Blacktip reef shark Image Source: National Oceanic and Atmospheric Administration (NOAA) ; Wikimedia Commons The presence of sharks in a reef is a sign of a healthy ecosystem. As top predators they help keep other carnivores from becoming too numerous and depleting herbivorous species. They also weed out sick and weak fish, leaving the fittest tor survive. This helps keep the reef diverse and vibrant.
Over 160 species of sharks inhabit the Great Barrier.Reef. For the most part they not dangerous predators of humans. While they can indeed be efficient killing machines, their targets are their traditional prey. The top apex predator at the Great Barrier Reef is — as is the case with many other large reefs — is the tiger shark. Tiger Sharks can reach lengths of five meters. Attacks involving them are rare, still I would’t turn my back to one. [Source: Great Barrier Reef.com]
The most common species of shark found in the Great Barrier Reef is the whitetip reef shark, a relatively passive shark that grows to a maximum length of two meters. Hammerhead sometimes show up. They can grow up to four meters in length and rarely attack swimmers although they do have a reputation for being aggressive. Great white sharks are generally not found at tropical reefs.
Whitetip reef sharks, grey reef shark and blacktip reef shark (all described in more detail below) often occupy reefs together along with other sharks and predators. Often each species occupies a particular niche and location within the reef system. Whitetip reef sharks live among the coral reefs, most commonly between the depths of eight and 40 meters (26 and 131 feet). Blacktip reef sharks are more likely to be found in shallow, high-energy coastal waters. The grey reef shark sticks to deeper clear waters off the reef edge.
Websites and Resources: Shark Foundation shark.swiss ; International Shark Attack Files, Florida Museum of Natural History, University of Florida floridamuseum.ufl.edu/shark-attacks ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems
Lemon Sharks and Nurse Sharks
Carribbean reef shark Lemon sharks (Scientific name: Negaprion brevirostris) are found mostly in tropical waters the eastern Pacific and the western and eastern Atlantic Oceans. Also known as galano and galano de ley, they are found around reefs and in shallow waters and can survive in brackish water in areas with low oxygen and feeds mainly on bony fishes, guitarfish and stingrays and may also eat crustaceans, mollusks and seabirds.
Nurse sharks(Scientific name: Ginglymostoma cirratum) are one of the most benign and sluggish shark species. Reaching a length of 4.3 meters (14 feet) and a weight of 150 kilograms (330 pounds), they spend much of their time cruising the bottom of the sea near the shore and searching through rocky crevices and caves for prey such as squid, crabs and lobsters. Their name comes from the powerful sucking sound made by their powerful throat muscle, small mouth and large pharynx which in the old days reminded some people who heard it of nursing children. They are also known as cat sharks. They source of the name nurse shark is a matter of debate.
Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas (sometimes of brackish or fresh water) and include such species as the bull shark, tiger shark, silky shark, dusky shark, spinner shark, blacknose shark, blacktip shark, blue shark, copper shark and oceanic whitetip shark. Among those found around coral reefs are thelemon shark, grey reef shark, blacktip reef shark and whitetip reef shark. ,
Many requiem sharks look similar and are difficult to tell apart. Grey reef sharks (Carcharhinus amblyrhynchos), for example, can be easily mistaken for similar species of requiem sharks. The blacktip shark (Carcharhinus limbatus) and the blacktip reef shark (Carcharhinus melanopterus) can be distinguised by a black tip on the dorsal fin, while the dorsal fin of C. amblyrhynchos is white or grey. Similarly, the silvertip shark (Carcharhinus albimarginatus) has white tips on its pectoral and caudal fins, while the grey reef shark does not. [Source: Animal Diversity Web (ADW)]
Requiem sharks are among the top five species involved in shark attacks on humans; however, due to the difficulty in identifying individual species, a degree of inaccuracy exists in attack records. Requiem sharks (Carcharhinus spp.) have accounted for 46 non-fatal attacks and 5 fatal attacks for of total of 51 attacks. [Source: International Shark Attack Files, Florida Museum of Natural History, 2023, Wikipedia]
According to International Shark Attack Files: Due to the similarity of small coastal species in this group in tooth shape, body size, and appearance, it is often difficult to assign a species in bite cases. Based on life history traits, ISAF suspects blacktip sharks (C. limbatus) account for the majority of these requiem bites in Florida. However, these cases lack enough evidence to be conclusive.
