawn controversy, as opponents argue that the sharks may learn to associate humans with food, increasing the chances of a shark attack, and that the removal of reef fishes for bait may damage the local ecosystem. Conversely, proponents maintain that shark feeds contribute to conservation by incentivizing the protection of sharks and educating people about them. Thus far, there has been little evidence that shark feeds have increased the risk of attack in the surrounding area.[8][15] Shark feeding has been outlawed off the coast of Florida, but continues at other locations in the Caribbean.[4]
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