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Whale sharks (Rhincodon typus) are often thought to be solitary behemoths that live and feed in the open ocean. Scientists at the Smithsonian Institution and colleagues, however, have found that this is not necessarily the case, finding that whale sharks can be gregarious and amass in the hundreds to feed in coastal waters.

The team of scientists also examined a nearby, less dense aggregation of whale sharks, known as the Cabo Catoche aggregation, off the northern tip of the Yucatn Peninsula. They found that the prey of this group mostly consisted of copepods (small crustaceans) and shrimp. Increased sightings at Afuera coincided with decreased sightings at Cabo Catoche, and both groups had the same sex ratio, implying that the same animals were involved in both aggregations.

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These sharks are recognizable not just for being the largest fish in the sea, but also for their unique patterns. They are filter feeders, often swimming near the surface of the open sea; they gulp in water and filter everything from plankton and fish eggs to crustaceans and schooling fish, to occasional larger prey like squid or tuna. Despite their size, they are considered harmless to humans, and will often interact docilely with divers.

Until 2008, Taiwan caught an average of 100 whale sharks annually, for meat, oil, fins, or aquaria. Although Whale shark fins are rarely seen on the market when they appear they are highly-priced because of their difficult preparation and trophy-like status. Because of their value, opportunistic finning began in several countries including India and Taiwan (Chen, 2002). In India, harpooning allowed access to liver oils and flesh of the shark. Even though whale sharks are now protected in India and the Philippines, harpooning fisheries developed in other countries such as Iran and Pakistan (Akhilesh, 2013). The liver oils are often used for waterproofing fishing boats and other appliances, for the manufacture of shoe polish, and as a treatment for some skin diseases, while the flesh is occasionally eaten.

Whale sharks have been kept in specialized aquaria in Japan, China, and in the Georgia Aquarium (U.S.), but their large size and specialized diet exclude this species from mainstream aquarium species. In a few locations where the presence of whale sharks appears to be predictable, they are increasingly targeted by commercial tourist operations. By taking advantage of the surface feeding habits of the whale shark, the tourism industry has rapidly expanded around the globe, generating millions of dollars per country annually (Topelko, 2005).

Generally considered harmless. However, there have been a few cases of whale sharks ramming sportfishing boats, possibly after being provoked. Usually, the sharks are more at risk of being struck accidentally by vessels whilst basking or feeding on the surface.

Recent research using mitochondrial DNA and microsatellite analysis has demonstrated that there exist two subpopulations of whale sharks. One lives in the Indo-Pacific Ocean and the other population in the Atlantic Ocean. The Indo-Pacific Ocean population ranges from the Western Indian Ocean, the Philippines, Taiwan, Thailand, and the Western and Central Pacific. The population size has shown a decrease from overfishing in this area. The Atlantic subpopulation is known to have more aggregations over feeding areas. The Atlantic population has decreased as well (Castro, 2007).

The whale shark has a very widespread distribution, occurring in all tropical and warm temperate seas, except in the Mediterranean. It occurs throughout the Atlantic Ocean, from New York through the Caribbean to central Brazil and from Senegal to the Gulf of Guinea. It also occurs in the Indian Ocean, throughout the region, including the Red Sea and the Arabian Gulf. In the Pacific Ocean, it is found from Japan to Australia, off Hawaii, and from California to Chile (Sequeira, 2013).

In contrast to most sharks from the same order (Orectolobiformes), which are benthic (live on or near the bottom) species, the whale shark is a pelagic (open sea) species. Studies reveal that this shark can reach depths of 1928 meters (6325.5 ft) (Tyminski, 2015) and prefers warm waters, with surface temperature around 21-30 C (69.8-86 F), marked by high primary productivity (plankton). They are often seen offshore but commonly come close inshore, sometimes entering lagoons or coral atolls. This species segregates by size and sex in most of the coastal feeding areas. The coastal feeding sites consist of mainly juvenile male sharks, with the largest congregation containing hundreds to thousands of individual sharks (Rohner, 2013). Whale sharks show site fidelity, where they continuously return to the same feeding site but are also highly migratory with daily movement of about 24-28 km (14.9-17.4 miles) (McCoy, 2018). Their movements might be related to local productivity and they are often associated with schools of pelagic fish that are probably feeding on the same prey organisms.