Grey Reef Sharks
Grey reef sharks (Scientific name:Carcharhinus amblyrhynchos) range across the Indian ocean, and the islands and atolls of Indonesia, the Philippines and the South Pacific. Attaining a length of six feet or more, these medium-size sharks prowl the reefs with "slow flicks of it black-edged tail." The longest known lifespan for a wild grey reef shark is 25 years. Their name is sometimes spelled gray reef shark. [Source: Bill Curtsinger, National Geographic January 1995]
Grey reef sharks are commonly seen by divers and snorkelers and usually present no problems they can be very aggressive. When an intruder such as a diver enters their territory, they often adopt an aggressive posture with their back arched, the pectoral fins lowered and snout raised, swimming from side to side in a "threat posture analogous to a rattlesnake.” Grey reef sharks have accounted for eight non-fatal unprovoked attacks and one fatal attack for of total of 9 attacks. [Source: International Shark Attack Files, Florida Museum of Natural History, 2023]
Grey reef shark are typically found at depths of zero to 280 meters (918.64 feet). They are widespread from the eastern Pacific Ocean (Costa Rica) through the western Pacific and Indian Oceans, and in the Red Sea. They are most commonly encountered off the islands of Tahiti, Micronesia, Fiji, Papua New Guinea, and Malaysia.[Source: Jessie Christel, Animal Diversity Web (ADW) /=]
Grey reef sharks are usually the top predators on coral reefs, controlling the fish populations under them. Their main known predators are larger sharks and orcas. The risk of predation for grey reef sharks decreases as they get older and bigger. Predation of grey reef sharks by silvertip sharks (Carcharhinus albimarginatus). has been observed in the Marshall Islands
Blacktip Reef Sharks
Blacktip reef sharks (Carcharhinus melanopterus) are the most commonly encountered shark in tropical waters in the the Pacific and Indian Oceans. They are found around reefs and in shallow waters. Their dorsal and tail fins often project above the water and have black tips, hence its name. Blacktip reef sharks are regarded as inquisitive but not dangerous. They occasionally bite divers, surfers and waders, seemingly accidently, as they chase schools of bait fish near the shore but are generally not aggressive. Blacktip reef sharks have accounted for 14 non-fatal unprovoked attacks and zero fatal attacks on humans, according to the International Shark Attack Files, Florida Museum of Natural History, between 1876 and 2023.
blacktip reef shark
Blacktip reef sharks reach lengths of two meters (six feet) and weight of about 45 kilograms. (100 pounds). They give birth to live young, have streamlined bodies and are excellent and powerful swimmers. Blacktip sharks are "gregarious creatures that travel in large groups and somersaults out of the water during feeding frenzies." Within their genus,, blacktip reef shark and sand tiger shark females illustrate their readiness to mate by reducing their speed and swimming with their tails in a more upward position and their snout pointing slightly down. The male will then come up to the female and place its snout below the female’s vent.
Studies of black tips indicates they head to warmer waters in the winter but return to their nursery ground when the weather warms. Research indicates they have a very sophisticated navigation system that allows them to migrate to certain points in the ocean at specific times. In waters off Aldabra Atoll in the Seychelles, blacktip reef sharks position themselves in water only a few centimeters deep and wait for the tide to refill the lagoon. According to National Geographic: With their bellies touching the sand, they point their snouts into the current to keep water flowing over their gills.
Whitetip Reef Sharks
Whitetip reef sharks (Scientific name: Triaenodon obesus) are found mostly in tropical waters in the Indo-Pacific region. Their dorsal and upper tail fins have distinctive white tips, hence their name. Also known a bluntheads and white-tipped shark, they reach a length of 2.1 meters and a weight of about 20 kilograms. They are slender and give birth to live young. Unlike most sharks which need to swim continuously to keep oxygen flowing through their gills, whitetip reef sharks can pump water across their gills and thus rest on the ocean floor.
