whitetip reef shark
Still and cave dwelling by day, highly active and aggressive hunting the reef at night
The Whitetip Reef shark (Triaenodon obesus) is a species of requiem shark, in the family Carcharhinidae, and the only member of its genus. It is a small shark that behaves very different in the day than at night. It is easily recognizable by its white tips on its fins.
Family: Carcharhinidae – Requiem sharks
Common Name– Ground Sharks
Common Name– Requiem Sharks
Status: IUCN Red List NEAR THREATENED
Average Size and Length: Whitetip Reef shark rarely exceed 5.2 feet. One account report that possibly they could reach 6.9 feet, however this is doubtful.
Average Weight: The maximum recorded weight is 40 pounds.
Teeth and Jaw: The mouth has a distinct downward slant with short furrows at the corners. There are 42–50 tooth rows in the upper jaw and 42–48 tooth rows in the lower jaw. Each tooth has a single narrow, smooth-edged cusp at the center, flanked by a pair of much smaller cusplets.
Head: The head is short and broad. The snout is flattened and blunt, with large flaps of skin in front of the nares that are furled into tubes. The eyes are small and oval with vertical pupils and prominent ridges above and are often followed by a small notch.
Denticles: The dermal denticles are small and overlapping, usually with 7 horizontal ridges, giving the skin a smooth feel.
Tail: The lower lobe of the caudal fin is half the length of the upper, which has a strong notch near the tip.
Demographic, Distribution, Habitat, Environment and Range: The Whitetip Reef shark is distributed widely across the entire Indo-Pacific region. In the Indian Ocean, it can be found from northern KwaZulu-Natal, South Africa to the Red Sea and the Indian subcontinent, including Madagascar, Mauritius, the Comoros, the Aldabra Group, the Seychelles, Sri Lanka, and the Chagos Archipelago. In the western and central Pacific, it can be found from off southern China, Taiwan, and the Ryukyu Islands, to the Philippines, Southeast Asia, and Indonesia, to northern Australia, and is also found around numerous islands in Melanesia, Micronesia, and Polynesia, as far as Hawaii to the north and the Pitcairn Islands to the southeast. In the eastern Pacific, it occurs from Costa Rica to Panama, and off the Galápagos Islands.
Whitetip Reef sharks are most often encountered exclusively in coral reef habitats. They are found around coral heads and ledges with high vertical relief, and additionally over sandy flats, in lagoons, and near drop-offs to deeper water. They prefer very clear water and rarely swim far from the bottom. They typically stay at a depth of 26–131 feet. On occasion, they may enter water less than 4 feet deep. There is one record of a Whitetip Reef shark being captured from a depth of 1,080 feet in the Ryukyu Islands.
Whitetip Reef sharks tend to stay in highly localized areas. Only rarely do they take on long movements. The daytime home range of a Whitetip Reef shark is limited to approximately 0.019 square miles; at night this range increases to 0.39 square miles.
Diet: Whitetip Reef sharks mainly eat bony fishes like, eels, squirrelfishes, snappers, damselfishes, parrotfishes, surgeonfishes, triggerfishes and goatfishes, as well as octopuses, spiny lobsters, and crabs.
With its slender, lithe body, the whitetip reef shark specializes in wriggling into narrow crevices and holes in the reef and extracting prey inaccessible to other reef sharks. Alternatively, it is rather clumsy when attempting to take food suspended in open water.
A Whitetip Reef shark can survive 6 weeks without food.
The Whitetip Reef shark is preyed on by larger sharks like the Galapagos shark. In addition, some accounts suggest that Goliath Groupers may eat them on occasion. A much smaller Whitetip Reef shark was found in the stomach contents of one.
Aesthetic Identification: The Whitetip Reef shark has a very slim body. The coloration is grayish to brownish above and counter-shaded white below, with a pattern of scattered small, dark spots unique to each shark. Most recognizable, the tips of the first dorsal fin and upper caudal fin lobe, and sometimes also the second dorsal fin and lower caudal fin lobe, are bright white.
