One of the true nocturnal and attention-catching sharks inhabiting the reef depths is the Whitetip Reef Shark (Triaenodon obesus). This shark is a requiem shark species from the family Carcharhinidae. It is the only species in its genus Triaenodon.
The whitetip reef shark is a moderately sized shark, slender with a characteristic white-tipped dorsal and tail fins. Hence, the origin of its common name. This shark’s slim body helps it in navigating through caves and crevices, thus, extracting hidden prey.
Whitetip reef sharks are popular for resting on sandy bottoms and reef caves throughout the day. On the other hand, they spend their nights hunting for food. Most times they return to the same resting spot repeatedly for days, weeks, or even longer. The day’s resting usually involves many individuals piling on top of each other. Of course, they do not need to move to breathe.
There are many captivating features of this shark species worth learning about, hence, the essence of this page.
Naming and Scientific Classification
Apart from the whitetip reef shark, this species has other common names which include light-tip shark, blunthead shark, and whitetip shark. In the Fische des Rothen Meere (Fishes of the Ted sea) published in 1837, Eduard Rüppell a German naturalist first described this species as Carcharias obesus. The choice of the specific name obesus did not go without arousing concern, because this shark is actually slender.
Later the same year, Johannes Müller and Friedrich Henle formed an entirely new genus Triaenodon for this species. They coined the name from two Greek words triaena which means “trident” and odon which means “tooth”.
The lectotype of this species is a 12.2-inch (31cm) long specimen caught off Jeddah, Saudi Arabia in 1960. This is because Eduard Rüppell failed to originally designate a type specimen as a holotype.
Many authors recognize these sharks as belonging to the family Carcharhinidae. This recognition is based on morphological build-up, for instance, the possession of a full nictitating membrane, strong lower caudal fin lobe, well-developed precaudal pit, and scroll-like intestinal valves. However, this species once belonged to the family Triakidae.
Morphology and Phylogentic Relatives
Based on morphological and phylogenetic analysis, the whitetip reef shark is a close relative to the lemon shark (Negaprion brevirostris) and the sliteye shark (Loxodon). They occupy the intermediate position on the evolutionary tree of carcharhinids. This position is between the most basal genera and the most derived.
Habitat and Distribution Range
Whitetip reef sharks live mostly in coral reefs. They prefer to stay around coral heads and ledges having high vertical relief. Also, these sharks occur in lagoons, near deepwater drop-offs, and over sandy flats. They prefer a clear water habitat and usually swim very close to the bottom of the reef.
The whitetip reef shark is most common within depths of 26 to 131 feet (8 to 40 m). Sometimes, they swim up to water depth less than 3.3 feet (1m). Also, in an exceptional record, a whitetip reef shark was captured from a depth of 1,080 feet (330 m), in the Ryukyu Island.
The distribution of this species cuts across the Indian and Pacific Oceans. In the Indian Ocean, this shark occurs from northern KwaZulu-Natal South Africa to the Red Sea and the subcontinent of India, which includes Madagascar, Comoros, Mauritius, Sri Lanka, Seychelles, the Aldabra Group, and the Chagos Archipelago.
On the other hand, in the western and central Pacific, this shark occurs from off southern China, the Ryukyu Island, and Taiwan to the Philippines, Southeast Asia, and Indonesia. It also ranges toward northern Australia and found around several islands in Polynesia, Micronesia, and Melanesia ranging far to the north of Hawaii and to the southeast of the Pitcairn Islands.
In the eastern Pacific, the whitetip reef shark occurs from Costa Rica to Panama and off the Galápagos Islands.
Do Whitetip Reef Sharks Occur in the Atlantic Ocean?
For now, there is no record of whitetip reef sharks inhabiting the Atlantic Ocean. Though, this species was once thought to have existed in the Atlantic due to the fossil teeth dating to the Miocene epoch discovered in North Carolina. But, later research proved that this fossil belonged to a mackerel shark and not the whitetip shark.
Whitetip Reef Shark Description
The whitetip reef shark has a slim body, with a short and wide head. The face of this species is distinctive with a blunt and flattened snout, a tubular nasal flaps formed by large flaps of skin. They have small eyes with vertical pupils and pronounced ridges above. At times, a small notch follows the ridges.
