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Source: science.direct.com

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Summary

Marine ecosystems are suffering severe depletion of apex predators worldwide 1, 2, 3, 4; shark declines are principally due to conservative life-histories and fisheries overexploitation 5, 6, 7, 8. On coral reefs, sharks are strongly interacting apex predators and play a key role in maintaining healthy reef ecosystems 9, 10, 11. Despite increasing fishing pressure, reef shark catches are rarely subject to specific limits, with management approaches typically depending upon no-take marine reserves to maintain populations 12, 13, 14. Here, we reveal that this approach is failing by documenting an ongoing collapse in two of the most abundant reef shark species on the Great Barrier Reef (Australia). We find an order of magnitude fewer sharks on fished reefs compared to no-entry management zones that encompass only 1% of reefs. No-take zones, which are more difficult to enforce than no-entry zones, offer almost no protection for shark populations. Population viability models of whitetip and gray reef sharks project ongoing steep declines in abundance of 7% and 17% per annum, respectively. These findings indicate that current management of no-take areas is inadequate for protecting reef sharks, even in one of the world's most-well-managed reef ecosystems. Further steps are urgently required for protecting this critical functional group from ecological extinction.

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Ongoing Collapse of Coral-Reef Shark Populations

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Marine ecosystems are suffering severe depletion of apex predators worldwide 1, 2, 3, 4; shark declines are principally due to conservative life-histories and fisheries overexploitation 5, 6, 7, 8. On coral reefs, sharks are strongly interacting apex predators and play a key role in maintaining healthy reef ecosystems 9, 10, 11.

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Image Source: ProjectAware.com

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The Coral Reef is a Marine Ecosystem home to billions of diverse plant and animal species. Here is a brief introduction to this beautiful biome below.

Video Source: YouTube, National Geographic

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-Coral
-Fish
-Seahorses
-Sea Sponge
-Mollusks
-Crab
-Lobster
-Clam
-Sea Turtle
-Urchins
-Sting Rays
-Anemone
-Octopuses
-Reef Sharks

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Average Temperatures:
70-80 degrees Fahrenheit

Water location: Shallow

Salinity: 32-40 PSU (practical Salinity Units)

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Currently, coral reefs around the world are dying. This ecosystem is highly fragile. The coral reefs of the world are dying because of pollution, coral mining, blast fishing, over-fishing and digging canals.

The NOAA Coral Reef Conservation Program is here to help. This program actively participates in the following:
- Increased resilience to climate change
- Reducing land-based pollution
- Improving fishery sustainability
- Restoration of viable coral populations

With billions of members worldwide, the NOAA is making good progress to slow the extinction of coral reefs, and possibly even prevent it.

Once coral population is back to normal, new-coming fish will be sure to reproduce quickly. That's where the Whitetip Reef Shark comes into play. A few sharks will be raised in captivity and simulated to know what to du in the wild. When the coral reef inhabitants begin to overpopulate, the human raised sharks will be released into the wild to help keep the numbers normal.

Sources used:

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Coral Reef Ecosystems: Valuable and Threatened

A reefscape in the waters offshore of southwestern Guam demonstrates some of the biodiversity found in this region. Photo Credit : Dave Burdick

Healthy coral reefs are among the most biologically diverse, culturally significant, and economically valuable ecosystems on Earth. They provide billions of dollars in food, jobs, recreational opportunities, coastal protection, and other important goods and services to people around the world.

Coral reefs face an increasing number of threats, including pollution, unsustainable fishing practices, and global climate change. According to the Word Resource Institute, more than 60 percent of the world's reefs are under threat from local stressors, like fishing and land-based pollution. That number jumps to 75 percent when local threats to reefs are combined with the threat of thermal stress from a changing climate. As a result, in the U.S. 22 species of coral are now listed as threatened under the Endangered Species Act.

Given their incredible value, it is now more important than ever to address and reverse the threats impacting coral reef ecosystems. The NOAA Coral Reef Conservation Program is leading efforts to study and conserve these precious resources for current and future generations.