Whitetip reef sharks were originally described by Eduard Ruppell in 1837. They have been around a long time. Fossils of them have been found in North Carolina from the Miocene Period (23 million to 5.3 million years ago) indicating that the shark existed in the Atlantic Ocean several million years ago; though they are not found there now. Their lifespan in the wild is estimated to be up to 25 years. The most dangerous predator of the whitetip reef shark is humans but they can be preyed upon by large sharks, such as the tiger shark and silvertip shark.[Source: Andrew Feldkamp, Animal Diversity Web (ADW)]
Whitetip reef shark are important predators in reef ecosystems. They use coral reefs as a habitat, as well as a source for food. Their predation of fishes may serve as a sort of population control. This is particularly important in those fishes, such as the parrotfish, that consume the coral. /=\ However the whitetip reef shark does occasionally have a negative effect on the coral, damaging iti n their aggressive pursuit of prey fish. The whitetip reef shark also serves as host to small cleaner fish such as gobies or striped cleaner wrasses who feed on the parasites infesting the shark.
Whitetip reef sharks live in tropical, saltwater, and/or marine environments and they are found in reefs, coastal areas and on or near the sea bottom as well as in caves at depths of one to 330 meters (3.28 to 1082.68 feet) at an average depth of 8-40 meters (26-131 feet). Found in both the Indian and Pacific oceans, they have been spotted as far west as the coasts of South Africa and Sri Lanka in the Indian Ocean and have been observed as far east as the coasts of Costa Rica and Panama in the Pacific Ocean. They are most numerous around Indo-Pacific islands and along the southern coast of the Indian sub-continent.
Whitetip Reef Shark Characteristics and Behavior
Whitetip reef shark Whitetip reef sharks reach lengths of 213 centimeters (84 inches), with their average length being 165 centimeters (65 inches). They reach weights of 27.7 kilograms (61 pounds), with their average weight being 20 kilograms (44 pounds). Males are larger than females. [Source: Andrew Feldkamp, Animal Diversity Web (ADW)]
The whitetip reef sharks are grey in color with a white belly and characteristic white tips on its first dorsal, upper caudal and occasionally the pelvic fins. According to Animal Diversity: The snout is short and broad with a mouth full of smooth edged teeth on both jaws. Both the mouth and nostrils are located on the underside of the head. The skin is very tough and the lateral fins are highly flexible. Both of these characteristics allow them to exist more easily among the rough and jagged edges of a coral reef. A diagnostic feature that distinguishes Whitetip reef sharks from the similar silvertip and oceanic whitetip sharks is the second dorsal fin. In the whitetip reef shark it is significantly larger in comparison to the other species.
Whitetip reef shark are nocturnal (mainly active at night), occasionally motile (move around as opposed to being stationary) and occasionally sedentary (remain in the same area). Their average territory size is two square kilometers. They are considered docile and non-aggressive. Being nocturnal, they spend much of the day in caves and deep crevices in coral reefs and coral reef lagoons.
Whitetip reef sharks have the ability to pump water across their gills without moving forward, so they can sit motionless on the sea floor. However the shark prefers the safety and seclusion of caves when they are hunting and return to the same cave day after day for several months. Whitetip reef sharks remain in a relatively small area throughout their life. The longest recorded travel over the coarse of a year by an individual was three kilometers. The whitetip reef shark is non-territorial. It sharing its range with other whitetip reef sharks and sharks of other species.
Whitetip reef sharks communicate with vision, touch and chemicals usually detected by smelling and sense using vision, touch, sound, chemicals detected by smelling and electric signals. /=\ As with most sharks the main form of perception is visual. Their eyes are large and oval in shape. They share caves, and occasionally hunt together, however how they communicate is not well understood. Tactile communication — the male biting the fins of the female — is employed during mating.