The mouth of the whitetip reef shark shows a noticeable downward slant which gives it a disgruntled look. By the corners of the mouth are short furrows. This shark has in its upper jaws 42 to 50 tooth rows and in the lower jaw, it has 42 to 48 tooth rows. Each tooth has a single narrow cusp at the center with smooth edges, flanked by two smaller cusplets.
Like most sharks, this species has two dorsal fins. The position of the first dorsal fin is well back on the body, closer to the pelvic fin than the pectoral fins. Then, comes the second dorsal fin which is about half to three-quarter high as the first dorsal fin. There is no ridge existing between the first and second dorsal fins.
The anal fin is as large as the second dorsal fin. Originating slightly before the fifth gill slit level is the pectoral fins which are broad and triangular in shape. There is a strong notch near the tip of the upper lobe of the caudal fin, and the lower lobe is half the length of the upper lobe.
Covering the skin of whitetip reef sharks are small overlapping dermal denticles. Usually, they are with 7 horizontal ridges, thus making the skin have a smooth feel.
The whitetip reef shark has a predominantly greyish to brownish color on the backside. However, the underside is white. There is a pattern of small, scattered dark spots unique to each individual.
Then, on the tips of the first dorsal fin and the upper lobe of the caudal fin are bright white coloration. Sometimes, the tips of the second dorsal fin and the lower caudal-fin lobe also partake in the white coloration.
Size and Weight
Whitetip reef sharks are relatively small species of shark. Only a few specimens exceed 5.2 feet (1.6 m) in length. The maximum length of this species often adopted is 6.9 feet (2.1 m), but this is questionable since the figure from the onset bases on visual observation.
This shark has a maximum reported weight of 40 pounds (18.3 kg).
Typical Behavior of Whitetip Reef Sharks
The whitetip reef shark is a typical nocturnal shark that is most active at the night or in the slack tide. And, unlike other requiem sharks, these sharks can lie motionless on the bottom while actively pumping water over its gills for respiration. They spend most of their day resting singly within caves or in small groups piled atop one another or arranged in parallel.
These sharks may also shelter inside underwater lava tubes as observed off Hawaii. They also lie on sandy flats in the open as often seen off Costa Rica. Even while these species can lie still, they can also swim with strong undulations (wavelike motion) of their body.
Whitetip reef sharks rarely undertake long journeys. In fact, they prefer to remain within a highly localized area, only wandering for sometime when seeking out a new resting place. A study at Johnston Atoll discovered that of all the sharks examined, none traveled farther than 1.9 miles (3 km) away from their original capture location. The study period was up to one year.
To confirm the results, a second study that took place at Rangiroa Atoll in French Polynesia found that about 40% of the tagged individuals remained on the same reef of initial capture. This was after more than 3 years of the study. Thus, an individual may choose to rest within a particular cave and remain there for months to years.
Are Whitetip Reef Sharks Territorial?
Whitetip reef sharks are not territorial species. They tolerate the presence of others of their species within their home range. Unlike the grey reef shark (Carcharhinus amblyrhynchos), the whitetip reef shark does not perform threat displays.
During the daytime, their home range stays within a limited area of around 0.019 square miles (0.05 sq km). However, at night, this range expands to about 0.39 square miles (1 sq km).
Interaction with Other Reef Sharks
The whitetip reef shark along with the grey reef shark (Carcharhinus amblyrhynchos) and the blacktip reef shark (Carcharhinus melanopterus) are the three most common shark species inhabiting the reefs of the Indian and Pacific Oceans. These sharks’ habitat preferences tend to overlap. However, the whitetip reef shark, unlike the blacktip reef, does not frequent very shallow water, nor does it swim to the outer reef regularly as the grey reef shark.
Whitetip Reef Shark Predators
The popular predators of whitetip reef sharks include Galapagos sharks (Carcharhinus galapagensis) and tiger sharks (Galeocerdo cuvier). Others with records of preying on this species are silvertip shark (Carcharhinus albimarginatus) and giant grouper (Epinephelus lanceolatus). Though, the former inhabit greater depths than the whitetip reef shark and the latter is quite rare, thus not considered a significant predator of this species.
Parasites common with the whitetip reef shark are the copepod, Paralebion elongatus and the praniza which is the larvae of the isopod, Gnathia grandilaris.
The wrasse, Bodianus diplotaenia and the goby, Elacatinus puncticulatus when observed tends to clean these sharks as they are resting during the day. There is also an unusual report of the whitetip shark adopting a cleaning posture by leaving its mouth wide open and the gills flared, while amid a swarm of non-cleaning hyperiid amphipods.