About the NOAA Coral Reef Conservation Program

The program was established in 2000 by the Coral Reef Conservation Act to protect, conserve, and restore the nation's coral reefs by maintaining healthy ecosystem function. We focus on four main pillars of work:

Increase resilience to climate change

Reduce land-based sources of pollution

Improve fisheries' sustainability

Restore viable coral populations

A Multidisciplinary Approach

Damsel fish swim among corals in Guam. Photo Credit: Dave Burdick

The NOAA Coral Reef Conservation Program brings together expertise from across NOAA for a multidisciplinary approach to studying these complex ecosystems to inform more effective management. We work closely with NOAA scientists in the National Ocean Service, National Marine Fisheries Service, Office of Oceanic and Atmospheric Research, and National Environmental Satellite, Data and Information Service.

Collaboration is critical to coral reef conservation. We partner with state and territorial governments, academic institutions, non-governmental organizations, and community groups to take targeted approaches to local issues that impact coral reef ecosystems.

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national oceanic and atmospheric administration

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NOAA's Coral Reef Conservation Program (CRCP) - Who We Are

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Coral Reef Ecosystems: Valuable and Threatened Healthy coral reefs are among the most biologically diverse, culturally significant, and economically valuable ecosystems on Earth. They provide billions of dollars in food, jobs, recreational opportunities, coastal protection, and other important goods and services to people around the world.

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Keystone Species: The Whitetip Reef Shark

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Keystone Species: The Whitetip Reef Shark

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This Reef Shark is a prime example of a keystone species in this ecosystem.
Size: 4-5 feet (Adult)
Weight: Avg of 22 lbs
Species: Reiquiem Shark
Status: Near Threatened
Food: reef fish such as parrotfish, and octopuses and crustaceans.

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The whitetip reef shark ( Triaenodon obesus) is a species of requiem shark, in the family Carcharhinidae, and the only member of its genus. A small shark that does not usually exceed 1.6 m (5.2 ft) in length, this species is easily recognizable by its slender body and short but broad head, as well as tubular skin flaps beside the nostrils, oval eyes with vertical pupils, and white-tipped dorsal and caudal fins. One of the most common sharks found on Indo-Pacific coral reefs, the whitetip reef shark occurs as far west as South Africa and as far east as Central America. It is typically found on or near the bottom in clear water, at a depth of 8-40 m (26-131 ft).

During the day, whitetip reef sharks spend much of their time resting inside caves. Unlike other requiem sharks, which rely on ram ventilation and must constantly swim to breathe, this shark can pump water over its gills and lie still on the bottom. At night, whitetip reef sharks emerge to hunt bony fishes, crustaceans, and octopus in groups, their elongate bodies allowing them to force their way into crevices and holes to extract hidden prey. Individuals may stay within a particular area of the reef for months or years, frequently returning to the same shelter. This species is viviparous, in which the developing embryos are sustained by a placental connection to their mother.

Whitetip reef sharks are rarely aggressive towards humans, though they may investigate swimmers closely. However, spear fishers are at risk of being bitten by one attempting to steal their catch. This species is caught for food, though ciguatera poisoning resulting from its consumption has been reported. The IUCN has assessed the whitetip reef shark as Vulnerable, noting its numbers are dwindling due to increasing levels of unregulated fishing activity across its range. The slow reproductive rate and limited habitat preferences of this species renders its populations vulnerable to overfishing.

The whitetip reef shark was first described by the German naturalist Eduard Rüppell as Carcharias obesus, in the 1837 Fische des Rothen Meere ( Fishes of the Red Sea). His choice of the specific epithet obesus was curious, given that this shark is actually quite slender. Later in 1837, Johannes Müller and Friedrich Henle moved this species into its own genus Triaenodon, from the Greek triaena meaning "trident", and odon meaning "tooth". As Rüppell did not originally designate a holotype, in 1960 a 31-cm-long specimen caught off Jeddah, Saudi Arabia, was made the species lectotype. Other common names for this shark include blunthead shark, light-tip shark, reef whitetip shark, and whitetip shark.