Different geographic locations appear to be preferred at various times of the year. Whale sharks alternatively may undertake either fairly localized or large-scale transoceanic migrations, the movements governed by the timing and location of production pulses and possibly by breeding behavior. Seasonal migrations have been postulated for various areas but more information is needed to confirm these patterns. Each March and April, whale sharks are known to be aggregate on the continental shelf of the central western coast of Australia, particularly in the Ningaloo Reef area (Fitzpatrick, 2006). A study was done in this area to provide information on the short-term movements and behavior of this species of shark. Whale sharks are thought to migrate to Ningaloo Reef each year to take advantage of the high zooplankton concentrations (Martin, 2007).

A few whale sharks were tracked and some behavioral observations were made while snorkeling in the area. The reaction of the sharks to snorkelers varied between ignoring them to slowly diving. At times when water was flowing out from the reef lagoon, possibly transporting potential prey outside the reef, the tracked sharks swam in large circles adjacent to passes in the reef. The whale sharks also made numerous dives throughout the observation period. It appears that these movements, up and down through the water column, were associated with feeding (Gunn, 1999). Whale sharks have smaller livers than most sharks and could conceivably control their buoyancy by swallowing some air as do the sand tiger sharks (Ondontaspis taurus).

Whale sharks were also observed near La Paz, Mexico. Researchers reported that when these sharks were not feeding at the surface, they swam practically without the head-turning, gulping, and rhythmical opening and closing of the gill slits, seen during feeding behavior(Rowat, 2012). The mouth was held slightly open, and the skin over the gill openings was quivering as water flowed steadily out the gill slits in the typical ventilation of pelagic sharks (Rowat, 2012).

The whale shark has unique denticles (tooth-like scales structures), each with an extremely strong central keel, no lateral keels, and a tri-lobed rear margin. It would appear that the denticles are hydrodynamically important in its pelagic lifestyle (Martin, 2007).

Whale sharks feed on a wide variety of planktonic (microscopic) and nektonic (larger free-swimming) prey, such as small crustaceans, schooling fishes, and occasionally on tuna and squids (Martin, 2007). Also, phytoplankton (microscopic plants) and macroalgae (larger plants) may form a component of the diet. Unlike most plankton feeding vertebrates, they do not depend on slow forward motion to filter, rather, they rely on a versatile suction filter-feeding method, which enables them to draw water into the mouth at higher velocities than other dynamic filter-feeders, like the basking shark. This enables the whale shark to capture larger more active nektonic prey as well as zooplankton aggregations (Motta, 2010).

Therefore, they are dependent on dense aggregations of prey organisms. The denser filter screens are efficient filters for short suction intakes, in contrast to the flow through systems of basking shark. Whale sharks are always seen feeding passively in a vertical or near vertical position with the head at or near the surface (Motta, 2010).

The whale shark feeds actively by opening its mouth, distending the jaws and sucking. Then it closes its mouth and the water flows out its gills. During the slight delay between closing the mouth and opening the gill flaps, plankton may be trapped against the dermal denticles lining the gill plates and pharynx (Motta, 2010). The fine sieve-like apparatus, a unique modification of the gill rakers, forms an obstruction to the passage of anything but fluid, retaining all organisms above 2 to 3mm (.07- .12 inches) in diameter. Practically nothing but water goes through this sieve. Individuals have also been observed coughing, a mechanism that is thought to be employed to clear or flush the gill rakers of accumulated food particles (Motta, 2010).

Whale sharks move their heads from side to side, vacuuming in seawater rich in plankton, or aggressively cut swathes through schools of prey. Groups of individuals have been observed feeding at dusk or after dark (Martin, 2007). The density of plankton probably is sensed by the well-developed nostrils, located on either side of the upper jaw, on the leading edge of the terminal mouth. The frequent turns may keep the whale sharks in the denser parts of the plankton patches, searching and scanning when an olfactory cue weakens on one side or the other (Martin, 2007).

The egg-capsules of this whale shark were amber colored, with a smooth texture, and possessed a respiratory fissure (opening) on each side (Chang, 1997). The sex ratio was approximately 1:1. It would appear that female whale sharks give birth as they feed in the rich waters of the Kuroshio Current. It is also apparent that the southeast waters off Taiwan are an important birthing area during summer months. It is believed that the young measure 55-64 cm (21.7-25.2 in.) total length at birth (Chang, 1997). e24fc04721