Moving amphipods produces mechanical simulation which is thought to evoke the cleaning posture in the whitetip shark. Of course, the simulation of the amphipods is similar to actual cleaner organisms.
Whitetip reef sharks hunt mainly at night. This is the time many fishes are sleeping and easily taken. After it gets dark, these sharks come alive vigorously pursuing prey. They tend to hunt individually and in competition with others in the group. Multiple sharks may target the same prey blocking off escape from a particular coral head.
These sharks do not become more excited when feeding in groups, thus they are less likely thrown into feeding frenzy unlike the grey reef shark and the whitetip reef shark. This shark still feeds opportunistically while resting during the day, despite their nocturnal habit. They usually gather around reef drop-offs, off Borneo feeding on foods brought up by rising currents.
Individuals off Hawaii tends to follow Hawaiian monk seals (Monachus schauinslandi), attempting to steal their catches. The whitetip reef shark does not need to feed regularly as it can survive up to six weeks without feeding.
Choice of Food
The whitetip reef shark feeds mainly on bony fishes which include snappers, squirrelfishes, triggerfishes, damselfishes, goatfishes, eels, parrotfishes, and surgeonfishes. They also feed on crabs, octopuses, and spiny lobsters.
To track their prey, this shark species uses smell, sound, and detection of electrical signals given off by potential prey. The eyesight of this shark responds more to movement and contrast than to details of the object.
The whitetip reef shark is especially sensitive to low frequency sounds both natural and artificial. The sound range of 25 to 100 Hz brings to mind a struggling fish.
Mating and Reproduction
During mating, up to five males follow a female closely behind while biting her fins and body. They possibly get cues through pheromones produced by the female which indicates her readiness. Each male tries to get hold of one of her pectoral fins. At times, two males simultaneously seize a female on both sides.
Once the male (or males) successfully engages the female, they sink to the bottom where the male now rotates his claspers in an attempt to deposit sperm into the female through her vent. In many attempts, the female may reflect a choice of mate by pressing her belly against the bottom while arching her tail as a form of resistance on her part.
Because the male holds the female’s pectoral fin in his mouth, he has a limited time to achieve copulation. This is because he is not getting oxygen as he keeps holding the female. However, if the female is willing, the process is a lot easier. Thus, the pair settles side-by-side with their body inclined upward at an angle and their heads pressed against the bottom. Then, the male transfers the sperm successfully.
These sharks reach sexual maturity at a length of around 3.6 feet (1.1 m). They attain this size at the age of 8 to 9 years. Though, there are suggestions of regional variation in size of maturity. A record of a mature male whitetip reef shark at the length of just 37 inches (95 cm) exists. This individual was captured from the Maldives.
Gestation and Parturition
The whitetip reef shark just like other members of its family is viviparous. It sustains its developing embryo in a yolk sac which later transforms into a placental connection. The latter allows the mother to deliver nutrition directly until birth.
A mature female whitetip reef possesses two functional uteri and a single functional ovary on the left side. They have a biennial reproductive cycle.
Gestation lasts for about 10 to 13 months with the females giving birth to litters of 1 to 6 pups. However, the average number of pups is 2 – 3. The number of pups birthed by a female does not correlate to her size. On average, each female gives birth to 12 pups in her lifetime.
Parturition takes place at varying seasons in different regions. Thus, in French Polynesia, it occurs between autumn and winter from May to August, off Australia, it occurs in summer around October, and off Enewetak Atoll, it occurs in summer around July.
Females give birth to their young while swimming. They make violent twists and turns with their bodies as they try to deliver a pup. It generally takes less than an hour for a pup to fully emerge.
What is the Size of a Whitetip Reef Shark Pup at Birth?
The pups of whitetip reef sharks at birth measures around 20 to 24 inches (52 to 60 cm). At this time, the caudal fin tends to be longer when compared to body size than as adults.
Whitetip reef sharks develop quite slowly compared to other requiem sharks. They grow at an average rate of 6.3 inches (16 cm) per year as young sharks. However, as adults, they only achieve a growth rate of 0.8 to 1.6 inches (2 to 4 cm) per year.
