Details - Maldives Bio Diversity

Whitetip reef shark's description

Whitetip reef shark is a relatively small species, few whitetip reef sharks are longer than 1.6 m (5.2 ft). The maximum length this species attains is often given as 2.1 m (6.9 ft), though this was originally based on visual observations and may be dubious. The maximum reported weight is 18.3 kg (40 lb). The whitetip reef shark has a slim body and a short, broad head. 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. The mouth has a distinct downward slant (imparting a disgruntled expression to the shark), 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. 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. The lower lobe of the caudal fin is half the length of the upper, which has a strong notch near the tip. The dermal denticles are small and overlapping, usually with 7 horizontal ridges, giving the skin a smooth feel. The coloration is grayish to brownish above and white below, with a pattern of scattered small, dark spots unique to each individual. 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.

Whitetip reef shark's facts

The Whitetip Reef Shark is also known as the Triaenodon Obesus. Along with the Blacktip Reef Shark and Gray Reef Shark, it is one of the most frequent sharks in the Indo-Pacific. This species is easily spotted due to its curious, irregular, and waving swimming style and of course, the white tip on its dorsal fin.

Whitetip reef shark's Behavior & Ecology

The whitetip reef shark is one of the three most common sharks inhabiting the reefs of the Indo-Pacific, the other two being the blacktip reef shark (Carcharhinus melanopterus) and the grey reef shark (Carcharhinus amblyrhynchos). The habitat preferences of this species overlap those of the other two, though it does not tend to frequent very shallow water like the blacktip reef shark, nor the outer reef like the grey reef shark. The whitetip reef shark swims with strong undulations of its body, and unlike 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. These sharks may be found sheltering inside underwater lava tubes, and can be seen lying in the open on sandy flats. Whitetip reef sharks generally remain within a highly localized area, only rarely do they undertake long movements, wandering for a while before settling down somewhere new. An individual shark may rest inside the same cave for months to years. The daytime home range of a whitetip reef shark is limited to approximately 0.05 km2 (0.019 sq mi); at night this range increases to 1 km2 (0.39 sq mi). These sharks are not territorial and share their home ranges with others of their species; they do not perform threat displays. Important predators of the whitetip reef shark include tiger sharks (Galeocerdo cuvier), Galapagos sharks (Carcharhinus galapagensis), and possibly also silvertip sharks (Carcharhinus albimarginatus), though they usually occur at depths greater than those favored by whitetip reef sharks. An 80 cm (31 in) long whitetip reef shark has also been found in the stomach of a giant grouper (Epinephelus lanceolatus), though these groupers are unlikely to be significant predators of this species due to their rarity. Known parasites of the whitetip reef shark include the copepod Paralebion elongatus and the praniza (parasitic) larvae of the isopod Gnathia grandilaris. While resting during the day, these sharks have been observed being cleaned by the wrasse Bodianus diplotaenia and the goby Elacatinus puncticulatus. Unusually, there is also a report of seven whitetip reef sharks adopting a cleaning posture (mouth agape and gills flared) in the midst of a swarm of non-cleaning hyperiid amphipods; the mechanical stimulation from the moving amphipods are thought to have evoked this behavior through their similarity to actual cleaner organisms.

Whitetip reef shark's Feeding

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. This species feeds mainly on bony fishes, including eels, squirrelfishes, snappers, damselfishes, parrotfishes, surgeonfishes, triggerfishes and goatfishes, as well as octopuses, spiny lobsters, and crabs. 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 sharks hunt primarily at night, when many fishes are asleep and easily taken. After dusk, groups of sharks methodically scour the reef, often breaking off pieces of coral in their vigorous pursuit of prey. Multiple sharks may target the same prey item, covering every exit route from a particular coral head. Each shark hunts for itself and in competition with the others in its group. Unlike blacktip reef sharks and grey reef sharks, whitetip reef sharks do not become more excited when feeding in groups and are unlikely to be stirred into a feeding frenzy. Despite their nocturnal habits, whitetip reef sharks will hunt opportunistically in daytime. It is known that this species gathers around reef drop-offs to feed on food brought up by the rising current, and this spices do attempt to steal others catches. A whitetip reef shark can survive for six weeks without food.