Whitetip Reef Shark Food and Eating Behavior
According to Animal Diversity Web: Despite the docile nature of this shark during the day, during feeding at night they become very aggressive. It will thrash through coral reefs looking for food. The whitetip reef shark usually hunts alone but will work with other sharks to pursue prey throughout the coral reefs. Sometimes in pursuit of a fish, the shark will wedge the front half of its body into a crack or crevice on the reef and stay there until it catches the fish. [Source: Andrew Feldkamp, Animal Diversity Web (ADW)]
The whitetip reef shark is considered clumsy and slow in open water, however it is still considered a pelagic (living in the open ocean, far from land) predator. It is capable of catching fish in coral reefs because of its maneuverability. Despite its ability to catch fish, it specializes in bottom feeding. Its ventrally located mouth is ideal for picking crab, lobster and octopi off the sea floor, but its primary source of food is several types of boney fishes including but not restricted to damselfish, parrotfish, surgeonfish, goatfish, triggerfish, squirrelfish and eels
The large eyes are particularly useful to the whitetip because it is a nocturnal animal that does most of its hunting and traveling at night. Like other sharks, they have very strong chemosensory systems as well. This is most useful to the whitetip reef sharks in hunting and eating. Whitetip reef sharks respond to sounds in the water. They are believed to be attracted to the sounds of spearfishing in the water. Like other sharks, this species also has electroreceptive abilities to help them detect prey.
Whitetip Reef Shark Mating, Reproduction and Offspring
Whitetip reef sharks are viviparous (they give birth to live young that developed in the body of the mother) and iteroparous (offspring are produced in groups such as litters). They engage in internal reproduction in which sperm from the male fertilizes the egg within the female and engage in seasonal breeding but there is not enough evidence to indicate how often this species breeds. Fertilization occurs seasonally in autumn and winter. This is between May and August in the Southern Hemisphere. The number of offspring ranges from one to five, with the average number of offspring being two to three young each measuring about 60 centimeters (two feet) each. . The average gestation period is five months. On average males and females reach sexual or reproductive maturity at age five years. [Source: Andrew Feldkamp, Animal Diversity Web (ADW)]
According to Animal Diversity Web: Male whitetip reef sharks have been known to school in groups of nearly a hundred in pursuit of a female ready to mate. The sharks orient themselves parallel to each other and at about a 45 degree angle to the water column during copulation. They position themselves with their snouts in the sea floor, maintaining this vertical position with occasional simultaneous undulations of their bodies. The male then bites the pectoral fin of the female and inserts his clasper into the cloaca. This ritual of biting the female’s pectoral fin to hold position is common to several species.
During the pre-birth stage provisioning and protecting is done by females. While in the embryo stage, the juvenile receives all its nutrients from the mother via a yolk sac placenta. When the female has a a litter of shark pups insider her, she slower and less maneuverable and thus more vulnerable to attacks by predators. Juveniles are born alive and fully functional. Resembling mini-versions of adults, they are completely independent and capable of surviving on their own. They grow relatively slowly and reach sexual maturity at around age five.
Whitetip Reef Sharks and Humans
Whitetip reef sharks are regarded as not dangerous, passive and calm — easily approachable by divers. They are only a problem to humans if provoked and may attack in defense if they are cornered and escape is not possible. The sharks are attracted by boat engines, presumably by an opportunity for a free meal, often show up when fish are speared, and occasionally bite divers in struggles over possession of speared fish. It has been suggested that the sound of spear fishing arouses these sharks to leave their cave and pursue the speared fish. In April 2001, a surfer was bitten on the left hand by a small white-tip reef shark in 10-foot waters off Ewa Beach in Hawaii Whitetip reef sharks have accounted for five non-fatal unprovoked attacks and zero fatal attacks according to International Shark Attack Files.
White tips have been overfished. Many have been harvested for their fins. Although there are reports that their body parts, particularly the liver, may be toxic, the flesh of these sharks is sometimes eaten for food. The International Union for Conservation of Nature (IUCN) Red List: lists whitetip sharks as “Near Threatened.” They have no special status according to the Convention on the International Trade in Endangered Species (CITES). The shark currently have a wide tropical distribution however their slow rate of reproduction makes them vulnerable to overfishing.
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated March 2023