The first dorsal fin is positioned well back on the body, closer to the pelvic than the pectoral fins. The second dorsal and anal fins are large, about half to three-quarters as high as the first dorsal fin. The broad, triangular pectoral fins originate at or slightly before the level of the fifth gill slit. There is no ridge between the first and second dorsal fins.
Biology and Reproduction: Known parasites of the whitetip reef shark include the copepod Paralebion elongatus and the praniza larvae of the isopod Gnathia grandilaris.
While resting during the day, they have been observed being cleaned by the wrasse and goby. They gape their mouths, and flair their gills while the fish clean. In addition, a non-cleaning hyperiid amphipods have been observed cleaning them too.
The Whitetip Reef shark is viviparous. They have a biennial reproductive cycle.
Mating is initiated when up to five males follow closely behind a female and bite at her fins and body, possibly cued by pheromones indicating the female’s readiness. Sometimes, two males at a time, one on each side biting her fins. Once engaged, the sharks sink to the bottom. In many cases, the female resists by pressing her belly against the bottom and arching her tail; this may reflect mate choice on her part.
Gestation is between 10 and 13 months. Females give birth to 1 to 6 pups, but usually litters of 2 to 3 pups. It is estimated that females have an average of 12 pups over their entire lifespan. The number of litters is not associated to the size of the female.
Parturition occurs from May to August in French Polynesia, in July off Enewetak Atoll, and in October off Australia. Females give birth while swimming, making violent twists and turns of their bodies; each pup takes under an hour to fully emerge.
The newborns measure between 20–24 inches long and have relatively longer caudal fins than adults. They develop slowly in comparison to other species. Sexual maturity is reached at a length of around 3.6 feet and an age of 8–9 years.
On the Great Barrier Reef, males live to 14 years and females to 19 years; the maximum lifespan of this shark may be upwards of 25 years.
Research suggests they could possibly reproduce asexually.
Behavioral Traits, Sensing and Intelligence: The Whitetip Reef shark swims with strong undulations of its body, and unlike most other requiem sharks can lie motionless on the bottom and actively pump water over its gills for respiration. This species is most active at night or during slack tide and spends much of the day resting inside caves singly or in small groups, arranged in parallel or stacked atop one another. An individual shark may rest inside the same cave for months to years. Off Hawaii, they may be found sheltering inside underwater lava tubes, while off Costa Rica they are often seen lying in the open on sandy flats.
At night while hunting and active, they tend to be found in groups hunting competitively and aggressively search out prey. Whitetip Reef sharks hunt primarily at night because many fishes are asleep and easily taken. After dusk, groups of sharks systematically scour the reef, often breaking off pieces of coral in their energetic pursuit of prey. Multiple sharks may target the same fish, covering every exit route from a coral head. Each shark hunts for itself and in competition with the others in its group. They do not engage in feeding frenzies. Despite their nocturnal habits, Whitetip Reef sharks will hunt opportunistically in daytime.
Whitetip Reef sharks are not territorial and share their home ranges with others of their species; they do not perform threat displays.
The Whitetip Reef shark is highly responsive to the olfactory, acoustic, and electrical cues given off by potential prey, while its visual system is attuned more to movement and/or contrast than to object details. It is especially sensitive to natural and artificial low-frequency sounds in the 25–100 Hz range, which evoke struggling fish.
Whitetip Reef Shark Future and Conservation: The Whitetip Reef shark is taken by fisheries longlines, gillnets, and trawls. The meat and liver are eaten, though sharks from certain areas present a substantial risk of ciguatera poisoning, especially the liver, which contains a much higher concentration of the toxin than the meat.
Whitetip Reef Shark Recorded Attacks on Humans: They are relatively harmless unless provoked. ISAF lists 2 unprovoked attacks. Spear fisherman are more at risk.