Once placed in the family Triakidae, the whitetip reef shark is now recognized by most authors as belonging to the family Carcharhinidae on the basis of morphological characters, such as a full nictitating membrane, well-developed precaudal pit, strong lower caudal fin lobe, and scroll-like intestinal valves. Morphological and molecular phylogenetic analyses suggest the whitetip reef shark is grouped with the lemon sharks ( Negaprion) and the sliteye shark ( Loxodon) in occupying an intermediate position on the carcharhinid evolutionary tree, between most basal genera (Galeocerdo, Rhizoprionodon, and ) and the most derived (Carcharhinus and ).

The whitetip reef shark is distributed widely across the entire Indo-Pacific region. It was once thought to have formerly existed in the Atlantic Ocean, based on fossil teeth found in North Carolina dating to the Miocene epoch. However, more recent research indicates that the teeth belonged to a mackerel shark, and that this species has never colonized the Atlantic. In the Indian Ocean, it occurs 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 occurs 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.

Associated almost exclusively with coral reef habitats, whitetip reef sharks are most often encountered 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. This species is most common at a depth of 8-40 m (26-131 ft). On occasion, they may enter water less than 1 m deep, and there is an exceptional record of a whitetip reef shark being captured from a depth of 330 m (1,080 ft) in the Ryukyu Islands.

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.

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. Off Hawaii, these sharks may be found sheltering inside underwater lava tubes, while off Costa Rica they are often 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. One study at Johnston Atoll found that none of the sharks examined had moved more than 3 km (1.9 mi) away from their original capture location over periods of up to a year. Another study at Rangiroa Atoll in French Polynesia found that, after more than three years, around 40% of the originally tagged sharks were still present on the same reef where they were first captured. 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 km ² (0.019 sq mi); at night this range increases to 1 km ² (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.

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. Off Borneo, this species gathers around reef drop-offs to feed on food brought up by the rising current. Off Hawaii, they follow Hawaiian monk seals ( Monachus schauinslandi) and attempt to steal their catches. A whitetip reef shark can survive for six weeks without food.

Life history

Like other members of its 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 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).

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. Whitetip reef sharks are well-suited to ecotourism diving, and with conditioning they can be hand-fed by divers. In Hawaiian mythology, the fidelity (i.e. "loyalty") of whitetip reef sharks to certain areas of the reef for years at a time may have inspired belief in , the spirits of family ancestors that take animal form and protect their descendants.

The whitetip reef shark is taken by fisheries operating off Pakistan, India, Sri Lanka, Madagascar, and likely elsewhere, using 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). The International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable, 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. In June 2018 the New Zealand Department of Conservation classified the whitetip reef shark as "Vagrant" under the New Zealand Threat Classification System.

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2. Froese, Rainer; Pauly, Daniel (eds.) (2009). in FishBase. July 2009 version.

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7. ^ Coetzee, M.; N.J. Smit; A.S. Grutter & A.J. Davies (June 2008). "A new gnathiid (Crustacea: Isopoda) parasitizing two species of requiem sharks from Lizard Island, Great Barrier Reef, Australia". The Journal of Parasitology. 94 (3): 608-615. doi:10.1645/ge-1391r.1.

8. ^ Nelson, D.R. and R.H. Johnson. (1970). Acoustic studies on sharks: Rangiroa Atoll, July 1969. ONR Technical Report 2, No. N00014-68-C-0138.

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The whitetip reef shark ( Triaenodon obesus) is a species of requiem shark, in the family Carcharhinidae, and the only member of its genus. A small shark that does not usually exceed 1.6 m (5.2 ft) in length, this species is easily recognizable by its slender body and short but broad head, as well as tubular skin flaps beside the nostrils, oval eyes with vertical pupils, and white-tipped dorsal and caudal fins.