Whitetip reef shark's Reproduction

Like other members of shark family, the whitetip reef shark is viviparous; once the developing embryos exhaust their supply of yolk, the yolk sac is converted into a placental connection through which the mother delivers nourishment for the remainder of gestation. Mature females have a single functional ovary, on the left side, and two functional uteruses. The reproductive cycle is biennial. 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. Each male attempts to seize the female by engulfing one of her pectoral fins; at times two males might grasp a female on both sides simultaneously. Once engaged, the sharks sink to the bottom, whereupon the male (or males) rotates one of his claspers forward, inflates the associated siphon sac (a subcutaneous abdominal organ that takes in seawater that is used to flush sperm into the female), and attempts to make contact with the female's vent. 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. The male has a limited time in which to achieve copulation, as while he is holding the female's pectoral fin in his mouth he is being deprived of oxygen. On the other hand, if the female is willing, the pair settles side-by-side with their heads pressed against the bottom and their bodies at an upward angle. After a gestation period of 10–13 months, females give birth to litters of 1–6 (usually 2–3) pups. The number of offspring is not correlated with female size; each female produces an estimated average of 12 pups over her entire lifetime. Parturition occurs in Maldives from May to August (autumn and winter) in French Polynesia, in July (summer) off Enewetak Atoll, and in October (summer) 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 52–60 cm (20–24 in) long and have relatively longer caudal fins than adults. This shark develops slowly compared to other requiem sharks; newborns grow at a rate of 16 cm (6.3 in) per year while adults grow as a rate of 2–4 cm (0.79–1.57 in) per year. Sexual maturity is reached at a length of around 1.1 m (3.6 ft) and an age of 8–9 years, though mature males as small as 95 cm (37 in) long have been recorded from the Maldives, suggesting regional variation in maturation size. 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. In 2008, a whitetip reef shark produced a single pup through possibly asexual means at the Nyiregyhaza Centre in Hungary; previous instances of asexual reproduction in sharks have been reported in the bonnethead (Sphyrna tiburo) and the blacktip shark (Carcharhinus limbatus).

Whitetip reef shark's Conservation

Whitetip reef shark and other shark species are protected in the Maldives, there is a huge fine to anyone who catch or do any harm to this species.

Whitetip reef shark's Relationship with Humans

Unlike its Oceanic cousin, the white tip reef shark is more harmless and is seldom aggressive unless provoked. They are also fearless and curious, as the whitetip reef sharks may approach swimmers closely to investigate. However, these sharks readily attempt, and quite boldly, to steal catches from spear fishers, which has resulted in several people being bitten in the process. In some places, local whitetip reef sharks have learned to associate the sound of a speargun discharge or a boat dropping anchor with food and respond within seconds. As of 2008, the International Shark Attack File lists two provoked and three unprovoked attacks to this species but there is NO RECORD IN MALDIVES. Whitetip reef sharks are well-suited to ecotourism diving, and with conditioning they can be hand-fed by divers. In past, Maldivian fishermans use to catch the whitetip reef shark using longlines, gillnets, and trawls. The meat was eaten and liver used to make oil. Fins were sold and exported from maldives. The International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened, as its numbers have dropped in recent decades due to increasing, and thus far unregulated, fishing pressure in the tropics. Its restricted habitat, low dispersal, and slow reproduction are factors that limit this shark's capacity for recovering from overfishing. On the Great Barrier Reef, populations of whitetip reef sharks in fishing zones have been reduced by 80% relative to no-entry zones. Furthermore, populations in no-take zones, where boats are allowed but fishing prohibited, exhibit levels of depletion comparable to fishing zones due to poaching. Demographic models indicate that these depleted populations will continue to decline by 6.6–8.3% per year without additional conservation measures.

Whitetip reef shark habitat

The Whitetip Reef Shark is demersal on the continental shelves and around oceanic islands and reefs at depths of 0–330 m (Randall 1977). It is closely associated with coral reefs in clear tropical waters (Compagno 1984). It reaches a maximum size of 200 cm total length (TL) but adults are very rare over 160 cm. Size-at-maturity is about 105 cm TL (Randall 1977). Reproduction is viviparous with yolk-sac placenta, small litters of 1–5 (Last and Stevens 2009), an annual reproductive cycle, and a size-at-birth of 52–60 cm TL. Growth is slow in the wild, estimated at 2.1–4.2 cm year^-1 (Randall 1977), and they may attain sexual maturity at eight to nine years and live to about 16 years (Randall 1977, Smith et al. 1998). Generation length is estimated to be 12.3 years (Randall 1977).

Coral Reef

Whitetip reef shark threats

The Whitetip Reef Shark is caught throughout its range in industrial and small-scale longline, gillnet, trawl and handline fisheries that occur in the waters around coral reefs. Most is taken as incidental catch in general reef fisheries targeting teleost fishes. The species is often retained for its meat, fins, and liver. The species is also taken in small amounts by recreational fishers in some countries. In many parts of east Africa, and south and east Asian, there are large amounts of fishing effort targeted at carcharhinid sharks in continental shelf waters, and it continues to increase. For example, in the waters of Indonesia effort by small-scale fisheries has tripled when taking population into account (Ramenzoni 2017); and in Myanmar the International Labour Organisation (2015) estimated the number of vessels participating in the small scale inshore fishery to be about 26,000 in 2013, and the number of locally operated larger offshore vessels numbered 2,846 in 2013, having increased nearly 30% since 2009. Only in locations where fisheries are strictly regulated (e.g. Australia) (Espinoza et al. 2014), where human population densities are low (Nadon et al. 2009), or where dive-based tourism supports protection (Sutcliffe and Barnes 2018) are there low levels of threat that enable this species to remain common.

The reliance of this species on coral reefs makes it susceptible to declines in habitat quality. Global climate change has already resulted in large-scale coral bleaching events with increasing frequency causing worldwide reef degradation since 1997. Almost all warm-water coral reefs are projected to suffer significant losses of area and local extinctions, even if global warming is limited to 1.5ºC (IPCC Report, 2019). Destructive fishing practices in some nations (e.g. dynamite fishing) (McManus 1997) and declining water quality (MacNeil et al. 2019) have also led to the decline in coral reef habitat.