Whitetip Reef Sharks’ Interaction with Humans
Attacks on Humans
The International Shark Attack File (ISAF) as of 2008 listed 2 provoked and 3 unprovoked attacks on humans linked to the whitetip reef shark. Though, this shark is less aggressive and harmless compared to its cousin inhabiting the ocean.
They tend to approach divers or swimmers closely to investigate. This proves their tendency to be curious and fearless. Whitetip reef sharks readily make bold attempts to steal catches from spearfishers. This behavior has resulted in the biting of several people.
In some regions, local whitetip reef sharks have learned to relate with the sound of a speargun discharge or a dropping anchor from a boat with food. As such, they respond in seconds on such sounds.
Importance to Humans
Whitetip reef sharks are well suitable for ecotourism diving. Divers can hand-feed these sharks with conditioning.
Fisheries off Sri Lanka, Pakistan, India, Madagascar, and possibly other regions it occurs take this shark species using gillnets, longlines, and trawls. The flesh and liver can serve as food. However, sharks from certain regions present a considerable risk of ciguatera poisoning. This points especially at the liver since it contains a much higher toxin concentration than the flesh.
Whitetip Reef Sharks Myth
In some Hawaiian tradition, whitetip reef sharks are considered ʻaumākua which means guardian spirits. They believe they are spirits of their family ancestors that took the animal form to protect the descendants.
The loyalty of whitetip reef sharks to a particular home range may have inspired this myth.
The increasing and unregulated fishing pressure in the tropics poses a great threat to the population of the whitetip reef shark. Though several conservation actions are being put in place to reduce human threats by fishing.
On the Great Barrier Reef, populations of this species in fishing zones have reached an 80% reduction relative to no-entry zone. Further, in no-take zones where boats can enter but fish prohibited, populations of these sharks show levels of reduction comparable to fishing zones as a result of poaching.
Demographic models suggested further conservation measures as these depleted species will continue to decline at a rate of 6.6 to 8.3% yearly if neglected.
The IUCN in their Red List of Threatened Species listed the Triaenodon obesus as “Near Threatened (NT)”. Their numbers dropped in recent decades due to increased fishing pressure, slow reproduction, restricted habitat, and low distribution.
Amazing Whitetip Reef Shark Facts at a Glance
1. Got Its Name from the White Coloration at the Tip of the First Dorsal and Caudal Fins
The first dorsal fin and the upper lobe of the caudal fin have bright white color at the tip. Thus, the origin of the name “whitetip reef shark”. Sometimes, the white markings extend to the second dorsal fin and the lower lobe of the caudal fin.
2. Ability to Lie Motionless on the Reef Bottom
While resting, these sharks lie motionless at the bottom and pumping water over their gills for respiration. Other requiem sharks are not capable of this process.
3. These Sharks are Nocturnal Species
Whitetip reef sharks are most active at night. They rest through the daytime and emerge to hunt at night. They take advantage of sleeping prey which is most vulnerable.
4. They Can Navigate Through Caves and Crevices Extracting Preys.
Preys hiding within caves and crevices are not safe from the whitetip reef shark. The slender body of these species helps them to navigate through while extracting them.
5. Remaining Faithful to a Chosen Home Range
Whitetip reef sharks always return to a preferred home range and continue with it for long. They do not travel far from the region they occupy in a reef.
6. Considered ʻAumākua (Guardian Spirits) in Some Hawaii Tradition
Some traditions of Hawaii see this shark as the spirit of their ancestors in animal form protecting the descendants.
7. The Face Appears Grumpy
This shark’s protruding bow ridges and down-turned mouth gives it a grumpy facial appearance.
8. Exhibition of Social Grouping
While resting during the day, these sharks usually lie in groups on the bottom. Either they position themselves in a parallel form or they stack on top of each other.
9. Whitetip Reef Sharks are Bold and Fearless
Apart from approaching divers, these sharks also steal catch from spearfishers and other fishes such as the Hawaiian monk seal.
10. They Engage in Violent Mating Ritual
The male shark tends to bite the female on the fins and body as he tries to make her submit for copulation.
- “Triaenodon obesus, Whitetip reef shark”, FishBase.
- “Discover Fishes: Whitetip reef shark (Triaenodon obesus)“, FloridaMuseumof Natural History Ichthyology Department.
- “Triaenodon obesus, Whitetip reef shark”, IUCN Red List of Threatened Species.
- “Whitetip Reef Shark”, Wikipedia (assessed 02 April, 2020).