Social aggregation is well documented in grey reef sharks. In the northwestern Hawaiian Islands, large numbers of pregnant adult females have been observed slowly swimming in circles in shallow water, occasionally exposing their dorsal fins or backs. These groups last from 11:00 to 15:00, corresponding to peak daylight hours. Similarly, at Sand Island off Johnston Atoll, females 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 09:00, reaching a peak in numbers during the hottest part of the day in the afternoon, and dispersing by 19:00. Individual sharks return to the aggregation site every one to six days. These female sharks are speculated to be taking advantage of the warmer water to speed their growth or that of their embryos. The shallow waters may also enable them to avoid unwanted attention by males.
The grey reef shark has a streamlined, moderately stout body with a long, blunt snout and large, round eyes. The upper and lower jaws each have 13 or 14 teeth (usually 14 in the upper and 13 in the lower). The upper teeth are triangular with slanted cusps, while the bottom teeth have narrower, erect cusps. The tooth serrations are larger in the upper jaw than in the lower. 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 (sickle-shaped).
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.
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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. Commercial fishing for this species is prohibited in United States waters. 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.
WWF works to preserve the coral habitats where reef sharks live through the creation and improved management of marine protected areas, elaboration of fisheries management plans, and the introduction of fishing bans to protect vulnerable species including reef sharks. WWF also promoted the understanding that communities can derive more economic value from reef sharks through tourism than through their capture. We support local communities to set up appropriate ecotourism systems and infrastructure to ensure well-managed and sustainable shark tourism operations.
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.
Most observed displays by grey reef sharks have been in response to a diver (or submersible) approaching and following it from a few meters behind and above. They also perform the display towards moray eels, and in one instance towards a much larger great hammerhead (which subsequently withdrew). However, they have never been seen performing threat displays towards each other. This suggests the display is primarily a response to potential threats (i.e. predators) rather than competitors. As grey reef sharks are not territorial, they are speculated to be defending a critical volume of "personal space" around themselves. Compared to sharks from French Polynesia or Micronesia, grey reef sharks from the Indian Ocean and western Pacific are not as aggressive and less given to displaying.
Sandbar shark (C. plumbeus): The sandbar shark has a snout that is shorter than the width of its mouth and a large first dorsal fin originating over the axis of the pectoral fin (the Caribbean reef shark’s first dorsal fin is further from the head than the sandbar shark). Unlike the Caribbean reef shark, the sandbar shark has widely spaced non-overlapping dermal denticles that lack defined teeth on their free edges.
The Caribbean reef shark infrequently attacks humans. In general, a shark attack on a human is behaviorally similar to an attack upon natural prey. A human is more susceptible to being attacked if the shark is cornered and feels that there is no escape route. In situations like these, the shark may rake the victim during the attack resulting in lacerations.
This sturdy shark is abundant in the Caribbean, and because of its average features, is often confused with other requiem sharks. Usually growing 6.5 to 10 feet long, these are the apex predator of their food web. They have been found ‘sleeping’ in caves and on the ocean floor, behavior that is still unexplained. There has been concern over eating these sharks because of the build-up of toxins in their flesh, but now they are valued for tourism more than food, which brings its own safety issues.
The grey reef shark (Carcharhinus amblyrhynchos, sometimes misspelled amblyrhynchus or amblyrhinchos) is a species of requiem shark, in the family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as far east as Easter Island and as far west as South Africa. This species is most often seen in shallow water near the drop-offs of coral reefs. The grey reef shark has the typical "reef shark" shape, with a broad, round snout and large eyes. This species can be distinguished from similar species by the plain or white-tipped first dorsal fin, the dark tips on the other fins, the broad, black rear margin on the tail fin, and the lack of a ridge between the dorsal fins. Most individuals are less than 1.9 m (6.2 ft) long.
Reef Ambassadors are forever just passing through, crossing borders, taking in cultures, and exploring foreign shores. And now you can follow our ambassadors more closely, as we roll out a new monthly film series for 2016, showcasing their adventures in the best waves around the globe. This 10 Episode series will bring you along with our team to far off, exotic locales to iconic surf destinations.